Decreased retinal-choroidal blood flow in retinitis pigmentosa as measured by MRI

Abstract

Purpose: To evaluate retinal and choroidal blood flow (BF) using high-resolution magnetic resonance imaging (MRI) as well as visual function measured by the electroretinogram (ERG) in patients with retinitis pigmentosa (RP).

Methods: MRI studies were performed in 6 RP patients (29-67 years) and 5 healthy volunteers (29-64 years) on a 3-Tesla scanner with a custom-made surface coil. Quantitative BF was measured using the pseudo-continuous arterial spin-labeling technique at 0.5 × 0.8 × 6.0 mm. Full-field ERGs of all patients were recorded. Amplitudes and implicit times of standard ERGs were analyzed.

Results: Basal BF in the posterior retinal-choroid was 142 ± 16 ml/100ml/min (or 1.14 ± 0.13 μl/mm(2)/min) in the control group and was 70 ±19 ml/100ml/min (or 0.56 ± 0.15 μl/mm(2)/min) in the RP group. Retinal-choroidal BF was significantly reduced by 52 ± 8 % in RP patients compared to controls (P<0.05). ERG a- and b-wave amplitudes of RP patients were reduced, and b-wave implicit times were delayed. There were statistically significant correlations between a-wave amplitude and BF value (r=0.9, P<0.05) but not between b-wave amplitude and BF value (r =0.7, P=0.2).

Conclusions: This study demonstrates a novel non-invasive MRI approach to measure quantitative retinal and choroidal BF in RP patients. We found that retinal-choroidal BF was markedly reduced and significantly correlated with reduced amplitudes of the a-wave of the standard combined ERG.

Figure 1

Full-field ERGs from RP (thin trace) and non-RP eyes (thick trace) of the unilateral RP patient. ERG includes single flash cone (A), 30-Hz flicker (B), rod (C) and standard combined (D).

Figure 2

Basal BF (in color) overlaid on scout images from two representative RP eyes (A,C) and their matched control eyes (B,D). (A) and (B) were from the RP and non-RP eyes of the same RP patient.

Figure 3

Blood flow profiles from RP patients (dashed line) and control subjects (solid line) across the retinal-choroidal thickness from the sclera to the vitreous as shown in the inset. Error bars are standard errors of the mean (SEM).

Figure 4

Blood flow profile from RP patients (dash line) and control subjects (solid line) along the length of the retina from the nasal to the temporal side of fovea as shown in the inset. Error bars are SEM. Black arrow indicates the location of optic nerve head.

Figure 5

Scatterplot of individual BF values from RP patients (open square) and control subjects (solid square). The bars indicate the mean and SEM.

Figure 6

Scatterplots of standard combined ERG amplitudes (A) and ERG implicit time (B) from each RP patient as a function of retinal-choroidal BF for the same patient.