C L I N I C A L
A N D
E X P E R I M E N T A L
OPTOMETRY RESEARCH PAPER
Rigid gas-permeable contact lens related life quality in keratoconic patients with different grades of severity Clin Exp Optom 2015; 98: 150–154 Ye Wu MM Qi Tan MM Wenqiu Zhang PhD Jianglan Wang PhD Bi Yang PhD Wei Ma MM Xue Wang MM Longqian Liu MD PhD Department of Optometry, West China School of Medicine, Sichuan University, Chengdu, Sichuan Province, China E-mail: [email protected]
Submitted: 14 June 2014 Revised: 22 July 2014 Accepted for publication: 14 September 2014
DOI:10.1111/cxo.12237 Purpose: The aim was to compare the impact of rigid gas-permeable (RGP) contact lenses on vision-related quality of life (VR-QOL) in keratoconic patients with different grades of severity. Methods: This comparative study was conducted from December 2012 to September 2013 on 46 patients with bilateral keratoconus. Patients were divided into three groups according to the average of the steep keratometry (K) readings in the two eyes of each patient. Main outcome measures included binocular visual acuity (VA), lens wearing time, the 25-item National Eye Institute Visual Function Questionnaire (NEI-VFQ-25), foreign body (FB) sensation, comfort and overall satisfaction. Results: Patients with severe keratoconus showed significantly reduced wearing time compared with the other two groups (4.8 ± 2.5 hours per day). Regarding the subjective criteria, there was no significant difference on NEI-VFQ-25 scores, foreign body sensation, comfort and overall satisfaction between mild and moderate keratoconus groups but scores in the group with severe keratoconus were significantly lower than the other two groups. Binocular VA strongly correlated with NEI-VFQ-25 scores; however, NEI-VFQ-25 scores had no significant correlations with different disease severities. Conclusions: Appropriate correction with RGP lenses contributes to good VR-QOL for keratoconic patients; however, as the disease progresses to a steep keratometric value of more than 52 dioptres (6.50 mm), RGP lenses did not guarantee a relatively good VR-QOL. Other lens options with new designs might bring better life quality for these patients with severe keratoconus.
Key words: contact lenses, keratoconus, rigid gas-permeable, vision-related quality of life Keratoconus is a non-inflammatory, degenerative disease of the cornea, in which the cornea becomes progressively thinner, more distorted and steeper in curvature.1 These corneal changes may lead to irregular astigmatism and corneal scarring.2 The disease usually presents at puberty and may progress until later stages of life. Although the disease rarely results in blindness, the burden of decreased vision and its unpredictable characteristic changes can lead to a significant impact on the daily lives and mental development of young patients.3–6 Increasingly, patient-reported outcomes are being used to estimate the impact of ocular disease on vision-related quality of life (VR-QOL), which includes not only the biologic status of disease but also the full range of outcomes, such as mental health, social function and role difficulties. The National Eye Institute Visual Function Questionnaire-25 (NEI-VFQ-25) has been Clinical and Experimental Optometry 98.2 March 2015
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used widely to assess visual function of patients with various ocular disorders, such as glaucoma, cataract and retinal detachment.7–9 In the early stages of keratoconus, vision can be managed with spectacles but as the disease progresses, rigid gas-permeable (RGP) contact lenses are preferred for reducing distortion and providing better vision. Although RGP lenses are the primary method of non-surgical visual correction in keratoconic patients, a considerable number of more advanced cases can feel uncomfortable with RGP lenses due to the corneal irregularity and the inability to obtain an acceptable lens fit.10–12 Because of these factors, advanced cases may suffer symptoms of contact lens intolerance, unsatisfactory visual acuity (VA) and a generally poor quality of life. To our knowledge, no previous studies have evaluated the impact of RGP lenses on VR-QOL among patients
with different grades of keratoconus. Therefore, we performed this study to compare RGP lens-related VR-QOL in keratoconic patients with different grades based on objective and subjective performances, with the aim of improving the knowledge of the impact of RGP contact lens wear on the subjective aspects of daily living activities in keratoconic patients, and contact lens management options. MATERIALS AND METHODS
Subjects This prospective study was approved by the local ethics committee and written informed consent was obtained from all patients. Patients with bilateral keratoconus who attended the contact lens clinic in the West China Hospital of Sichuan University from December 2012 to September 2013 were © 2014 The Authors
Clinical and Experimental Optometry © 2014 Optometry Australia
RGP contact lens-related quality of life in keratoconus Wu, Tan, Zhang, Wang, Yang, Ma, Wang and Liu
enrolled. All the patients had been diagnosed with keratoconus by an ophthalmologist and referred to this clinic for RGP lens management rather than surgery. We excluded patients with a history of intraocular or corneal surgery, including penetrating keratoplasty (PK) or other ocular diseases, such as cataracts, retinal disease or glaucoma.
assessed on a slitlamp with fluorescein. The fit was judged to be good if there was apical clearance, or mild apical touch, good centration and adequate edge lift. If the ordered lenses gave an acceptable fit, vision and comfort, the patient was scheduled for the one-month study visit.
Statistical analyses Measurement protocol Corneal topography was performed using the Tomey KC screening system (Tomey Corporation, Tokyo, Japan). Patients were divided into three groups according to the average of the steep keratometry (K) readings in the two eyes of each patient: mild (average Sim K less than 45 D; 7.50 mm), moderate (average Sim K 45 to 52 D; 7.50 to 6.20 mm) and severe (average Sim K more than 52 D; 6.20 mm).13–14 All the recruited patients used RGP lenses for the first time. Demographic characteristics were documented based on medical records. Binocular VA and NEI-VFQ-25 scores were evaluated after one month of adaptation to RGP lenses. Binocular VA was measured using the Early Treatment Diabetic Retinopathy (ETDRS) chart. Results were reported as the number of letters correct, then adding zero (for testing at one metre) or plus 30 (for testing at four metres).15 A Chinese version of the NEIVFQ-25, which has been proven to be a reliable and valid tool in a previous study,16 was administered to all patients. The NEIVFQ-25 consists of 25 items that constitute 12 subscales. The scale scores were computed based on the algorithm developed by Mangione and colleagues17 and ranged from zero (worst) to 100 (best). After three months of RGP lens-wear, patients were asked to verbally grade the performance of RGP lenses using a Likert scale18,19 (in which 1 represents very poor and 5 represents excellent) with respect to foreign body sensation, comfort and overall satisfaction. Additionally, regarding lens wearing time, patients were asked to state how many hours a day they had been wearing the lenses. RGP lens designs available in our clinic were as follows: standard keratoconic (FreshKon, Shanghai, China), Rose K design (FreshKon, Shanghai, China), standard spherical surface and back surface multicurve design (Menicon Z E-1, Menicon, Nagoya, Japan). The patients were fitted with suitable RGP lenses and then
Descriptive data were presented as mean and standard deviation and percentages. We used non-parametric tests when the data were not normally distributed. There were no statistical differences in age and educational level among the groups. After adjustment for gender, binocular VA, lens-wearing time, NEI-VFQ-25 scores, foreign body sensation, comfort and overall satisfaction were compared among the different grades of keratoconus by using the Kruskal–Wallis H test. Spearman rank correlation analysis was performed to evaluate the relationship between NEI-VFQ-25 scores and clinical variables, including binocular VA and disease severity classification. A p-value less than 0.05 was considered statistically significant. To reduce the rate of false negatives, Bonferroni correction was used for multiple testing. Statistical analyses were performed with SPSS 18.0 for windows SPSS Inc, Chicago, Illinois, USA).
