Rapid RNFL thinning predictive of visual field decline in glaucoma
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Patients with glaucoma who experienced rapid thinning of the retinal nerve fiber layer during initial follow-up were more likely to have visual field decline over an extended period of time, according to a study.
“The purpose of this study was to investigate the relationship between the magnitude of RNFL thinning seen during an initial period of follow-up of glaucoma patients and the magnitude of concurrent and subsequent visual field loss seen during an extended follow-up period of the same cohort,” the study authors wrote. “We hypothesized that fast initial RNFL progression would be associated with fast visual field progression, justifying the rationale for and providing guidance to the use of longitudinal OCT results in assisting clinical decision-making in glaucoma.”
The authors conducted a retrospective cohort study using data from the Duke Glaucoma Registry of 1,150 eyes of 839 patients with glaucoma. They determined rates of retinal nerve fiber layer (RNFL) loss through global RNFL thickness values of the first five OCT scans and assessed rates of visual field loss using standard automated perimetry mean deviation (SAP MD) during the entire follow-up period.
Investigators used rates of RNFL loss to categorize eyes as slow progressors (change less than –1 µm per year), moderate progressors (change between –1 µm and –2 µm per year) and fast progressors (change greater than –2 µm per year).
Over the initial follow-up of 3.7 years, the rate of RNFL change was –0.76 ± 0.85 µm per year. The rate was –0.36 ± 0.54 µm per year among slow progressors (765 patients), –1.34 ± 0.25 µm per year in moderate progressors (328 patients) and –2.87 ± 1.39 µm per year in fast progressors (57 patients).
Over the extended follow-up period of 6.1 years, the rates of SAP MD were –0.16 ± 0.35 dB per year among slow progressors, –0.32 ± 0.43 dB per year among moderate progressors and –0.71 ± 0.65 dB per year among fast progressors (P < .001). Using a multivariable model, age, OCT progressor group and concurrent SAP rate were all associated with overall rate of SAP MD loss (all P < .001).
“Rapid RNFL thinning during an initial follow-up period was significantly predictive of concurrent and subsequent rates of visual field decline over an extended period,” the study authors wrote. “These findings are of value to the clinician, as fast rates of RNFL thinning portend rapid future worsening in SAP. Intensifying treatment based on rapid structural loss in order to mitigate future functional loss may be warranted.”
Perspective
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This study quantifies the effect of loss of neural tissue on future visual function. This is something that has been documented over many years in terms of the loss of circumpapillary retinal nerve fiber layer and macular measures and later effect on visual fields. What Dr. Medeiros and his team did was to set thresholds of loss of retinal nerve fiber layer over time and then measure the subsequent deterioration of visual fields. As you might expect, they found that the more retinal nerve fiber layer was being lost in a given amount of time, the more visual field loss would subsequently occur.
Prior studies, some of which were cited in this paper, have shown that if you start out with a thinner nerve fiber layer, you are more likely to lose visual field downstream. In looking at reports from the Advanced Imaging for Glaucoma Study, OCT progression predated visual field progression by 2 years in people who were glaucoma suspects or had preperimetric glaucoma and by 1 year in people who had perimetric glaucoma. So, we know that OCT macular and RNFL thinning are predictive of future visual field loss. However, Dr. Medeiros and his group have quantified what that relationship is between early OCT progression and the visual field loss that follows downstream.
This can help clinicians understand that if somebody is having progressive retinal nerve fiber layer thinning by OCT, what the likelihood is that there would be visual field loss in the future and how much visual field loss they are likely to have. This study shows the importance of starting intervention at the time of the identification of OCT RNFL thinning as opposed to waiting for that visual field loss to occur.
References:
Zhang X, et al. Am J Ophthalmol. 2016;doi:10.1016/j.ajo.2016.09.015.
Zhang X, et al. Am J Ophthalmol. 2017;doi:10.1016/j.ajo.2017.09.020.
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