Contact Lens & Anterior Eye 38 (2015) 28–33
Contents lists available at ScienceDirect
Contact Lens & Anterior Eye journal homepage: www.elsevier.com/locate/clae
Assessment of corneal morphological changes induced by the use of daily disposable contact lenses Antonio J. Del Águila-Carrasco ∗ , Alberto Domínguez-Vicent, Cari Pérez-Vives, Teresa Ferrer-Blasco, Robert Montés-Micó Optometry Research Group (GIO), Department of Optics, University of Valencia, Spain
a r t i c l e
i n f o
Article history: Received 28 January 2014 Received in revised form 5 August 2014 Accepted 28 August 2014 Keywords: Corneal thickness Corneal curvature Daily disposable contact lenses
a b s t r a c t Purpose: To assess the effect of different disposable soft contact lenses upon corneal thickness, and upon anterior and posterior corneal curvatures using a dual-Scheimpflug imaging based device. Methods: Twenty-eight young, healthy subjects wore four different types of daily disposable soft contact lenses on four different days: Dailies Total1, Proclear 1 Day, Clariti 1-Day and 1-Day Acuvue Moist. The lenses had different material and water content. Pachymetry maps and keratometry values were obtained using the Galilei G4 twice a day: one before putting the lens on and one after an eight-hour period of contact-lens wear. Measurements were also recorded without any contact lenses being worn during a day. Results: Clariti 1-Day lens caused the greatest thickening in the central (8.9 ± 2.8 m; p < 0.01) and in the peripheral cornea (10.1 ± 4.6 m; p < 0.01), whereas Dailies Total1 was the lens that had the most similar behaviour to the non-contact lens scenario. All the lenses caused a slight flattening in the anterior corneal curvature, except Clariti 1-Day, which induced a very slight steepening. The four lenses caused a steepening of different magnitude in the posterior corneal curvature. Conclusions: The magnitude of the changes introduced by the use of soft contact lenses over the eighthour wearing period was rather small. Thus it is probable it will not influence the vision nor the comfort of the subject. Also, variations on corneal parameters seem to depend on the type of contact lens used. © 2014 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.
1. Introduction Disposable soft contact lenses are very popular nowadays for people who have refractive errors, such as myopia, hyperopia, astigmatism or presbyopia. There are also contact lenses for aesthetic purposes. It seems logical that disposable soft contact lenses could modify the morphology of the anatomical surface where they are fit: the cornea. There are a lot of studies documenting the changes undergone by the cornea which are induced by the use of contact lenses, both rigid gas permeable [1,2] and soft [3–5] ones. These changes in corneal shape or morphology were evaluated using different techniques. It is also well known that the cornea undergoes through some changes during the day. These changes are natural and happen as a result of the own metabolism of the cornea and the tear layer.
∗ Corresponding author at: Optometry Research Group (GIO), Department of Optics, University of Valencia, C/Dr Moliner, 50, 46100 Burjassot, Spain. Tel.: +34 963544764; fax: +34 963544715. E-mail address: [email protected] (A.J. Del Águila-Carrasco).
The natural modifications experienced by the cornea are generally small in magnitude, but it is important to have them in consideration for clinical – e.g. refractive surgery – and research purposes. The natural diurnal changes suffered by the cornea in its thickness [6,7] and curvatures [8,9] are well studied. In order to comprehend better the changes in corneal shape caused by the wearing of contact lenses, diurnal changes that cornea goes through need to be known. This way, the real modifications that contact lenses introduce in the cornea can be studied. Currently, there are several techniques which allow us to measure the corneal changes previously mentioned. The Galilei G4 (Ziemer, Switzerland) is a non-invasive optical diagnostic system designed for the analysis of the anterior segment of the eye, based on a rotating Dual-Scheimpflug and a Placido tomography system. This device allows the evaluation of the diurnal natural changes undergone by the corneal shape (thickness and curvatures) and also the changes caused by the use of soft contact lenses in a fast and easy way. Disposable soft contact lenses are in constant evolution and there are a wide variety of materials, water content, designs, etc. It is expected that this range of different parameters causes a variety
http://dx.doi.org/10.1016/j.clae.2014.08.004 1367-0484/© 2014 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.
A.J. Del Águila-Carrasco et al. / Contact Lens & Anterior Eye 38 (2015) 28–33
of results in the change of the curvatures and thickness of the cornea. Wearing time and frequency in the use of soft contact lenses may also affect the modifications of these corneal parameters. To the best author’s knowledge, no previous study has been carried out evaluating these changes in corneal shape, using the Galilei G4. The purpose of this study was to evaluate changes that may occur in corneal shape (i.e. curvatures and thickness) as a result of wearing four different types of disposable soft contact lenses during an eight hours period of time. In order to achieve this, a non-invasive technique was performed, using the Galilei G4. This method allows us to determine whether or not corneal parameters suffer modifications over time due to the wearing of each soft contact lens that took part in this study. 2. Methods 2.1. Subjects Twenty-eight left eyes [7] from twenty-eight individuals, 11 male and 17 female, aged from 21 to 36 years (mean: 25.7 ± 5.1 years). Spherical refractive errors ranged between −3.50 and −2.75 diopters (D), being the mean spherical refractive error −3.12 ± 0.24 D. All of the subjects had best-corrected visual acuity of 6/6 or better. None of the subjects were a regular user of contact lenses and they were not using any ocular or systemic medication. They presented clear intraocular media and no known ocular pathology. All patients were informed about the details of this study, and a written informed consent was obtained after verbal and written explanation of the nature and possible consequences of the study, in accordance with the Helsinki Declaration. Institutional Review Board approval was required for this study. Subjects having ocular or systemic disease, ocular surgery history, intraocular pressure higher than 21 mmHg, presence of retinal or optic disc pathology were excluded from this study. A series of preliminary tests were conducted to ensure that all subjects had normal anterior segment, and central corneal thickness. 2.2. Contact lenses Four different types of daily disposable contact lenses, each one from a different commercial brand, were evaluated: Dailies Total1 (Alcon, www.alcon.com), Proclear 1 Day (CooperVision, www.cooopervision.com), 1-Day Acuvue Moist (Johnson & Johnson Vision Care, www.jnjvision.com) and Clariti 1-Day (Sauflon, www.sauflon.com). The main technical specifications of the lenses under evaluation are summarized in Table 1. All the contact lenses used on every subject’s eye were fitted in an optimal or acceptable way and all of them had a power of −3 D. The lens power and total diameter were checked by one of the authors and found to conform to the manufacturers stated tolerances. Subjects wore a different type of contact lens in the left eye on four separate days, during a period of 8 h each day. New lenses were used for each subject and for each trial. All the four types of contact lenses were worn by each study participant in a randomized order. 2.3. Galilei G4 The Galilei G4 is a non-invasive optical diagnostic system designed for the analysis of the anterior segment of the eye, based on a rotating Dual-Scheimpflug and a Placido tomography system. The Galilei uses a monochromatic diode emitting blue light at 470 nm and combines dual Scheimpflug cameras and a Placido disc to measure both anterior and posterior corneal surfaces. During the rotating scan, the Placido and Scheimpflug data of the corneal information are simultaneously obtained. Two Scheimpflug slit images are made by the dual camera from opposite sides of the illuminated
29
slit, and the data are averaged. Meanwhile, the dual camera simultaneously tracks decentration due to eye movements. Studies have reported the Galilei to be highly repeatable and reasonably accurate for measuring corneal thickness [10,11] and corneal curvatures [12]. Anterior and posterior corneal topography and regional corneal thickness were measured using the Galilei G4. Baseline measurements, approximately at 10 am (at least 2 h after subjects reported time of waking, in order to avoid the peak in corneal thickness immediately after waking [13]) and at 6 pm, were taken during two days on the left eye without any contact lenses being worn in order to record each individual’s natural diurnal variations in corneal thickness and curvature. For the contact-lens scenario, measurements of the cornea were also taken twice a day: once before the contact-lens insertion around 10 am; at least 2 h after subjects reported time of waking. The other one was taken around 6 pm, after an eight-hour period of wearing each contact lens, and it was completed within 10 min of lens removal for each lens. A recovery period of 3 days was allowed for the individuals between lenses, in order to let the cornea to restore its normal state in case any changes were caused by the lenses.