RESULTS A total of 53 Chinese patients were diagnosed with bilateral keratoconus in our contact lens clinic. Of these, four patients refused to wear RGP lenses due to lack of affordability or intolerance of the rigid lens material and three patients were lost to follow-up after dispensing the RGP lenses. Therefore, 46 of the 53 patients (87 per cent) were actually included in all analyses. The mean age of the participants was 23.2 ± 6.5 years (range, 16 to 40 years). There were more male patients in the sample (30 of 46, 65 per cent). Nine patients had mild, 19 patients had moderate and 18 patients had severe keratoconus. The mean binocular VA scores in mild, moderate and severe keratoconus groups were 89.7 ± 6.2 (Snellen equivalent 6/6), 82.1 ± 9.4 (Snellen equivalent 6/7.5) and 73.3 ± 8.6 (Snellen equivalent 6/12) respectively (Kruskal–Wallis H test, p < 0.001). As the majority of patients did not drive (for non-eye-related reasons), we omitted
© 2014 The Authors Clinical and Experimental Optometry © 2014 Optometry Australia
this subscale according to the suggestion of a previous study.16 Table 1 shows the results of the NEI-VFQ-25 scores. There was no significant difference on subscale scores between mild and moderate keratoconus groups; however, the NEI-VFQ-25 scores in both of the groups were significantly higher than in the severe keratoconus group, except the score for ‘colour vision’ (Kruskal–Wallis H test with Bonferroni correction for multiple testing, p < 0.001). Comparing foreign body sensation, comfort and overall satisfaction, the differences between mild and moderate keratoconic groups were borderline significant (p = 0.051, p = 0.062 and p = 0.059, respectively), with significantly lower scores in the advanced keratoconus group as shown in Table 2 (Kruskal–Wallis H test with Bonferroni correction for multiple testing, p < 0.001). The mean and SD lens wearing time in mild, moderate and severe keratoconus groups were 10.4 ± 1.4 hours per day, 9.6 ± 1.7 hours per day and 4.8 ± 2.5 hours per day, respectively (Figure 1). Table 3 presents the correlations between NEI-VFQ-25 scores and binocular VA against disease severity classification. NEI-VFQ-25 scores correlated significantly with binocular VA except those for ‘colour vision’ and ‘ocular pain’. All the correlation coefficients (r) were greater than 0.7 except that for ‘general health’ (p < 0.001). There was no significant correlation between the NEIVFQ-25 scores and mild, moderate or severe keratoconic groups (p > 0.05).
DISCUSSION RGP lenses provide keratoconic patients with better visual performance and greater reduction of ocular aberrations compared to soft contact lenses or spectacles.20 RGP lenses mask the underlying irregular corneal surface and provide excellent tear exchange but may be uncomfortable to wear for most of the patients with severe keratoconus.10–12 Therefore, it is of great significance to evaluate RGP contact lensrelated functional abilities in daily activities of keratoconic patients with different severity grades. These findings may prove beneficial to ophthalmologists and optometrists given that they provide the patients’ perspectives, which can be integrated into the decision-making process for any treatment being planned, such as penetrating keratopasty. Clinical and Experimental Optometry 98.2 March 2015
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RGP contact lens-related quality of life in keratoconus Wu, Tan, Zhang, Wang, Yang, Ma, Wang and Liu
Subscale
Mild
Moderate
Severe
Overall p-value
Multiple test
(n = 9)
(n = 19)
(n = 18)
(Mean ± SD)
(Mean ± SD)
(Mean ± SD)
General health
83.0 ± 8.2
82.6 ± 11.3
60.5 ± 14.1
p < 0.001
a, b‡, c‡
General vision
87.4 ± 9.8
83.9 ± 10.2
63.3 ± 13.5
p < 0.001
a, b‡, c‡
Ocular pain
61.3 ± 12.5
59.9 ± 9.1
37.4 ± 16.8
p < 0.001
a, b‡, c‡
Near activities
94.7 ± 13.6
90.3 ± 10.7
72.1 ± 11.0
p < 0.001
a, b‡, c‡
Distance activities
90.4 ± 6.6
87.7 ± 16.0
68.8 ± 18.4
p < 0.0011
a, b‡, c‡
Social function
94.6 ± 14.1
91.3 ± 16.2
66.2 ± 15.9
p < 0.001
a, b‡, c‡
Mental health
77.1 ± 11.6
75.6 ± 15.5
51.4 ± 12.8
p < 0.001
a, b‡, c‡
Role difficulties
84.8 ± 11.7
83.1 ± 10.0
61.5 ± 16.6
p < 0.001
a, b‡, c‡
Dependency
91.6 ± 15.1
87.0 ± 17.8
62.7 ± 18.5
p < 0.001
a, b‡, c‡
Colour vision
99.3 ± 8.4
97.9 ± 9.8
94.3 ± 10.7
p < 0.05
a, b, c
Peripheral vision
93.3 ± 11.9
91.4 ± 8.9
78.2 ± 10.1
p < 0.001
a, b‡, c‡
a: mild versus moderate group, b: moderate versus severe group, c: mild versus severe group. Those significant at the 0.05 level are marked by *, those significant at the 0.01 level are marked by † , those significant at the 0.001 level are marked by ‡.
