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Editors Selection IGR 20-3

Clinical Forms of Glaucoma: Rate of Conversion from Narrow Angle to PACG

Comment by Harsha Rao & Zia Pradhan on:

105119 Rates and Patterns of Diagnostic Conversion from Anatomical Narrow Angle to Primary Angle-Closure Glaucoma in the United States, Yoo K; Apolo G; Zhou S et al., Ophthalmology. Glaucoma, 2023; 6: 169-176

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Understanding the progression from anatomical narrow angles (ANA) to primary angle-closure glaucoma (PACG) has been addressed by epidemiological studies from India and China.^1-4 Yoo et al. researched this question in the United States using the data of newly-diagnosed ANA patients enrolled in the national healthcare claims database for at least eight years (3985 subjects).⁵ They found that 11.52% of ANA cases (459 of 3985) converted to PACG which is higher than the conversion rate of 1.25-5.7% found in previous studies.^1,2 One possible explanation for this discrepancy is that when a patient is first noted to have occludable angles on gonioscopy, their exact diagnosis within the primary angle-closure disease spectrum is unclear, and they are often labelled ANA. After the acquisition of additional information from IOP measurements, corneal pachymetry, visual fields, and a dilated disc examination (which may be after a laser peripheral iridotomy, LPI), the final diagnosis is often revised to PACG. Yoo et al. found that the conversion rate dropped from 10.59% per year during the first 6 months of an ANA diagnosis to 3.54% per year thereafter; the latter is therefore likely to be more accurate.

The authors also examined the factors associated with this diagnostic conversion. They found that LPI and IOP-lowering drops started within six months were positively associated with conversion to PACG. However, the authors appropriately state that this is unlikely a causative relationship. More likely, several patients initially labelled ANA probably had more severe disease and the diagnosis was revised after additional tests were performed. They also found that cataract surgery performed any time after the ANA diagnosis was associated with a reduced risk of diagnostic conversion. This is biologically plausible as removal of the lens addresses the ANA by relieving pupillary block and reducing the lens vault. However, the present study analyzed patient-level rather than eye-level data as they included ICD-9 codes which lack laterality.

A third of the subjects analyzed in this study (1281 of 3985) did not have a second ocular examination after being diagnosed as having ANA (index date), in spite of being continuously enrolled in the database

A significant point to note is that close to a third of the subjects analyzed in this study (1281 of 3985) did not have a second ocular examination after being diagnosed as having ANA (index date), in spite of being continuously enrolled in the database. And, close to a third of the remaining subjects (858 of 2704) did not have an ocular examination beyond one year of being diagnosed as ANA. This essentially makes the estimates and the associations found in the study weak and larger epidemiological studies with robust clinical data and follow-up are required to validate these results.

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