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Macular thickness differentiates occult BRAO, POAG
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Macular scanning may be important in baseline glaucoma evaluation to differentiate occult branch retinal artery occlusion from primary open-angle glaucoma and lead to fewer clinical implications from inaccurate diagnosis.
“Although acute branch retinal artery occlusion is typically straightforward to diagnose, its late stage can mimic primary open-angle glaucoma if the patient is unaware of past acute vision loss events and the optic nerve portends glaucoma suspicion,” researchers wrote.
A total of 437 subjects had comprehensive eye examinations including retinal nerve fiber layer (RNFL) and macular thickness using spectral domain OCT.
Researchers divided macular thickness scans into 64 individual thickness blocks, with thin macular thickness blocks defined by the lower 99% confidence interval from a group of normal eyes.
Eleven subjects met the criteria for the occult branch retinal artery occlusion (BRAO) group, which researchers defined by the presence of regional inner thinning with lack of inner layer stratification on macular SD-OCT B-scan images that spatially corresponded with arteriolar distribution and visual field loss location, according to researchers.
Fifty-two primary open-angle glaucoma (POAG) subjects were selected after matching for age and visual field mean defect.
The retinal thickness block distribution analysis in 42 normal, age-matched eyes showed that 99.5% of thickness blocks exceeded 200 µm in the normal eyes.
They found no differences in age, IOP, central corneal thickness, mean defect, pattern standard deviation, inter-eye cup-to-disc ratio asymmetry, global RNFL thickness, inter-eye global RNFL thickness asymmetry, and total, inferior and superior macular thicknesses.
BRAO eyes had a shorter axial length, smaller cup-disc ratio, higher intra-eye macular thickness asymmetry, higher inter-eye macular thickness asymmetry and higher frequency of thin macular thickness blocks of less than 200 µm.
All BRAO eyes exhibited at least three contiguous macular thickness blocks of less than 200 µm, and only 4% of POAG eyes and no normal control eyes demonstrated this finding, researchers concluded. – by Abigail Sutton
Perspective
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Lisa M. Young, OD, FAAO
Technologic advances in OCT enhance our clinical abilities by allowing detailed in vivo analysis of microscopic change to ocular structures.
For example, in the early 2000s, macular thickness scans via OCT were found to correlate with changes in RNFL structure in glaucoma. These scans have evolved to become commonplace, as many practitioners use them to aid in the diagnosis and management of ocular disease and, more specifically, glaucoma. However, OCT data may be altered by coincidental nonglaucoma pathology. How might we differentiate?
Sullivan-Mee and colleagues have found that SD-OCT macular scanning has the potential to confound glaucoma-related changes in the presence of occult branch retinal vein occlusion, with the latter presenting with a shorter axial length, smaller cup-to-disc ratio, higher intereye and intraeye macular thickness asymmetry, and higher frequency of thin macular thickness blocks less than 200 µm.
Based on these astute clinical findings, I plan on evaluating macular scans with a new-found vigor, specifically evaluating for symmetry, or lack thereof, and comparing each individual quadrant and contrasting them to the contralateral eye. Careful analysis will allow accurate interpretation, especially in those cases where the clinical data isn’t cohesive or doesn’t quite coincide with glaucoma-related findings.
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