Biomedical subjects

N Sayles

Publications and source records attributed to N Sayles.

6 recordsLinked to original sources

PubMed1987

Accommodation in infants as measured by photorefraction.

We developed a video camera photorefractive procedure that allows on-line monitoring of accommodation from a distance of 1-2m, and have used it to study accommodation in twenty-nine 2- to 10-month-old human infants. We presented square wave gratings and random checkerboard targets at 25, 33, 50, and 100 cm from the infant. All infants altered their accommodation in the appropriate direction for changing target distances. We also presented infants with a slowly rotating circular striped target. We did not observe any systematic change in accommodation of the astigmatic infants to the rotating striped target, nor any significant change in their accommodation to stationary targets as a function of target type. Measured speeds of accommodation in infants were at least 4.6 D/sec, comparable to that found for adults.

Accommodation, Ocular↗

PubMed1987

Simple pointspread retinoscope suitable for vision screening.

A simple pointspread retinoscope and method of retinoscopy are described which use optical principles similar to those of photoretinoscopy or static photographic skiascopy. In this instrument the degree of defocus of an eye is estimated from the disappearance of the bright fundal reflex or "crescent" in the eye of the subject when the distance between the light source and the eye of the observer is increased systematically. The instrument is particularly suitable for large scale screening efforts because it is easy to use and can be constructed from inexpensive materials. The pointspread retinoscope was calibrated against an artificial eye of known defocus. Additionally, results from pointspread retinoscopy were compared against meridional photorefractive data from a sample of infants and young children, and a significant correlation was found to exist between measurements made by the two methods.

Child↗

PubMed1987

A photorefractive characterization of focusing ability of infants and young children.

The authors have used isotropic and orthogonal photorefraction to examine the focusing ability of 360 normal uncyclopleged infants and young children (ages, 2 mo to 5 yr). Photorefractive reflexes were recorded on 400 ASA color transparency film at 1.5 m, and the subject viewed the photographer's face located directly above the camera. The photographs of reflexes were projected at X 20 on a computer-driven digitizing tablet and converted to the ophthalmic prescriptions that would correct the subject for the camera distance. Using these prescriptions the authors established 95% confidence limits as a function of age for each of four different tests: net sphere of most defocused eye; cylinder of most astigmatic eye; difference in spheres between two eyes; and difference in cylinder between two eyes. Spheric defocus was found to decrease uniformly as a function of age, as did the cylinder of the most astigmatic eye. However, the symmetry of focus of the eyes, as judged by spheric and cylindric differences, was established within the first year of life. By relaxing the limits of each individual test, a test battery was constructed that was failed by 5% of the subject population, with the individual tests contributing in approximately equal proportions to the failure rate. The use of this test battery for detecting focusing conditions in infancy and early childhood that can lead to amblyopia is discussed.

Child, Preschool↗

PubMed1985

Photokeratometric and photorefractive measurements of astigmatism in infants and young children.

We have measured corneal and total astigmatism on 161 eyes of 90 normal infants and young children aged 2 months to 5 years using the techniques of photorefraction and photokeratometry. Both the mean corneal and mean total astigmatism were found to decrease with increasing age. We found large and significant correlations between corneal and total astigmatism in the 0-1, 1-2 and 2-3 year-old infants and children. Previous studies have shown that photorefractive measurements of astigmatism compare well with retinoscopic measurements of the same infants. As part of this study we measured the corneal astigmatism of 19 adults (38 eyes) by photokeratometry and with a clinical keratometer and found that the two measures were well correlated (r = 0.820). We conclude that the major component of total astigmatism seen in uncyclopleged infants of ages 0-3 years is corneal in nature.

Adult↗

PubMed1984

Photorefractive measurements of astigmatism in infants and young children.

We have photorefracted 312 infants and young children in Tompkins county in New York state and characterized the magnitude and axes of their astigmatisms. The population was solicited by letter from birth announcements or photographed at nursery schools, and was composed of children free of ocular problems. As had been previously reported, we found that the prevalence of astigmatisms of greater than 1 diopter decreased with increasing age. Roughly 7 of 10 infants aged 1 year of younger had one eye with at least 1 diopter of astigmatism or more, while only 1 out of 10 children of age four or more had an eye with 1 or more diopters of astigmatism. A longitudinal study of 26 infants also showed a decrease in the amount of astigmatism over the first three years of life. In infants up to 2 years of age from Tompkins County, the ratio of against-the-rule:oblique:with-the-rule astigmatisms was 15:9:1 in the most astigmatic eye. Generally the axes of oblique astigmatism showed bilateral symmetry. Photorefraction of a group of 159 infants from the city of Seattle showed a similar prevalence of astigmatism, but a slightly different ratio of kinds of astigmatism.

Astigmatism↗

PubMed1983

Photorefractive studies of normal and handicapped infants and children.

We have photorefracted 360 infants and children of ages 2 months to 5 years from and around Tompkins County, New York, who were free of any obvious ocular pathology. From these studies we have established 95% confidence limits for largest cylinder, largest sphere, and spherical and cylindrical differences between eyes as a function of age. Using this normal data we have begun to photorefract handicapped children from special childrens' centers in and around Tompkins County. Our preliminary data indicate a higher prevalance (greater than 4 X ) of refractive anomalies in handicapped children, as compared to normal children, even when allowance for ocular pathology is made.

Child, Preschool↗