Corneal hysteresis and glaucoma-related quantitative traits in the EPIC-Norfolk Eye Study

Abstract

 

Purpose

 

Controversy exists regarding whether corneal biomechanical properties are related to glaucoma risk independently of intraocular pressure. The aim of this study was to determine if an association exists between corneal hysteresis (CH) and glaucoma-related quantitative traits in a population-based sample.

 

Methods

 

Ophthalmic examination took place cross-sectionally between 2004-2011. Goldmann-correlated intraocular pressure (IOP) and CH were measured using the Ocular Response Analyzer (single best value from 3 readings). Average retinal nerve fibre layer (RNFL) thickness and the nerve fibre indicator (NFI) were measured using the GDxVCC (quality score ≥7). Optic disc rim area and linear cup-to-disc ratio (CDR) were measured using the HRT II (topographic SD ≤40). Axial length was measured using the IOLMaster. Linear regression models were used to examine the association between CH and RNFL/disc parameters. Models with GDx parameters were adjusted for typical scan score (TSS) to handle scans with atypical retardation, and models with HRT parameters were adjusted for disc area. Maximally adjusted models were further adjusted (linearly) for IOP, axial length, age, sex, body mass index, height and systolic blood pressure. Generalised estimating equations were used to analyse data from both eyes of participants.

 

Results

 

Complete data were available from 8,615 eyes of 5,354 predominantly white participants. The mean age was 67yrs (48-89) and 43% were men. Summary measures for the 8,615 eyes are shown in Table 1. Table 2 summarises results from the regression analyses. Higher CH was significantly associated with a larger rim area (p<0.001), smaller linear CDR (p<0.001) and thicker RNFL (p<0.001) in maximally adjusted models. Higher CH was associated with lower NFI in crude analysis (p<0.001) but not following maximal adjustment (p=0.18). Results were similar if adjustment was for corneal-compensated IOP, rather than Goldmann-correlated values.

 

Conclusions

 

In a population of British adults, higher CH was significantly associated with RNFL and optic disc parameters in a direction suggestive of a protective effect against glaucoma. This may support the theory that corneal biomechanical measures reflect lamina properties and thus glaucoma risk. Residual confounding by IOP is another possible explanation for the association. Regression coefficients were small, indicating a small effect.

 

 

 

Keywords: 464 clinical (human) or epidemiologic studies: risk factor assessment • 627 optic disc • 610 nerve fiber layer