Relationship between Visual Fields and the Electroretinogram in RPGR-X-linked Retinitis Pigmentosa

Abstract

Purpose: To quantify disease severity by investigating the relationship between Goldmann visual field (GVF) area and the full-field electroretinogram (ERG) parameters in patients with RPGR^ORF15 and RPGR^1-19 mutations.

Methods: A retrospective chart review of both eyes of 20 RPGR^ORF15 patients, ages 6 -42 yrs., and 12 RPGR^1-19 patients, ages 6 - 56 yrs. The horizontal diameter (HD) and GVF planimetric areas were measured for isopters IV4e and I4e. Normal range from 8 normally sighted observers ages 23 to 50 yrs. was IV4e: 4.2±0.04 SD log deg² for area and 149.7±6.73° SD for HD and I4e: 4.09±0.026 SD log deg² for area, and 131.32±5.86° SD for HD. ERG parameters included amplitude and implicit time for the ISCEV standard.

Results: In all subjects visual acuity ranged from 20/20 to 20/200. Square root of GVF area was statistically significantly related linearly to HD for both isopters and for each genotype. RPGR^ORF15: 16 of 20 (80%) patients had < 30% normal photopic flash and flicker amplitude including 3 with non-detectable (ND) ERG. These subjects had retained 23% to 80% of normal IV4e area and about 1% to 53% of I4e area. Their IV4e HD was in the range 23.9° to 139° and I4e HD from 5.7 to 53°. There was a significant linear correlation between scotopic rod-cone b-wave (Bmax) for I4e (R=0.8, p<0.0001) and for IV4e (R=0.6, p<0.0086). The relationship was poor between photopic amplitude and GVF area. However, both flicker and flash ERG implicit time had a statistically significant linear relationship with I4e (R=-0.89, p<0.0001) and with IV4e (R=-0.66, p<0.0015). RPGR^1-19 patients had more severely affected ERG and GVF. Ten of 12 patients had ND scotopic ERG; of these, 6 had ND photopic ERG. Photopic implicit times fell in one of two clusters, ND or delayed (>35 ms). There were no significant correlations for any of the ERG parameters with GVF area. Patients in these categories had 2.4% - 44% normal area or 21.5° - 55° HD with IV4e and 0.18% - 2.2% normal area or 5.8° - 14.5° HD with I4e.

Conclusions: The strongest relationship was for decreasing GVF area with increasing photopic ERG implicit time and for decreasing scotopic Bmax amplitude in RPGR^ORF15. Central GVF areas were retained despite reduced ERGs in both groups, but were variable when the photopic and/or scotopic ERG was non-detectable.

Keywords: 696 retinal degenerations: hereditary • 758 visual fields • 509 electroretinography: clinical