Table 1. Analysis on National Eye Institute Visual Function Questionnaire (NEI-VFQ-25) scores among groups divided by disease severity
Dimension
Mild
Moderate
Severe
(n = 9)
(n = 19)
(n = 18)
(Mean ± SD)
(Mean ± SD)
(Mean ± SD)
Overall p-value
Multiple test
FB sensation 4.2 ± 1.1 (3.0–5.0) 3.3 ± 1.4 (2.0–5.0) 1.9 ± 1.6 (1.0–3.0) p < 0.001 a, b‡, c‡ Comfort
4.4 ± 0.9 (4.0–5.0) 3.8 ± 1.2 (3.0–5.0) 2.5 ± 1.4 (2.0–4.0) p < 0.001 a, b‡, c‡
Overall satisfaction
4.5 ± 0.7 (4.0–5.0) 3.7 ± 1.5 (3.0–5.0) 2.3 ± 1.7 (1.0–4.0) p < 0.001 a, b‡, c‡
FB: foreign body, a: mild versus moderate group, b: moderate versus severe group, c: mild versus severe group. Those significant at the 0.05 level are marked by *, those significant at the 0.01 level are marked by † , those significant at the 0.001 level are marked by ‡.
Table 2. Comparisons of foreign body sensation, comfort, overall satisfaction among groups divided by disease severity
In the present study, as the disease severity progressed, the binocular VA became worse. Keratoconus typically does not lead to uncorrectable visual loss. Ten to 20 per cent of patients with keratoconus require a penetrating keratoplasty or similar procedure as a result of insufficient correction of visual acuity with a contact lens or contact lens intolerance.21–22 One study by Weed, Macewen and McGhee23 studying a Scottish Clinical and Experimental Optometry 98.2 March 2015
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population showed that 97 per cent of their subjects achieved a binocular visual acuity of 6/9 (0.17 logMAR) or better wearing their rigid contact lenses; however, we found that nearly 40 per cent of our subjects have VA with RGP lenses worse than 6/7.5. This inconsistency in this study may be attributed to the fact that patients might not completely adapt to RGP lenses after only one month of wear. All the patients used RGP
lenses for the first time, so that a longer time to completely adapt to RGP lenses may be necessary. Further analysis concerning NEI-VFQ-25 scores among groups of different grades revealed that there was no significant difference in NEI-VFQ-25 scores between patients with mild and moderate keratoconus but patients in the severe keratoconus group showed the lowest NEI-VFQ-25 scores compared with the other two groups, especially in the subscales of ocular pain, mental health and role difficulties. Thus, patients with mild and moderate keratoconus could have similar VR-QOL by wearing RGP lenses; however, when the disease became much worse with a steep keratometric value of more than 52 D (6.50 mm), the patients appeared to have a significantly poorer VR-QOL. Regarding additional subjective criteria after three months of RGP lens-wearing, the significantly lower scores of the more advanced patients in foreign body sensation, comfort and overall satisfaction confirmed this finding. Hashemi and colleagues18 reported that overall satisfaction, comfort and VR-QOL were greater in keratoconic patients with the ClearKone-Synergeyes lens compared to simple RGP lens designs. From the patients’ perspectives, our study further confirms the results of previous studies,18,24 namely as the cornea gets thinner and more distorted in the advanced stages of keratoconus, the extreme irregularity of the ocular surface and the inability to achieve an ideal lens fit make these patients unhappy with their lenses, including poor comfort and an unstable lens fit. The present study showed that patients with mild and moderate keratoconus were able to achieve a sufficient lens wearing time (mean, 10.4 hours per day; 9.6 hours per day) to allow them to have a relatively normal work and social life, whereas the severe keratoconic patients showed a significantly reduced wearing time (mean, 4.8 hours per day) compared with other two groups. Several studies have reported longer wearing times in patients with scleral lenses.19,25,26 This inconsistency may be due to different lens options used in the study groups and may also depend on the various definitions of wearing time in patients who wear their lenses all day long. According to our findings, wearing RGP lenses by patients with severe keratoconus can result in discomfort, ocular pain and foreign body sensation. Such problems lead to a reduced © 2014 The Authors
Clinical and Experimental Optometry © 2014 Optometry Australia
RGP contact lens-related quality of life in keratoconus Wu, Tan, Zhang, Wang, Yang, Ma, Wang and Liu
Lens wearing time (hr/day)
15
*** ***
10
5
0 Mild
Moderate
Severe
Figure 1. Comparisons of mean rigid gas-permeable (RGP) contact lens wearing time in mild, moderate and severe keratoconus groups. ***p < 0.001 for multiple testing with Bonferroni correction.
Subscale
Binocular VA
Disease severe classification
r
p
r
p
General health
0.41
0.000
-0.14
0.362
General vision
0.73
0.000
-0.29
0.070
Ocular pain
0.10
0.463
-0.07
0.581
Near activities
0.84
0.000
-0.22
0.086
Distance activities
0.79
0.000
-0.13
0.387
Social function
0.83
0.000
-0.18
0.196
Mental health
0.74
0.000
-0.09
0.545
Role difficulties
0.82
0.000
-0.11
0.421
Dependency
0.88
0.000
-0.16
0.230
Colour vision
0.067
0.601
-0.02
0.893
Peripheral vision
0.70
0.000
-0.05
0.611
r: Spearman correlation coefficient
Table 3. Correlation analysis between National Eye Institute Visual Function Questionnaire (NEI-VFQ-25) scores and binocular visual acuity (VA) against disease severity classification wearing time with the lenses and can have a negative impact on the patients’ work schedules and social life. This issue is important because most keratoconic patients are adolescents or young adults, constituting the active population of society. Therefore, especially for severe patients, other lens options, such as scleral lenses and hybrid lenses, may provide better comfort and increased lens tolerance. It may also show the limitation of pre-designed keratoconic lenses compared to custom-designed lenses.
