The summer studentship programme offers an insight into practical optometric research through participation in ongoing projects. The current placement was in the Myopia and Accommodation Research Laboratory working under the supervision of Dr. Edward Mallen and Dr. Karen Hampson. The main task undertaken was to participate in the design of an experiment to study Longitudinal Chromatic Aberration (LCA) and the effect of accommodation on chromatic focus.
Measurement of LCA in the eye is already well-documented, therefore an appreciation of published data was required before proceeding further. The next stage was to design the apparatus and experimental procedure.
The instrument to be constructed was a chromatic Vernier optometer. Collimated light from a tungsten halogen lamp was split into component wavelengths using a monochromator. This monochromatic light was directed towards a 1mm slit, bisected by a 1 ? Dioptre prism, to create a Vernier target which could be viewed by the subject via a Badal optometer. An additional illuminated target was placed on the opposite end of the apparatus platform to act as a stimulus to accommodation. The target was illuminated by white, collimated light from a tungsten source. A rotating mirror was located between the target and the Vernier at the focal distance of the Badal optometer lens. The mirror was designed to alternate between the target and Vernier such that the observer viewed the latter for only 0.4 seconds to avoid accommodation, but viewed the accommodative target for 4 seconds to remain focussed for the correct viewing distance. The mirror was aligned with the Badal optometer lens through which the observer would view the Vernier.
Several experiments were planned for this system. Initially it would be used to measure LCA. Therefore once the apparatus was assembled, the experimental procedure was tested. Four wavelengths of light were selected: 400, 450, 600, 650 nm. The observer viewed the Vernier through the Badal lens and mirror and moved the Vernier until the two halves of the target were aligned. The distance between the Vernier unit and the mirror was recorded and converted into a dioptric value. The difference in dioptres between the measurements for 400 nm and 650 nm was considered as the observer’s chromatic interval for LCA. An average of 1.85D for the magnitude of the chromatic interval was found for 5 young adult observers. One observer repeated the procedure twice: once with refractive correction and the target focussed at infinity, and once without correction with the target focussed at their far point. The chromatic interval with refractive correction was -0.25D less than when no correction was worn.
Collection of the pilot data helped to identify several elements key to the success of the experiment:
· correct alignment of the optical equipment;
· good instruction of the observer;
· sufficient method training for the observer prior to data collection.
By the end of the placement the apparatus had been tested and was ready for data collection.
The summer placement is an extremely valuable experience for any student who wishes to consolidate their studies. It demonstrates how basic optical techniques and skills can be put to practical use outside of direct clinical practice and how current research ideas may help to shape patient treatment in the future.
Research by Aleksandra Mankowska, University of Bradford