Abstract
PurposeTo investigate the validity and reliability of macular rod photoreceptor function measurement with a microperimeter.MethodsMacular sensitivity in dark-adapted retinitis pigmentosa (RP) patients (22 eyes; 9–67 years of age) and controls (five eyes; 22–55 years of age) was assessed with a modified Humphrey field analyzer (mHFA), as well as a scotopic microperimeter (Nidek MP-1S). Sensitivity loss (SL) was estimated at rod-mediated locations. All RP eyes were re-evaluated at a second visit 6 months later. The dynamic range of the MP-1S was expanded with a range of neutral-density filters (NDFs).ResultsIn controls, a 4 NDF was used at all macular locations tested. In patients with RP, 0 to 3 NDFs were used, depending on the local disease severity. At rod-mediated locations (n = 281), SL estimates obtained with the MP-1S were highly correlated (r = 0.80) with those of the mHFA. The inter-perimeter difference of SL averaged less than 3 decibels (dB) with all NDFs, except those with most severe locations evaluated with a 0 NDF, where the difference averaged more than 6 dB. The results were similar on the second visit.ConclusionsThe MP-1S estimates of SL are highly correlated with those of the mHFA over a wide range of disease severity replicated at two visits; however, there was an unexplained bias in the magnitude of SL estimated by the MP-1S especially at loci with severe disease.Translational RelevanceMP-1S scotopic microperimetry can be used to evaluate changes to macular rod function, but evaluation of treatment potential by quantitative comparison of SL to retinal structure will be more challenging.
Highlights
Mutations in >300 genes cause inherited retinal diseases (IRDs), due to dysfunction and/or degeneration of photoreceptors.[1,2] Retinitis pigmentosa (RP) is one of the more common clinical diagnoses associated with IRDs
The MP-1S estimates of sensitivity loss (SL) are highly correlated with those of the modified Humphrey field analyzer (mHFA) over a wide range of disease severity replicated at two visits; there was an unexplained bias in the magnitude of SL estimated by the MP-1S especially at loci with severe disease
The ceiling effect implied that the instrument was not producing dim enough stimuli to measure true dark-adapted sensitivities
Summary
Mutations in >300 genes cause inherited retinal diseases (IRDs), due to dysfunction and/or degeneration of photoreceptors.[1,2] Retinitis pigmentosa (RP) is one of the more common clinical diagnoses associated with IRDs. The photoreceptor identity and disease severity vary with molecular defect and with retinal location. In terms of understanding the phenotype, stage of disease severity, natural history, and response to treatments, it is important to measure the spatial distribution of rod and cone function and any changes over time. On the other hand, estimating rod function in IRDs can be more challenging despite the rod photoreceptors being the dominant cell type across most of the normal human retina. In dark-adapted normal eyes, light sensitivity is dominated by the rods across the retina except at the rod-free foveola. In dark-adapted IRD eyes, the photoreceptor source of sensitivity at
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