|Year : 1983 | Volume
| Issue : 4 | Page : 383-387
Retinal visual acuity in ametropia
OP Billore, AP Shroff
Rotary Eye Institute Navsari, India
O P Billore
Rotary Eye Institute Navsare
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Billore O P, Shroff A P. Retinal visual acuity in ametropia. Indian J Ophthalmol 1983;31:383-7
The Retinometer measures retinal and cortical function independent of the difference optical of the media of the eye. There are so many methods for qualitative estimation of the retinal function but none is to estimate quantitatively. Recently Rodenstock Retinometer and Haag Streit visometer are available for quantitative estimation of the retinal function.
| Materials and methods|| |
In the present study retinal visual acuity was measured in 500 cases whose visual acuity with Suellen's Chart was 6/6. Accuracy and reliability of the retinometer was tested by recording retinal visual acuity in normal cases.
Retinal visual acuity was measured in 500 ametropia cases before refraction and results were compared after spectacle or contact lens correction. Retinal visual acuity was recorded in 200 myopia, 200 hypermetropia and 100 astigmatism cases.
The Rodenstock Retinometer is mounted on RO 2000 slit lamp. The slit lamp is adjusted to the eye to be measured and a thin slit image is focussed sharply on the cornea as usual. Now retinometer is switched on. When the examiner observes the two small red dots in the pupil of the patient's eye then by moving the Joy Stick of the slit lamp, these are adjusted in the centre of the pupil or transparent area of the optical media of the eye. With clear media normal setting should be used by rotating knob (3) to setting 1. The rotating knob (1) serves for changing the density of interference fringes, in steps corresponding to values of the retinal visual acuity from 0.03 to 1.0. In order to have an independent criteria for to exclude wrong or false answers given by the patient, the direction of fringe pattern can be set to four different positions-horizontal, vertical, and two oblique settings-by means of dove prism operated by turning knob 2. Patient is asked whether he can see a fringe pattern but also which direction it has. Special importance must be attached to the direction in which lines are lying.
| Observations|| |
In the present study retinal visual acuity was measured in 500 cases in which visual acuity was 6/6 when recorded with Suellen's test chart. Retinal visual acuity was measured in these normal cases to test the reliability and accuracy of the Retinometer. It was observed that in 99.5%, cases retinal visual acuity (RVA) was corresponding to Snellens letter's visual acuity (LVA 1). In 0.5%, cases RVA was not corresponding due to error on the part of the patient and examiner as he could not make understand the patient such a simple procedure or lack of patience on the part of the examiner. It was observed that retinometer predicts very correctly when the optical media of the eye is transparent. Retinal visual acuity was recorded in illitrate patients and children also and it gives idea that his visual acuity is normal or not. Retinal visual acuity was recorded in 200 myopic cases before refraction and fundus examination was done. 23 cases had central myopic degeneration. It was observed that retinal visual acuity (RVA) was higher than letter's visual acuity (LVA1) in 93% cases of myopia. [Table - 1] RVA was equal to LVA1 in 52 cases and less than LVA1 in 1.5% cases only probably due to error on the part of the examiner and patient. In 93% cases of myopia RVA was higher than LVA1 which shows that vision can be improved by glasses or by contact lens. In 41.5% cases RVA was equal to LVA2 (corrected visual acuity by spectacle or contact lens). It means that in 41.5% cases expected visual acuity was gained which was indicated by Retinometer before refraction. In 48.62% cases LVA2 was less than RVA suggesting that there is some disturbance in the transparencp of the media. 23 cases of myopic had central myopic degeneration and retinal visual acuity in these cases were higher than the corrected visual acuity. From [Table - 2] LVA2 was 6/12 to 6/6 in 64.8 and 69.0% cases only while RVA was 89.44% and 91.5% cases was between 6/12 to 6/6. Between 6/12 to 6/6 RVA was seen in 40% cases (18 cases) of myopia with central degenerative but it could be improved in 17.78% only (4 cases). From the [Table - 3] It is clear that visual acuity in high myopia with central degenerative could not be improved with glasses or contact lens as expected by Retinometer. Vision must be improved to 6/12 to 6/6 in 89.44 and 91.5°0 in right eye and left respectively in myopia but it was achieved in 64.8 and 69.0% cases in right eye and left eye respectively. This shows that RVA is more than LVA2 mentioned, eye has a potentiality of improvement of vision how to improve the vision according to retinometer is a matter of further research.
Retinal visual acuity was measured in 200 hypermetropia cases before refraction was done. As shown in [Table - 4] in 47 cases (23.42%) RVA was equal to LVA1. In 70% cases RVA was more than LVAI. In 51.5% cases RVA was equal to LVA2. In 37.5% cases RVA was more than LVA2 in which vision cannot improved further with glasses. From the [Table - 5] it appears that corrected visual acuity between 6/12 to 6/6 was in 79.5% in right eye and 78.0°0 in the left eye. RVA was in between 6/12 to 6/6 in 95.5 and 95% cases. Which shows that there is potentiality of improvement of vision which in routine course could not be improved by glasses or contact lens.
Retinal visual acuity was measured in 100 astigmatism eases before refraction. As shown in [Table - 4] in 91 cases RVA was more than LVAL. In 9 cases it was same as LVAI. In 54 cases RVA was equal to LVA2. In 39 cases RVA was more than LVA2. From [Table - 7], it appears that RVA between 6/12 to 6/6 in 95% and 99% in right and left eye respectively andLVA2 in 82% and 93% lans.
| Discussion|| |
Retinometer measure the retinal visual acuity irrespective of the optical media of the eye by interference fringe method. Quantitative estimation of the retinal visual acuity by this instrument is really a guide in normal and diseased conditions of the eye in which it indicates potential vision of the eye which can be improved. In ametropic condition retinometer indicates possibility of improvement of vision by glasses or contact lens and in diseased condition by appropriate treatment.
In myopia cases retinal visual acuity was higher than Snellen's visual acuity in 93%, cases. In 41.5% cases expected visual acuity was gained by glasses or contact lens which was indicated by Retinometer before refraction. In unilateral high myopia with central myopia degeneration it was observed that retinal visual acuity was higher than the LVAI and LVA2 This shows that there are chances of improvement of vision by appropriate measures. From review cases records itw as observed that in some cases vision was improved fully as shown by retinometer or in some cases improved partially with medical line of treatment. Why we cannot improve vision in every case of high myopia with central degeneration is difficult to answer.
In hypermetropia cases in 69.8% cases RVA was more than LVA2. In 51.9% cases RVA was equal to LVA2. It means in these cases vision could be improved with glasses or contact lens as shown by Retinometer before refraction.
In astigmatism cases in 93% of cases RVA indicated the expected corrected visual acuity fairly accurately,
Retinometer is a quick, easy and dependable method to quantitative assessment of retinal visual acuity. Test is full proof as it has both objective and subjective check. It is applicable to children and illitrate too, as it requires more appreciation of direction of interference fringes.
| References|| |
Lotmar, W., 1982, acuity of the retina. Appl. optics 11:1266.
Lotmar. W., 1980, Invest. Ophthalmol. 19 : 393.
[Table - 1], [Table - 2], [Table - 3], [Table - 4], [Table - 5], [Table - 6], [Table - 7]