Optic disc characteristics of glaucoma eyes with and without high myopia

Abstract

Purpose : To characterize structural differences in glaucomatous optic discs in eyes with high, low and no myopia using optical coherence tomography (OCT) and OCT angiography (OCTA).

Methods : All glaucoma patients enrolled in the Diagnostic Innovations in Glaucoma Study with axial length (AL), visual field (VF) measurements and good quality Spectralis OCT ONHRC (optic nerve head radial circle) scans for calculation of minimum rim width (MRW) and retinal nerve fiber layer (RNFL) thickness were included. Participants were classified into 3 myopia groups by AL (mm); no (<24), low (24-26) and high (>26) axial myopia. Optic disc ovality index (OI), tilt and torsion were calculated using custom analysis of segmented OCT volumes. AngioVue OCTA ONH whole image vessel density (wiVD) was also analyzed. Linear mixed models were used to compare eye characteristics between groups, and univariable and age and mean deviation (MD) adjusted models were used to evaluate the association between AL and ocular parameters.

Results : 326 glaucoma patients (553 eyes) were classified into 3 groups: no myopia (n=116, VF MD=-6.69 dB), low myopia (n=168, VF MD=-7.1 dB), and high myopia (n=42, VF MD=-8.19 dB) (VF MD differences; p=0.1). Mean (95% CI) OI was significantly lower (more oval) in the high myopia group (0.84 (0.82-0.87)), compared to the low myopia (0.89; (0.87-0.9)) and no myopia group (0.88; (0.87-0.89)) (p=0.01), while disc tilt angle was highest in the high myopia group (9.6° (8.4-10.9)) compared to the no (4.0° (3.3-4.6)) and low myopia group (5.1° (4.5-5.7)) (p<0.001). Disc torsion angle was similar across the 3 groups (22.1°, 22.6°, and 17.7° (p=0.92), respectively) as was mean RNFL thickness (67.0µm, 65.1µm and 64.5µm (p=0.73), respectively). Mean (95% CI) MRW was significantly lower in the high myopia group than in the no- and low-myopia group (170µm (153-188), 198µm (189-208), and 192µm (184-200) respectively, p=0.03)). Mean (95% CI) OCTA wiVD was significantly lower in high myopes (38.1% (36.0-40.2)), compared to low myopes (38.7% (37.7-39.7)), and non-myopes (40.2% (39.0-41.4)) (p=0.01). Disc tilt, wiVD and MRW were significantly associated (all p<0.04) with increasing AL in age, and VF MD adjusted multivariable models.

Conclusions : Caution should be exercised when using ONH MRW and vessel density for glaucoma management decisions in high axial myopia as these global structural parameters are associated with AL.

This is a 2020 ARVO Annual Meeting abstract.