2.4. Data analysis Corneal thickness and curvature data were exported from the Galilei. In order to compare the baseline measurements with postlens removal measurements, thickness and curvature difference values were calculated for all the 28 subjects and for each of the four lens types. Also, diurnal changes were obtained calculating the difference between measurements taken in the morning and the ones taken in the afternoon when the subjects were not wearing any lenses. In this study, the data from all the subjects were averaged. A repeated measures analysis of variance (ANOVA) was used to analyze changes in corneal curvature and thickness because of contact lens wear, with lens type, corneal region and time as within-subject factors using SPSS Statistics v.17.0 (www.ibm.com/ software/analytics/spss/). Statistical significance was set at p = 0.05.
3. Results 3.1. Diurnal changes Data was averaged considering two corneal zones: a central and mid-peripheral zone of 5 mm diameter and a peripheral annulus from 5 to 8 mm (Fig. 1a). A significant difference was found between the morning and the afternoon measurements when the subjects were not wearing any contact lenses. The group mean diurnal change in corneal thickness for the non-contact lens scenario showed a significant thinning of −2.0 ± 1.7 m (p = 0.037) in the central corneal region and −4.6 ± 2.8 m (p = 0.012) in the peripheral annular corneal region. Considering the cornea divided in four different zones (nasal, temporal, inferior and superior), as it can be seen in Fig. 1b, a significant thinning was found in each one of the four zones: −1.8 ± 1.6 m for the nasal quadrant, −2.4 ± 2.6 m in the temporal one, −2.0 ± 2.1 m in the inferior one, and −3.1 ± 2.7 m in the superior quadrant. The anterior corneal curvature showed a slight significant steepening of −0.01 ± 0.01 mm (p = 0.047), whereas the posterior corneal curvature exhibited a slight non-significant flattening of 0.01 ± 0.02 mm (p = 0.055). All these changes should and were taken into consideration when analyzing corneal changes using contact lenses, due to their magnitude.
30
A.J. Del Águila-Carrasco et al. / Contact Lens & Anterior Eye 38 (2015) 28–33
Table 1 Main features of the daily soft contact lenses assessed in this study. Parameter
1-Day Acuvue Moist
Dailies Total1
Clariti 1-Day
Proclear 1 Day
FDAa Group Water content Material BOZRb (mm) TDc (mm) tcd (mm) @ −3.00 D DK/te (@ −3.00 D) Design Manufacturer
IV 58% Etafilcon A 8.5 14.2 0.084 26 Spherical lens Johnson & Johnson Vision care
II 33% to >80% Delefilcon A 8.5 14.1 0.09 156 Bicurve lens Alcon
II 56% Filcon II 3 8.6 14.1 0.07 86 Aspheric lens Sauflon
II 60% Omafilcon A 8.7 14.2 0.09 36.6 Aspheric front surface CooperVision
a b c d e
FDA: Food & Drug Administration (USA). BOZR: back optic zone radius. TD: total diameter. tc: central thickness. DK/t: oxygen transmissibility.
Table 2 Central and peripheral corneal thickness variation for all of the contact lenses under study. Lens type
Central mean change (m)
Acuvue Moist Dailies Total1 Clairiti 1 Day Proclear 1-Day
5.6 1.8 8.9 5.0
± ± ± ±
3.0a (p = 0.02) 1.5 (p = 0.11) 2.8a (p < 0.01) 2.9a (p = 0.03)
Peripheral mean change (m) 7.3 3.9 10.1 4.3
± ± ± ±
3.7a (p = 0.01) 2.1 (p = 0.09) 4.6a (p < 0.01) 3.0a (p = 0.02)
a Values that revealed significant changes from baseline after a pair-wise comparison were performed.
3.2. Changes in corneal thickness Repeated measures ANOVA revealed that both type of contact lens and corneal zone (central and peripheral annulus) had a significant effect in corneal thickness after 8 h of lens wear (p < 0.001 and p = 0.012, respectively). The mean change in corneal thickness with each of the four contact lenses is shown in Table 2. It is necessary to remind that these corneal thickness variations are relative to the baseline condition, since diurnal changes existed and were significant. The greatest magnitude of corneal variation in the central zone was caused by the Clariti 1-Day lens, which provoked a thickening of 8.9 ± 2.8 m (1.52 ± 0.48%; p < 0.01). In the peripheral zone, also the Clariti 1-Day lens was the one that caused the greatest
magnitude in corneal variation, being 10.1 ± 4.6 m of thickening (1.60 ± 0.75%; p < 0.01). Dailies Total1 is the lens that induces the smallest variation in both corneal zones (central and peripheral). In order to better illustrate the variations in corneal thickness, data from several zones were averaged. On one hand, Fig. 2 shows profiles of corneal thickness variation for all the contact lenses used in this study and also for the non-contact lens scenario, averaged in four different zones: centre and three consecutives annulus. On the other hand, Fig. 3 shows the same corneal thickness changes, but the data was averaged from nasal, temporal, inferior and superior quadrants, and it represents percentages values. As Fig. 2 shows, the Clariti 1-Day and the 1-Day Acuvue Moist lenses are the ones that introduce the greatest changes in corneal thickness. Changes caused by the Dailies Total1 are quite small, keeping some resemblance with the non-contact lens profile. Fig. 3 shows that the Dailies Total1 lens is the one that barely modifies corneal thickness in any of the quadrants. The other three lenses introduce bigger changes; being the Clariti 1-Day lens the one that introduced the greatest changes in corneal thickness. Another repeated measures ANOVA was run for the case in which the cornea is divided in four quadrants, showing that type of lens and position (nasal, temporal, inferior and superior) had significant effect on corneal thickness (p < 0.001 for both). The greatest thickening appeared in the temporal and inferior quadrants of the cornea with the Clariti 1-Day lens, whereas the smallest changes
Fig. 1. Diagram representing (a) the two areas of the cornea were data were averaged. Central zone is coloured as light green; a darker green represents the peripheral cornea. And (b) the four quadrants in which the cornea was divided for averaging the data for a left eye. N: Nasal, T: Temporal, I: Inferior and S: Superior.
