Association between retinal steepness and central myopic shift in children.

PURPOSE: Retinal steepness at the posterior pole was shown to be associated with peripheral refraction, and there exists strong evidence that peripheral refraction influences central refractive development. The purpose of this study was to investigate whether retinal steepness is associated with central myopic shift in children. METHODS: Central refraction was measured in OD of 140 children aged 7 to 11 years as central sphere equivalent refraction (CSER) and central sphere refraction at baseline and after ~30 months. For the estimation of retinal steepness, relative peripheral eye length (RPEL) was determined in OD by measuring length axially with a custom-made optical low coherence interferometer and subtracting it from eye length measured peripherally at 20° in the nasal, inferior, temporal, and superior fields. Association between baseline RPEL at the various locations and shift in central refraction was evaluated with a Structural Equation Modeling analysis. RESULTS: CSER at baseline measured +0.05 ± 0.54 diopters (D) (mean ± SD). Shift in CSER, as standardized over a 30-month interval to account for individual differences in the follow-up period, was -0.21 ± 0.56 D. A weak, but significant, correlation was observed between baseline RPEL in the temporal retina and myopic shift in CSER (r = 0.207, p = 0.049), steeper retinas displaying greater myopic shifts. Myopic shift was correlated with axial elongation but not correlated with baseline refraction. Analyses were performed for both CSER and central sphere refraction with near-identical results. RPEL did not change significantly. CONCLUSIONS: The significant correlation between temporal RPEL and central myopic shift, with the latter being independent of baseline refraction, supports the hypothesis that eye shape at the posterior pole is one of the factors influencing visually guided axial eye growth, possibly through associated peripheral defocus. Its predictive value for refractive development and limitation to the temporal retina require further investigation.

Highly precise eye length measurements in children aged 3 through 12 years.

OBJECTIVE: To determine the feasibility, reliability, and validity of using partial coherence interferometry, a noncontact method that detects interference patterns from various layers of the eye, to measure axial length in young children. METHODS: The right eye of 64 subjects (mean age, 8.4 y; age range, 3.4-12.9 y; best-corrected visual acuity >or=20/30) was measured. Subjects fixated monocularly on the collimated light pattern from a laser diode (the alignment beam) and the operator used a video monitor to align the corneal reflection in the optical path. Axial length was measured during an 0.8-second scan using interference patterns from a collimated short coherence superluminescence diode aligned coaxially with the laser diode. Five series of 16 readings each were obtained. The average axial length for each of the 5 series of readings was calculated. Main Outcome Measure Axial length. RESULTS: Within-subject precision of axial length measurements was high, with an overall SE of measurement of 8 micro m for individual subjects across the 5 sessions (95% confidence interval, +/-16 micro m). Subgroup analysis showed that sex, age, spherical equivalent, and refractive error exerted statistically significant effects on precision, but all of the differences among subgroups were 3 micro m or less and likely to be insignificant clinically. Axial length measured by partial coherence interferometry varied systematically, with factors known to influence eye length (ie, age and refractive error), further validating the measurement method. CONCLUSION: The partial coherence interferometry technique provides reproducible, extraordinarily precise eye length measurements in young children and should enable novel approaches to study eye growth and refractive development.

Axial and peripheral eye length measured with optical low coherence reflectometry.

An optical low-coherence reflectometer (OLCR device) is described that allows the precise and noncontact measurement of eye length. The device measures eye length both on-axis and off-axis, thus enabling the determination of eye shape, an ocular parameter thought to be important in the development of refractive error. It is essential for several applications in ophthalmology and vision science. This improved OLCR device operates using a single-beam interferometer with a beam deflection mechanism that allows the precise measurement of eye length along the visual axis and within 15 deg horizontally and vertically from the fovea. The validity of this instrument and its revised software is evaluated by measuring the reproducibility of axial length results in an adult eye and an artificial eye, and by correlating axial eye length measured in a group of ten adult eyes with axial eye length obtained with A-scan ultrasound in the same eyes. The precision obtained with adult subjects is compared with that obtained with children.

Variability of retinal steepness at the posterior pole in children 7-15 years of age.

PURPOSE: Considerable evidence suggests that both axial and peripheral refraction play important roles in eye growth control. The large variability in peripheral refraction seen in adults and children indicates that the peripheral retina is exposed to a wide range of refractive errors. The current lack of appropriate measurement techniques has hampered the determination of whether variability in peripheral refraction between individuals can be correlated with variability in retinal steepness. An Optical Low Coherence Reflectometer (OLCR) was developed to determine retinal steepness. METHODS: Retinal steepness was assessed in right eyes of 63 children 7-15 years of age by measuring eye length (EL) and spherical equivalent refraction (SER) axially and at 15 degrees temporally, nasally, inferiorly and superiorly with OLCR and Binocular Auto-Refractometry, respectively, during cycloplegia. At each peripheral location, relative peripheral EL and SER (i.e., the difference between peripheral and axial readings) were compared between myopic, emmetropic and hyperopic eyes, and the correlation between relative peripheral EL and SER was analyzed. RESULTS: Although the standard deviations were large, significant differences in relative peripheral EL and SER between refractive groups as well as a significant correlation between relative peripheral EL and SER were observed at several of the assessed locations. CONCLUSIONS. The results strongly suggest that peripheral refraction is correlated with retinal steepness and that previously observed variability in peripheral refraction chiefly reflects variability in retinal steepness. If peripheral refraction represents a determining parameter in the control of eye growth, the precise measurement of retinal steepness could be used not only to improve estimates of myopic progression, but also to identify children who are at high risk of developing myopia. It may lead to specialized clinical/optical treatments, e.g. the correction of not only axial but also peripheral refractive errors, which are more effective than current treatments in individuals who are at risk of myopia development or progression.

