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Alexandra Davies, Anika Nanda, Robert E MacLaren; Effect of reduced visual acuity on microperimetry performance in patients with inherited retinal degenerations. Invest. Ophthalmol. Vis. Sci. 2019;60(9):1820.
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© ARVO (1962-2015); The Authors (2016-present)
Microperimetry assesses sensitivity of rods and cones in the central 10 degrees of retina. Patients can have difficulties in performing this examination due to poor visual acuity (VA) that leads to poor fixation and reliability. The aim of this study was to audit the reliability of microperimetry in terms of fixation for patients with impaired vision caused by two types of inherited retinal degeneration (IRD) – RPGR related retinitis pigmentosa and choroideremia (CHM).
This was a non-interventional, retrospective analysis of anonymised data acquired during routine clinical care. VA was tested using the Early Treatment Diabetic Retinopathy Study protocol. Patients performed a 10-2 threshold strategy on the Macular Integrity Assessment Microperimeter after 20 minutes dark adaptation. This compares fixation against the retinal image. Fixation stability can be defined as the percentage of fixation points within the central 1 degrees (P1) or 2 degrees (P2). In total, plots from 29 patients (12 RPGR, 17 CHM, aged 24-84) were analysed.
Results were divided into two groups: RPGR retinitis pigmentosa and CHM. Statistical analysis was performed on P1 and P2 with BCVA using Spearman’s rank correlation coefficient. For CHM both P1 and P2 were strongly correlated to VA (p<0.01 for both). CHM patients with a BCVA of at least 67 letters were able to maintain accurate fixation with 100% of the fixation points located within P1. Patients with over 75% of fixation points in P1 had a BCVA of at least 47 letters. For RPGR, P1 and P2 were similarly correlated to VA (p=0.06 for P1 and p<0.01 for P2). RGPR patients who maintained 100% fixation in P1 had a BCVA of at least 66 letters, whilst 39 letters was the minimum cut off for gaining at least 75% of P1 fixation.
Patients with IRD were able to maintain 100% fixation within the central 1 degrees with a minimum VA of 66 letters. This compares favourably to a recent study in macular diseases (Estudillo et al., 2017), in which none of 18 patients with impaired VA ranging from 6 to 92 letters could achieve 100% P1. This may be due to the significant loss of peripheral visual field in IRD patients, which might assist in fixation as VA decreases. Since a P1 score of at least 75% was seen with VA as low as 39-47 letters, microperimetry may still provide reliable endpoints for more advanced CHM and RPGR patients.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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