A.J. Del Águila-Carrasco et al. / Contact Lens & Anterior Eye 38 (2015) 28–33
31
Fig. 2. Percentage of variation in corneal thickness for each contact lens under study normalized to the naked eye, after the 8-h wearing period. The data correspond to the central zone (dark grey) and the peripheral zone (lighter grey) of the cornea.
were evident in the temporal and superior quadrants, wearing the Dailies Total1 lens.
3.4. Association between changes in thickness and curvatures
3.3. Changes in anterior and posterior curvatures Anterior and posterior curvature data was averaged from the values given by the Galilei G4. Table 3 shows the mean values of the changes that happened on the anterior and posterior axial corneal curvature relative to the baseline days, for each of the four contact lenses used in this study. Repeated measures ANOVA indicated that type of lens had a significant effect on the change of both curvatures (p = 0.031 and p = 0.005 respectively). Anterior corneal curvature changes were slight and pair-wise comparison revealed that 1-Day Acuvue Moist and Proclear 1 Day introduced significant changes in anterior corneal curvature (p < 0.05). Posterior corneal curvature showed a steepening, and the comparison with the baseline days data revealed that all the contact lenses used in this study, except
Table 3 Variation suffered by the anterior and posterior corneal curvatures for all the lenses under study. Lens type Acuvue Moist Dailies Total1 Clariti 1-Day Proclear 1 Day
Anterior curvature change (mm) 0.02 0.01 −0.01 0.02
± ± ± ±
0.02a (p = 0.03) 0.02 (p = 0.10) 0.02 (p = 0.12) 0.02a (p = 0.03)
for the Dailies Total1, caused significant changes (p < 0.05) in this curvature.
Posterior curvature change (mm) −0.04 −0.01 −0.10 −0.02
± ± ± ±
0.07a (p = 0.01) 0.02 (p = 0.08) 0.03a (p = 0.04) 0.03a (p = 0.02)
a Values that revealed significant changes from baseline after a pair-wise comparison were performed.
Pearson’s correlation and significance were calculated between variables in order to evaluate if changes in corneal thickness, anterior and posterior corneal curvature are associated. There was a very weak and non-significant negative correlation between the changes suffered by the mean corneal thickness (averaged from the whole maps of 8 mm diameter) and the changes in anterior corneal curvature (R2 = 0.17, p > 0.05). A strong negative correlation was found between the changes in the mean corneal thickness and the ones in posterior corneal curvature (also averaged from the whole maps of 8 mm diameter). This correlation resulted nonsignificant (R2 = 0.95, p = 0.058). Hence, no associations can be identified between the changes in corneal thickness and changes in corneal anterior curvature. There could exist a relationship between changes in posterior corneal curvature and modifications in corneal thickness. 4. Discussion The results obtained in this study highlight that the wearing of daily disposable soft contact lenses induces additional changes in corneal morphology (i.e. thickness and curvatures), whose magnitude and pattern depend on the particular lens fitted. Both corneal thickness and corneal curvatures in contact-lens wearing were different from the non-contact lens condition. Dailies Total1 is the lens which yielded similar values than the non-contact lens scenario,
32
A.J. Del Águila-Carrasco et al. / Contact Lens & Anterior Eye 38 (2015) 28–33
Fig. 3. Variation in corneal thickness (%) experienced by each of the four quadrants of the cornea for each contact lens under study.
followed by the Proclear 1 Day lens. Clariti 1-Day lens showed the most different behaviour from the non-contact lens condition. The largest changes suffered by the corneal thickness and corneal curvatures are typically found upon waking [13], as it is reported in previous studies [3]. The diurnal variation in corneal thickness that has been observed here is consistent with previous investigations [3,14–17]. We have found the cornea to suffer a small but significant thinning. These thinning increases as we move to the periphery of the cornea, which could be caused by the stromal collagen fibrils. These fibrils present different arrangement in the central zone of the cornea than in the periphery. According to Boote et al. [18], the diameter of stromal collagen fibrils is the same from the central fibrils and for the peripheral ones, however the fibril spacing is greater in the peripheral cornea. The smallest thinning in the central cornea could be caused by the denser packed of fibrils within this area. A small steepening was found in anterior corneal curvature during the 8 h period, which is consistent with previous studies documenting these changes [3,8]. There are very few studies documenting diurnal changes in posterior corneal curvature. In this case, a small flattening was found, which is in agreement with Tyagi et al. [3] It seems that environmental factors could influence corneal thickness [17]. For example, a reduction in blinking frequency with reading has previously been suggested to have an effect on corneal thickness variations [19]. Low humidity induced by heating systems could affect corneal thickness variations too [20]. Corneal thickness may therefore be either directly affected by environmental factors and/or due to alterations of the functions of the various tissues of the eye in response to these environmental conditions. With regard to the modifications on the corneal thickness and curvatures while disposable soft contact lenses are fitted, it is needed to say that these changes are quite small, but rather
significant, which is why it is important to keep them in consideration for any research or clinical applications. There are a lot of studies evaluating changes in anterior corneal curvature [3,4,22,23] and corneal thickness [3,5,21–23], and a few ones evaluating changes in posterior corneal curvature [3,23,24], caused by the use of different types of contact lenses. The lenses’ parameters (material, water content, etc.), period of wearing and whether the subject wears contact lenses regularly or just occasionally are some examples of factors that have influence in corneal morphology. There are several studies which evaluate extended contact lens wear [25–27]. These studies typically report that under extended wear conditions, cornea experiments a small swelling during the firsts weeks. Then, the cornea deswells gradually until it reaches similar values to those reported before the use of the contact lenses. Obviously, it depends on each subject and the type of lens under consideration. In the present study, we evaluated the changes in corneal thickness and corneal anterior and posterior curvatures caused by the use of disposable soft contact lenses, during a wearing period of 8 h (approximately from 10 am to 6 pm). It is difficult to establish a comparison between the results showed in different studies [3,23] that evaluated changes caused in corneal morphology by the use of contact lenses and the ones obtained here, since they depend on the subjects, the type of lenses under study, and the measurement methods. Still, the changes introduced by the daily use of well fitted soft contact lenses are quite small, sometimes even smaller than the daily variations, which indicate that the design and manufacture of contact lenses are improving. In the present study, Dailies Total1 and Proclear 1 Day are the lenses which modified less the corneal thickness. The anterior corneal curvature showed a slight flattening with all the contact lenses under study, except for the Clariti 1-Day, which introduce a very small steepening. All the four lenses
A.J. Del Águila-Carrasco et al. / Contact Lens & Anterior Eye 38 (2015) 28–33
provoked a steepening in the posterior corneal curvature. The greatest one was caused by the Clariti 1-Day lens. No correlation was found between corneal thickness and anterior corneal curvature; however, a strong but not significant correlation was found between the changes in corneal thickness and in posterior corneal curvature by the use of contact lenses, which would be interesting to analyze in future studies. Corneal swelling or oedema can affect visual quality and visual acuity if it is big enough, so it is very interesting to analyze the corneal swelling that a particular contact lens can induce. The oxygen transmissibility has an essential role in corneal oedema, and it depends on some lens parameters like thickness, material and water content. Hess and Garner [28] studied the effect of corneal oedema on visual function, enlightening that when the cornea swells due to anoxia, visual function is slightly compromised when the change in corneal thickness is about 6%. Visual acuity changed from 6/5 to 6/6 for the clinical Snellen letter chart, and 6% oedema affects as well contrast sensitivity, but only the spatial high frequency region of the contrast function. Higher values of oedema or corneal swelling (>6% of corneal thickness) have greater effects on the visual function. It is important to know that the developing of corneal oedema is very variable from one subject to another [29]. Then, it is possible to affirm that the changes on corneal thickness caused by all these soft contact lenses under study are not clinically significant, since none of the lenses studied here introduced changes in corneal thickness above 2% (see Fig. 3). Currently, a big amount of contact-lens wearers are interested in refractive surgery. It is very important then to know the possible changes that the use of contact lenses can cause in the cornea, in order to give better information about the procedure and to obtain the best possible outcome from the surgery. Also, this would provide better knowledge for clinicians to prescribe the best type of contact lens for each subject, depending on their diurnal variations and how their corneas respond to the wear of each lens. In summary, the Galilei G4 device is good for evaluating the changes that different soft contact lenses cause in corneal morphology; particularly in its thickness and in its anterior and posterior corneal curvatures in a quick and non-invasive way. Corneal thickness variation and the changes suffered by corneal curvatures allow us to analyze how well a soft contact lens is fit and how the eye behaves in the case of wearing these kinds of lenses. We measured the natural diurnal variation of all the corneal parameters under consideration and then use these data to obtain the true change in the cornea associated with contact lens wear. The natural diurnal variations in corneal thickness that we measured from mid-morning to afternoon were sometimes larger than the changes caused by different soft contact lenses, and this factor should be considered in short-term studies of contact lens-induced corneal swelling.
