PubMed Health⌕ Search

Biomedical subjects

D Pickwell

Publications and source records attributed to D Pickwell.

6 recordsLinked to original sources
PubMed1995

The effect of red and neutral density filters on the degree of eccentric fixation.

The reported shift of fixation to a more central position when a red filter is placed before an eye which fixates eccentrically, has never been satisfactorily explained. To further investigate this phenomenon, 14 subjects with eccentric fixation were recruited. A Wratten No. 92 filter was placed before the eccentrically fixating eye, and any change of fixation was assessed by the after-image transfer test. A neutral density (ND) filter was then used, to mimic the reduced retinal illumination caused by the red filter. The results suggest that there is a significant reduction in the eccentricity of fixation, when placing the red filter before an eccentrically fixating eye, and also when placing the ND filter. No significant difference in the effects produced by either filter was found. This suggests that it is the reduction in retinal illuminance caused by the red filter which contributes towards such improvements in fixation.

Afterimage↗
PubMed1989

The accommodative contribution to binocular vergence eye movements.

Forced vergence fixation disparity curves were generated for both with and without an accommodative stimulus (accommodative closed and open loop conditions respectively) for fifteen asymptomatic subjects. All subjects exhibited an exophoric shift in fixation disparity for the accommodative open loop condition at the forced convergence side of the curve. No corresponding bias was found at the forced divergence side of the curve. The findings are discussed in terms of the results of previous studies and the existing models of vergence eye movements.

Accommodation, Ocular↗
PubMed1987

World optometry.

The International Optometric and Optical League (IOOL) sent out a questionnaire to contacts in countries across the world in order to formulate an "Optometry Profile" on as many countries as possible. The information from the 58 replies is summarized. The very varied distribution of optometric services that is revealed is discussed in the light of experience gained by the author in his own visits and correspondence relating to the worldwide situation of optometry.

Africa↗
PubMed1987

The effect on fixation disparity and associated heterophoria of reading at an abnormally close distance.

It is well established that prism stress on binocular vision produces fixation disparity. It is therefore suggested that fixation disparity is a sign of stress on binocular vision. The authors have previously looked at the stress caused by reading in reduced levels of illumination, and found that the average fixation disparity and associated heterophoria become more exophoric. In this paper the effect on fixation disparity and associated heterophoria of reading at an abnormally close distance is reported. It was found that in 50 young adults fixation disparity and associated heterophoria increased to a greater degree of exo-disparity. An analysis of the visual symptoms indicated that there was also an increase in the visual discomfort and other symptoms.

Adult↗
PubMed1987

The clinical assessment of binocular vision before and after a working day.

This paper looks at the clinical investigative and measurement procedures used in assessing binocular vision at the beginning of a normal working day and compared with the same procedures carried out in the afternoon which included several hours of close work. In 84 young adults, it was found that dissociated heterophoria, associated heterophoria and fixation disparity increased. This was accompanied by visual symptoms. It is likely that any decompensation of heterophoria is worse at the end of a working day. The results of this investigation raise the question of the value of some clinical tests for binocular assessment carried out at the beginning of the day.

Adolescent↗