Abstract
Purpose: :
In the macula, the cones reach maturity later than do the parafoveal rods. We hypothesized that the parafoveal rods are less affected by ROP than the later maturing central cones.
Methods: :
Psychophysical measurements of the dark adapted threshold for the parafoveal rods and age appropriate measurements of light adapted visual acuity were obtained in infancy and childhood in subjects with a history of preterm birth. Threshold for detecting 2° diameter, 50 ms duration stimuli presented parafoveally (10° eccentric) was estimated using a two-alternative, forced choice preferential looking method. At age 6 months, the Teller Acuity Card (TAC) procedure was used to estimate grating acuity. At age 3 years and older, either TAC grating acuity or symbol acuity was determined. The subjects’ threshold and acuity values were expressed relative to age-matched normal values. The subjects were categorized according to maximum acute-phase ROP as severe, treated ROP (n = 10); mild, untreated ROP (n = 57); or no ROP (n = 27).
Results: :
In 6 month olds, parafoveal rod mediated thresholds were elevated in mild and severe ROP compared to term born infants and former preterms who never had ROP; PL grating acuity was normal for age in all preterm groups. At age 3 years and older, parafoveal rod thresholds were normal in 80% of subjects with mild ROP but in only 40% of subjects with severe ROP; acuity deficits were uncommon and minimal in mild ROP but frequent and moderate in severe ROP.
Conclusions: :
ROP appears to have more frequent and relatively more severe effects on the later maturing central cones than on the parafoveal rods. This contrasts the more marked effect of ROP on peripheral rods than cones; in the periphery, cones mature earlier than rods.
Keywords: retinopathy of prematurity • visual acuity • retinal development