Financial disclosure The authors have no proprietary interest in any of the products or devices mentioned in this article. Acknowledgements This research was partly supported by an Atracció de Talent (Universidad de Valencia) research scholarship granted to Antonio
33
J. Del Águila Carrasco and to Alberto Domínguez Vicent, and by a VALi+D research scholarship (Generalitat Valenciana) granted to Cari Pérez Vives. References [1] Yebra-Pimentel E, Giráldez MJ, Arias FL, González J, González JM, Parafita MA, et al. Rigid gas permeable contact lens and corneal topography. Ophthal Physiol Opt 2001;21:236–42. [2] Schwallie JD, Barr JT, Carney LG. The effects of spherical and aspheric rigid gas permeable contact lenses: corneal curvature and topography changes. Int Contact Lens Clin 1995;22:67–79. [3] Tyagi G, Collins M, Read S, Davis B. Regional changes in corneal thickness and shape with soft contact lenses. Optomet Vis Sci 2010;87:567–75. [4] Alba-Bueno F, Beltran-Masgoret A, Sanjuan C, Biarnes M, Marin J. Corneal shape changes induced by first and second generation silicone hydrogel contact lenses in daily wear. Cont Lens Anterior Eye 2009;32:88–92. [5] Snyder C, Schoessler JP. Corneal thickness changes associated with daily and extended contact lens wear. Am J Optomet Physiol Opt 1983;60:830–8. [6] Handa T, Mukuno K, Niida T, Uozato H, Tanaka S, Shimizu K. Diurnal variation of human corneal curvature in young adults. J Refract Surg 2002;18:58–62. [7] Read SA, Collins MJ, Carney LG. The diurnal variation of corneal topography and aberrations. Cornea 2005;24:678–87. [8] Reynolds DR, Poynter III HL. Diurnal variation in central corneal curvature. Am J Optom Arch Am Acad Optom 1970;47:892–9. [9] Cronje S, Harris WF. Short-term keratometric variation in the human eye. Optom Vis Sci 1997;74:420–4. [10] Karimian F, Feizi S, Faramarzi A, Doozandeh A, Yaseri M. Evaluation of corneal pachymetry measurements by Galilei dual Scheimpflug camera. Eur J Ophthalmol 2012;22:33–9. [11] Huang J, Ding X, Savini G, Pan C, Feng Y, Cheng D, et al. A comparison between scheimpflug imaging and optical coherence tomography in measuring corneal thickness. Ophthalmology 2013;120:1951–8. [12] Menassa N, Kaufmann C, Goggin M, Job OM, Bachmann LM, Thiel MA. Comparison and reproducibility of corneal thickness and curvature readings obtained by the Galilei and the Orbscan II analysis systems. J Cataract Refract Surg 2008;34:1742–7. [13] Mertz GW. Overnight swelling of the living human cornea. J Am Optom Assoc 1980;51:211–4. [14] Read SA, Collins MJ. Diurnal variation of corneal shape and thickness. Optom Vis Sci 2009;86:170–80. [15] Harper CL, Boulton ME, Bennett D, Marcyniuk B, Jarvins-Evans JH, Tullo AB, et al. Diurnal variations in human corneal thickness. Bri J Ophthalmol 1996;80:1068–72. [16] Feng Y, Varikooty J, Simpson TL. Diurnal variation of corneal and corneal epithelial thickness measured using optical coherence tomography. Cornea 2001;20:480–3. [17] Du Toit R, Vega JA, Fonn D, Simpson T. Diurnal variation of corneal sensitivity and thickness. Cornea 2003;22:205–9. [18] Boote C, Dennis S, Newton RH, Puri H, Meek KM. Collagen fibrils appear more closely packed in the prepupillary cornea: optical and biomechanical implications. Invest Ophthalmol Vis Sci 2003;44:2941–8. [19] Odenthal MTP, Nieuwendaal CP, Venema HW, Oosting J, Kok JHC, Kijlstra A. In vivo human corneal hydration control dynamics: a new model. Invest Ophthalmol Vis Sci 1999;40:312–9. [20] O’Neal M, Polse KA. In vivo assessment of mechanisms controlling corneal hydration. Invest Ophthalmol Vis Sci 1985;26:849–56. [21] Kaluzny JJ, Orzalkiewicz A, Czajkowski G. Changes of corneal thickness in patients wearing frequent-replacement contact lenses. Eye Contact Lens 2003;29:23–6. [22] Liu Z, Pflugfelder SC. The effects of long-term contact lens wear corneal thickness, curvature, and surface regularity. Ophthalmology 2000;107:105–11. [23] Moezzi AM, Fonn D, Simpson TL, Sorbara L. Contact lens-induced corneal swelling and surface changes measured with the Orbscan II corneal topographer. Optom Vis Sci 2004;81:189–93. [24] Martin R, Izquierdo M, Saber A. Investigation of posterior corneal curvature in CL-induced corneal swelling. Contact Lens Anterior Eye 2009;32:288–93. [25] Hirji NK, Larke JR. Corneal thickness in extended wear of soft contact lenses. Br J Ophthalmol 1979;63:274–6. [26] Schoessler JP, Barr JT. Corneal thickness changes with extended contact lens wear. Am J Optom Physiol Opt 1980;57:729–33. [27] Bonanno JA, Polse KA. Central and peripheral corneal swelling accompanying soft lens extended wear. Am J Optom Physiol Opt 1985;62:74–81. [28] Hess RF, Garner LF. The effect of corneal edema on visual function. Invest Ophthalmol Vis Sci 1977;16:5–13. [29] Sarver MD, Polse KA, Baggett DA. Intersubject difference in corneal edema response to hypoxia. Am J Optom Physiol Opt 1983;60:128–31.
