Year : 1976 | Volume
: 24 | Issue : 3 | Page : 10--13
Meena Bhatia, VB Pratap
Dept. of Opthalmology, K.G.'s Medical College, Lucknow, India
Dept. of Opthalmology, K.G.«SQ»s Medical College, Lucknow
|How to cite this article:|
Bhatia M, Pratap V B. Anisometropic Amblyopia.Indian J Ophthalmol 1976;24:10-13
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Bhatia M, Pratap V B. Anisometropic Amblyopia. Indian J Ophthalmol [serial online] 1976 [cited 2021 Oct 22 ];24:10-13
Available from: https://www.ijo.in/text.asp?1976/24/3/10/31290
Amblyopia is derived from a Greek word meaning "Blunting of vision" and is defined as a condition of diminished visual form of sense which is not associated with any structural abnormality or disease of the media, fundi or visual pathways and which is not overcome by correction of refractive error. In the recent years amblyopia has been classified by Noorden and Maumenee as strabismic amblyopia, stimulus deprivation amblyopia and anisometropic amblyopia.
The term anisometropic amblyopia (without strabismus) is suggested for use when the degree of refractive error alone accounts for poor visual acuity in the more defective eye, because it describes the condition without implying the exact mechanism. Studies of Helvestons, and Malik, Gupta and Chowdhry have shown that there may be no correlation bet ween degree of anisometropia and depth of amblyopia.
The present work is undertaken to study the correlation of visual acuity and amount of anisometropia in cases without strabismus.
Method and Material
This study covers the cases who reported in the orthoptic clinic of the Eye Department of K. G.'s Medical College, Lucknow during the period from January 1973 to June 1974. In all 931 patients were examined, out of which 61 cases who had unilateral amblyopia without strabismus were selected for this study.
The criterion for anisometropia was a difference between two eyes of 0.50 D or more, either of sphere or cylinder. Patients with visual acuity of 6/9 or less in the eye which could not be improved even after correction of refractive error, having no organic disease of media or fundus and who showed no manifest deviation with or without glasses for all distances on cover test, were regarded as cases of "Straight amblyopia". In every case refraction and examination of fundus and media was done under cycloplegia (Atropine in children and Homatropine in adults) and best visual acuity with glasses was recorded. Each case was also examined for the grade of binocular functions as well as for any evidence of suppression on synoptophore.
Observations and Results
Amblyopia was seen more commonly in males (76.6%) than in females (23.3%). Majority of 36 cases (60%) were seen in the age group of 11-20 years.
Out of the 61 cases of straight amblyopia, 60 cases had anisometropia. Majority of 48 cases (80%) showed anisohypermetropia. Anisometropia of 2-4 diopters was commonest (22 casses-36.%). Anisomyopia was seen in only 1 I cases (18.3%) and only one case (1.7%) showed myopia in one eye and hypermetropia in the other eye. (Hypermetropic eye being amblyopic).
[Table 5] shows that there is no direct relation between the degree of anisometropia and the depth of amblyopia (in terms of visual acuity. Anisometropia of 0.5-1 D is compatible with visual acuity of 6/9 to 6/60 whereas that of 5-6 D or even 7.0 D is compatible with visual acuity of 6;18 to less than 6/60. 19 cases (31.7%) showed visual acuity from 6/9 to 6/18, out of whom majority of 12 cases had anisometropia of 1-4 D. 37 cases (61.6%) had visual acuity of 6/36 to 6/60 and in this group also, most of the cases (25) had anisometropia of 1-4 D. Only 4 cases had visual acuity less than 6) 60 and they showed anisometropia of 4-7D, Thus it was seen that there is tendency for better visual acuity in eyes with low or moderate degree of anisometropia (1-40).
Incidence of anisometropia in straight amblyopia is variable as reported by many authors,,. In our series incidence is slightly higher being 98.2%. Regarding age and sex incidence it was noted in the present study that straight amblyopia is more common in males (76.7%) than in females (23.3%), and maximum incidence was seen in the age group of 11-20 yrs. In 34 cases (56.7%) left eye was involved and in rest of the 26 cases (43.3%) right eye was involved. Contrary to these findings Feldman and Taylor reported that there was no predilection for either eye in the development of amblyopia nor was there any sex influence.
In our series it was observed that in almost all the cases anisometropia led to amblyopia in the eye with greater error of refraction which conform to the findings of Copps.
Out of the total of 60 cases of anisometropic straight amblyopes, 48 cases (80%) had hypermetropic anisometropia varying from 0.5 to 7.0 D, whereas only 11 cases (18.3%) showed myopic anisometropia. These findings very well square with the study of Copps who mentioned that amblyopia accompanying anisometropia was greater in hyperopic than in myopic eyes.
It is a universally accepted fact that anisometropia is associated with amblyopia of variable degrees but the controversy remains about the depth of amblyopia in relation to the degree of anisometropia. The view of points of various authors may be categorised as follows :
(1) Helveston has suggested that there is no relationship between the degree of anisometropia and depth of amblyopia in anisometropic amblyopia with or without strabismus. (2) Copps is of the view that intensity of amblyopia varies directly with the amount of anisometropia (3) Malik et all and Gupta et a1 observed that there is no strict relationship between the depth of amblyopia and amount of anisometropia but there is tendency for visual acuity to be better in low anisometropia.
The results of present study are inaccordance with the findings of 3rd view point that visual acuity is better where anisometropia is from 1-4 D and here too it was observed that visual acuity of 6/60 may be seen with anisometropia of 0.5-1.0 D azid visual acuity of 6/18 or more with anisometropia of 6-7D.
The retina of the more ametropic eyes has never received such clearly defined images as its fellow. Therefore the development of visual acuity does not progress to complete as in the eye with the lower refraction, thereby fusion of images is not possible and suppression develops in the more ametropic eye. This at a late stage leads to suppression at higher centres, first of faculative type later becoming obligatory in nature. These explanations can justify development of amblyopia in anisometropia of 2-3 D or more but no justification can be provided for situations where anisometropia is of low degree with visual acuity of 6/60. It is seen very commonly in daily practice that some patients can tolerate a difference of 2-3 D between the two eyes whereas others are very uncomfortable even with a difference of 0.5 D. Thus it may be assumed that anisometropia alone is not resposible for amblyopia but adaptbility of the individual has also its role to play.
The available literature reveals that mention has also been made of factors like age of onset of anisometropia, degree of eccentric fixation,,, degree of anisicconia, difference in the axial length of the eyeballs and certain "un-know factors". Yet anisotnetropia remains in important factor, although it is not the only cause for producing amblyopia and much work remains to be done in this field.
1. From 51 cases of "Straight amblyope', 98.2% show anisometropia ranging from 0.5 to 7D.
2. Males show a higher incidence (76.7%) than females (23.3%) in anisometropia without strabismus.
3. 11-20 years age group has the maximum number of cases having amblyopia in straight eyes.
4. Hypermetropic anisometropia is observed in 80% of the cases.
5. No direct relationship can be established between the degree of anisometropia and depth of amblyopia, but there seems to be a tendency for better visual acuity in low or moderate degree of anisometropia (1-4D).
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