|LETTER TO THE EDITOR
|Year : 2009 | Volume
| Issue : 1 | Page : 71-72
Pradeep Sharma, Rohit Saxena, Makarand Narvekar, Ritu Gadia, Vimla Menon
Strabismology Service, Dr. R.P. Center for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi-110 029, India
|Date of Web Publication||12-Dec-2008|
Dr. Rajendra Prasad Center for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi-110 029
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Sharma P, Saxena R, Narvekar M, Gadia R, Menon V. Authors' reply. Indian J Ophthalmol 2009;57:71-2
We thank Pandey et al .  for taking keen interest in our article.  It is interesting that they have raised the issue of dissociated horizontal deviations (DHDs), decompensated monofixational exotropia, and exotropia accompanying neurological diseases as differentials of intermittent exotropia (XT). All these conditions were excluded by history and relevant examination as indicated. Reverse fixation test as described earlier by Mattheus et al . and Graf and recently highlighted by Brodsky et al .,  and specific binocular tests can differentiate the conditions described above. In short, a proper orthoptic workup can never be underestimated.
We agree that subnormal vision can affect the stereoacuity. Therefore, all our cases had the best corrected Snellen acuity of 20/20 or better in each eye. As already mentioned in the article, patients with amblyopia, anisometropia over 2 diopter (D), and any horizontal and/or vertical incomitance were excluded from the study.
It is nice that they have raised the issue of different types of convergence movements. Although under laboratory conditions, we may distinguish the tonic, proximal, accommodative, and fusional vergences,  clinically they work in conjunction and in different combinations under different situations. So, in pencil pushups all may be working together, but in prism bar exercises with the object at a distance, the tonic and fusional vergences work but not the proximal. And any accommodative convergence would induce a change in the image size that can be appreciated. The use of accommodative vergences can be easily tested and controlled on the synoptophore by using lenses controlling the accommodation, even if a specialized accommodation synoptophore is not used. In our methodology, the prism bars were used for measuring the vergences and may have tested for tonic and fusional vergences only. Clinically, there is not much gain by splitting the two.
Again it is obvious that the effect of orthoptic exercises is temporary and needs to be done continuously, as any body-builder knows that the effect of gym workouts wears off if they are not sustained. That is because the muscles are a dynamic organ. Improvement of fusional vergences after surgery is explained by the ease with which home exercises can be done after surgical alignment, whereas preoperatively a neutralization of deviation was required. It could also imply "improved efficiency of the feedback mechanism following surgery, or alternatively could be conceptualized as an epiphenomenon of surgical intervention," as suggested by them.
Finally regarding the Frisby Davis distance (FD2) stereo test, we agree that the responses are variable, and this could be possibly due to the parallax between the two eyes because of the real depth that may be judged even in the absence of true stereopsis. We are evaluating the role of FD2 in intermittent XT in another study.
To conclude, we thank them for evoking interesting issues regarding intermittent XT, convergence insufficiency, stereopsis, and the role of convergence exercises and surgery.
| References|| |
Pandey PK, Vats P, Amar A, Jain P, Bansal Y. Evaluation of distance and near stereoacuity and fusional vergence in intermittent exotropia. Indian J Ophthalmol 2009;57:71.
Sharma P, Saxena R, Narvekar M, Gadia R, Menon V. Evaluation of distance and near stereoacuity and fusional vergence in intermittent exotropia. Indian J Ophthalmol 2008;56:121-5.
Brodsky MC, Graf MH, Kommerell G. The reversed fixation test: A diagnostic test for dissociated horizontal deviations. Arch Ophthalmol 2005;123:1083-7.
Arnoldi K, Reynolds JD. A review of convergence insufficiency: What are we really accomplishing with excercises? Am Orthop J 2007;57:123-30.