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G. Sobaci, G. Özge, F. C. Gündogan; Usability of OCT-Assessed RNFL Analysis in Definition of Potential Candidates for Successful Replacement/Restoration Therapies in the Retina. Invest. Ophthalmol. Vis. Sci. 2009;50(13):6272.
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Integrity of the inner retinal layer (IRL) has been suggested as a prerequisite for successful replacement/restoration therapy in the outer retinal layer (ORL). Recently, variability in OCT-assessed retinal nerve fiber layer (RNFL) thickness of patients with retinitis pigmentosa (RP) has been shown. Thinner RNFL has been related to the optic atrophy (OA); however, the reason(s) for thicker RNFL seen in considerable percentage of patients have not yet been clarified. We need better understanding of the cause(s) of the thicker RNFL to make use of OCT-RNFL thickness as a measure of the integrity of the IRL in RP. In the light of recent hard evidences which highlight transsynaptic anterograde and retrograde neural degeneration in the retina, we hypothesize that thicker RNFL in RP might be related to relative preservation of cones in the ORL.
Twenty-seven patients with RP, 10 patients with traumatic OA, and 30 healthy subjects were enrolled. They were selected among conscripts between ages 20 to 27. One of eyes with better visual acuity in the RP and the control groups, and the traumatized eye in OA group were studied. Patients who had visual acuity (VA) of less than 1 logMAR (20/200 Snellen equivalent), refractive errors with spherical equivalent of more than 3 diopters, the larger or smaller optic disk, intraocular pressure and visual fields suggesting glaucoma, and cystoid macular edema were excluded. ERG recordings according to the ISCEV standards (Roland Retiport®, Wiesbaden, Germany), and RNFL and central macular thickness (CMT) measurements by fast RNFL algorithm (Stratus-3, Zeiss, Basel) were performed in the groups.
In RP group, thicker RNFL (> 95% CI upper limit) were observed in more than 2 different sectors in 10 eyes (37%). Eight (29.6%) eyes in RP group, and all eyes in OA group had thinner RNFL (p=0.01, Fisher test). Significant correlations (p<0.05), especially in temporal sectors (p<0.01), were found between RNFL and ERG parameters (scotopic rod a wave amplitude, cone b implicit time, 30Hz Flicker P1 amplitude and implicit time) in RP and OA groups. Insignificant correlations were found between CMT and VAs in both groups. No correlation existed between ERG parameters and VAs in OA and RP groups. When thicker RNFL compared to thinner ones, only cone ERG b wave implicit times showed significantly less values (p=0.008) in RP group.
Thicker RNFL values in RP might be the result of relative preservation of the cone functions in RP which may be indicative of successful visual outcome.
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