Deactivation of the rod response in retinopathy of prematurity

Abstract

It is known that retinopathy of prematurity (ROP) alters the activation of rod photoreceptors, but the effect of ROP on deactivation has not been investigated. We studied deactivation using an electroretinographic (ERG) paired flash procedure in 22 subjects (12 infants and 10 older subjects) with a history of preterm birth and ROP. The amplitude of the rod-isolated a-wave response to a flash presented 2-120 s after a test flash was measured, and the time at which it reached 50% of the single flash amplitude (t(50)) was determined by linear interpolation. Deactivation results were compared to those in former preterms who never had ROP (n = 6) and term-born controls. In infants, t(50) values of ROP subjects did not differ from those in subjects who never had ROP or term-born controls. Among mature ROP subjects, eight of 12 had t(50) values longer than any control subject. Prolonged deactivation in these mature ROP subjects may indicate lack of maturation of the deactivation process (t(50)) or progressive compromise of retinal function with increasing age.

Fig. 1

Sample results from a 14 year old subject with a history of mild ROP and t₅₀ value (10 s) close to the ROP median. Rod isolated ERG a-wave responses are shown in the left panel; the responses to the single flash and to the probe flash at the indicated inter-stimulus intervals (ISI) are shown. In the right panel, a-wave amplitude (R) expressed as a proportion of the response to the single flash (R_MAX) is plotted as a function of ISI. The ISI (arrow) that would produce a half maximum response was determined by linear interpolation.

Fig. 2

Values of t₅₀ and S_ROD. Upper panel: Values of t₅₀ are plotted for the mild ROP subjects (filled circles), the no ROP subjects (filled triangles), and term born control subjects (open circles). The horizontal bars indicate the median for each group. Lower panel: Values of S_ROD are plotted for the same subjects; all features are as described for the upper panel. S_ROD values for these subjects were reported previously [1].

Fig. 3

Deactivation parameter (t₅₀) versus activation parameter (S_ROD). In both panels, the shaded bands indicate the range of t₅₀ and S_ROD values in control subjects; t he cross hatched area represents the locus of control data [11]. Data from infant ROP subjects (n=10) are plotted in the upper panel and from mature ROP subjects (n=12) in the lower panel. The same scales are used in both panels to facilitate comparison across age groups.