Assessment of corneal thickness and tear meniscus during contact-lens wear.

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Assessment of corneal thickness and tear meniscus during contact-lens wear夽 Antonio J. Del Águila-Carrasco ∗ , Teresa Ferrer-Blasco, Santiago García-Lázaro, José J. Esteve-Taboada, 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 20 November 2014 Received in revised form 10 December 2014 Accepted 26 January 2015 Keywords: Corneal thickness Tear meniscus volume Contact lenses OCT Cornea

a b s t r a c t Purpose: To assess the effect of seven different daily disposable contact lenses upon corneal thickness, as well as upon tear meniscus volume, by using optical coherence tomography (OCT). Methods: Thirty-four young healthy subjects wore seven different types of daily disposable soft contact lenses, each for a period of 12 h: Delefilcon A, Nelfilcon A, Omafilcon A, Filcon II3, Narafilcon A, Etafilcon A and Hilafilcon B. Central and mid-peripheral corneal thickness and lower tear meniscus volume (TMV) were measured using an OCT device during contact-lens wear at 4-h intervals throughout a 12-h period. Measurements were also recorded without any contact lenses being worn during a day. Results: In the no-lens scenario a small but significant (p < 0.05) thinning in the cornea was observed after the 12-h period. Overall, as for contact-lens wear, it was the Hilafilcon B lens that caused the greatest thickness increase in the central area, whereas the Etafilcon A caused it in the mid-peripheral cornea. Delefilcon A was the lens that showed the most similar behavior to the naked eye. As for TMV, it decreased with all the lenses, but it was the Delefilcon A lens the one that caused the smallest drop in TMV (p = 0.007). Conclusions: OCT makes it possible to evaluate both corneal thickness variations and TMV changes as a result of contact-lens wear. The changes in corneal thickness hereafter presented are not clinically significant. On the other hand, TMV drop could indicate discomfort for contact-lens users. © 2015 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.

1. Introduction The change in corneal thickness with contact-lens wear can be considered to be a measure of corneal hypoxic stress induced by the contact lenses [1]. Many studies have demonstrated central corneal swelling after short periods of soft-contact-lens wear [2–4]. It is well known that the cornea undergoes small but significant diurnal changes in thickness, the most pronounced of which occur upon awakening [5,6]. Studies have also shown a slight thinning of the cornea as the day progresses (morning to afternoon) [5,7]. Failure to adequately account for these natural corneal diurnal changes can potentially lead to inaccurate outcomes in those studies investigating contact lens-induced corneal changes, for both daily and

夽 This research was supported in part by a Alcon research grant (IIS Grant ID 8645837) and an Atracció de Talent (University of Valencia) research scholarship granted to Antonio J. Del Águila (UV-INV-PREDOC14-179135). The authors have no proprietary interest in any of the products or devices mentioned in this article. ∗ Corresponding author at: 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).

extended-wear conditions. It is important to quantify the possible changes in corneal thickness due to the contact-lens wear, since edema (corneal swelling due to hypoxia) can compromise the visual function [8]. Moreover, contact lenses can also cause changes in the tear film of the eye [9]. Tear volume is essential to preserve a smooth optical surface, corneal health and transparency, among others [10–12]. Tear volume is distributed across three continuous compartments: the cul–de–sac, the conjunctival tear menisci, and the preocular tear film, and it depends on the rates of tear production, drainage, and evaporation. It has been reported that tear meniscus variables, such as height, width, cross-sectional area, and meniscus curvature are useful for the diagnosis of dry eye [13–19]. It is reasonable to use lower tear meniscus parameters as objective indicators of tearfilm status, since Wang et al. [20] showed that upper and lower tear menisci have almost identical volume in healthy eyes. All these structures (cornea, lens, lower tear meniscus, etc.) can be easily assessed nowadays thanks to the various non-invasive techniques that have been developed for the evaluation of the eye’s anterior segment, such as Scheimpflug techniques, Placido’s disc based techniques, optical coherence tomography (OCT), etc. Among them, OCT [21] is one of the most suitable methods to

http://dx.doi.org/10.1016/j.clae.2015.01.010 1367-0484/© 2015 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.

