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Review
. 2009 Jun;86(6):E653-8.
doi: 10.1097/OPX.0b013e3181a6a237.

Development of Rod Function in Term Born and Former Preterm Subjects

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Free PMC article
Review

Development of Rod Function in Term Born and Former Preterm Subjects

Anne B Fulton et al. Optom Vis Sci. .
Free PMC article

Abstract

Purpose: To provide an overview of some of our electroretinographic (ERG) and psychophysical studies of normal development of rod function and their application to retinopathy of prematurity (ROP).

Methods: ERG responses to full-field stimuli were recorded from dark adapted subjects. Rod photoreceptor sensitivity (SROD) was calculated by fit of a biochemical model of the activation of phototransduction to the ERG a-wave. Dark adapted psychophysical thresholds for detecting 2 degrees spots in parafoveal (10 degrees eccentric) and peripheral (30 degrees eccentric) retina were measured and the difference between the thresholds, Delta10-30, was examined as a function of age. SROD and Delta10-30 in term born and former preterm subjects were compared.

Results: In term born infants, (1) the normal developmental increase in SROD changes proportionately with the amount of rod visual pigment, rhodopsin, and (2) rod-mediated function in central retina is immature compared with that in peripheral retina. In subjects born prematurely, deficits in SROD persist long after active ROP has resolved. Maturation of rod-mediated thresholds in the central retina is prolonged by mild ROP.

Conclusions: Characterization of the development of normal rod and rod-mediated function provides a foundation for understanding ROP.

Figures

Figure 1
Figure 1
Rhodopsin growth curve and the preterm onset of ROP. Rhodopsin content is plotted as percent of the adult mean. The large arrow indicates the age at which prethreshold ROP is diagnosed. The small arrow indicates a preterm age.
Figure 2
Figure 2
Procedures for assessment of retinal function in dark adapted infants. (A) Electroretinography. A 10 week old infant is positioned under an integrating sphere that is used for presenting full-field stimuli. A bipolar contact electrode on the infant's right eye registers changes in the transretinal potential, the ERG, that are evoked by brief flashes of light. (B) Psychophysical Δ10-30 test. An older infant reaches toward a test spot presented on a rear projection screen. For younger infants, an adult observer reports on every trial the infant's looking response to the right or left of the screen. Details of the procedure are given in Barnaby et al. A color version of this figure is available online at www.optvissci.com.
Figure 3
Figure 3
Rod photoreceptor sensitivity, SROD, in former preterms. The solid curve represents the average normal growth curve for SROD; dashed lines show the upper and lower 95% prediction limits of normal. Each symbol represents one subject with ROP category as indicated in the key. The 50% point on the SROD growth curve is at approximately 10 weeks post term and thus within the 95% confidence interval for the growth curve for rhodopsin. Re-plotted from Fulton et al. and Moskowitz et al. with additional data added.
Figure 4
Figure 4
Psychophysical Δ10-30 test. (A) ROP zones and location of stimuli on the retina. The position of the parafoveal and peripheral stimuli (filled circles) are superimposed on the circular diagram of the ROP zones. (B) Schematic diagram of the screen and stimuli. The 2° diameter stimuli at the parafoveal (10° eccentric) and peripheral (30° eccentric) sites are indicated. The + indicates the central fixation display. Re-plotted from Figure 1 in Barnaby et al.
Figure 5
Figure 5
Dark adapted thresholds in former preterms. The difference between parafoveal and peripheral thresholds (Δ10-30) is plotted as a function of corrected age. Panel A shows data from subjects with a history of mild, untreated ROP (N=12); panel B shows data from former preterms who never had ROP (N=12). Data points from an individual are connected by line segments. Values above zero indicate that the parafoveal threshold was elevated relative to the peripheral threshold. In term born infants aged 6 months, as in adults, Δ10-30 is zero. The dashed lines in each panel indicate the upper and lower limits of the 99% prediction interval of normal. Re-plotted from figures 2 and 3 in Barnaby et al.

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