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| LETTER TO EDITOR |
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| Year : 2006 | Volume
: 54
| Issue : 4 | Page : 288-289 |
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Authors' reply
Simi Zaka-ur-rab
2 - Wazir Manzil, Luxmibai Marg, Aligarh - 202001, India
Correspondence Address:
Simi Zaka-ur-rab
2 - Wazir Manzil, Luxmibai Marg, Aligarh - 202001
India
 Source of Support: None, Conflict of Interest: None  | Check |
How to cite this article:
Zaka-ur-rab S. Authors' reply. Indian J Ophthalmol 2006;54:288-9 |
Dear Editor,
In response to the queries regarding my article published in the June 2006 issue of Indian Journal of Ophthalmology entitled "Evaluation of relationship of ocular parameters and depth of anisometropic amblyopia with the degree of anisometropia",[1] my point-wise comments on the same are as under:
1. Though it is not uncommon to have patients reading partial lines in Snellen's test types, there was, however, no such case in the present study.[1] This fact already stands unambiguously mentioned in my article. The line acuity, therefore, was measured in all the cases by using Snellen's chart by a refractionist and counterchecked by the author.
2. Anisometropic amblyopia and meridional amblyopia are two different well-recognized entities. [2],[3],[4],[5],[6] Menon et al.[5] reported 5.56% cases of meridional amblyopia in a hospital referral practice have defined meridional amblyopia as "Patients with regular astigmatism of 1.5 D in any meridian or those with irregular astigmatism in both eyes, resulting in a decrease in vision in one or both eyes and with no associated strabismus". They had excluded patients with significant anisometropia along with a difference of 1.5D or greater astigmatism between the two eyes from the aforementioned category and grouped them under the anisometropic amblyopia group.
The present study was conducted on cases of anisometropic amblyopia.[1] Since this anisometropia was mainly due to myopic or hypermetropic refractive errors associated in some cases with lesser degree of astigmatism, these cases were classified as anisohypermetropic and anisomyopic amblyopia.
Meridional amblyopia results from an uncorrected 'significant' astigmatic error.[3],[6] The lesser degree of astigmatism observed in the present study, therefore, was unlikely to cause meridional amblyopia. The cases of astigmatism were not studied separately as there was no case in which anisometropia could be attributed mainly to astigmatism.
3. Difference in spherical equivalent was used to calculate the degree of anisometropia in the present study. Townshend et al .[7] had calculated an index of anisometropia to give greater weight to asymmetric axes, observed that this index of anisometropia was at least 'as good as' spherical equivalent in predicting the depth of amblyopia. They further concluded that of the three indices they had studied, such as spherical equivalent, root mean square and index of anisometropia, the depth of amblyopia correlated strongly with the difference in spherical equivalent, which is easy to calculate and therefore convenient.
4. I agree that it would be enlightening to know the relationship of the amount of anisometropia and the depth of amblyopia with ocular parameters, such as keratometry and axial length in meridional amblyopia, especially mixed astigmatism. Since this was beyond the purview of my present study, it would be improper on my part to make comments on the same. This subject matter, nevertheless, deserves to be separately researched upon in order to arrive at any unequivocal conclusions in this regard.
| References | |  |
| 1. | Zaka-ur-Rab S. Evaluation of relationship of ocular parameters and depth of anisometropic amblyopia with the degree of anisometropia. Indian J Ophthalmol 2006;54:99-103.  [ PUBMED] [ FULLTEXT] |
| 2. | Harvey EM, Dobson V, Miller JM, Clifford CE. Amblyopia in astigmatic children: Development and treatment. J Vision 2005;5:38a http://journalofvision.org/5/12/38/, doi:10.1167/5.12.38. |
| 3. | Goel BS. Meridional amblyopia. In : Nema HV and Nema N, editors. Recent advances in ophthalmology 5. Jaypee Brothers: New Delhi; 2000. p. 131-40. |
| 4. | Polat U, Bonneh Y, Ma-Naim T, Sagi D. Spatial interactions in amblyopia: Effects of stimulus parameters and amblyopia type. Vision Res 2005;45:1471-9. [ PUBMED] [ FULLTEXT] |
| 5. | Menon V, Chaudhuri Z, Saxena R, Gill K, Sachdev MM. Profile of amblyopia in a hospital referral practice. Indian J Ophthalmol 2005;53:227-34. [ PUBMED] [ FULLTEXT] |
| 6. | Quah BL, Tay MT, Chew SJ, Lee LK. A study of amblyopia in 18 -19 year old males. Singapore Med J 1991;32:126-9. [ PUBMED] |
| 7. | Townshend AM, Holmes JM, Evans LS. Depth of Anisometropic amblyopia and difference in refraction. Am J Ophthalmol 1993;116:431-6. [ PUBMED] |
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