Abstract
Purpose :
Age and intraocular pressure (IOP) are the strongest predictors of primary open-angle glaucoma (POAG), which is associated with retinal nerve fibre layer (RNFL) thinning. IOP is associated with vertical cup-to-disc ratio (VCDR) in population-based studies, but several studies have shown no relationship between RNFL and IOP. This study aimed to investigate the relationship between average peripapillary RNFL thickness (RNFLT) and IOP using the TwinsUK Cohort.
Methods :
Data from 1560 adults from the population-representative TwinsUK volunteer cohort was analysed (mean age[SD] 57.0[15.7], range 19-92 years, 88% female). RNFLT was measured by spectral-domain optical coherence tomography (sd-OCT: Optovue, Inc., Fremont, CA). VCDR was graded from sd-OCT scans and corrected for optic disc area, a known association of RNFLT and VCDR. Only data from left eyes were used and outliers (>3SD) were excluded. Subjects were divided into 20-year age groups (20-40, 41-60, 61-80) to investigate the impact of age. Correlations between RNFL and IOP and between VCDR and IOP were tested using linear mixed models adjusted for age, sex, disc area and twin-relatedness. P-values of <0.05 were considered significant.
Results :
The mean RNFLT[SD] was 97.3µm[9.58µm]. RNFLT had a linear decrease with age (β=-0.136µm/year, 95%CI=-0.167,-0.105, p=<0.001), and as expected, was inversely associated with VCDR (β=-9.52µm, 95%CI=-13.55,-5.48, p=<0.001). The mean IOP[SD] in this cohort was 13.4mmHg[2.78mmHg].
Across the whole cohort, there was no significant association between RNFLT and IOP (β=-0.136µm/mmHg, 95%CI=-0.306, 0.033, p=0.116). However, for subjects aged 61-80 years, RNFLT was thinner as IOP increased (β=-0.253µm/mmHg, 95%CI=-0.515, 0.009, p=<0.001). While VCDR correlated with IOP overall, the effect of IOP increased with age, and was most significant in the 61-80 years age group (β=0.00481, 95%CI=-0.00135, 0.00828, p=<0.05).
Conclusions :
Our data shows that although RNFLT gradually thins with age, IOP only appears to significantly influence RNFLT in subjects aged over 60 years, and also has a greater effect on VCDR with increasing age. Therefore, factors other than IOP appear to determine RNFL loss in younger people. As glaucoma-related factors may only have an impact with advancing age, it is important to consider this when using RNFLT as an endophenotype for glaucoma in research studies.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.