Ocular Effects of Scleral Lens Wear on Dry Eye Patients

Abstract

Purpose: Dry eye disease (DED) is among the most complex ocular surface diseases to treat. Complaints of ocular discomfort and dryness are common in DED patients and in contact lens wearers. The use of SL to restore the integrity of the ocular surface in a more severe DED has become increasingly accepted among eye care practitioners. However, little is known about this treatment regimen and its impact on ocular surface in mild to moderate DED. Also, the potential impact of coated SL designs incorporating Hydra-PEG (polyethylene glycol) technology on ocular surface health has not yet been fully investigated. This thesis aimed to address this gap in knowledge and determine whether SL (uncoated or Hydra-PEG) could be used as a viable option for patients who are experiencing milder forms of DED. Over the course of the study, participants were asked to complete DE questionnaires; lens settling and vision, corneal thickness, osmolarity and matrix metalloproteinase 9 (MMP-9) in the pre-corneal tear film were investigated. The study also examined the relationship between the respective parameters and compared the two lens pairs.

Methods and Materials: The study was a prospective, double-masked, randomized, dispensing, crossover clinical trial involving five visits, where 20 subjects with mild to moderate dry eye disease (DED) were enrolled. Eligibility of the participants was confirmed following the Tear Film and Ocular Society (TFOS) Diagnostic Report in the first visit: presence of symptoms using the Ocular Surface Disease Index (OSDI) and Standardized Patient Evaluation of Eye Dryness (SPEED) questionnaires (OSDI ≥ 13, SPEED ≥ 4), plus osmolarity values (> 308 mOsmol/L in either eye or interocular difference of > 8 mOsmol/L) and or a positive MMP-9 result (using InflammaDry® test kit) or both. The second visit involved randomization and dispensing of customized hydra-PEG coated or uncoated SL, where each pair of lenses were worn on a daily wear basis for four weeks. Prior to dispensing the lenses, high contrast (HCVA) and low contrast acuities (LCVA) were recorded. The central corneal clearance (CCC) was measured with VisanteTM OCT to determine lens settling over time. Two standard clinical questionnaires (contact lens impact on quality of life (CLIQ) and contact lens dry eye questionnaire 8 (CLDEQ-8)) and an internally developed wearing habit and subjective rating questionnaire were provided to subjects and completed. The third visit (after 4 weeks) involved follow-up of the first randomized SL, where the lenses were evaluated, and clinical measurements repeated. A wash-out period of at least 48 hours was allowed before dispensing (visit 4) and follow-up (visit 5) of the other pair of SL, using the same procedures, measurement protocols and visit schedule. The SL used in the study were Zen™ RC (Alden Optical, Bausch & Lomb, Lancaster, NY, USA) available in only two diameters (14.80 and 15.40 mm), with a central thickness of 250 µm.

Results: Eighteen females and two males, mean age 29.10 ± 7.48 years, participated in the study. The overall OSDI and SPEED scores were 36.45 ± 17.08 and 12.50 ± 4.03 respectively. There was no significant difference in the CLIQ and CLDEQ-8 scores between uncoated and coated SL. In terms of wearing habit and subjective ratings, no statistically significant differences were observed in any of the parameters (wear time, dryness, burning, vision, and comfort). This suggests that the use of hydra-PEG coated SL did not show greater performance compared to the uncoated SL. The central corneal clearance (CCC) at the dispensing visit was 260 ± 40 (range: 200 - 300 µm) for both lens pairs. This significantly reduced to 190 ± 40 µm (lens settling: 70 ± 42 µm) for the uncoated SL and 200 ± 30 µm (lens settling: 70 ± 43 µm) for the coated SL at the follow-up visits, (all, p < 0.001). Comparing the CCC for the two lens pairs at the follow-up visits, no significant difference was observed, thus, the lens pairs settled at similar rates. In terms of HCVA and LCVA between the two lens pairs at both the dispensing and follow-up visits, there were no significant differences between them. Also, no significant correlations were found comparing the CCC with HCVA and LCVA of each lens pair at both visits. The CCT at the baseline and follow-up visits were: baseline: 560.55 ± 32.28 µm, post wear of uncoated SL: 557.65 ± 32.10 µm, and post wear of coated SL: 560.50 ± 34.02 µm. There were no significant differences for either lens type for central corneal thickness (CCT) at the baseline and follow-up visits (all, p > 0.05). Also, no significant correlations between CCC and CCT were observed at baseline or follow-up visits. These results demonstrated there were minimal corneal hypoxic effects when these SL were worn on a daily wear basis. For osmolarity measures, there was a statistically significant difference between the baseline and follow-up visit for the coated lenses (311.00 ± 14.86 vs 302.85 ± 7.96 mOsmol/L; p = 0.04). While this is statistically significant, the clinical relevance of this small difference remains questionable. Comparing the two lens pairs, no significant difference was found at all visits. The inflammaDry® test results indicated that 80 % of the participants tested positive for elevated MMP-9 at the baseline visit. There was a reduction in MMP-9 positive test results following the SL wear, however, there were no significant differences between the baseline and follow-up visits for each lens pair. Comparing the two lens pairs, no significant difference was observed. For either lens, no correlation was observed between osmolarity and MMP-9 test results.

Conclusion: There is a potential for using SL to manage symptoms in subjects suffering from mild to moderate DED, as the overall wearing habit and subjective ratings showed > 70 % of lens tolerance among the study cohort. SL wear over the month of wear in this cohort induced little change to the cornea or conjunctival tissue. Furthermore, SL may appear to marginally reduce tear film osmolarity, however, further studies are needed to confirm this result and its impact on subjective dryness. The clinical phenomenon of lens settling needs further investigation, especially on its impact on conjunctival morphology. In this cohort of subjects of mild to moderate DED, the hydra-PEG coating technology did not show superior performance over the uncoated lens for any of the factors assessed.

Keywords: dry eye disease. scleral contact lens, hydra-PEG, osmolarity, inflammadry, cornea