The neural retina in retinopathy of prematurity

Abstract

Retinopathy of prematurity (ROP) is a neurovascular disease that affects prematurely born infants and is known to have significant long term effects on vision. We conducted the studies described herein not only to learn more about vision but also about the pathogenesis of ROP. The coincidence of ROP onset and rapid developmental elongation of the rod photoreceptor outer segments motivated us to consider the role of the rods in this disease. We used noninvasive electroretinographic (ERG), psychophysical, and retinal imaging procedures to study the function and structure of the neurosensory retina. Rod photoreceptor and post-receptor responses are significantly altered years after the preterm days during which ROP is an active disease. The alterations include persistent rod dysfunction, and evidence of compensatory remodeling of the post-receptor retina is found in ERG responses to full-field stimuli and in psychophysical thresholds that probe small retinal regions. In the central retina, both Mild and Severe ROP delay maturation of parafoveal scotopic thresholds and are associated with attenuation of cone mediated multifocal ERG responses, significant thickening of post-receptor retinal laminae, and dysmorphic cone photoreceptors. These results have implications for vision and control of eye growth and refractive development and suggest future research directions. These results also lead to a proposal for noninvasive management using light that may add to the currently invasive therapeutic armamentarium against ROP.

Keywords: Electroretinogram; Infant visual psychophysics; Retinal development; Retinopathy of prematurity.

Figure 1

Rhodopsin content and large vessel coverage of the temporal retina. The purple curve shows the developmental increase in retinal rhodopsin content in the human eye, normalized to the median adult rhodopsin content, 7.19 nmol/retina (Fulton et al., 1999a). At age 5-weeks post-term, rhodopsin content reached 50% of the adult value (95% confidence interval: 0–10 weeks). Data from Fulton et al. (Fulton et al., 1999a) copyright Association for Research in Vision and Ophthalmology. The red arrow indicates the onset of prethreshold ROP at 32 weeks gestation (Palmer et al., 1991) which coincides with the period of rapid developmental increase in rhodopsin content. The points show percent vessel coverage, estimated from Figure 6 in Provis, 2001 (Provis, 2001); a logistic growth curve (brown line) is fit to the points.

Figure 2

Rod ring superimposed on diagram used to describe location (zones) and extent (clock hours) of retinopathy (ICROP, 2005). The “rod ring” (Hendrickson, 1994), indicated by the purple oval band, is an annular region with a high density of rods that is concentric with the fovea and extends horizontally to the approximate eccentricity of the optic nerve head. N indicates nasal; T indicates temporal.

Figure 3

Sample rod mediated full-field ERG records and model fits of the a-wave and b-wave from a 1 year old subject with Severe ROP. Upper panel: Dark adapted ERG responses to a series of blue flashes increasing in strength from top to bottom, left to right. The troland values are indicated to the left of each trace. Calibration bars pertain to all waves. Lower left panel: The solid lines show the first 40 ms of the response to the five brightest flashes; the red dashed lines show fits of Equation 3 to the a-waves. The parameters rod photoreceptor sensitivity (S_ROD), amplitude of the saturated rod response (R_ROD), and a brief time delay (t_d) are indicated. Lower right panel: The points indicate b-wave amplitude plotted as a function of stimulus intensity; the curve shows the fit of Equation 4 to the b-waves. The parameters post-receptor sensitivity (log σ) and saturated amplitude (V_MAX) are indicated.

Figure 4

Growth curves for ERG parameters and rhodopsin. The photoreceptor parameters (S_ROD and R_ROD), and the post-receptor parameters (σ and V_MAX) are plotted as a function of log age. Parameters of these curves are shown in Table 3. Data from all but 14 of these term born subjects have been reported previously (Fulton & Hansen, 2000; Fulton et al., 2009). The rhodopsin growth curve (Fulton et al., 1999a), normalized to the median adult value, is also shown.

Figure 5

Photoreceptor sensitivity (S_ROD) and post-receptor sensitivity (log σ) for two subjects tested in infancy and later in childhood. One subject had a history of Mild ROP and the other a history of Severe ROP.