This study showed that binocular VA correlated significantly with the NEI-VFQ-25 scores. Unexpectedly, there were no significant correlations between the NEI-VFQ-25 scores and the three grades divided by disease severity. Although several studies reported that a steeper corneal curvature was associated with more visual impairment and poorer VR-QOL,13,27 the present study showed that, RGP lens-related VR-QOL had a strong correlation with binocular VA rather than the keratometric value. To this
© 2014 The Authors Clinical and Experimental Optometry © 2014 Optometry Australia
extent, RGP contact lenses changed the impact of the disease severity on VR-QOL. Although it is generally accepted that the severity classification is based on keratometric readings, it only partially explains the natural course of progression in keratoconus. Taken together, we might suggest that we should combine VA assessment, keratometric reading or other subjective measures with VR-QOL, as a comprehensive appraisal of keratoconus in future clinical studies, which covers both objective and subjective aspects, respectively. There are several limitations to this study. First, we evaluated the VR-QOL of patients with keratoconus based on binocular VA, which may facilitate the comparison among different studies of keratoconus.13,14,27 Second, the functional outcomes with more recent lens designs, such as scleral lenses and hybrid lenses, were not studied. Comparison of RGP lens-intolerant patients with these other lens options or custom-designed lenses may have been helpful. In conclusion, keratoconus has an extensive impact on patient-reported VR-QOL. RGP lenses provide a significantly better VR-QOL; however, when the disease progresses to a keratometric value of more than 52 D (6.50 mm), RGP lenses do not necessarily ensure a relatively good QOL. This study stresses the importance of prescribing the appropriate contact lenses for different grades of keratoconus. These findings suggest that comprehensive evaluation of keratoconus requires measures of VA, keratometry and VR-QOL, which translate objective outcome measures into areas of functioning in daily activities that are more meaningful to patients, their families, optometrists and ophthalmologists. ACKNOWLEDGMENT
We thank Dr Fei Li of the Department of Radiology, West China Hospital of Sichuan University, for assistance in revision of the manuscript. REFERENCES 1. Krachmer JH, Feder RS, Belin MW. Keratoconus and related non-inflammatory corneal thinning disorders. Surv Ophthalmol 1984; 28: 293–322. 2. Zadnik K, Barr JT, Gordon MO, Edrington TB. Biomicroscopic signs and disease severity in keratoconus. Cornea 1996; 15: 139–146. 3. Mannis MJ, Morrison TL, Zadnik K, Holland EJ, Krachmer JH. Personality trends in keratoconus. An analysis. Arch Ophthalmol 1987; 105: 798–800. 4. Rudisch B, D’Orio B, Compton MT. Keratoconus and psychosis. Am J Psychiatry 2003; 160: 1011.
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5. Giedd KK, Mannis MJ, Mitchell GL, Zadnik K. Personality in keratoconus in a sample of patients derived from the internet. Cornea 2005; 24: 301– 307. 6. Kaprelyan AG, Tzoukeva AJ, Dimitrov IN, Ivanov B, Deleva NS. Subjective cognitive complaints in a patient with keratoconus: cognitive impairment or ‘keratoconic personality’? J IMAB 2012; 18: 312– 314. 7. McKean-Cowdin R, Wang Y, Wu J, Azen SP, Varma R, Los Angeles Latino Eye Study group. Impact of visual field loss on health-related quality of life in glaucoma: the Los Angeles Latino Eye Study. Ophthalmology 2008; 115: 941–948. 8. Chatziralli IP, Sergentanis TN, Peponis VG, Papazisis LE, Moschos MM. Risk factors for poor vision-related quality of life among cataract patients. Evaluation of baseline data. Graefes Arch Clin Exp Ophthalmol 2013; 251: 783–789. 9. Okamoto F, Okamoto Y, Hiraoka T, Oshika T. Vision-related quality of life and visual function after retinal detachment surgery. Am J Ophthalmol 2008; 146: 85–90. 10. Barnett M, Mannis MJ. Contact lenses in the management of keratoconus. Cornea 2011; 30: 1510– 1516. 11. Jhanji V, Sharma N, Vajpayee RB. Management of keratoconus: current scenario. Br J Ophthalmol 2011; 95: 1044–1050. 12. Vazirani J, Basu S. Keratoconus: current perspectives. Clin Ophthalmol 2013; 7: 2019–2030. 13. Kymes SM, Walline JJ, Zadnik K, Gordon MO, Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study Group. Quality of life in keratoconus. Am J Ophthalmol 2004; 138: 527–535. 14. Gothwal VK, Reddy SP, Fathima A, Bharani S, Sumalini R, Bagga DK, Sudharman PM. Assessment of the impact of keratoconus on vision-related quality of life. Invest Ophthalmol Vis Sci 2013; 54: 2902–2910. 15. Ferris FL 3rd, Kassoff A, Bresnick GH, Bailey I. New visual acuity charts for clinical research. Am J Ophthalmol 1982; 94: 91–96. 16. Wang CW, Chan CL, Jin HY. Psychometric properties of the Chinese version of the 25-item National Eye Institute Visual Function Questionnaire. Optom Vis Sci 2008; 85: 1091–1099. 17. Mangione CM, Lee PP, Pitts J, Gutierrez P, Berry S, Hays RD. Psychometric properties of the National Eye Institute Visual Function Questionnaire (NEIVFQ). NEI-VFQ Field Test Investigators. Arch Ophthalmol 1998; 116: 1496–1504. 18. Hashemi H, Shaygan N, Asgari S, Rezvan F, Asgari S. ClearKone-Synergeyes or rigid gas-permeable contact lens in keratoconic patients: a clinical decision. Eye Contact Lens 2014; 40: 95–98. 19. Visser ES, Visser R, van Lier HJ, Otten HM. Modern scleral lenses part II: patient satisfaction. Eye Contact Lens 2007; 33: 21–25. 20. Jinabhai A, Radhakrishnan H, Tromans C, O’Donnell C. Visual performance and optical quality with soft lenses in keratoconus patients. Ophthalmic Physiol Opt 2012; 32: 100–116. 21. Rabinowitz YS. Keratoconus. Surv Ophthalmol 1998; 42: 297–319. 22. Edrington TB, Gundel RE, Libassi DP, Wagner H, Pierce GE, Walline JJ, Barr JT et al. Variables affecting rigid contact lens comfort in the collaborative longitudinal evaluation of keratoconus (CLEK) study. Optom Vis Sci 2004; 81: 182–188. 23. Weed KH, MacEwen CJ, McGhee CN. The Dundee University Scottish Keratoconus Study II: a pro-
Clinical and Experimental Optometry 98.2 March 2015
154
24.
25.
26.
27.
spective study of optical and surgical correction. Ophthalmic Physiol Opt 2007; 27: 561–567. Sengor T, Kurna SA, Aki S, Ozkurt Y. High Dk piggyback contact lens system for contact lensintolerant keratoconus patients. Clin Ophthalmol 2011; 5: 331–335. Segal O, Barkana Y, Hourovitz D, Behrman S, Kamun Y, Avni I, Zadok D. Scleral contact lenses may help where other modalities fail. Cornea 2003; 22: 308–310. Romero-Rangel T, Stavrou P, Cotter J, Rosenthal P, Baltatzis S, Foster CS. Gas-permeable scleral contact lens therapy in ocular surface disease. Am J Ophthalmol 2000; 130: 25–32. Kymes SM, Walline JJ, Zadnik K, Sterling J, Gordon MO, Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study Group. Changes in the quality-of-life of people with keratoconus. Am J Ophthalmol 2008; 145: 611–617.
