|Year : 1992 | Volume
| Issue : 2 | Page : 44-47
"A retrospective cohort study for prognostic significance of visual acuity for near over that for distance in anisometropic amblyopia.".
Vinita Singh, Suman Sinha, GK Singh
Department of Ophthalmology, K G's Medical College, Lucknow, India
Department of Ophthalmology, K G's Medical College, Lucknow
Source of Support: None, Conflict of Interest: None
A cohort of 50 anisometropic amblyopes, between the ages of 2.5 to 10 years, was studied retrospectively to assess the prognostic significance of visual acuity for near over that for distance. There is ample evidence in the literature for a significantly lower accommodative response in the anisometropic amblyopic eye. It has been proposed that the efferent accommodative dysfunction may be a fundamental and causative factor in anisometropic amblyopia. A reduced visual acuity for near over that for distance was found in 17 [34%] patients and in 11 out of these the near vision improved after an addition of +3.0D sph. When a reduced visual acuity for near, was obtained it was difficult to determine whether the visual afferent system (due to insufficient visual input), or the accommodation efferent mechanism was responsible. However an improvement in corrected near vision by addition of +3.0D sph. suggested an accommodative dysfunction. In patients with reduced visual acuity for near over that for distance, not only was the final visual outcome poor but also the onset of visual improvement in response to amblyopia therapy was delayed.
|How to cite this article:|
Singh V, Sinha S, Singh G K. "A retrospective cohort study for prognostic significance of visual acuity for near over that for distance in anisometropic amblyopia.". Indian J Ophthalmol 1992;40:44-7
| Introduction|| |
Amblyopia occurs at an age at which the integrity of the visual system is susceptible to modifications in the visual experience. Clinical experience suggests that this period ranges from birth to approximately 5 years 
The asymmetrical visual experience, no matter what the underlying factor, causes neurological anomalies in the striate and prestriate cortex and morphological changes in the lateral geniculate body 
Reduced amount of accommodation in the eye with anisometropic amblyopia, has been documented ,, and efferent accommodative dysfunction, has been suggested as a fundamental and causative factor in anisometropic amblyopia ,, Reports that the relative visual acuity for near over that for distance is related to the response to amblyopia therapy  form the basis of this study.
| Material and methods|| |
This is a retrospective cohort study of 50 children aged 2.5 to 10 years with anisometropic amblyopia, selected out of 410 similar patients who visited the orthoptic clinic in the period 1985-1989. Prognostic significance of visual acuity for near over that for distance was studied. The children were selected on the basis of (i) availability of upto 12 weeks follow up. (ii) absence of erratic fixation and (iii) ability to co-operate for visual assessment. The selection of nearly 1 in 8 patients could bias the association if cases were differentially selected from one of the prognostic groups. However comparison of base line data like age, sex, socio-economic status and initial distant visual acuity between the 50 selected and 50 riot selected revealed that the two were comparable. Thus our selection can be considered quasi-random and non differential.
These patients were subjected to a complete orthoptic evaluation including refraction, assessment of corrected and uncorrected visual acuity for distance on Snellen's chart as well as for near on Jaeger's types held at a distance of 33 cms. Any improvement in the corrected near vision with the addition of + 3.0 D sph. was noted. In the case of small children who were unable to co-operate for the visual assessment during the first visit, the parents were told to teach them to react and tell the E chart with their hands. In the subsequent visits when the children became more familiar and less hesitant, it was easier to elicit co-operation for visual assessment. These assessments were used to place the patients in the two prognostic groups I & If [Table - 1].
After the visual status was satisfactorily determined the patient were treated for amblyopia by giving necessary refractive correction for constant use along with full time conventional occlusion and reading, writing and drawing exercises using the amblyopic eye. The children in the pre-school going age were encouraged to draw and colour small figures of their interest using the amblyopic eye. The vision of the amblyopic eye as well as that of the sound eye was observed at two weekly intervals for 8 weeks and there after at monthly intervals. The amblyopia treatment was discontinued if there was no improvement after 12 weeks of treatment. When the visual acuity became stationary the treatment was continued with gradually reduced periods of occlusion and periodic monitoring of visual acuity till occlusion was completely withdrawn and visual acuity maintained. However, in this study the observations for a period of 12 weeks follow up have been evaluated, as this period was considered sufficient to get a response to amblyopia therapy.