Please cite this article in press as: Del Águila-Carrasco AJ, et al. Assessment of corneal thickness and tear meniscus during contact-lens wear. Contact Lens Anterior Eye (2015), http://dx.doi.org/10.1016/j.clae.2015.01.010

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Table 1 Main features of the daily soft contact lenses assessed in this study. Parameter

Delefilcon A

Nelfilcon A

Narafilcon A

Etafilcon A

Hilafilcon B

Omafilcon A

Filcon II 3

FDA group Water content BOZR (mm) TD (mm) tc (mm) @ −3.00D DK/t (@ −3.00D) Design

II 33% to >80% 8.5 14.1 0.09 156 Bicurve lens

I 46% 8.5 14.2 0.085 118 Spherical lens

IV 58% 8.5 14.2 0.084 26 Spherical lens

II 59% 8.6 14.2 0.09 24 Aspheric lens

Alcon

Johnson & Johnson Vision Care

Johnson & Johnson Vision Care

Bausch & Lomb

II 60% 8.7 14.2 0.09 36.6 Aspheric front surface Cooper vision

II 56% 8.6 14.1 0.07 86 Aspheric lens

Manufacturer

II 69% 8.7 14.0 0.10 26 Tri-curve front and back surfaces Alcon

Sauflon

FDA: food and drug administration (USA); BOZR: back optic zone radius; TD: total diameter; tc: central thickness; DK/t: oxygen transmissibility.

image the human eye’s anterior segment (i.e., cornea and contact lens) [22,23], thanks to its ability to capture cross-sectional (or volumetric) images of tissue with high axial resolution, along with its high-speed acquisition rates. Fourteen studies using OCT technology for contact-lens assessment were recently identified and reviewed in the literature [24]. The aim of this study was to investigate the effect of one-day contact-lens wear upon the central, mid-peripheral corneal thickness and also in the tear meniscus volume. For this purpose, several types of soft contact lenses were evaluated. Moreover, natural (i.e., naked eye; no contact-lens scenario) diurnal changes occurring in corneal thickness were also measured and used as baseline data, which allowed us to provide an accurate measure of the corneal changes directly attributable to the contact lenses. 2. Subjects and methods 2.1. Subjects This study included 34 left eyes from 34 individuals, 15 male and 19 female, aged 23–34 (mean: 25.40 ± 1.94 years). Spherical refractive errors ranged between −3.50 and −3.00 diopters (D) (mean: −3.21 ± 0.18D). They all had clear intraocular media and no known ocular pathologies. All subjects 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 Declaration of Helsinki. Institutional Review Board approval was required for this study. Subjects having best-corrected visual acuity worse than 0.0 logMAR, ocular or systemic diseases, a history of ocular surgery, intraocular pressure above 21 mmHg or presence of retinal or optic disc pathology, were excluded from this study. None of the subjects were regularly using either contact lenses, or any ocular or systemic medication. A series of preliminary tests were conducted to ensure that all subjects had normal tear film (BUT of more than 10 s and Schirmer test score of more than 5 mm) and central corneal thickness. 2.2. Contact lenses In order to have a representative sample of the daily disposable soft contact lenses available in the market, the following seven types of soft-contact lenses from five different lens manufacturers were evaluated: Delefilcon A and Nelfilcon A (Alcon Laboratories, TX, United States), Omafilcon A (CooperVision, CA, United States) Narafilcon A and Etafilcon A (Johnson & Johnson Vision Care, NJ, United States), Hilafilcon B (Bausch & Lomb, NY, United States), and FIlcon II 3 (Sauflon, Twickenham, United Kingdom). The main technical specifications of the lenses under evaluation are summarized in Table 1. The lens power and total diameter were also