© 2014 The Authors Clinical and Experimental Optometry © 2014 Optometry Australia
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A N D
E X P E R I M E N T A L
OPTOMETRY RESEARCH PAPER
Rigid gas-permeable contact lens related life quality in keratoconic patients with different grades of severity Clin Exp Optom 2015; 98: 150–154 Ye Wu MM Qi Tan MM Wenqiu Zhang PhD Jianglan Wang PhD Bi Yang PhD Wei Ma MM Xue Wang MM Longqian Liu MD PhD Department of Optometry, West China School of Medicine, Sichuan University, Chengdu, Sichuan Province, China E-mail: [email protected]
Submitted: 14 June 2014 Revised: 22 July 2014 Accepted for publication: 14 September 2014
DOI:10.1111/cxo.12237 Purpose: The aim was to compare the impact of rigid gas-permeable (RGP) contact lenses on vision-related quality of life (VR-QOL) in keratoconic patients with different grades of severity. Methods: This comparative study was conducted from December 2012 to September 2013 on 46 patients with bilateral keratoconus. Patients were divided into three groups according to the average of the steep keratometry (K) readings in the two eyes of each patient. Main outcome measures included binocular visual acuity (VA), lens wearing time, the 25-item National Eye Institute Visual Function Questionnaire (NEI-VFQ-25), foreign body (FB) sensation, comfort and overall satisfaction. Results: Patients with severe keratoconus showed significantly reduced wearing time compared with the other two groups (4.8 ± 2.5 hours per day). Regarding the subjective criteria, there was no significant difference on NEI-VFQ-25 scores, foreign body sensation, comfort and overall satisfaction between mild and moderate keratoconus groups but scores in the group with severe keratoconus were significantly lower than the other two groups. Binocular VA strongly correlated with NEI-VFQ-25 scores; however, NEI-VFQ-25 scores had no significant correlations with different disease severities. Conclusions: Appropriate correction with RGP lenses contributes to good VR-QOL for keratoconic patients; however, as the disease progresses to a steep keratometric value of more than 52 dioptres (6.50 mm), RGP lenses did not guarantee a relatively good VR-QOL. Other lens options with new designs might bring better life quality for these patients with severe keratoconus.
Key words: contact lenses, keratoconus, rigid gas-permeable, vision-related quality of life Keratoconus is a non-inflammatory, degenerative disease of the cornea, in which the cornea becomes progressively thinner, more distorted and steeper in curvature.1 These corneal changes may lead to irregular astigmatism and corneal scarring.2 The disease usually presents at puberty and may progress until later stages of life. Although the disease rarely results in blindness, the burden of decreased vision and its unpredictable characteristic changes can lead to a significant impact on the daily lives and mental development of young patients.3–6 Increasingly, patient-reported outcomes are being used to estimate the impact of ocular disease on vision-related quality of life (VR-QOL), which includes not only the biologic status of disease but also the full range of outcomes, such as mental health, social function and role difficulties. The National Eye Institute Visual Function Questionnaire-25 (NEI-VFQ-25) has been Clinical and Experimental Optometry 98.2 March 2015
150
used widely to assess visual function of patients with various ocular disorders, such as glaucoma, cataract and retinal detachment.7–9 In the early stages of keratoconus, vision can be managed with spectacles but as the disease progresses, rigid gas-permeable (RGP) contact lenses are preferred for reducing distortion and providing better vision. Although RGP lenses are the primary method of non-surgical visual correction in keratoconic patients, a considerable number of more advanced cases can feel uncomfortable with RGP lenses due to the corneal irregularity and the inability to obtain an acceptable lens fit.10–12 Because of these factors, advanced cases may suffer symptoms of contact lens intolerance, unsatisfactory visual acuity (VA) and a generally poor quality of life. To our knowledge, no previous studies have evaluated the impact of RGP lenses on VR-QOL among patients
with different grades of keratoconus. Therefore, we performed this study to compare RGP lens-related VR-QOL in keratoconic patients with different grades based on objective and subjective performances, with the aim of improving the knowledge of the impact of RGP contact lens wear on the subjective aspects of daily living activities in keratoconic patients, and contact lens management options. MATERIALS AND METHODS
Subjects This prospective study was approved by the local ethics committee and written informed consent was obtained from all patients. Patients with bilateral keratoconus who attended the contact lens clinic in the West China Hospital of Sichuan University from December 2012 to September 2013 were © 2014 The Authors
Clinical and Experimental Optometry © 2014 Optometry Australia
RGP contact lens-related quality of life in keratoconus Wu, Tan, Zhang, Wang, Yang, Ma, Wang and Liu
enrolled. All the patients had been diagnosed with keratoconus by an ophthalmologist and referred to this clinic for RGP lens management rather than surgery. We excluded patients with a history of intraocular or corneal surgery, including penetrating keratoplasty (PK) or other ocular diseases, such as cataracts, retinal disease or glaucoma.
assessed on a slitlamp with fluorescein. The fit was judged to be good if there was apical clearance, or mild apical touch, good centration and adequate edge lift. If the ordered lenses gave an acceptable fit, vision and comfort, the patient was scheduled for the one-month study visit.
Statistical analyses Measurement protocol Corneal topography was performed using the Tomey KC screening system (Tomey Corporation, Tokyo, Japan). Patients were divided into three groups according to the average of the steep keratometry (K) readings in the two eyes of each patient: mild (average Sim K less than 45 D; 7.50 mm), moderate (average Sim K 45 to 52 D; 7.50 to 6.20 mm) and severe (average Sim K more than 52 D; 6.20 mm).13–14 All the recruited patients used RGP lenses for the first time. Demographic characteristics were documented based on medical records. Binocular VA and NEI-VFQ-25 scores were evaluated after one month of adaptation to RGP lenses. Binocular VA was measured using the Early Treatment Diabetic Retinopathy (ETDRS) chart. Results were reported as the number of letters correct, then adding zero (for testing at one metre) or plus 30 (for testing at four metres).15 A Chinese version of the NEIVFQ-25, which has been proven to be a reliable and valid tool in a previous study,16 was administered to all patients. The NEIVFQ-25 consists of 25 items that constitute 12 subscales. The scale scores were computed based on the algorithm developed by Mangione and colleagues17 and ranged from zero (worst) to 100 (best). After three months of RGP lens-wear, patients were asked to verbally grade the performance of RGP lenses using a Likert scale18,19 (in which 1 represents very poor and 5 represents excellent) with respect to foreign body sensation, comfort and overall satisfaction. Additionally, regarding lens wearing time, patients were asked to state how many hours a day they had been wearing the lenses. RGP lens designs available in our clinic were as follows: standard keratoconic (FreshKon, Shanghai, China), Rose K design (FreshKon, Shanghai, China), standard spherical surface and back surface multicurve design (Menicon Z E-1, Menicon, Nagoya, Japan). The patients were fitted with suitable RGP lenses and then
Descriptive data were presented as mean and standard deviation and percentages. We used non-parametric tests when the data were not normally distributed. There were no statistical differences in age and educational level among the groups. After adjustment for gender, binocular VA, lens-wearing time, NEI-VFQ-25 scores, foreign body sensation, comfort and overall satisfaction were compared among the different grades of keratoconus by using the Kruskal–Wallis H test. Spearman rank correlation analysis was performed to evaluate the relationship between NEI-VFQ-25 scores and clinical variables, including binocular VA and disease severity classification. A p-value less than 0.05 was considered statistically significant. To reduce the rate of false negatives, Bonferroni correction was used for multiple testing. Statistical analyses were performed with SPSS 18.0 for windows SPSS Inc, Chicago, Illinois, USA).