Contents lists available at ScienceDirect
Contact Lens & Anterior Eye journal homepage: www.elsevier.com/locate/clae
Assessment of corneal morphological changes induced by the use of daily disposable contact lenses Antonio J. Del Águila-Carrasco ∗ , Alberto Domínguez-Vicent, Cari Pérez-Vives, Teresa Ferrer-Blasco, Robert Montés-Micó Optometry Research Group (GIO), Department of Optics, University of Valencia, Spain
a r t i c l e
i n f o
Article history: Received 28 January 2014 Received in revised form 5 August 2014 Accepted 28 August 2014 Keywords: Corneal thickness Corneal curvature Daily disposable contact lenses
a b s t r a c t Purpose: To assess the effect of different disposable soft contact lenses upon corneal thickness, and upon anterior and posterior corneal curvatures using a dual-Scheimpflug imaging based device. Methods: Twenty-eight young, healthy subjects wore four different types of daily disposable soft contact lenses on four different days: Dailies Total1, Proclear 1 Day, Clariti 1-Day and 1-Day Acuvue Moist. The lenses had different material and water content. Pachymetry maps and keratometry values were obtained using the Galilei G4 twice a day: one before putting the lens on and one after an eight-hour period of contact-lens wear. Measurements were also recorded without any contact lenses being worn during a day. Results: Clariti 1-Day lens caused the greatest thickening in the central (8.9 ± 2.8 m; p < 0.01) and in the peripheral cornea (10.1 ± 4.6 m; p < 0.01), whereas Dailies Total1 was the lens that had the most similar behaviour to the non-contact lens scenario. All the lenses caused a slight flattening in the anterior corneal curvature, except Clariti 1-Day, which induced a very slight steepening. The four lenses caused a steepening of different magnitude in the posterior corneal curvature. Conclusions: The magnitude of the changes introduced by the use of soft contact lenses over the eighthour wearing period was rather small. Thus it is probable it will not influence the vision nor the comfort of the subject. Also, variations on corneal parameters seem to depend on the type of contact lens used. © 2014 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.
1. Introduction Disposable soft contact lenses are very popular nowadays for people who have refractive errors, such as myopia, hyperopia, astigmatism or presbyopia. There are also contact lenses for aesthetic purposes. It seems logical that disposable soft contact lenses could modify the morphology of the anatomical surface where they are fit: the cornea. There are a lot of studies documenting the changes undergone by the cornea which are induced by the use of contact lenses, both rigid gas permeable [1,2] and soft [3–5] ones. These changes in corneal shape or morphology were evaluated using different techniques. It is also well known that the cornea undergoes through some changes during the day. These changes are natural and happen as a result of the own metabolism of the cornea and the tear layer.
∗ Corresponding author at: Optometry Research Group (GIO), Department of Optics, University of Valencia, C/Dr Moliner, 50, 46100 Burjassot, Spain. Tel.: +34 963544764; fax: +34 963544715. E-mail address: [email protected] (A.J. Del Águila-Carrasco).
The natural modifications experienced by the cornea are generally small in magnitude, but it is important to have them in consideration for clinical – e.g. refractive surgery – and research purposes. The natural diurnal changes suffered by the cornea in its thickness [6,7] and curvatures [8,9] are well studied. In order to comprehend better the changes in corneal shape caused by the wearing of contact lenses, diurnal changes that cornea goes through need to be known. This way, the real modifications that contact lenses introduce in the cornea can be studied. Currently, there are several techniques which allow us to measure the corneal changes previously mentioned. The Galilei G4 (Ziemer, Switzerland) is a non-invasive optical diagnostic system designed for the analysis of the anterior segment of the eye, based on a rotating Dual-Scheimpflug and a Placido tomography system. This device allows the evaluation of the diurnal natural changes undergone by the corneal shape (thickness and curvatures) and also the changes caused by the use of soft contact lenses in a fast and easy way. Disposable soft contact lenses are in constant evolution and there are a wide variety of materials, water content, designs, etc. It is expected that this range of different parameters causes a variety
http://dx.doi.org/10.1016/j.clae.2014.08.004 1367-0484/© 2014 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.
A.J. Del Águila-Carrasco et al. / Contact Lens & Anterior Eye 38 (2015) 28–33
of results in the change of the curvatures and thickness of the cornea. Wearing time and frequency in the use of soft contact lenses may also affect the modifications of these corneal parameters. To the best author’s knowledge, no previous study has been carried out evaluating these changes in corneal shape, using the Galilei G4. The purpose of this study was to evaluate changes that may occur in corneal shape (i.e. curvatures and thickness) as a result of wearing four different types of disposable soft contact lenses during an eight hours period of time. In order to achieve this, a non-invasive technique was performed, using the Galilei G4. This method allows us to determine whether or not corneal parameters suffer modifications over time due to the wearing of each soft contact lens that took part in this study. 2. Methods 2.1. Subjects Twenty-eight left eyes [7] from twenty-eight individuals, 11 male and 17 female, aged from 21 to 36 years (mean: 25.7 ± 5.1 years). Spherical refractive errors ranged between −3.50 and −2.75 diopters (D), being the mean spherical refractive error −3.12 ± 0.24 D. All of the subjects had best-corrected visual acuity of 6/6 or better. None of the subjects were a regular user of contact lenses and they were not using any ocular or systemic medication. They presented clear intraocular media and no known ocular pathology. All patients were informed about the details of this study, and a written informed consent was obtained after verbal and written explanation of the nature and possible consequences of the study, in accordance with the Helsinki Declaration. Institutional Review Board approval was required for this study. Subjects having ocular or systemic disease, ocular surgery history, intraocular pressure higher than 21 mmHg, presence of retinal or optic disc pathology were excluded from this study. A series of preliminary tests were conducted to ensure that all subjects had normal anterior segment, and central corneal thickness. 2.2. Contact lenses Four different types of daily disposable contact lenses, each one from a different commercial brand, were evaluated: Dailies Total1 (Alcon, www.alcon.com), Proclear 1 Day (CooperVision, www.cooopervision.com), 1-Day Acuvue Moist (Johnson & Johnson Vision Care, www.jnjvision.com) and Clariti 1-Day (Sauflon, www.sauflon.com). The main technical specifications of the lenses under evaluation are summarized in Table 1. All the contact lenses used on every subject’s eye were fitted in an optimal or acceptable way and all of them had a power of −3 D. The lens power and total diameter were checked by one of the authors and found to conform to the manufacturers stated tolerances. Subjects wore a different type of contact lens in the left eye on four separate days, during a period of 8 h each day. New lenses were used for each subject and for each trial. All the four types of contact lenses were worn by each study participant in a randomized order. 2.3. Galilei G4 The Galilei G4 is a non-invasive optical diagnostic system designed for the analysis of the anterior segment of the eye, based on a rotating Dual-Scheimpflug and a Placido tomography system. The Galilei uses a monochromatic diode emitting blue light at 470 nm and combines dual Scheimpflug cameras and a Placido disc to measure both anterior and posterior corneal surfaces. During the rotating scan, the Placido and Scheimpflug data of the corneal information are simultaneously obtained. Two Scheimpflug slit images are made by the dual camera from opposite sides of the illuminated
29
slit, and the data are averaged. Meanwhile, the dual camera simultaneously tracks decentration due to eye movements. Studies have reported the Galilei to be highly repeatable and reasonably accurate for measuring corneal thickness [10,11] and corneal curvatures [12]. Anterior and posterior corneal topography and regional corneal thickness were measured using the Galilei G4. Baseline measurements, approximately at 10 am (at least 2 h after subjects reported time of waking, in order to avoid the peak in corneal thickness immediately after waking [13]) and at 6 pm, were taken during two days on the left eye without any contact lenses being worn in order to record each individual’s natural diurnal variations in corneal thickness and curvature. For the contact-lens scenario, measurements of the cornea were also taken twice a day: once before the contact-lens insertion around 10 am; at least 2 h after subjects reported time of waking. The other one was taken around 6 pm, after an eight-hour period of wearing each contact lens, and it was completed within 10 min of lens removal for each lens. A recovery period of 3 days was allowed for the individuals between lenses, in order to let the cornea to restore its normal state in case any changes were caused by the lenses.