rechecked by one of the authors and were found to conform to the manufacturer’s stated tolerances. All the contact lenses used in this study had the same power of −3D, and for each contact lens type and subject, the fitting was performed in an optimal or acceptable way. Subjects wore in their left eye each type of contact lens for 12 h. Each lens type was worn and assessed on a different day, following a randomized order. New lenses were used for each subject and for each trial. 2.3. Ocular coherence tomography The Topcon SL SCAN-1 is a spectral-domain OCT instrument that provides high-resolution cross-sectional images of the posterior and anterior segments of the eye. The SL SCAN-1, using as light source a super-luminescent diode (SLD) with a wavelength of 840 nm, has an axial resolution of 8–9 ␮m, a lateral resolution below 20 ␮m and a scanning speed of 5000 A-scans/s. This device has the following options for scan patterns: horizontal line, vertical line, cross, raster, grid, radial and circle. For each subject, lens type and time of the day, an 6-mm width grid-pattern scan was acquired. This pattern comprises six scanning lines, the distance between adjacent vertical or horizontal lines being 3 mm. With this approach, six scans are obtained with just one simple measure, as shown in the left part of Fig. 1. The central point can be measured with both the vertical and horizontal scans, that is the reason why only five scans are showed in the right part of Fig. 1. The instrument has an eye preview camera to assist with the alignment of the subject. External illumination was used in order to improve the eye preview image quality. 2.4. Corneal thickness Measurements of the cornea were taken four times throughout the 12-h period that the subjects wore each contact lens. The first measurements were taken around 9 a.m., right after the fitting of the contact lens, but we made sure that the subject had been awake for at least 2 h to avoid the well-known corneal thickness peak that occurs immediately after waking up [5]. Then, successive measurements were taken every 4 h, until approximately 9 p.m. After each day of lens wear, the subject was allowed a 2-day recovery period before being fitted with the next lens. Baseline measurements i.e., with the subject wearing no contact lenses were also recorded in a similar manner: on the left eye starting at 9 a.m. until 9 p.m. at 4-h intervals, so as to record each individual’s natural diurnal variations in corneal thickness. All these measures were recorded with the abovementioned OCT device, while the subject was looking at an external fixation target. Three sets of measures were taken at the center of the pupil, using the grid scanning pattern (Fig. 1) where corneal thickness was measured at different positions. Once the set of scans was saved, corneal thickness were measured at the center of the cornea and


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Fig. 1. Grid scan pattern over an eye (left) and the five different tomograms obtained using this pattern (right). The red dots indicate the point where measurements were recorded.

at the center of each scanning line, which corresponds to points that are 3 mm apart from the corneal center in each one of the four cardinal directions (superior, inferior, nasal and temporal). 2.5. Determination of lower tear meniscus volume Following each corneal thickness measurement, three OCT vertical scans were recorded at the center of the lower eyelid, allowing us to see the lower tear meniscus (see Fig. 2). For each scan, the subject was instructed to look straight ahead at an external fixation target while the scan reference was located at the center of the lower eyelid margin, at around the 6-o’clock position from the corneal center. The scan was recorded approximately 6 s after the subject’s blinking since, according to the literature [25], it is at this time when film stability in normal subjects is achieved. All measurements were taken under the same illumination and temperature conditions. The initial measurement (0 h) was taken approximately 15–20 min after the lens was fitted so as to avoid the peak in TMV that occurs as result of the lens insertion [26]. The

volume of the meniscus was calculated from the local area conformed by the tomogram obtained from the OCT system (Fig. 2), assuming a uniform distribution [27] of the tear meniscus across the lower eyelid (this assumption may not always be correct, however, if tear film volume is not optimal or if the contact lens lead to a disruption of the tear film) and using the software ImageJ (http://imagej.nih.gov/ij/), which allows us to calculate the area of interest. As was suggested by Tiffany et al. [28], a factor of 1.294 was included in the calculation in order to compensate for the eyelid’s curvature. Therefore, tear meniscus volume (TMV) was computed as follows TMV = Area (␮m2 ) · lower eyelid length (␮m) · 1.294 The lower eyelid length was measured from a photograph of each eye with a reference scale and using also the software ImageJ. All measurements were taken by the same observer in order to avoid potential variations in tear film meniscus volume due to interobserver differences, as reported by Bitton et al. [29].