| Observation|| |
In this series of 50 children of anisometropic amblyopia near visual acuity corresponding to the distance visual acuity was found in 26 [52%] patients and near vision better than distance vision in 7 [14%] patients. For the purpose of analysing the response to amblyopia therapy patients in both these categories [33 patients] have been placed in group I. The remaining 17 [34%] patients had a poorer visual acuity for near over that for distance and these have been placed in group II. By addition of +3.0 D sph. an improvement in the corrected near vision by 1 line or more was found in 11 patients in group II and none in group I thereby indicating an accommodative dysfunction [Table - 1]
The age distribution among prognostic groups is shown in [Table - 2] and rules out the possibility of age being a confounder because it was not related to the prognostic groups (p>0.05) similarly the sex [Table - 3] and the initial visual acuity [Table - 4] were not confounders because they had no significant relation with the prognostic groups. All the patients were hypermetropes.
The patients were treated for amblyopia on the lines defined earlier and the visual acuity determined at regular intervals. The response to amblyopia therapy Considering the time taken for initiation of visual improvement in response to amblyopia therapy [Table - 5], a significantly large fraction (>50%) of patients in group I showed visual improvement at two weeks as compared to none in group II.
Considering the time taken for significant visual improvement (one full line or more on Snellen's chart) in response to amblyopia therapy [Table - 6], 10 out of 33 patients showed this response in group I as compared to none in group II (P<0.05 using Fishers exact test) within the first 4 weeks. Between 4 - 6 weeks also group I patients mere 7 times more likely to show a response as compared to group II (P<0.05). The difference between the response rates in the two prognostic groups was not statistically significant between 6 - 12 weeks. Overall the patients in group I were 1.8 times more likely to show significant improvement at alpha error values of P=0.003. The MHRR (Mantel Hanzel Relative Risk) adjusted for time was 2.67 with 95% confidence interval ranging from 1.26 to 5.66 (p <0.05).
A comparison of visual acuity at 12 weeks follow up of amblyopia therapy [Table - 7], [Figure - 1] suggests that patients in group I are 2.29 times more likely to show a vision better than 6/12 than patients in group II. The 95% confidence limit is 1.01 to 5.20. (P<0.01 using Fisher's exact one tailed test).
| Discussion|| |
50 patients of anisometropic amblyopia between the age group of 2.5 to 10 years were studied for assessing the prognostic significance of a reduced visual acuity for near over that for distance for response to amblyopia therapy.
A reduced visual acuity for near over that for distance was found in 17 (34%) patients. Not only was the visual outcome at the end of 12 weeks poorer in these patients but the initiation of visual improvement and continued improvement thereafter was delayed. When a reduced visual acuity for near was observed it was difficult to determine whether the visual system (due to insufficient visual input) or the accommodative efferent mechanism was responsible. Significant improvement in near vision by addition of +3.0 D sph. in 11 out of the above 17 patients suggested an accommodative dysfunction.
Inability to do fine reading, writing and drawing exercises due to reduced vision for near may be one of the factors responsible for a poorer response to amblyopia therapy. It is felt that if amblyopia therapy and exercises are given to these patients with suitable correction for near (bifocals), the response to amblyopia therapy should be comparable to the rest of the patients of anisometropic amblyopia. With recovery in vision it may be possible to gradually reduce and finally withdraw the near correction.
| References|| |
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Lennarson. L.W. Thomas C.O. France. D; Portnoy. M.D.; Jane, M.D.; Scott. M.D. "A comparison of distance and near vision in amblyopia": Transaction fifth international orthoptic congress. Cannes. France. Oct. 10-13. 1983: 329-336.
Takashi Utusunni. M.D. Jun Sugasa M.D., Yukuki Ishida C.O. and Yumiko Nobe C.O.: "Accommodative response in anisometropic amblyopia with successfully recovered visual acuity. Transaction fifth International Orthoptic Congress Cannes. France. Oct 10-13. 1983: 337-341.
Abraham 1961. "Accommodation in the amblyopia eye." American Journal of Ophthalmology: 52: 197-200.
Mann 1975. "Amblyopia: Accomodation as a causative factor" Optom Weekly 67-177.
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[Figure - 1]
[Table - 1], [Table - 2], [Table - 3], [Table - 4], [Table - 5], [Table - 6], [Table - 7]