Figure 6

Photoreceptor sensitivity (S_ROD) and post-receptor sensitivity (σ) for ROP subjects and term born controls. For S_ROD (left panel) and for σ (right panel), the mean (±1 SEM) for each group is plotted as the log difference from normal for age in infancy (median age 10 weeks) and in childhood (median age 10 years). Data from 85 of the ROP subjects were reported in Harris et al. (2011); 13 new ROP subjects were included in the current analysis.

Figure 7

Deficits in post-receptor sensitivity (log σ) as a function of the sum of deficits in photoreceptor sensitivity (S_ROD) and saturated amplitude (R_ROD) in term born subjects. Data are shown for 4 and 10 week old infants and for adults. Each point represents data from an individual subject. The range of deficits in adult post-receptor sensitivity is indicated by the horizontal red dashed lines, the range of adult photoreceptor sensitivity by the vertical red dashed lines; the median adult value is at (0,0). The dotted line has a slope of 1.0. Data from all but 14 of these subjects were reported in Fulton et al., 2009; data from 14 new term born subjects were added.

Figure 8

Deficits in post-receptor sensitivity (log σ) as a function of the sum of deficits in photoreceptor sensitivity (S_ROD) and saturated amplitude (R_ROD) in the three groups of ROP subjects [median age 7.5 (range 0.1 to 23.3) years]. Each point represents data from an individual subject. All other features of the graph are the same as in Figure 7. Data from 70 of the subjects were reported in Harris et al. (2011); data from 13 new ROP subjects were added. Subjects tested using skin electrodes in the Harris study were excluded from the analysis because of the uncertainty in specifying saturated rod amplitude (R_ROD) from skin electrode recordings.

Figure 9

Rod-mediated spatial summation. Upper panel: Spatial summation functions are shown for a representative subject from each group. Middle panel: Log threshold is plotted as a function of log stimulus area. Average D_CRIT values are used to construct a summary function for each group. For small spots, threshold depends on the total energy of the stimulus (slope = −1 on log-log coordinates) up to a critical diameter (D_CRIT). For stimuli larger than (D_CRIT), threshold changes little (slope ≈ 0). The two lines intersect at D_CRIT. Lower panel: Values of D_CRIT are plotted for individual subjects in the three ROP groups and for each term born control. The mean D_CRIT value for each group is indicated by the color-coded dotted line. Data from Hansen et al., 2014; copyright Association for Research in Vision and Ophthalmology.

Figure 10

Rod mediated temporal summation. Upper panel: Temporal summation functions are shown for a representative subject from each group. Middle panel: Log threshold is plotted as a function of log stimulus duration. Thresholds were recorded for seven stimulus durations (10 to 640 ms); the x-axis has been truncated to emphasize the range of durations that show complete summation. For brief stimulus durations, threshold depends on the total energy of the stimulus (slope = −1 on log-log coordinates) up to a critical duration (T_CRIT). For stimuli longer than T_CRIT, threshold changes little (slope ≈ 0). The two lines intersect at T_CRIT. Lower panel: Values of t_CRIT are plotted for each subject in the three ROP groups and for each term born control. The mean T_CRIT value for each group is indicated by the color-coded dotted line. Data from Hansen et al., 2015; copyright Association for Research in Vision and Ophthalmology.

Figure 11

Rod increment threshold functions and deficits in dark adapted threshold (T_DA) and the Eigengrau (A₀). Upper panel: Log threshold in No ROP, Mild ROP, and Severe ROP as a function of log background intensity; the function for term born controls (not shown) does not differ significantly from that in the No ROP subjects. The stimulus was a 50 ms, 5° diameter flash presented 20° eccentric. The curves plot Equation 6 using median T_DA and A₀ from each group. Dotted lines: For the No ROP curve, the horizontal asymptote is at T_DA; the oblique line (slope = 1) intersects T_DA at A₀, the background level that elevates threshold by a factor of 2 (0.3 log units). Lower panel: Deficit in T_DA plotted as a function of deficit in A₀. Each point represents an individual subject. The range of T_DA values in term born controls is indicated by the horizontal red dashed lines, the range of control A₀ values by the vertical red dashed lines; the median control value is at (0,0). The prediction for a preadaptation site effect is shown by the dotted diagonal line with slope = 1.0. Data from Hansen et al., 2016; copyright Association for Research in Vision and Ophthalmology.

