The optimum time to achieve initial adequate surgical alignment in congenital esotropia is any time before the age of two years. I base this opinion on a study1 1 personally performed of over 150 adequately aligned congenital esotropes from the practices of seven strabismologists in three countries followed for an average of 8.4 years. A correlation was made of adequate surgical alignment (which was within 10 prism diopters of orthophoria for a minimum of six months) with standard motor and sensory tests. It is important to realize I performed all the tests on all patients in the study without knowledge of the age of initial adequate surgical alignment. After the results were tabulated, the records were then scrutinized for the age of adequate surgical alignment and the patients were divided into four subgroups according to the age at which the surgeons achieved adequate surgical alignment.
Although sensory tests showed a high percentage of binocularity in patients aligned by 24 months of age, and although the results showed no statistically significant difference between those aligned by 6 months vs. 12 months vs. 24 months, those aligned after 24 months of age demonstrated a significantly lower percentage with sensory evidence for binocularity (p < 0.001).
The four subgroups were remarkably similar in the following aspects: the age of diagnosis confirmed by ophthalmologist's exam, length of follow-up from initial adequate surgical alignment, the length of follow-up from the last surgical procedure, the initial refractive error, the initial deviation, the number of horizontal procedures, the number of patients who received vertical muscle surgery, the number of patients who received glasses or miotics, the incidence of amblyopia, the present motor alignment and the number of patients with dissociated vertical divergence.
It is important to emphasize that the motor tests performed revealed no statistically significant difference in the four subgroups.
Interestingly, although there was usually an agreement on the binocularity assessment between myself and the patients' own ophthalmologists, a few cases had been rated "bifoveal" by their own surgeon, and 1 found definite (but small) motor shifts and absolutely no sensory evidence for binocularity in these patients. If one realizes that occasionally, in the ensuing years, the alignment in patients will slide from an esotropie into an exotropic position, it is not hard to postulate that at some point in time, these same patients will appear straight or very nearly straight and yet have no binocularity!
One must realize in discussing this subject that most previous studies have been based on the age of first surgery rather than the age of first adequate surgical alignment and that the tests utilized for the evaluation of binocularity had not been standardized.
Also, personal bias could not be ruled out in previous studies since in these studies either the surgeon or his associates analyzed their own cases. In my study, I minimized prejudicial bias by masking myself from the age of initial adequate alignment until after the examination was performed, and I analyzed other surgeons cases rather than my own.
A prospective, randomized, masked study is not possible for this type of investigation because the age of initial adequate alignment cannot be predetermined since many cases are not adequately aligned until the second or third surgery. It is generally assumed that adequate motor alignment is a necessary precursor of binocularity, and that is why I made this feature such an important one in this study. Admittedly, refined stereopsis was rarely found and most cases considered cured fell within the confines of the monofixation syndrome described by Parks.
One last comment about a study such as I described is in order. I believe it is best to turn over data gathered like this for statistical analysis to a professional. A biostatistician can usually tell us if we have enough cases to prove or disprove a point, and it probably is just as important in a study as the surgical technique and criteria for surgery.
The data referred to above influence my current management of patients with congenital esotropia in the following way: I try to eliminate all the motor misalignment before the age of two as soon as I feel I have enough consistent measurements in a patient to do so. I do not try to "titrate" surgery, but prefer to eliminate all the angle by as much surgery as is necessary even if it means surgery for both medial recti and both lateral recti at the first session. The initial surgical procedure is recession of both medial recti if the defect is 50 prism diopters or less. A resection of one lateral rectus is included initially for all deviation angles above 60 prism diopters. An additional lateral rectus resection and re-weakening of a medial rectus is done for any residual angle over 10 prism diopters that does not respond to full hyperopic correction and/or miotics within six weeks of the first surgery. Presently, I do not feel pressured to try to achieve alignment before or by six months of age because I honestly feel now that these results are no better than those aligned by 24 months of age. On the other hand, I do not defer surgery if I have consistent measurements.
1. Ing MR: Early surgical alignment for congenital esotropia. TYans Am Ophthalmol Soc 1981; 79:625-663.