Kathryn J. Saunders

Early refractive development in humans

Over recent years much interest has been directed toward understanding the process by which refractive errors develop, how this is controlled and the effect of refractive errors on subsequent visual status. There are obvious difficulties in studying such mechanisms in human subjects and for this reason many studies have employed animal models. The present paper compiles the evidence available from human subjects, examining the significance of different aspects of refractive status, normal and abnormal patterns of development and their significance in the development of normal binocular function.

Emmetropisation in human infancy: Rate of change is related to initial refractive error

Animal studies show that the rate of recovery from experimentally induced refractive errors is related to the level of ametropia induced. The present study examined the rate of emmetropisation occurring in a sample of 22 human infants refracted by near retinoscopy during the first six months of life and then again between 12 and 17 months old. None of the subjects were myopic. Regression analysis revealed that emmetropisation occurred more rapidly in the presence of high refractive errors (P < 0.005 and P = 0.001 for hyperopia and astigmatism respectively). These data confirm the findings of the animal studies and suggest that non-reducing hyperopia and astigmatism in the second year of life may require correction.

Emmetropisation following preterm birth

Background/aims: Even in the absence of retinopathy of prematurity (ROP), premature birth signals increased risk for abnormal refractive development. The present study examined the relation between clinical risk factors and refractive development among preterm infants without ROP. Methods: Cycloplegic refraction was measured at birth, term, 6, 12, and 48 months corrected age in a cohort of 59 preterm infants. Detailed perinatal history and cranial ultrasound data were collected. 40 full term (plus or minus 2 weeks) subjects were tested at birth, 6, and 12 months old. Results: Myopia and anisometropia were associated with prematurity (p<0.05). More variation in astigmatic axis was found among preterm infants (p<0.05) and a trend for more astigmatism (p<0.1). Emmetropisation occurred in the preterm infants so that at term age they did not differ from the fullterm group in astigmatism or anisometropia. However, preterm infants remained more myopic (less hyperopic) than the fullterm group at term (p<0.05) and those infants born <1500 g remained more anisometropic than their peers until 6 months (p<0.05). Infants with abnormal cranial ultrasound were at risk for higher hyperopia (p<0.05). Other clinical risk factors were not associated with differences in refractive development. At 4 years of age 19% of the preterm group had clinically significant refractive errors. Conclusion: Preterm infants without ROP had high rates of refractive error. The early emmetropisation process differed from that of the fullterm group but neither clinical risk factors nor measures of early refractive error were predictive of refractive outcome at 4 years.

Cortical visual dysfunction in children: a clinical study.

Damage to the cerebral cortex was responsible for impairment in vision in 90 of 130 consecutive children referred to the Vision Assessment Clinic in Glasgow. Cortical blindness was seen in 16 children. Only 2 were mobile, but both showed evidence of navigational blind-sight. Cortical visual impairment, in which it was possible to estimate visual acuity but generalised severe brain damage precluded estimation of cognitive visual function, was observed in 9 children. Complex disorders of cognitive vision were seen in 20 children. These could be divided into five categories and involved impairment of: (1) recognition, (2) orientation, (3) depth perception, (4) perception of movement and (5) simultaneous perception. These disorders were observed in a variety of combinations. The remaining children showed evidence of reduced visual acuity and/ or visual field loss, but without detectable disorders of cognitive visual function. Early recognition of disorders of cognitive vision is required if active training and remediation are to be implemented.

Refractive error and visual impairment in school children in Northern Ireland

Aims To describe the prevalence of refractive error (myopia and hyperopia) and visual impairment in a representative sample of white school children. Methods The Northern Ireland Childhood Errors of Refraction study, a population-based cross-sectional study, examined 661 white 12–13-year-old and 392 white 6–7-year-old children between 2006 and 2008. Procedures included assessment of monocular logarithm of the minimum angle of resolution (logMAR), visual acuity (unaided and presenting) and binocular open-field cycloplegic (1% cyclopentolate) autorefraction. Myopia was defined as −0.50DS or more myopic spherical equivalent refraction (SER) in either eye, hyperopia as ≥+2.00DS SER in either eye if not previously classified as myopic. Visual impairment was defined as >0.30 logMAR units (equivalent to 6/12). Results Levels of myopia were 2.8% (95% CI 1.3% to 4.3%) in younger and 17.7% (95% CI 13.2% to 22.2%) in older children: corresponding levels of hyperopia were 26% (95% CI 20% to 33%) and 14.7% (95% CI 9.9% to 19.4%). The prevalence of presenting visual impairment in the better eye was 3.6% in 12–13-year-old children compared with 1.5% in 6–7-year-old children. Almost one in four children fails to bring their spectacles to school. Conclusions This study is the first to provide robust population-based data on the prevalence of refractive error and visual impairment in Northern Irish school children. Strategies to improve compliance with spectacle wear are required.