2.4. Data analysis Corneal thickness and curvature data were exported from the Galilei. In order to compare the baseline measurements with postlens removal measurements, thickness and curvature difference values were calculated for all the 28 subjects and for each of the four lens types. Also, diurnal changes were obtained calculating the difference between measurements taken in the morning and the ones taken in the afternoon when the subjects were not wearing any lenses. In this study, the data from all the subjects were averaged. A repeated measures analysis of variance (ANOVA) was used to analyze changes in corneal curvature and thickness because of contact lens wear, with lens type, corneal region and time as within-subject factors using SPSS Statistics v.17.0 (www.ibm.com/ software/analytics/spss/). Statistical significance was set at p = 0.05.
3. Results 3.1. Diurnal changes Data was averaged considering two corneal zones: a central and mid-peripheral zone of 5 mm diameter and a peripheral annulus from 5 to 8 mm (Fig. 1a). A significant difference was found between the morning and the afternoon measurements when the subjects were not wearing any contact lenses. The group mean diurnal change in corneal thickness for the non-contact lens scenario showed a significant thinning of −2.0 ± 1.7 m (p = 0.037) in the central corneal region and −4.6 ± 2.8 m (p = 0.012) in the peripheral annular corneal region. Considering the cornea divided in four different zones (nasal, temporal, inferior and superior), as it can be seen in Fig. 1b, a significant thinning was found in each one of the four zones: −1.8 ± 1.6 m for the nasal quadrant, −2.4 ± 2.6 m in the temporal one, −2.0 ± 2.1 m in the inferior one, and −3.1 ± 2.7 m in the superior quadrant. The anterior corneal curvature showed a slight significant steepening of −0.01 ± 0.01 mm (p = 0.047), whereas the posterior corneal curvature exhibited a slight non-significant flattening of 0.01 ± 0.02 mm (p = 0.055). All these changes should and were taken into consideration when analyzing corneal changes using contact lenses, due to their magnitude.
30
A.J. Del Águila-Carrasco et al. / Contact Lens & Anterior Eye 38 (2015) 28–33
Table 1 Main features of the daily soft contact lenses assessed in this study. Parameter
1-Day Acuvue Moist
Dailies Total1
Clariti 1-Day
Proclear 1 Day
FDAa Group Water content Material BOZRb (mm) TDc (mm) tcd (mm) @ −3.00 D DK/te (@ −3.00 D) Design Manufacturer
IV 58% Etafilcon A 8.5 14.2 0.084 26 Spherical lens Johnson & Johnson Vision care
II 33% to >80% Delefilcon A 8.5 14.1 0.09 156 Bicurve lens Alcon
II 56% Filcon II 3 8.6 14.1 0.07 86 Aspheric lens Sauflon
II 60% Omafilcon A 8.7 14.2 0.09 36.6 Aspheric front surface CooperVision
a b c d e
FDA: Food & Drug Administration (USA). BOZR: back optic zone radius. TD: total diameter. tc: central thickness. DK/t: oxygen transmissibility.
Table 2 Central and peripheral corneal thickness variation for all of the contact lenses under study. Lens type
Central mean change (m)
Acuvue Moist Dailies Total1 Clairiti 1 Day Proclear 1-Day
5.6 1.8 8.9 5.0
± ± ± ±
3.0a (p = 0.02) 1.5 (p = 0.11) 2.8a (p < 0.01) 2.9a (p = 0.03)
Peripheral mean change (m) 7.3 3.9 10.1 4.3
± ± ± ±
3.7a (p = 0.01) 2.1 (p = 0.09) 4.6a (p < 0.01) 3.0a (p = 0.02)
a Values that revealed significant changes from baseline after a pair-wise comparison were performed.
3.2. Changes in corneal thickness Repeated measures ANOVA revealed that both type of contact lens and corneal zone (central and peripheral annulus) had a significant effect in corneal thickness after 8 h of lens wear (p < 0.001 and p = 0.012, respectively). The mean change in corneal thickness with each of the four contact lenses is shown in Table 2. It is necessary to remind that these corneal thickness variations are relative to the baseline condition, since diurnal changes existed and were significant. The greatest magnitude of corneal variation in the central zone was caused by the Clariti 1-Day lens, which provoked a thickening of 8.9 ± 2.8 m (1.52 ± 0.48%; p < 0.01). In the peripheral zone, also the Clariti 1-Day lens was the one that caused the greatest
magnitude in corneal variation, being 10.1 ± 4.6 m of thickening (1.60 ± 0.75%; p < 0.01). Dailies Total1 is the lens that induces the smallest variation in both corneal zones (central and peripheral). In order to better illustrate the variations in corneal thickness, data from several zones were averaged. On one hand, Fig. 2 shows profiles of corneal thickness variation for all the contact lenses used in this study and also for the non-contact lens scenario, averaged in four different zones: centre and three consecutives annulus. On the other hand, Fig. 3 shows the same corneal thickness changes, but the data was averaged from nasal, temporal, inferior and superior quadrants, and it represents percentages values. As Fig. 2 shows, the Clariti 1-Day and the 1-Day Acuvue Moist lenses are the ones that introduce the greatest changes in corneal thickness. Changes caused by the Dailies Total1 are quite small, keeping some resemblance with the non-contact lens profile. Fig. 3 shows that the Dailies Total1 lens is the one that barely modifies corneal thickness in any of the quadrants. The other three lenses introduce bigger changes; being the Clariti 1-Day lens the one that introduced the greatest changes in corneal thickness. Another repeated measures ANOVA was run for the case in which the cornea is divided in four quadrants, showing that type of lens and position (nasal, temporal, inferior and superior) had significant effect on corneal thickness (p < 0.001 for both). The greatest thickening appeared in the temporal and inferior quadrants of the cornea with the Clariti 1-Day lens, whereas the smallest changes
Fig. 1. Diagram representing (a) the two areas of the cornea were data were averaged. Central zone is coloured as light green; a darker green represents the peripheral cornea. And (b) the four quadrants in which the cornea was divided for averaging the data for a left eye. N: Nasal, T: Temporal, I: Inferior and S: Superior.
