Visual Field Defects Are Consistent in Macular Measurements Among Those With Glaucoma, High Myopia

In patients with primary open-angle glaucoma (POAG) and high myopia, changes in macular measurements were in accordance with visual field defects, and retinal nerve fiber layer (RNFL) thickness did not consistently decline with visual field defects due to the effects of high myopia, study results showed. The findings published in BMC Ophthalmology, suggest that during diagnosis and follow-up of glaucoma with high myopia, more attention ought to be focused on structure and functional defects in macular areas, the researchers wrote.

Glaucoma—characterized by progressive retinal ganglion cell apoptosis and subsequent visual field defects—is the second leading cause of blindness worldwide. Myopia, or nearsightedness, is a risk factor for glaucoma as “the prevalence of open-angle glaucoma and suspected glaucoma is 2 to 3 times greater in patients with myopia than in individuals without myopia.”

Diagnosis and monitoring of glaucoma are based on consistent structural and functional changes. Therefore, understanding the relationship between retinal structural changes and visual function defects is essential to disease management.

Because the influence of high myopia on the relationship between RNFL thickness or macular structure and visual field defects in patients with glaucoma is unclear, researchers aimed to evaluate the correlations and level of agreement between the structural and functional characteristics of patients with glaucoma with or without high myopia. Specifically, the study sought to determine the influence of high myopia on the consistency between optical coherence tomography (OCT) and visual field in patients with POAG.

All study participants were recruited from a single hospital in Shanghai, China. Patients were split into 3 groups: those with POAG and high myopia (n = 37, POAG-HM), those with POAG without high myopia (n = 27, POAG) and those with high myopia without glaucoma (n = 29, HM). Any patients with pathologic myopia, media opacities, or any other ocular disease were excluded from the study.

Participants underwent comprehensive ophthalmologic exams including best-corrected visual acuity (BCVA), and digital fundus photography while those with glaucoma underwent Humphrey perimetry (30–2 and 10–2 algorithms). OCT data collection was also performed on all patients and peripapillary scans were performed on each eye to measure RNFL thickness.

“The axial length (AL) of all patients was > 26 mm, and the BCVA was ≥ 20/25. During the data collection period, the intraocular pressures (IOPs) of patients with glaucoma were all controlled at < 21 mmHg by using antiglaucoma drugs. High myopia was defined as a refractive error < −6.0D,” the authors wrote.

Cross-classification and κ analyses revealed:

• In the POAG group, there was a strong agreement between the inferior temporal ganglion cell-inner plexiform layer (GCIPL) thickness and the mean sensitivity (MS) of 10–2 algorithms (κ = 0.5447, P = .0048), and good agreement between the superior and inferior RNFL thicknesses and 30–2 MS (κ = 0.4407 and 0.4815; P < .05)
• In the POAG-HM group, only the inferior temporal GCIPL thickness showed good agreement with 10–2 MS (κ = 0.3155, P = .0289) and none of the RNFL sectors were in good agreement with the corresponding MS
• In the HM group, no significant interexamination relationship and agreement between structural abnormity and functional defects could be found

Overall, results showed visual field defects in patients with glaucoma and high myopia are consistent in macular measurements but not in RNFL thicknesses. Investigators hypothesize the discrepancy “is due to peripapillary atrophy in high myopia that affects the relationship between the structural and functional defects, whereas macula is less likely to be affected by high myopia.”

A relatively small sample size in addition to the cross-sectional study design mark limitations to the study.

“For patients with POAG, with or without high myopia, the decline in retinal function occurred along with structural damage. In contrast to patients with POAG without high myopia, we observed consistency between visual field and macular measurements, but not with RNFL thicknesses, in patients with POAG and high myopia,” researchers concluded.

Reference

Wen W, Zhang Y, Zhang T, and Sun x. Consistency between optical coherence tomography and Humphrey visual field for evaluating glaucomatous defects in high myopic eyes. BMC Ophthalmol. Published online November 20, 2020. doi:10.1186/s12886-020-01724-2