Fig. 2. OCT B-Scans showing the lower tear meniscus without wearing any contact lens (left) and wearing a soft contact lens (right). A detail of the measurement of the lower tear meniscus’ area with ImageJ is shown in the left image. C: cornea; LTM: lower tear meniscus; L: lens.




Fig. 3. Central corneal thickness variations for each contact lens under study, including the no-contact lens condition, in the three time intervals.

2.6. Statistical analysis All the data collected from the subjects’ left eyes were analyzed using the SPSS Statistics software v.17.0 (www.ibm.com/ software/analytics/spss/). For each scenario, the differences in corneal thickness for each time interval were calculated by subtracting the initial value to the final one and then the average of the three subtractions was performed. Values of tear meniscus volume were calculated as the mean of three repeated measurements. After normality of the data was verified by means of the Kolmogorov–Smirnov test, a two-way repeated measurements analysis of variance (ANOVA) of 8 (seven contact lenses plus naked eye scenario) × 3 (three different time intervals) factorial analysis was performed for the center measurements and another for the mid-peripheral ones. In one case, the dependent variable was the variation in corneal thickness, while in the other it was the tear meniscus volume. Multiple comparison tests with the Holm Sidak method were performed when the two-way repeated measurements ANOVA revealed differences. Statistical significance was set at p = 0.05. 3. Results 3.1. Changes in corneal thickness Corneal thickness variation occurring over the course of the day was calculated by subtracting the initial value (9 a.m.) from the final one, recorded once the 12-h wearing period was over (9 p.m.). For the thirty-four subjects that took part in this study, the mean variation in corneal thickness for the no-contact lens scenario amounted −3.7 ± 3.3 ␮m for the center of the cornea and −5.7 ± 3.1 ␮m for the mid-periphery, indicating that both areas experienced a small but significant (p = 0.01 and p = 0.004) thinning. Fig. 3 shows a plot of central corneal thickness variations for each contact lens under study and in the three different time intervals (0–4 h, 4–8 h, 8–12 h). Each color corresponds to either one of

the seven daily disposable contact lenses analyzed in this study or the no-contact lens scenario. A general look at Fig. 3 reveals that the central corneal thickness tends to decrease slightly, starting from the second time interval (around 4 h) toward the end of the day. The plot also reveals that there are differences across lenses: the Delefilcon A lens was the one that modified the least the central corneal thickness regardless the time interval, while, in general, the Hilafilcon B was the lens which had greater differences with respect to the naked eye. Statistical analysis of these values (two-way repeated measurements ANOVA) revealed differences across groups and interactions between both factors, namely type of contact lens and time interval (p = 0.013). Multiple pairwise comparison by means of the Holm Sidak method showed that, for the first time interval (0–4 h), Etafilcon A, Hilafilcon B and Filcon II 3 lenses were statistically different from the no-contact lens scenario (p = 0.003, p < 0.001 and p = 0.003, respectively), whereas the other lenses did not show significant differences with respect to the naked eye. For the second time interval (4–8 h), the lenses that presented significant differences with regard to the naked eye were the Nelfilcon A and the Etafilcon A (p = 0.002 and p < 0.001). The values obtained in the last interval (8–12 h) were significantly different from those acquired in the naked eye condition, except for the Delefilcon A and the Omafilcon A lenses (p > 0.05). Furthermore, similarly to Fig. 3, Fig. 4 also depicts corneal thickness variations for each one of the contact lenses under study, but in this case they correspond to the mid-peripheral zone (3 mm away from the center). It is clear that the Delefilcon A, Omafilcon A and Nelfilcon A are the lenses whose behavior is most similar to the naked eye scenario; that is, they are the ones that induce the smallest modifications to the mid-peripheral cornea. On the contrary, Etafilcon A lens yielded the highest mid-peripheral corneal thickness variations, especially during the first 4 h of wearing. The two-way repeated measurements ANOVA of these mid-peripheral values, revealed again differences across groups and interactions between both factors; namely type of contact lens and time interval (p = 0.02). Multiple pairwise comparison by means of the Holm




