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  • Extra OCT Scans May Be Needed to Determine Glaucoma Progression Rate

    By Lynda Seminara
    Selected by Russell N. Van Gelder, MD, PhD
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    Journal Highlights

    Ophthalmology, January 2023

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    Thickness of the peripapillary retinal nerve fiber layer (RNFL) as measured by OCT is a common metric to assess glaucoma progression and guide treat­ment, but how many scans are needed to accurately establish the progression rate? Bradley et al. set out to answer this question, with the goal of provid­ing evidence-based guidelines for prac­titioners. In their large cohort of adults with confirmed or suspected glaucoma, they found that increasing the number of scans obtained in a two-year period from three to seven could boost accura­cy by 20% or more.

    For this descriptive simulation study, the researchers included 12,150 eyes (7,392 adults) who were suspected or confirmed to have glaucoma and received follow-up at Wilmer Eye In­stitute during a nine-year period. Each eye had at least five measurements of RNFL thickness by Cirrus OCT, with signal strength of six or higher. Linear regression was applied to measure rates of RNFL worsening for average RNFL thickness and for each of the four quadrants.

    Simulations were used to estimate the accuracy of detecting worsening, defined as the proportion of patients for whom the true rate of RNFL worsening was at or below different criterion rates of worsening when the OCT-measured rate was also at or be­low the same rates. Two measurement strategies were used: evenly spaced (equal time intervals between measure­ments) and clustered (approximately 50% of measurements obtained at each period’s end point). Main outcome measures were the 75th percentile (moderate) and the 90th percentile (rapid) rates of RNFL worsening for average RNFL thickness, as well as accuracy of the diagnosed worsening at both rates.

    The mean RNFL thickness at baseline was 87.50 μm, and the mean interval between measurements was 390 days. The 75th and 90th percentile rates of worsening for average RNFL thickness were –1.09 μm/year and –2.35 μm/year, respectively.

    The simulations demonstrated that, for the average measurement frequency in the study population (approximately three OCT scans within two years), the diagnosis of moderate and rapid RNFL worsening was accurate for only 47% and 40%, respectively. According to the analysis, achieving accuracy of at least 60% would require seven scans. Ac­curacy of 70% would require 14 scans for moderate-rate progression and 16 scans for rapid-rate progression. The clustered-measurement strategy was more accurate.

    The authors suggest using a clus­tered-measurement strategy when practical, with multiple scans obtained at each visit. They emphasized that OCT scans take little time and are patient-friendly. They recommend further research to define the best approach for obtaining clustered OCT measurements. To their knowledge, the currently available OCT software does not permit inclusion of clustered mea­surements in linear regression models of RNFL progression.

    The original article can be found here.