A.J. Del Águila-Carrasco et al. / Contact Lens & Anterior Eye 38 (2015) 28–33
31
Fig. 2. Percentage of variation in corneal thickness for each contact lens under study normalized to the naked eye, after the 8-h wearing period. The data correspond to the central zone (dark grey) and the peripheral zone (lighter grey) of the cornea.
were evident in the temporal and superior quadrants, wearing the Dailies Total1 lens.
3.4. Association between changes in thickness and curvatures
3.3. Changes in anterior and posterior curvatures Anterior and posterior curvature data was averaged from the values given by the Galilei G4. Table 3 shows the mean values of the changes that happened on the anterior and posterior axial corneal curvature relative to the baseline days, for each of the four contact lenses used in this study. Repeated measures ANOVA indicated that type of lens had a significant effect on the change of both curvatures (p = 0.031 and p = 0.005 respectively). Anterior corneal curvature changes were slight and pair-wise comparison revealed that 1-Day Acuvue Moist and Proclear 1 Day introduced significant changes in anterior corneal curvature (p < 0.05). Posterior corneal curvature showed a steepening, and the comparison with the baseline days data revealed that all the contact lenses used in this study, except
Table 3 Variation suffered by the anterior and posterior corneal curvatures for all the lenses under study. Lens type Acuvue Moist Dailies Total1 Clariti 1-Day Proclear 1 Day
Anterior curvature change (mm) 0.02 0.01 −0.01 0.02
± ± ± ±
0.02a (p = 0.03) 0.02 (p = 0.10) 0.02 (p = 0.12) 0.02a (p = 0.03)
for the Dailies Total1, caused significant changes (p < 0.05) in this curvature.
Posterior curvature change (mm) −0.04 −0.01 −0.10 −0.02
± ± ± ±
0.07a (p = 0.01) 0.02 (p = 0.08) 0.03a (p = 0.04) 0.03a (p = 0.02)
a Values that revealed significant changes from baseline after a pair-wise comparison were performed.
Pearson’s correlation and significance were calculated between variables in order to evaluate if changes in corneal thickness, anterior and posterior corneal curvature are associated. There was a very weak and non-significant negative correlation between the changes suffered by the mean corneal thickness (averaged from the whole maps of 8 mm diameter) and the changes in anterior corneal curvature (R2 = 0.17, p > 0.05). A strong negative correlation was found between the changes in the mean corneal thickness and the ones in posterior corneal curvature (also averaged from the whole maps of 8 mm diameter). This correlation resulted nonsignificant (R2 = 0.95, p = 0.058). Hence, no associations can be identified between the changes in corneal thickness and changes in corneal anterior curvature. There could exist a relationship between changes in posterior corneal curvature and modifications in corneal thickness. 4. Discussion The results obtained in this study highlight that the wearing of daily disposable soft contact lenses induces additional changes in corneal morphology (i.e. thickness and curvatures), whose magnitude and pattern depend on the particular lens fitted. Both corneal thickness and corneal curvatures in contact-lens wearing were different from the non-contact lens condition. Dailies Total1 is the lens which yielded similar values than the non-contact lens scenario,
32
A.J. Del Águila-Carrasco et al. / Contact Lens & Anterior Eye 38 (2015) 28–33
Fig. 3. Variation in corneal thickness (%) experienced by each of the four quadrants of the cornea for each contact lens under study.
followed by the Proclear 1 Day lens. Clariti 1-Day lens showed the most different behaviour from the non-contact lens condition. The largest changes suffered by the corneal thickness and corneal curvatures are typically found upon waking [13], as it is reported in previous studies [3]. The diurnal variation in corneal thickness that has been observed here is consistent with previous investigations [3,14–17]. We have found the cornea to suffer a small but significant thinning. These thinning increases as we move to the periphery of the cornea, which could be caused by the stromal collagen fibrils. These fibrils present different arrangement in the central zone of the cornea than in the periphery. According to Boote et al. [18], the diameter of stromal collagen fibrils is the same from the central fibrils and for the peripheral ones, however the fibril spacing is greater in the peripheral cornea. The smallest thinning in the central cornea could be caused by the denser packed of fibrils within this area. A small steepening was found in anterior corneal curvature during the 8 h period, which is consistent with previous studies documenting these changes [3,8]. There are very few studies documenting diurnal changes in posterior corneal curvature. In this case, a small flattening was found, which is in agreement with Tyagi et al. [3] It seems that environmental factors could influence corneal thickness [17]. For example, a reduction in blinking frequency with reading has previously been suggested to have an effect on corneal thickness variations [19]. Low humidity induced by heating systems could affect corneal thickness variations too [20]. Corneal thickness may therefore be either directly affected by environmental factors and/or due to alterations of the functions of the various tissues of the eye in response to these environmental conditions. With regard to the modifications on the corneal thickness and curvatures while disposable soft contact lenses are fitted, it is needed to say that these changes are quite small, but rather
significant, which is why it is important to keep them in consideration for any research or clinical applications. There are a lot of studies evaluating changes in anterior corneal curvature [3,4,22,23] and corneal thickness [3,5,21–23], and a few ones evaluating changes in posterior corneal curvature [3,23,24], caused by the use of different types of contact lenses. The lenses’ parameters (material, water content, etc.), period of wearing and whether the subject wears contact lenses regularly or just occasionally are some examples of factors that have influence in corneal morphology. There are several studies which evaluate extended contact lens wear [25–27]. These studies typically report that under extended wear conditions, cornea experiments a small swelling during the firsts weeks. Then, the cornea deswells gradually until it reaches similar values to those reported before the use of the contact lenses. Obviously, it depends on each subject and the type of lens under consideration. In the present study, we evaluated the changes in corneal thickness and corneal anterior and posterior curvatures caused by the use of disposable soft contact lenses, during a wearing period of 8 h (approximately from 10 am to 6 pm). It is difficult to establish a comparison between the results showed in different studies [3,23] that evaluated changes caused in corneal morphology by the use of contact lenses and the ones obtained here, since they depend on the subjects, the type of lenses under study, and the measurement methods. Still, the changes introduced by the daily use of well fitted soft contact lenses are quite small, sometimes even smaller than the daily variations, which indicate that the design and manufacture of contact lenses are improving. In the present study, Dailies Total1 and Proclear 1 Day are the lenses which modified less the corneal thickness. The anterior corneal curvature showed a slight flattening with all the contact lenses under study, except for the Clariti 1-Day, which introduce a very small steepening. All the four lenses
A.J. Del Águila-Carrasco et al. / Contact Lens & Anterior Eye 38 (2015) 28–33
provoked a steepening in the posterior corneal curvature. The greatest one was caused by the Clariti 1-Day lens. No correlation was found between corneal thickness and anterior corneal curvature; however, a strong but not significant correlation was found between the changes in corneal thickness and in posterior corneal curvature by the use of contact lenses, which would be interesting to analyze in future studies. Corneal swelling or oedema can affect visual quality and visual acuity if it is big enough, so it is very interesting to analyze the corneal swelling that a particular contact lens can induce. The oxygen transmissibility has an essential role in corneal oedema, and it depends on some lens parameters like thickness, material and water content. Hess and Garner [28] studied the effect of corneal oedema on visual function, enlightening that when the cornea swells due to anoxia, visual function is slightly compromised when the change in corneal thickness is about 6%. Visual acuity changed from 6/5 to 6/6 for the clinical Snellen letter chart, and 6% oedema affects as well contrast sensitivity, but only the spatial high frequency region of the contrast function. Higher values of oedema or corneal swelling (>6% of corneal thickness) have greater effects on the visual function. It is important to know that the developing of corneal oedema is very variable from one subject to another [29]. Then, it is possible to affirm that the changes on corneal thickness caused by all these soft contact lenses under study are not clinically significant, since none of the lenses studied here introduced changes in corneal thickness above 2% (see Fig. 3). Currently, a big amount of contact-lens wearers are interested in refractive surgery. It is very important then to know the possible changes that the use of contact lenses can cause in the cornea, in order to give better information about the procedure and to obtain the best possible outcome from the surgery. Also, this would provide better knowledge for clinicians to prescribe the best type of contact lens for each subject, depending on their diurnal variations and how their corneas respond to the wear of each lens. In summary, the Galilei G4 device is good for evaluating the changes that different soft contact lenses cause in corneal morphology; particularly in its thickness and in its anterior and posterior corneal curvatures in a quick and non-invasive way. Corneal thickness variation and the changes suffered by corneal curvatures allow us to analyze how well a soft contact lens is fit and how the eye behaves in the case of wearing these kinds of lenses. We measured the natural diurnal variation of all the corneal parameters under consideration and then use these data to obtain the true change in the cornea associated with contact lens wear. The natural diurnal variations in corneal thickness that we measured from mid-morning to afternoon were sometimes larger than the changes caused by different soft contact lenses, and this factor should be considered in short-term studies of contact lens-induced corneal swelling.