Exaggerated eye growth in IRBP-deficient mice in early development.

PURPOSE: Because interphotoreceptor retinoid-binding protein (IRBP) is expressed before being needed in its presumptive role in the visual cycle, we tested whether it controls eye growth during development. METHODS: The eyes of congenic IRBP knockout (KO) and C57BL/6J wild-type (WT) mice ranging in age from postnatal day (P)2 to P440 were compared by histology, laser micrometry, cycloplegic photorefractions, and partial coherence interferometry. RESULTS: The size and weight of IRBP KO mouse eyes were greater than those of the WT mouse, even before eye-opening. Excessive ocular enlargement started between P7 and P10, with KO retinal arc lengths becoming greater compared with WT from P10 through P30 (18%; P < 0.01). The outer nuclear layer (ONL) of KO retinas became 20% thinner between P12 to P25, and progressed to 38% thinner at P30. At P30, there were 30% fewer cones per vertical section in KO than in WT retinas. Bromodeoxyuridine (BrdU) labeling indicated the same number of retinal cells were born in KO and WT mice. A spike in apoptosis was observed in KO outer nuclear layer at P25. These changes in size were accompanied by a large decrease in hyperopic refractive error, which reached -4.56 ± 0.70 diopters (D) versus +9.98 ± 0.993 D (mean ± SD) in WT, by postnatal day 60 (P60). CONCLUSIONS; In addition to its role in the visual cycle, IRBP is needed for normal eye development. How IRBP mediates ocular development is unknown.

In vivo human choroidal thickness measurements: evidence for diurnal fluctuations.

PURPOSE: The authors applied partial coherence interferometry (PCI) to estimate the thickness of the human choroid in vivo and to learn whether it fluctuates during the day. METHODS: By applying signal processing techniques to existing PCI tracings of human ocular axial length measurements, a signal modeling algorithm was developed and validated to determine the position and variability of a postretinal peak that, by analogy to animal studies, likely corresponds to the choroidal/scleral interface. The algorithm then was applied to diurnal axial eye length datasets. RESULTS: The postretinal peak was identified in 28% of subjects in the development and validation datasets, with mean subfoveal choroidal thicknesses of 307 and 293 microm, respectively. Twenty-eight of 40 diurnal PCI datasets had at least two time points with identifiable postretinal peaks, yielding a mean choroidal thickness of 426 microm and a mean high-low difference in choroidal thickness of 59.5 +/- 24.2 microm (range, 25.9-103 microm). The diurnal choroidal thickness fluctuation was larger than twice the SE of measurement (24.5 microm) in 16 of these 28 datasets. Axial length and choroidal thickness tended to fluctuate in antiphase. CONCLUSIONS: Signal processing techniques provide choroidal thickness estimates in many, but not all, PCI datasets of axial eye measurements. Based on eyes with identifiable postretinal peaks at more than one time in a day, choroidal thickness varied over the day. Because of the established role of the choroid in retinal function and its possible role in regulating eye growth, further development and refinement of clinical methods to measure its thickness are warranted.

Emmetropisation under continuous but non-constant light in chicks.

It has been suggested that ambient lighting at night influences eye growth and might play a causal role in human myopia. To test this hypothesis, we reared newly hatched chicks under 12 hr light-dark or light-dim cycles with a light phase intensity of 1500 microW/cm(2) and variable dim phase intensities between 0.01 and 500 microW/cm(2). Other chicks were reared under constant light conditions with intensities between 1 and 1500 microW/cm(2). After three weeks, the chicks were examined by refractometry, ultrasound and caliper measurements of enucleated eyes. To relate ocular parameters with a retinal neurotransmitter likely involved in eye growth control, retinal and vitreal levels of dopamine and its principal metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), were measured by high performance liquid chromatography with electrochemical detection in the light, dark and dim phases. Diurnal fluctuations in axial length and choroidal thickness also were measured twice daily by partial coherence interferometry (PCI) in chicks under light-dark and the two brightest light-dim conditions. The eyes of chicks reared under most light-dim conditions had refractions and ocular dimensions comparable to those reared under light-dark conditions. At dim phase light intensities of 10 microW/cm(2) and above, the day-night changes in retinal dopamine metabolism were not observed. The daily fluctuations of axial length and choroidal thickness were altered with rearing under the two brightest dim light intensities, compared to the light-dark condition. Rearing under constant light with intensities ranging between 1 and 1500 microW/cm(2) produced a shallow anterior chamber and other eye alterations previously described for constant light rearing even though rearing under continuous light that fluctuated between these same intensities generally permitted normal eye growth. Thus, continuous but fluctuating light exerts different developmental effects on the eye than constant non-fluctuating light. Light-dim rearing may be more relevant to daily human light exposures than other laboratory lighting conditions and may provide an opportunity to study developmental interactions of visual quality (e.g. blur, defocus, etc.) and features of the light-dark cycle under conditions that perturb daily rhythms in dopamine metabolism and ocular dimensions. Such studies also could provide mechanistic insights into whether and how daily rhythms in retinal dopamine metabolism, axial length or choroidal thickness modulate refractive development.