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Fig. 4. Mid-peripheral corneal thickness variations for each contact lens under study, including the no-contact lens condition, in the three time intervals.

Sidak method showed that, in the first time interval (0–4 h), the only two lenses that did not differ significantly from the naked eye scenario were the Delefilcon A and the Nelfilcon A (p > 0.05). Contrariwise, for the other four types of contact lenses, statistically significant differences were observed relative to the no-contact lens scenario (p < 0.05). Omafilcon A and Filcon II 3 were the lenses that did not show significant differences with respect to the no-contact lens condition in the second interval (8–12 h). In the last interval (8–12 h), Narafilcon A was the only lens which showed significant differences from the naked eye scenario (p < 0.001). To better illustrate the change in corneal thickness caused by each type of daily disposable contact lens after the whole diurnal wearing period, Fig. 5 shows for each lens under evaluation, the variation in corneal thickness during the whole period of measurements (12 h). It is important to notice that the horizontal axes in this figure are located in the variations values experienced by the naked eye in each corneal area. For both central corneal thickness and mid-peripheral corneal thickness, Delefilcon A, Omafilcon A and Nelfilcon A showed the lowest variation, while Hilafilcon B showed the highest variation for central corneal thickness and Etafilcon A for the mid-peripheral cornea. Nevertheless, none of the contact lenses under study induced a percentage variation in corneal thickness above 1.5%. 3.2. Tear meniscus volume Values for the TMV and its standard deviation for every scenario can be found in Table 2. Fig. 6 represents TMV as a function of the measuring time for each contact lens under evaluation, plus the no-contact lens scenario. A first look reveals that when the subject wears no contact lens TMV values remain almost unchanged over the 12 h period. A similar trend is observed with the Etafilcon A and the Filcon II 3 lenses, although the TMV values are quite lower. In fact, these two lenses are the ones that caused the greatest drop in TMV compared to the no contact lens scenario. An interesting

finding is that wearing contact lenses, regardless of the specific type, leads to a decrease in TMV relative to the no-contact lens scenario. The two-way repeated measurements ANOVA shows that type of lens and also wearing time have both a significant influence upon the change in TMV (p < 0.05). Multiple pairwise comparisons by means of the Holm Sidak method revealed that TMV values for the seven contact lenses under test are significantly different from the no-contact lens scenario. Also, it reveals that Delefilcon A, Omafilcon A and Nelfilcon A present the highest values of TMV from all the seven lenses; while Filcon II 3 and Etafilcon A have the lowest values of TMV. To illustrate the changes in TMV as a function of the contact lens analyzed and wearing time, Fig. 7 displays a set of tomograms showing the lower tear meniscus from the left eye of the same subject wearing each one of the seven different lenses at the four measuring times. 4. Discussion It is a well-known fact that the cornea swells over night [30–34], reaching its peak thickness upon waking. Following sleep, it takes an average of 2 h for the cornea to deswell [33,35]. This is the reason why the first measure of each day was taken at least 2 h after the reported time of awakening. In this study, small but significant diurnal changes on corneal thickness were found (without lens wearing) both at the center and in the mid-periphery. The majority of studies [6,7,36–38] that evaluate diurnal changes in corneal thickness agree that corneal thickness slightly decreases during the day, until it starts swelling during the night. For example, Feng et al. [7] reported a central corneal thinning of −4.24 ␮m for the control group. The first measurement was taken at 8.30 a.m. and the last one, at 4.30 p.m. du Toit et al. [6] also reported a small central corneal thinning during the day, although this study stated that from 2 p.m. onward corneal thickness did not show any significant changes until the subsequent night swelling. Read and Collins [5] also found a thinning of the cornea both in the center and


