The influence of soft contact lens materials on the central, para-central and peripheral corneal endothelium

Abstract

PURPOSE: To examine the influence of a variety of soft contact lens (SCL) materials on the corneal endothelium, prior to and following two weeks cessation of SCL wear. METHODS: Corneal endothelial cells were examined using a CEM-530 specular microscope (Nidek, Japan). Full-time SCL wearers (n = 31 eyes) were compared to a non-contact lens (NCL) control group (n = 28 eyes) of a similar age (SCL: 20.82 ± 1.69 years, NCL: 21.14 ± 2.85 years, p = 0.58). Parameters analysed were endothelial cell density (ECD; cell/mm2), mean cell area (MCA; μ2), coefficient of variation (COV) and hexagonality (%). RESULTS: Prior to SCL cessation, two-way ANOVA testing showed significant differences between silicone hydrogel (SiH) SCL materials for the COV at 0o, with generation 2 SiH (G2SiH) wearers showing increased COV (27.67 ± 3.78) compared to generation 3 SiH (G3SiH) wearers (24.50 ± 3.73, p = 0.01). COV at the superior periphery was significantly lower in the NCL group (25.63 ± 2.79) compared to the hydrogel group (29.92 ± 6.22, p = 0.02). The MCA in the inferior periphery was also significantly higher in the NCL group (346.92 ± 36.75) compared to the hydrogel group (314.92 ± 16.57, p = 0.02). Following 14 days SCL cessation, no statistically significant differences in stability of endothelial parameters were detected between NCL and SCL material groups (all p values >0.05). CONCLUSION: SCL wear has an effect on paracentral and peripheral corneal endothelial measurements in SCL wearers compared to NCL wearers; with largest significant differences seen between NCL and hydrogel SCL wearers. Following two weeks SCL cessation, there were no significant differences in the stability of all endothelial measurements, regardless of which SCL material was worn. BACKGROUND Aoife Lloyd McKernan BSc (Hons) Optom FAOI1 , Luisa Simo Mannion DOO EU PhD2 , Veronica O'Dwyer DipOpt FAOI PhD 1 1Dublin Institute of Technology, Ireland, 2Plymouth University, United Kingdom Corneal hypoxia due to over-wear of low oxygen transmissibility (DK/t) SCLs results in endothelial polymegathism and corneal thinning 1. High DK/t SiH materials are reported to have negligible effects on the corneal endothelium 2. Hypothesis: endothelial parameters would show greater variation in a full-time low DK/t hydrogel SCL wearing group compared to a high DK/t SiH wearing group or NCL control group. Refitting previous low DK/t CL wearers with higher DK/t CLs results in reversal of hypoxia-induced endothelial changes 2. It is proposed that this reversal is linked to both the resolution of hypoxia and due to a mechanical reorganisation of the corneal endothelium following resolution of oedema-induced increased corneal thickness2. The stability of endothelial parameters in this study was examined over a two week period following cessation of SCL wear. This time period was chosen as it is the recommended SCL cessation time prior to corneal refractive surgery 3 and it has been previously demonstrated4 that the resolution of corneal and curvature and thickness following SCL cessation occurs within this time. Hypothesis: it was expected that endothelial corneal parameters in full time hydrogel SCL wearers would be more unstable after two weeks SCL wear cessation than SiH SCL wearers or NCL wearers METHODS  Inclusion criteria • Myopic prescriptions with low astigmatism ( 5 days per week for at least one year). • NCL group: no history of CL wear in the year prior