Biomedical subjects

H Whitefoot

Publications and source records attributed to H Whitefoot.

3 recordsLinked to original sources

PubMed1992

Dynamic retinoscopy and accommodation.

The added positive lens power required for low and high neutrals at a distance of 1/3 m is determined as a function of age for a sample of 221 clinically normal subjects, aged between 10 and 80 years. These dynamic retinoscopy results are compared with corresponding laser optometer measurements of the levels of accommodation under each condition. Dark focus (tonic accommodation) measurements are carried out on a further sample of 58 subjects. Although the mean results of dynamic retinoscopy agree with those found by earlier authors, on the basis of our sample it is concluded that the considerable scatter in neutral values found in normal subjects at any age limits the usefulness of the technique as an indication of abnormality in near responses. Much of this scatter in pre-presbyopic subjects appears to be related to individual variation in the level of tonic accommodation, although near phoria may also play some role.

Accommodation, Ocular↗

PubMed1979

Speckle motion in laser refraction. II. Experimental.

The validity of expressions for the position of the plane of stationarity, apparent speed of speckle movement, and estimated observer ametropia is examined for laser refraction, using a cylindrical drum. The agreement between theory and experiment is satisfactory. It appears unlikely, however, that methods of subjective refraction depending on estimation of speckle velocity can match the accuracy and precision of those based on rendering the plane of stationarity conjugate with the observer's retina. Even with experienced observers, refractive values based on estimates of speckle speed showed the unsatisfactorily large standard deviation of approximately 0.5 D.S.

Humans↗

PubMed1978

The refraction of the eye in the relation to spherical aberration and pupil size.

Available theoretical and experimental data on the dependence of the subjective refraction of the eye on spherical aberration and pupil size are reviewed and additional experimental results are presented. Under photopic conditions, refraction varies little (similar to 0.3 DS) with pupil diameter, even when substantial amounts of spherical aberration are present (similar to 1.0 DS). It is argued that this result may be attributed to the insensitivity of optimal focus to spherical aberration at the spatial frequencies involved in photopic refraction, to the Stiles-Crawford effect and to the influence of aberrations other than primary spherical aberration in the outer zones of the pupil. The signficance of these findings is indicated in relation to possible discrepancies between the results of objective and subjective refractions when large pupils are in use.

Humans↗