|Year : 1981 | Volume
| Issue : 3 | Page : 207
New test drum for recording distant vision
Yash Pal Singh, PL Rao
Department of Ophthalmology, S.N. Medical College and Hospital, Agra, India
Yash Pal Singh
Head of Deptt. of Ophthalmology, S.N. Medical College and Hospital, Agra
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Singh Y, Rao P L. New test drum for recording distant vision. Indian J Ophthalmol 1981;29:207
The apppratus consists of the following
- The Chart.
- The switch system.
- Illumination Box.
The test chart is placed in front of a box containing the illumination system. Letters of verious sizes conforming to 6/60, 6/36, 6/24, 6/13, 6/12, 6/9, 6/6 and 6/5 are arranged in rows from top to bottom. Each letter can be illuminated either singly or collectively with other letters in its own horizontal line. The first letters in all the horizontal lines can again be illuminated simultaneously.
The switch system consists of a box with piano-key pattern switches available in the market. The keys are so connected that either one bulb lights up at a time or all the bulbs in a line get lighted on pressing one switch only. Similarly all the first letters of the various horizontal rows can be lighted at the same time by pressing one particular key.
The drum is a rectangular cube containing charts in Dev Nagari, Roman, I andolt C and charts of any script. The drum may be designed to exhibit six charts instead of four and revolves on a strong metal roal resting on a metal base.
The illumination box is constructed into compartments of differing sizes corresponding to letters on the test charts, each has a socket for a bulb. The box can be shifted backwards or forwards while changing the script on the drum.
Thus a person to be tested may be asked to read from the top only the first lighted letters till he reaches the bottom letter. If he stops at the 4th or 5th letter from the top the other letter in the same line can be illuminated and his sight recorded.
Some subjects find it difficult to concentrate their attention on a single letter while subjective testing is being done, to facilitate,this, it is convenient to illuminate one letter only at a time, so that he may be able to appreciate any minor difierence by a change in lenses.
Illumination of a single letter and one line at a time is likely to be of particular benefit while testing children, illiterates or persons with a comparatively low. I.Q. The advantages of the system are numerous and obvious.