RESULTS A total of 53 Chinese patients were diagnosed with bilateral keratoconus in our contact lens clinic. Of these, four patients refused to wear RGP lenses due to lack of affordability or intolerance of the rigid lens material and three patients were lost to follow-up after dispensing the RGP lenses. Therefore, 46 of the 53 patients (87 per cent) were actually included in all analyses. The mean age of the participants was 23.2 ± 6.5 years (range, 16 to 40 years). There were more male patients in the sample (30 of 46, 65 per cent). Nine patients had mild, 19 patients had moderate and 18 patients had severe keratoconus. The mean binocular VA scores in mild, moderate and severe keratoconus groups were 89.7 ± 6.2 (Snellen equivalent 6/6), 82.1 ± 9.4 (Snellen equivalent 6/7.5) and 73.3 ± 8.6 (Snellen equivalent 6/12) respectively (Kruskal–Wallis H test, p < 0.001). As the majority of patients did not drive (for non-eye-related reasons), we omitted
© 2014 The Authors Clinical and Experimental Optometry © 2014 Optometry Australia
this subscale according to the suggestion of a previous study.16 Table 1 shows the results of the NEI-VFQ-25 scores. There was no significant difference on subscale scores between mild and moderate keratoconus groups; however, the NEI-VFQ-25 scores in both of the groups were significantly higher than in the severe keratoconus group, except the score for ‘colour vision’ (Kruskal–Wallis H test with Bonferroni correction for multiple testing, p < 0.001). Comparing foreign body sensation, comfort and overall satisfaction, the differences between mild and moderate keratoconic groups were borderline significant (p = 0.051, p = 0.062 and p = 0.059, respectively), with significantly lower scores in the advanced keratoconus group as shown in Table 2 (Kruskal–Wallis H test with Bonferroni correction for multiple testing, p < 0.001). The mean and SD lens wearing time in mild, moderate and severe keratoconus groups were 10.4 ± 1.4 hours per day, 9.6 ± 1.7 hours per day and 4.8 ± 2.5 hours per day, respectively (Figure 1). Table 3 presents the correlations between NEI-VFQ-25 scores and binocular VA against disease severity classification. NEI-VFQ-25 scores correlated significantly with binocular VA except those for ‘colour vision’ and ‘ocular pain’. All the correlation coefficients (r) were greater than 0.7 except that for ‘general health’ (p < 0.001). There was no significant correlation between the NEIVFQ-25 scores and mild, moderate or severe keratoconic groups (p > 0.05).
DISCUSSION RGP lenses provide keratoconic patients with better visual performance and greater reduction of ocular aberrations compared to soft contact lenses or spectacles.20 RGP lenses mask the underlying irregular corneal surface and provide excellent tear exchange but may be uncomfortable to wear for most of the patients with severe keratoconus.10–12 Therefore, it is of great significance to evaluate RGP contact lensrelated functional abilities in daily activities of keratoconic patients with different severity grades. These findings may prove beneficial to ophthalmologists and optometrists given that they provide the patients’ perspectives, which can be integrated into the decision-making process for any treatment being planned, such as penetrating keratopasty. Clinical and Experimental Optometry 98.2 March 2015
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RGP contact lens-related quality of life in keratoconus Wu, Tan, Zhang, Wang, Yang, Ma, Wang and Liu
Subscale
Mild
Moderate
Severe
Overall p-value
Multiple test
(n = 9)
(n = 19)
(n = 18)
(Mean ± SD)
(Mean ± SD)
(Mean ± SD)
General health
83.0 ± 8.2
82.6 ± 11.3
60.5 ± 14.1
p < 0.001
a, b‡, c‡
General vision
87.4 ± 9.8
83.9 ± 10.2
63.3 ± 13.5
p < 0.001
a, b‡, c‡
Ocular pain
61.3 ± 12.5
59.9 ± 9.1
37.4 ± 16.8
p < 0.001
a, b‡, c‡
Near activities
94.7 ± 13.6
90.3 ± 10.7
72.1 ± 11.0
p < 0.001
a, b‡, c‡
Distance activities
90.4 ± 6.6
87.7 ± 16.0
68.8 ± 18.4
p < 0.0011
a, b‡, c‡
Social function
94.6 ± 14.1
91.3 ± 16.2
66.2 ± 15.9
p < 0.001
a, b‡, c‡
Mental health
77.1 ± 11.6
75.6 ± 15.5
51.4 ± 12.8
p < 0.001
a, b‡, c‡
Role difficulties
84.8 ± 11.7
83.1 ± 10.0
61.5 ± 16.6
p < 0.001
a, b‡, c‡
Dependency
91.6 ± 15.1
87.0 ± 17.8
62.7 ± 18.5
p < 0.001
a, b‡, c‡
Colour vision
99.3 ± 8.4
97.9 ± 9.8
94.3 ± 10.7
p < 0.05
a, b, c
Peripheral vision
93.3 ± 11.9
91.4 ± 8.9
78.2 ± 10.1
p < 0.001
a, b‡, c‡
a: mild versus moderate group, b: moderate versus severe group, c: mild versus severe group. Those significant at the 0.05 level are marked by *, those significant at the 0.01 level are marked by † , those significant at the 0.001 level are marked by ‡.