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Fig. 5. Variation in corneal thickness for each contact lens under study after 12-h wearing period. The data correspond to the center of the cornea (left) and the mid-periphery (right). The horizontal axis has been displaced to the value corresponding to the naked eye for more clarity.

Table 2 Lower tear meniscus volume for every lens under study (and for the no contact lens scenario) at different wearing times. Each value represents the average volume and the standard deviation. Lens material Wearing time (h)

Naked eye Delefilcon A Lower tear meniscus volume (␮L)

0 4 8 12

1.08 1.09 0.99 1.07

± ± ± ±

0.29 0.26 0.15 0.17

1.05 1.04 0.90 0.82

± ± ± ±

0.17 0.21 0.20 0.19

Nelfilcon A 0.89 0.85 0.77 0.77

± ± ± ±

0.23 0.20 0.12 0.18

Narafilcon A 0.78 0.78 0.69 0.60

in the mid-periphery. They analyzed the variations in the course of a 24-h period, but from the data it can be inferred that from early in the morning until 12 h later (from around 9 a.m. to 9 p.m.), the corneal thinning ranges between 3 and 4 ␮m at the center of the cornea, and between 4 and 5 ␮m for the mid-peripheral area. These values are very similar to the ones obtained in the present study, despite the fact that their measuring areas were different from ours (they measured corneal thickness in a central area with a radius of 3.5 mm, and in a peripheral annulus from 3.5 mm to

± ± ± ±

0.31 0.25 0.21 0.21

Omafilcon A 0.90 0.95 0.88 0.80

± ± ± ±

0.18 0.26 0.24 0.27

Filcon II 3 0.60 0.56 0.55 0.51

± ± ± ±

0.30 0.27 0.21 0.23

Hilafilcon B 0.82 0.80 0.60 0.66

± ± ± ±

0.15 0.22 0.23 0.20

Etafilcon A 0.65 0.60 0.61 0.52

± ± ± ±

0.19 0.21 0.26 0.21

7 mm). Tyagi et al. [36] analyzed the diurnal variation in corneal thickness in a similar way. The main difference was that the measures were taken during an eight-(instead of twelve-) hour period and that, in this case, the central zone had a 4 mm radius and the peripheral annulus had an inner radius of 4 mm and an outer one of 8 mm. They reported a diurnal thinning of 7.9 ± 1.0 ␮m for the central zone, and of 9.3 ± 1.7 ␮m in the periphery. These values are slightly higher than ours, probably due to their measuring areas being bigger, since corneal thickness variations seem to be bigger

Fig. 6. Tear meniscus volume (TMV) values as a function of the wearing time (h) for each contact lens under study and for the no-contact lens scenario.




Fig. 7. Lower tear meniscus (LTM) as a function of wearing time (h), for each of the contact lenses under study. All images correspond to the same subject (subject #3).


