Changes of cone electroretinograms to colour flash stimuli after successful retinal detachment surgery

Abstract

Aim: To examine the changes in the short wavelength (S) and mixed long (L) and middle (M) wavelength sensitive cone (L,M-cone) electroretinograms (ERGs) after successful retinal detachment surgery.

Methods: Cone ERGs elicited by different colour flashes were recorded from 19 eyes with unilateral rhegmatogenous retinal detachment treated successfully by conventional buckling surgery. Ganzfeld colour flashes on a bright white background were used to elicit S-cone and L,M-cone ERGs. The ratio (operated eye/fellow eye) of the S-cone b-wave elicited by a 450 nm stimulus and the ratio (operated eye/fellow eye) of the L,M-cone b-wave elicited by a 633 nm stimulus were evaluated preoperatively and 1, 3, and 6 months after surgery.

Results: Preoperatively, no significant difference was observed between the ratio of the S-cone ERG amplitudes and the ratio of the L,M-cone ERG amplitudes. Postoperatively, the ratio of the L,M-cone ERGs increased significantly over the preoperative value (p=0.001) but the ratio of the S-cone ERG did not improve. There were significant differences between the ratios of the S-cone and the L,M-cone ERGs at 1, 3, and 6 months after surgery. The postoperative recovery of the S-cone ERG was significantly greater in eyes treated within 4 weeks after the onset of the detachment than in eyes treated later than 4 weeks.

Conclusions: These results indicate that the impairment of the L,M-cone system caused by retinal detachment may be reversible. However, the S-cone system may have more profound permanent damage.

Figure 1

Cone ERGs elicited by different colour flash stimuli in the presence of bright white background. The ERGs recorded before surgery (left), 6 months after surgery (middle), and from the normal fellow eye of a 22 year old patient whose macula was involved are shown. The numbers on the left indicate the nominal wavelength of maximum transmission of each filter and the numbers in parentheses indicate the neutral density filter used to adjust flash energy to produce approximately equal L,M-cone b-waves. The broken lines indicate the S-cone b-wave that was measured. S = S-cone b-waves; L,M = mixed L,M-cone b-waves. The calibration marker represents 0.62 µV vertically and 10 ms horizontally.

Figure 2

(A) Relation between the ratio of the S-cone ERG b-wave amplitude (S_op/S_norm) to 450 nm stimuli recorded at 6 months after surgery and the preoperative area of retinal detachment. The linear regression line for all patients was y=-0.00007x + 0.44 and the coefficient of correlation was r=-0.024, p=0.92. (B) Relation between ratio of the L,M-cone ERG b-wave amplitude to 633 nm stimuli (L,M_op/L,M_norm) at 6 months postoperatively and the preoperative area of retinal detachment. The linear regression line for all patients was y=-0.0003 + 0.78 and the coefficient of correlation was r=-0.25, p=0.61.