Stimulus deprivation amblyopia in human congenital ptosis: a study of 100 patients.

AIM: To investigate the frequency of stimulus deprivation amblyopia (SDA) in comparison with other reasons for amblyopia in human congenital ptosis.
METHODS: The frequency and causes of amblyopia were evaluated in the 200 eyes of 100 patients. Congenital ptosis was present in 128 eyes (72 unilateral, 28 bilateral). The age at investigation was one year and older, with an average of 11 years and 10 months. Amblyopia was defined as best corrected visual acuity less than 1.0 or a difference between the two eyes of at least 0.2. The following causes of amblyopia were identified: amblyopiogenic refractive errors: astigmatism > or = 1 dpt, anisometropia > or = 1 dpt (79% cycloplegia) and strabismus. In cases with no other reasons for amblyopia, SDA was assumed. Statistical analysis was performed using the chi-square and the sign tests.
RESULTS: The overall incidence of amblyopia in ptotic eyes was 89/128 (70%). In 3.9% of the cases (5/128; 2 eyes with unilateral and 3 eyes with bilateral ptosis) we assumed SDA. A comparison of ptotic eyes with (unilateral: n = 35, bilateral: n = 34) and without covered optical axis revealed the following: in the case of unilateral ptosis, amblyopia was found more often in ptotic eyes with covered optical axis: 30 out of 35 vs. 24 out of 37 (p = 0.06); in the case of bilateral ptosis this difference was significant: 27 out of 34 vs. 8 out of 22 (p < 0.05). In the case of SDA, the optical axis was covered in only a single eye, in a patient with bilateral ptosis. There was no difference in the incidence of anisometropia: 19 out of 53 vs. 14 out of 47 (p = 0.52). Astigmatism was found more frequently in ptotic eyes with covered optical axis in unilateral ptosis: 23 out of 35 vs. 16 out of 37 (p = 0.06) but not in bilateral ptosis: 21 out of 34 vs. 13 out of 22 (p > 0.9). Strabismus was found significantly more frequently in ptotic eyes with covered optical axis: 13 out of 35 vs. 4 out of 37 (p < 0.05) in unilateral ptosis and 7 out of 34 vs. 1 out of 22 (p = 0.13) in bilateral ptosis.
CONCLUSION: In contrast to the classical animal models of stimulus deprivation amblyopia, this entity is rare in human congenital ptosis, perhaps because of the counter effect of compensating head posture. Disruption of fusion resulting in strabismus might be an additional indirect cause of amblyopia in congenital ptosis. Prophylactic amblyopia treatment in ptosis cases is important as long as no testing of visual acuity is possible in a child.