Table 1. Analysis on National Eye Institute Visual Function Questionnaire (NEI-VFQ-25) scores among groups divided by disease severity
Dimension
Mild
Moderate
Severe
(n = 9)
(n = 19)
(n = 18)
(Mean ± SD)
(Mean ± SD)
(Mean ± SD)
Overall p-value
Multiple test
FB sensation 4.2 ± 1.1 (3.0–5.0) 3.3 ± 1.4 (2.0–5.0) 1.9 ± 1.6 (1.0–3.0) p < 0.001 a, b‡, c‡ Comfort
4.4 ± 0.9 (4.0–5.0) 3.8 ± 1.2 (3.0–5.0) 2.5 ± 1.4 (2.0–4.0) p < 0.001 a, b‡, c‡
Overall satisfaction
4.5 ± 0.7 (4.0–5.0) 3.7 ± 1.5 (3.0–5.0) 2.3 ± 1.7 (1.0–4.0) p < 0.001 a, b‡, c‡
FB: foreign body, a: mild versus moderate group, b: moderate versus severe group, c: mild versus severe group. Those significant at the 0.05 level are marked by *, those significant at the 0.01 level are marked by † , those significant at the 0.001 level are marked by ‡.
Table 2. Comparisons of foreign body sensation, comfort, overall satisfaction among groups divided by disease severity
In the present study, as the disease severity progressed, the binocular VA became worse. Keratoconus typically does not lead to uncorrectable visual loss. Ten to 20 per cent of patients with keratoconus require a penetrating keratoplasty or similar procedure as a result of insufficient correction of visual acuity with a contact lens or contact lens intolerance.21–22 One study by Weed, Macewen and McGhee23 studying a Scottish Clinical and Experimental Optometry 98.2 March 2015
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population showed that 97 per cent of their subjects achieved a binocular visual acuity of 6/9 (0.17 logMAR) or better wearing their rigid contact lenses; however, we found that nearly 40 per cent of our subjects have VA with RGP lenses worse than 6/7.5. This inconsistency in this study may be attributed to the fact that patients might not completely adapt to RGP lenses after only one month of wear. All the patients used RGP
lenses for the first time, so that a longer time to completely adapt to RGP lenses may be necessary. Further analysis concerning NEI-VFQ-25 scores among groups of different grades revealed that there was no significant difference in NEI-VFQ-25 scores between patients with mild and moderate keratoconus but patients in the severe keratoconus group showed the lowest NEI-VFQ-25 scores compared with the other two groups, especially in the subscales of ocular pain, mental health and role difficulties. Thus, patients with mild and moderate keratoconus could have similar VR-QOL by wearing RGP lenses; however, when the disease became much worse with a steep keratometric value of more than 52 D (6.50 mm), the patients appeared to have a significantly poorer VR-QOL. Regarding additional subjective criteria after three months of RGP lens-wearing, the significantly lower scores of the more advanced patients in foreign body sensation, comfort and overall satisfaction confirmed this finding. Hashemi and colleagues18 reported that overall satisfaction, comfort and VR-QOL were greater in keratoconic patients with the ClearKone-Synergeyes lens compared to simple RGP lens designs. From the patients’ perspectives, our study further confirms the results of previous studies,18,24 namely as the cornea gets thinner and more distorted in the advanced stages of keratoconus, the extreme irregularity of the ocular surface and the inability to achieve an ideal lens fit make these patients unhappy with their lenses, including poor comfort and an unstable lens fit. The present study showed that patients with mild and moderate keratoconus were able to achieve a sufficient lens wearing time (mean, 10.4 hours per day; 9.6 hours per day) to allow them to have a relatively normal work and social life, whereas the severe keratoconic patients showed a significantly reduced wearing time (mean, 4.8 hours per day) compared with other two groups. Several studies have reported longer wearing times in patients with scleral lenses.19,25,26 This inconsistency may be due to different lens options used in the study groups and may also depend on the various definitions of wearing time in patients who wear their lenses all day long. According to our findings, wearing RGP lenses by patients with severe keratoconus can result in discomfort, ocular pain and foreign body sensation. Such problems lead to a reduced © 2014 The Authors
Clinical and Experimental Optometry © 2014 Optometry Australia
RGP contact lens-related quality of life in keratoconus Wu, Tan, Zhang, Wang, Yang, Ma, Wang and Liu
Lens wearing time (hr/day)
15
*** ***
10
5
0 Mild
Moderate
Severe
Figure 1. Comparisons of mean rigid gas-permeable (RGP) contact lens wearing time in mild, moderate and severe keratoconus groups. ***p < 0.001 for multiple testing with Bonferroni correction.
Subscale
Binocular VA
Disease severe classification
r
p
r
p
General health
0.41
0.000
-0.14
0.362
General vision
0.73
0.000
-0.29
0.070
Ocular pain
0.10
0.463
-0.07
0.581
Near activities
0.84
0.000
-0.22
0.086
Distance activities
0.79
0.000
-0.13
0.387
Social function
0.83
0.000
-0.18
0.196
Mental health
0.74
0.000
-0.09
0.545
Role difficulties
0.82
0.000
-0.11
0.421
Dependency
0.88
0.000
-0.16
0.230
Colour vision
0.067
0.601
-0.02
0.893
Peripheral vision
0.70
0.000
-0.05
0.611
r: Spearman correlation coefficient
Table 3. Correlation analysis between National Eye Institute Visual Function Questionnaire (NEI-VFQ-25) scores and binocular visual acuity (VA) against disease severity classification wearing time with the lenses and can have a negative impact on the patients’ work schedules and social life. This issue is important because most keratoconic patients are adolescents or young adults, constituting the active population of society. Therefore, especially for severe patients, other lens options, such as scleral lenses and hybrid lenses, may provide better comfort and increased lens tolerance. It may also show the limitation of pre-designed keratoconic lenses compared to custom-designed lenses.