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as the distance to the corneal center increases. Knowledge of the diurnal changes experimented by corneal parameters is necessary for any clinical or research task that requires accurate and precise measurements of the cornea. Also, it is important to compare these diurnal variations with the measurements obtained while contact lenses are fitted in the eye, in order to assess the real change (due to the contact lens only) experimented by corneal thickness. Regarding the variation in corneal thickness while wearing contact lenses, it is highly important to mention that measuring corneal thickness with a contact lens using OCT leads to a wrong result, due to the appearance of distortions as a result of the difference between the refractive indexes of the contact lens and the cornea [39,40]. This is the reason why we chose differences of corneal thickness as our data to analyze, since when two corneal thickness (measured with the same contact lens) values are subtracted, the distortion does not play any role. Also, by doing it in this way, there is no need to manipulate the contact lens every 4 h until the end of the 12 h period. It is also important to bear in mind the fact that the thickness profile of −3 D contact lenses may be assumed to increase toward the periphery, thus reducing Dk/t and increasing the risk of peripheral edema. Since the area considered in this study is the mid-periphery, changes here could not be as noticeable as in the periphery. Now the question to answer is: does the wearing of soft contact lenses for a 12-h period modify the normal diurnal variation in corneal thickness that occurs in the naked eye? Our results indicate that wearing daily disposable soft contact lens slightly modifies the pattern of diurnal variation of corneal thickness. The magnitude of this change depended on the specific lens model that the eye was fitted with (ranging from 0.1% to 1.3%). The important fact here is that no lens induced more than 1.3% of corneal thickness variation, because the incidence of corneal edema is negligible when corneal thickness increase is below 6%. Hess and Garner [8] studied the effect of corneal edema upon visual function, concluding that corneal swelling due to hypoxia leads to a slightly compromised visual function only when the change in corneal thickness exceeded 6%. In those cases, visual acuity (clinical Snellen letter chart), changed from 6/5 to 6/6. Edema also had an impact upon contrast sensitivity, but only for high spatial frequencies. More severe edema or corneal swelling (>6% of corneal thickness) have a greater impact upon the visual function. It has to be kept in mind that some subjects are more prone than others to developing corneal edema [41]. Consequently, it can be stated that the changes in corneal thickness caused by all these soft contact lenses under study are not clinically significant, since none of them induced a corneal thickness variation that was even close to the 6% threshold established by Hess and Garner [8]. There are several studies that analyzed morphological changes of the cornea after using contact lenses. Some of them use rigid gas permeable (RGP) contact lenses [42,43]. Up to date, there is no other study in the literature that had analyzed the change of corneal thickness induced during the course of the day by different types of daily disposable soft contact lenses, using OCT. Tyagi et al. [36] compared two types of spherical soft contact lenses (without providing brands or models) when worn for an 8-h period. They observed a small thinning in the central zone. However, since this behavior depends on the type of contact lens, we cannot draw further conclusions. We decided to expand the wearing period to 12 h, because daily disposable soft contact lenses are currently very popular and there are plenty of people who usually wear them for increasingly longer periods of time. Kaluzny et al. [4] studied changes in corneal thickness after long periods of frequent-replacement contact lens wear, observing a corneal swelling after 2 weeks of wear, which normally subsided after 6 weeks of wear. In the periphery the changes were bigger, which generally is in agreement with our results. Alonso-Caneiro