Financial disclosure The authors have no proprietary interest in any of the products or devices mentioned in this article. Acknowledgements This research was partly supported by an Atracció de Talent (Universidad de Valencia) research scholarship granted to Antonio
33
J. Del Águila Carrasco and to Alberto Domínguez Vicent, and by a VALi+D research scholarship (Generalitat Valenciana) granted to Cari Pérez Vives. References [1] Yebra-Pimentel E, Giráldez MJ, Arias FL, González J, González JM, Parafita MA, et al. Rigid gas permeable contact lens and corneal topography. Ophthal Physiol Opt 2001;21:236–42. [2] Schwallie JD, Barr JT, Carney LG. The effects of spherical and aspheric rigid gas permeable contact lenses: corneal curvature and topography changes. Int Contact Lens Clin 1995;22:67–79. [3] Tyagi G, Collins M, Read S, Davis B. Regional changes in corneal thickness and shape with soft contact lenses. Optomet Vis Sci 2010;87:567–75. [4] Alba-Bueno F, Beltran-Masgoret A, Sanjuan C, Biarnes M, Marin J. Corneal shape changes induced by first and second generation silicone hydrogel contact lenses in daily wear. Cont Lens Anterior Eye 2009;32:88–92. [5] Snyder C, Schoessler JP. Corneal thickness changes associated with daily and extended contact lens wear. Am J Optomet Physiol Opt 1983;60:830–8. [6] Handa T, Mukuno K, Niida T, Uozato H, Tanaka S, Shimizu K. Diurnal variation of human corneal curvature in young adults. J Refract Surg 2002;18:58–62. [7] Read SA, Collins MJ, Carney LG. The diurnal variation of corneal topography and aberrations. Cornea 2005;24:678–87. [8] Reynolds DR, Poynter III HL. Diurnal variation in central corneal curvature. Am J Optom Arch Am Acad Optom 1970;47:892–9. [9] Cronje S, Harris WF. Short-term keratometric variation in the human eye. Optom Vis Sci 1997;74:420–4. [10] Karimian F, Feizi S, Faramarzi A, Doozandeh A, Yaseri M. Evaluation of corneal pachymetry measurements by Galilei dual Scheimpflug camera. Eur J Ophthalmol 2012;22:33–9. [11] Huang J, Ding X, Savini G, Pan C, Feng Y, Cheng D, et al. A comparison between scheimpflug imaging and optical coherence tomography in measuring corneal thickness. Ophthalmology 2013;120:1951–8. [12] Menassa N, Kaufmann C, Goggin M, Job OM, Bachmann LM, Thiel MA. Comparison and reproducibility of corneal thickness and curvature readings obtained by the Galilei and the Orbscan II analysis systems. J Cataract Refract Surg 2008;34:1742–7. [13] Mertz GW. Overnight swelling of the living human cornea. J Am Optom Assoc 1980;51:211–4. [14] Read SA, Collins MJ. Diurnal variation of corneal shape and thickness. Optom Vis Sci 2009;86:170–80. [15] Harper CL, Boulton ME, Bennett D, Marcyniuk B, Jarvins-Evans JH, Tullo AB, et al. Diurnal variations in human corneal thickness. Bri J Ophthalmol 1996;80:1068–72. [16] Feng Y, Varikooty J, Simpson TL. Diurnal variation of corneal and corneal epithelial thickness measured using optical coherence tomography. Cornea 2001;20:480–3. [17] Du Toit R, Vega JA, Fonn D, Simpson T. Diurnal variation of corneal sensitivity and thickness. Cornea 2003;22:205–9. [18] Boote C, Dennis S, Newton RH, Puri H, Meek KM. Collagen fibrils appear more closely packed in the prepupillary cornea: optical and biomechanical implications. Invest Ophthalmol Vis Sci 2003;44:2941–8. [19] Odenthal MTP, Nieuwendaal CP, Venema HW, Oosting J, Kok JHC, Kijlstra A. In vivo human corneal hydration control dynamics: a new model. Invest Ophthalmol Vis Sci 1999;40:312–9. [20] O’Neal M, Polse KA. In vivo assessment of mechanisms controlling corneal hydration. Invest Ophthalmol Vis Sci 1985;26:849–56. [21] Kaluzny JJ, Orzalkiewicz A, Czajkowski G. Changes of corneal thickness in patients wearing frequent-replacement contact lenses. Eye Contact Lens 2003;29:23–6. [22] Liu Z, Pflugfelder SC. The effects of long-term contact lens wear corneal thickness, curvature, and surface regularity. Ophthalmology 2000;107:105–11. [23] Moezzi AM, Fonn D, Simpson TL, Sorbara L. Contact lens-induced corneal swelling and surface changes measured with the Orbscan II corneal topographer. Optom Vis Sci 2004;81:189–93. [24] Martin R, Izquierdo M, Saber A. Investigation of posterior corneal curvature in CL-induced corneal swelling. Contact Lens Anterior Eye 2009;32:288–93. [25] Hirji NK, Larke JR. Corneal thickness in extended wear of soft contact lenses. Br J Ophthalmol 1979;63:274–6. [26] Schoessler JP, Barr JT. Corneal thickness changes with extended contact lens wear. Am J Optom Physiol Opt 1980;57:729–33. [27] Bonanno JA, Polse KA. Central and peripheral corneal swelling accompanying soft lens extended wear. Am J Optom Physiol Opt 1985;62:74–81. [28] Hess RF, Garner LF. The effect of corneal edema on visual function. Invest Ophthalmol Vis Sci 1977;16:5–13. [29] Sarver MD, Polse KA, Baggett DA. Intersubject difference in corneal edema response to hypoxia. Am J Optom Physiol Opt 1983;60:128–31.