This study showed that binocular VA correlated significantly with the NEI-VFQ-25 scores. Unexpectedly, there were no significant correlations between the NEI-VFQ-25 scores and the three grades divided by disease severity. Although several studies reported that a steeper corneal curvature was associated with more visual impairment and poorer VR-QOL,13,27 the present study showed that, RGP lens-related VR-QOL had a strong correlation with binocular VA rather than the keratometric value. To this
© 2014 The Authors Clinical and Experimental Optometry © 2014 Optometry Australia
extent, RGP contact lenses changed the impact of the disease severity on VR-QOL. Although it is generally accepted that the severity classification is based on keratometric readings, it only partially explains the natural course of progression in keratoconus. Taken together, we might suggest that we should combine VA assessment, keratometric reading or other subjective measures with VR-QOL, as a comprehensive appraisal of keratoconus in future clinical studies, which covers both objective and subjective aspects, respectively. There are several limitations to this study. First, we evaluated the VR-QOL of patients with keratoconus based on binocular VA, which may facilitate the comparison among different studies of keratoconus.13,14,27 Second, the functional outcomes with more recent lens designs, such as scleral lenses and hybrid lenses, were not studied. Comparison of RGP lens-intolerant patients with these other lens options or custom-designed lenses may have been helpful. In conclusion, keratoconus has an extensive impact on patient-reported VR-QOL. RGP lenses provide a significantly better VR-QOL; however, when the disease progresses to a keratometric value of more than 52 D (6.50 mm), RGP lenses do not necessarily ensure a relatively good QOL. This study stresses the importance of prescribing the appropriate contact lenses for different grades of keratoconus. These findings suggest that comprehensive evaluation of keratoconus requires measures of VA, keratometry and VR-QOL, which translate objective outcome measures into areas of functioning in daily activities that are more meaningful to patients, their families, optometrists and ophthalmologists. ACKNOWLEDGMENT
We thank Dr Fei Li of the Department of Radiology, West China Hospital of Sichuan University, for assistance in revision of the manuscript. REFERENCES 1. Krachmer JH, Feder RS, Belin MW. Keratoconus and related non-inflammatory corneal thinning disorders. Surv Ophthalmol 1984; 28: 293–322. 2. Zadnik K, Barr JT, Gordon MO, Edrington TB. Biomicroscopic signs and disease severity in keratoconus. Cornea 1996; 15: 139–146. 3. Mannis MJ, Morrison TL, Zadnik K, Holland EJ, Krachmer JH. Personality trends in keratoconus. An analysis. Arch Ophthalmol 1987; 105: 798–800. 4. Rudisch B, D’Orio B, Compton MT. Keratoconus and psychosis. Am J Psychiatry 2003; 160: 1011.
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5. Giedd KK, Mannis MJ, Mitchell GL, Zadnik K. Personality in keratoconus in a sample of patients derived from the internet. Cornea 2005; 24: 301– 307. 6. Kaprelyan AG, Tzoukeva AJ, Dimitrov IN, Ivanov B, Deleva NS. Subjective cognitive complaints in a patient with keratoconus: cognitive impairment or ‘keratoconic personality’? J IMAB 2012; 18: 312– 314. 7. McKean-Cowdin R, Wang Y, Wu J, Azen SP, Varma R, Los Angeles Latino Eye Study group. Impact of visual field loss on health-related quality of life in glaucoma: the Los Angeles Latino Eye Study. Ophthalmology 2008; 115: 941–948. 8. Chatziralli IP, Sergentanis TN, Peponis VG, Papazisis LE, Moschos MM. Risk factors for poor vision-related quality of life among cataract patients. Evaluation of baseline data. Graefes Arch Clin Exp Ophthalmol 2013; 251: 783–789. 9. Okamoto F, Okamoto Y, Hiraoka T, Oshika T. Vision-related quality of life and visual function after retinal detachment surgery. Am J Ophthalmol 2008; 146: 85–90. 10. Barnett M, Mannis MJ. Contact lenses in the management of keratoconus. Cornea 2011; 30: 1510– 1516. 11. Jhanji V, Sharma N, Vajpayee RB. Management of keratoconus: current scenario. Br J Ophthalmol 2011; 95: 1044–1050. 12. Vazirani J, Basu S. Keratoconus: current perspectives. Clin Ophthalmol 2013; 7: 2019–2030. 13. Kymes SM, Walline JJ, Zadnik K, Gordon MO, Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study Group. Quality of life in keratoconus. Am J Ophthalmol 2004; 138: 527–535. 14. Gothwal VK, Reddy SP, Fathima A, Bharani S, Sumalini R, Bagga DK, Sudharman PM. Assessment of the impact of keratoconus on vision-related quality of life. Invest Ophthalmol Vis Sci 2013; 54: 2902–2910. 15. Ferris FL 3rd, Kassoff A, Bresnick GH, Bailey I. New visual acuity charts for clinical research. Am J Ophthalmol 1982; 94: 91–96. 16. Wang CW, Chan CL, Jin HY. Psychometric properties of the Chinese version of the 25-item National Eye Institute Visual Function Questionnaire. Optom Vis Sci 2008; 85: 1091–1099. 17. Mangione CM, Lee PP, Pitts J, Gutierrez P, Berry S, Hays RD. Psychometric properties of the National Eye Institute Visual Function Questionnaire (NEIVFQ). NEI-VFQ Field Test Investigators. Arch Ophthalmol 1998; 116: 1496–1504. 18. Hashemi H, Shaygan N, Asgari S, Rezvan F, Asgari S. ClearKone-Synergeyes or rigid gas-permeable contact lens in keratoconic patients: a clinical decision. Eye Contact Lens 2014; 40: 95–98. 19. Visser ES, Visser R, van Lier HJ, Otten HM. Modern scleral lenses part II: patient satisfaction. Eye Contact Lens 2007; 33: 21–25. 20. Jinabhai A, Radhakrishnan H, Tromans C, O’Donnell C. Visual performance and optical quality with soft lenses in keratoconus patients. Ophthalmic Physiol Opt 2012; 32: 100–116. 21. Rabinowitz YS. Keratoconus. Surv Ophthalmol 1998; 42: 297–319. 22. Edrington TB, Gundel RE, Libassi DP, Wagner H, Pierce GE, Walline JJ, Barr JT et al. Variables affecting rigid contact lens comfort in the collaborative longitudinal evaluation of keratoconus (CLEK) study. Optom Vis Sci 2004; 81: 182–188. 23. Weed KH, MacEwen CJ, McGhee CN. The Dundee University Scottish Keratoconus Study II: a pro-
Clinical and Experimental Optometry 98.2 March 2015
154
24.
25.
26.
27.
spective study of optical and surgical correction. Ophthalmic Physiol Opt 2007; 27: 561–567. Sengor T, Kurna SA, Aki S, Ozkurt Y. High Dk piggyback contact lens system for contact lensintolerant keratoconus patients. Clin Ophthalmol 2011; 5: 331–335. Segal O, Barkana Y, Hourovitz D, Behrman S, Kamun Y, Avni I, Zadok D. Scleral contact lenses may help where other modalities fail. Cornea 2003; 22: 308–310. Romero-Rangel T, Stavrou P, Cotter J, Rosenthal P, Baltatzis S, Foster CS. Gas-permeable scleral contact lens therapy in ocular surface disease. Am J Ophthalmol 2000; 130: 25–32. Kymes SM, Walline JJ, Zadnik K, Sterling J, Gordon MO, Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study Group. Changes in the quality-of-life of people with keratoconus. Am J Ophthalmol 2008; 145: 611–617.
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