et al. [44] studied with OCT corneoscleral morphology after soft contact-lens wear, but they analyzed several layers of the corneoscleral junction and proximities, which cannot be compared with our results. Regarding tear volume, as it has already been mentioned, it is essential for many functions in eye health. Lower meniscus parameters can be used as objective estimators of tear films status. The goal here was to evaluate how the wearing of soft contact lenses alters the eye’s tear volume. For this purpose we measured the lower tear meniscus volume (LTMV). Naked eye (i.e., no contact lens) TMV values obtained here are similar to those provided by García-Lázaro et al. [45] (1.35 ± 1.18 ␮L). However, the values of LTMV obtained by Li et al. [46] are quite lower than ours. They determined TMV (both upper and lower) over 8-h period. Even the TMV from the normal group of patients was lower (ranging between 0.37 ± 0.28 ␮L and 0.53 ± 0.43 ␮L) than the values obtained in this study. Our results are consistent with the ones published previously in some studies [47–50], which stated that tear meniscus volume decreased in contact lens wearers and the thickness of the tear film decreased as well after the insertion of a contact lens. As it is already known, tear volume is variable and difficult to determine, as it depends on many factors, which may explain the discrepancies across studies. Wang et al. [26] measured the upper and lower tear menisci areas, which are proportional to the volume of both menisci, comparing two different soft contact lenses with the naked-eye (i.e., no contact lens) scenario. They found that the TMV increased in the moment of the lens insertion (relative to no-contact lens wear). Nevertheless, after 20 min of wear, TMV values were lower than the ones obtained in the naked-eye scenario. This is the reason why we decided to take the first TMV measurement (0 h) approximately 15–20 min after lens insertion, since our main interest was to evaluate the behavior of the TMV during the wearing time. This increase in TMV is probably due to reflex tearing upon insertion. Etafilcon A and Filcon II 3 were the daily disposable contact lenses that affected most the volume of the tear meniscus, cutting it almost by half. Probably this fact is due to the geometry of the lenses or to some of the contact lens surface properties such as ionicity, wettability, etc. For instance, an unstable pre-lens tear film on a lens of low wettability may rapidly flow toward the menisci and/or evaporate. Also, with the lens in place the geometrical configuration of the region used to determine tear film area is different (the area previously occupied by tear film is now occupied by a contact lens). This may partially explain the reduction in tear volume aforementioned described. Delefilcon A was the lens which modify the least the behavior of the TMV relative to the no-contact lens scenario. Tear volume is a very important parameter regarding the comfort of the contact-lens wear. If TMV values drop, it could indicate discomfort in the contact-lens wear [51]. Some studies analyzed the possible variations on optical quality [52] and on visual performance [53] of daily disposable contact lenses during the day. In summary, corneal thickness variations are present, although their magnitude is quite small; however changes in tear meniscus volume are more noticeable. Material, water content and other lens parameters seems to play an important role in morphological changes of the cornea and in the quantity of the tear as well. The knowledge of changes in corneal thickness and, especially in TMV while wearing a particular type of daily disposable soft contact lens provides information about comfort and corneal health [51] and could provide valuable information for eye care practitioners, like which type of soft contact lens is better for a particular subject, especially when wearing time is considered. Differences in corneal thickness and in TMV variations could be attributed to inherent lens properties, such as material and water content. Whether or not these differences translate into clinically relevant outcomes has yet to be determined.




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Meniscus tear surgery and meniscus replacement.

Correlation between tear osmolarity and tear meniscus.

Prominent Decrease of Tear Meniscus Height With Contact Lens Wear and Efficacy of Eye Drop Instillation.

Corneal thickness in extended wear of soft contact lenses.

Measurement of central corneal thickness and pre-corneal tear film thickness of rabbits using the Scheimpflug system.

Ipsilateral Medial and Lateral Discoid Meniscus with Medial Meniscus Tear.

The Wear and Tear of Medical Life.

The wear and tear of teeth.

Tear calcium levels and contact lens wear.

Optical Coherence Tomography Reveals Changes to Corneal Reflectivity and Thickness in Individuals with Tear Hyperosmolarity.

Assessment of tear meniscus with optical coherence tomography in thyroid-associated ophtalmopathy.

Tear plasmin activity with contact lens wear.

A Special Tear Pattern of Anterior Horn of the Lateral Meniscus: Macerated Tear.

Anterior horn lateral meniscus tear, repair, and meniscectomy.

Tear meniscus dimensions in tear dysfunction and their correlation with clinical parameters.

Discoid Medial Meniscus Tear, with a Literature Review of Treatments.

The double bucket handle tear of the medial meniscus.

Automatic dynamic tear meniscus measurement in optical coherence tomography.

Second-look arthroscopic assessment and clinical results of modified pull-out suture for posterior root tear of the medial meniscus.

Wear and tear injuries in athletes--an overview.

Medial meniscus posterior root tear: a comprehensive review.

Quantitative tear meniscus cytology versus quantitative conjunctival fluid cytology.

Effect of hydrogel lens wear on tear film stability.

Assessment of lower tear meniscus measurements obtained with Keratograph and agreement with Fourier-domain optical-coherence tomography.