Figure 12

Rod mediated, dark adapted thresholds. Mean (±SEM) threshold in term born, No ROP, and ROP subjects (both Mild and Severe) is plotted as function of age in the parafovea (10° eccentricity; left panel) and in the periphery (30° eccentricity; right panel). The analysis includes 29 term born control subjects and 127 preterm subjects, many of whom were tested at more than one age; data obtained at all sessions were included in the analysis. Twenty-six new ROP subjects have been added; 101 of the 127 ROP subjects were reported by Reisner et al., 1997 and Barnaby et al., 2007; all 29 control subjects were reported by Hansen & Fulton, 1995 and Hansen & Fulton, 1999.

Figure 13

ERG ON and OFF responses to a long flash. Upper panel: ERG responses to a 150 msec full-field flash presented on a steady background recorded from a term born 10 week old infant and from an adult control subject. The ON and OFF responses are indicated. The time course of the stimulus is represented by the horizontal line above the x-axis. Lower panel: Implicit time of the OFF response (d-wave) for individual 10-week old infants and adults. The horizontal dotted lines indicate the median for each group. Data from Altschwager et al, 2015 ARVO presentation; copyright Association for Research in Vision and Ophthalmology.

Figure 14

Photopic b-wave stimulus-response relationship. Upper panel: The model of the photopic b-wave stimulus-response relationship combines the sum of a Gaussian function that assesses the OFF component (solid green curve) and a logistic function that assesses the ON component (solid blue curve) to model the photopic b-wave (dashed red curve) (Hamilton et al., 2007). Lower panels: The amplitude of the b-wave is plotted as a function of flash intensity in a 10 week old term born infant (left) and an adult control subject (right). The red dashed curve in each of the lower panels shows a fit of the model to the data. Data from Altschwager et al, 2015 ARVO presentation; copyright Association for Research in Vision and Ophthalmology.

Figure 15

Drawings of macular cross sections. These drawings represent micrographs of cross sections of the macula at ages ranging from preterm to post term. From Bach and Seefelder, 1914; digital image from https://archive.org/stream/b21288008#page/n3/mode/2up

Figure 16

Optical coherence tomography (OCT) images. OCT images from a term born control subject and subjects with Severe and Mild ROP; the central ~15° (± 7.5° from the center of the pit) are shown. All three subjects were adolescents (age 13–18).

Figure 17

Adaptive optics scanning light ophthalmoscopy (AO-SLO) images. Representative registered and averaged images (0.25°×0.25°) obtained from a term born subject, a Mild ROP subject, and a Severe ROP subject at four temporal eccentricities (4.5°, 9°, 13.5°, and 18°) using confocal aperture (upper panel) and offset aperture (lower panel) are shown. Adapted from Ramamirtham et al., 2016; copyright Association for Research in Vision and Ophthalmology.

Figure 18

Spherical equivalent refraction in ROP subjects as a function of age. Data are shown for 1,087 refractions of one eye in 284 ROP subjects. For subjects who had ERG recording and/or retinal image, data from the tested eye was used; for subjects who participated in the binocularly performed psychophysical experiments, data from the left eye was used. One to 22 (median = 2) refractions were performed on an individual; all refractions are shown. Upper panel: 309 refractions from 44 Severe ROP subjects; middle panel: 581 refractions from 151 Mild ROP subjects; lower panel 197 refractions from 89 No ROP subjects. Data from 279 of the subjects and 1,027 of the refractions were reported by Moskowitz et al., 2016; data from five new subjects and 50 new refractions have been added. The black lines indicate the 95% prediction limits for normal refractive error, plotted using values from Mayer et al. (2001) for 1 to 48 month olds and from Zadnick et al. (2003) for school aged children.

Figure 19

Percent of individuals with ametropia in each ROP group. Each of the 284 subjects whose data are shown in Figure 18 was counted only once. Severe ROP, n = 44; Mild ROP, n = 151; No ROP, n = 89.