Abstract
Purpose: :
To compare the sensitivity of 2 measures of cone–mediated function in patients with advanced retinitis pigmentosa (RP) and correlate sensitivity with in–vivo morphology assessment.
Methods: :
Patients with RP who had non–recordable full–field ERGs, Goldman visual fields smaller than 20º and visual acuity (VA) in the better eye (index eye) of ≤ 1.0 log MAR (ETDRS) were included. Each patient was tested with a static photopic visual field test (VF) (Humphrey visual field analyzer, stimulus size III, background light 10 cd/m2) and cone–mediated multifocal electroretinogram [(mfERG), VerisTM stimulus–camera–refractor unit, m–sequence–length 214 –1, flash intensity 2.67 cd /sec/m2 (A) and 5.33 cd/sec/m2 (B) on a dark background (1 cd /m2)]. VF and mfERG were tested at the same 103 retinal locations. Optical coherence tomography (OCT) scans (OCT 3, Carl Zeiss Ophthalmic Systems, Inc.) were obtained from the macular area (scan length 4.5mm). Data were compared with an age–matched control group.
Results: :
20 patients with non–syndromic and syndromic RP [simplex RP (11), XLRP (2), ADRP (1); Usher type 1 (2), 2 (3), 3 (1)] aged 21 to 68 years were tested. VF sensitivity was detectable in all patients, whereas mfERG 1st order–kernel responses, within 4º retinal eccentricity, were detectable only in 8 patients. MfERG responses above noise were associated with better VA, higher VF sensitivity in the central 4º and normal VF foveal threshold. They were not associated with retinal thickness at the fovea or in the central 4º. MfERG responses (N1, P1, N2) were reduced more often in response density than in implicit time. The number of retinal responses above noise did not differ significantly for either mfERG flash intensities. Retinal thickness was significantly decreased in the perifoveal areas but not in the foveal area.
Conclusions: :
Well–preserved measurable central psychophysical function is a prerequisite for obtaining recordable cone–mediated mfERG responses in patients with advanced RP. The VF appears to give a better functional outcome measure of central visual function than the mfERG in this patient cohort.
Keywords: retinal degenerations: hereditary • electrophysiology: clinical • visual fields