OCT and Visual Field Tests Yield Diverging Values Based on Glaucoma Stage

There are distinct challenges involved in monitoring the progression of a patient’s glaucoma, and yet a watchful approach is crucial to best manage care and track prognosis. Typically, benchmarks are obtained with structural and functional metrics, but the 2 methods sometimes offer diverging indications of disease progression, according to a paper presented at the Association for Research in Vision and Ophthalmology (ARVO) Annual Meeting, held virtually from May 1 to 7, 2021.

The team of researchers from several US states was led by Ou Tan, PhD of the Casey Eye Institute at Oregon Health & Science University, in Portland. Investigators determined that nerve fiber layer (NFL) thickness scanned with optical coherence tomography (OCT), and visual field (VF) readings varied depending on severity of a patient’s glaucoma. Further, the study finds that calculating both the VF mean deviation (VF_MD) and NFL mean deviation (NFL_MD) may help to gauge disease progression.

“Compared to VF MD, NFL thickness tends to overestimate the progression speed in the early stages of glaucoma and underestimate it in the later stages,” according to the study.

Results are based on the analysis of an Advanced Imaging for Glaucoma study of 332 individuals who were either glaucoma suspect (n=75), diagnosed with pre-perimetric glaucoma (n=160), early perimetric glaucoma (n=77), or moderate to severe perimetric glaucoma (n=20). Participants underwent testing every 6 months on 7 or more occasions, including global VF assessment and NFL thickness measurement with OCT optic nerve head (ONH) scan. Follow-up time was 54±8 months. 

Investigators derived NFL MD from “VF-equivalent dB-scale quantities based on sector-wise nonlinear regression of NFL thickness with VF deviation using cross-sectional data” covering early to later disease phases. Regarding NFL MD and VF MD, the consistent rate of advancement in measurements reflected progression through the disease range. NFL thickness changed the fastest in pre-perimetric glaucoma and early perimetric glaucoma; however it decelerated during the moderate to severe stages.

The percentage of change in NFL thickness in relation to the VF metric was significantly different in the various levels of severity (P <.006). When looking at NFL MD compared with VF MD, progression rate was slower, but not meaningfully different through the glaucoma continuum (P =.08). Faster progression speed of NFL MD and VF MD was found in participants with more advanced disease at baseline, but progression speed of NFL thickness change was not associated with glaucoma severity at baseline.

Based on these findings, the study recommends that clinicians convert NFL thickness metrics to NFL MD to obtain measurements which potentially compare better to VF MD when evaluating progression through the developing levels of glaucoma.

Disclosure: Some of the study authors declared affiliations with a medical device company. Please see the original reference for a full list of authors’ disclosures.

Reference

Tan O, Huang D, Greenfield DS, et al. Harmonizing OCT and VF parameters in the assessment of glaucoma progression speed. Paper Presentation. Presented at the Association for Research in Vision and Ophthalmology (ARVO) annual meeting; May 1-7, 2021. Abstract 3531652.