Refractive errors in young children with Down syndrome.

Significant refractive errors are common among older children and adults with Down syndrome. We examined infants and children with Down syndrome to determine the prevalence of these errors at younger ages. Noncycloplegic retinoscopy was used to determine the refractive state of 92 infants and children with Down syndrome, aged 4 months to 12 years. The results for infants show a similar distribution of refractive errors in patients with Down syndrome and an age-matched control group. However, rather than a narrower distribution for the older age groups, as is the case with the controls, the distribution is wider, and the prevalence of refractive errors (including astigmatism) is higher among young children with Down syndrome than among controls. This high prevalence of refractive defects cannot be explained by the presence of strabismus or other pathologies.

The repeatability and validity of dynamic retinoscopy in assessing the accommodative response

Dynamic retinoscopy (DR) is an objective technique that has been used successfully to examine accommodative function of non‐communicative patients. However, there are few studies examining its repeatability and validity. This paper addresses the repeatability and validity of a form of DR (a modified Nott technique), by comparing results to the Shin‐Nippon SRW‐5000 Autorefractor whose validity and repeatability have previously been demonstrated. Accommodative responses of 41 subjects (aged 6–43 years) were assessed using DR and the Shin‐Nippon SRW‐5000 Autorefractor. Three different target demands were used (10, 6 and 4 D). DR was shown to be repeatable for all target demands (paired t‐test, p > 0.05). The results demonstrated good agreement between the autorefractor and DR. The results of the present study suggest that DR is a repeatable and valid objective technique for assessing accommodative function.

Investigation of changes in the myopic retina using multifocal electroretinograms, optical coherence tomography and peripheral resolution acuity

We investigated relationships between retinal structure using optical coherence tomography (OCT) and retinal function using peripheral resolution acuity and multifocal electroretinograms (mfERG) in 56 subjects with a range of refractive errors (+0.50 to -15.00 D). Retinal thinning occurred in moderate and high myopia which appeared to be primarily due to reduced thickness of the middle to inner retina (MIR) (outer plexiform layer to the nerve fiber layer). MIR thickness was correlated with reduced spatial resolution and delayed mfERG timing in the peripheral retina. The findings suggest the structure and function of the post-receptor retina is susceptible to disruption in moderately and highly myopic eyes.

Prognostic value of flash visual evoked potentials in preterm infants.

This paper investigates the prognostic value of flash visual evoked potentials (VEPs) recorded in preterm infants at birth and at term age with respect to severe neurological outcome. Flash VEPs were recorded in 81 preterm infants at birth (i.e. <35 weeks’ gestation) and repeated in 56 of these infants at term age. The preterm infants were assigned to either a healthy or at‐risk subgroup based on clinical birth factors. Normal ranges of flash‐VEP latencies, amplitudes, and number of components present were obtained from the subgroup of healthy preterm infants and from 68 term infants tested postnatally. The flash‐VEP results of the entire preterm group were compared with the normal ranges and any abnormalities noted. Seven preterm infants in the at‐risk group died, six of whom had abnormal flash VEPs before term age. Of the five infants from the at‐risk group diagnosed with cerebral palsy (CP), three had abnormal flash VEPs before term age. Thus the sensitivity and specificity of the flash VEP with respect to survival was 86% and 89% respectively, and with respect to the development of CP was 60% and 92%. The abnormal features of the flash VEP associated with adverse outcomes comprised a delayed N3 component before term age and the absence of a positive component (P2) at term age.

Comparison between near retinoscopy and cycloplegic retinoscopy in the refraction of infants and children.

We investigated the validity of replacing cycloplegic retinoscopy with a noncycloplegic, “near” retinoscopy technique. We refracted a group of 31 infants (<2 years) and 43 children (>2 years) with both techniques, grading our level of confidence in the result. Near retinoscopy gave on average a less hypermetropic result than cycloplegic retinoscopy by 0.39 D. The difference was significant in infants and for low levels of examiner confidence. However, a repeatability study showed that much of the variability in the infant group could be attributed to the poor repeatability of either retinoscopy technique. Agreement between the two techniques is improved by changing the suggested adjustment factor from 1.25 to 1.00 D for children and to 0.75 D for infants.