Refraction-associated congenital ptosis has been investigated in previous studies.2–4 Eyelid ptosis affects the anterior corneal surface, which then induces refractive changes because of corneal refractive error and astigmatism.4 Huo et al8 found that unilateral ptosis was associated with myopia. Paik et al2 reported that ptotic eyes had higher amounts of astigmatism, with the OA and WTR types being the most common. Consistent with previous studies,2–4, 8 we found a higher amount of astigmatism in the ptotic eyes compared with the fellow eyes, and WTR astigmatism was the most common type of astigmatism in ptotic eyes (70.6%).
Amblyopia has also been found to be higher in those with congenital ptosis compared to the general population.2,7 According to one study, childhood-ptosis-associated amblyopia was reported in about 7.9 per 100,000 births.9 Other previous studies2,7,9,10 found that the incidence of amblyopia was between 14% and 21%. Our study showed a higher incidence of amblyopia (46.4%) in the Thai patients under this study. This resulted from more than half of our cases (62.8%) demonstrating severe ptosis and 53.9% from the visual deprivation. The main etiology of amblyopia was occlusion of the visual axis, which is similar to the results of Grinpentrog et al,9 who reported that half of ptosis-associated amblyopia cases were the result of visual deprivation. Another cause of amblyopia was the correlation between the amounts of anisometropia. Ptotic eyes showed higher amounts of both SE and astigmatism, compared with the fellow eyes. Previous studies3,7 also reported that more than half of amblyopia cases came from refractive error, which is not different from our study (46.2%).
There has been controversy regarding the benefit of the timing for correction of ptotic eyes, in terms of anisometropic amblyogenic ptosis. Surgical intervention at an earlier age might provide benefits in terms of early refractive change to the cornea, better visual outcome and less emotional trauma associated with the surgery. Conversely, waiting to perform surgical correction at an older age allows patients to be more cooperative with examinations, producing better anatomical results and refractive stability. Wu et al11 reported that there was no significant visual benefit from surgical correction of congenital ptosis in patients at 2 years or younger, compared with patients operated upon between 2 to 5 years of age. Based on a retrospective chart review of 62 patients, Cadera et al12 reported that changes in cylinder were not statistically significant between patients in their younger and older-age groups (< 4 years old and ≥ 4 years old, respectively). A recent study2 in an Asian population also reported no significant change in the magnitude of astigmatism between age groups after surgical correction, but a significant increase OA in postoperative eyes.
Our study is the first prospective study, apart from that by Kumar et al,13 to include all ages of patients with congenital ptosis, especially those under the age of 5. We compared the astigmatic change after surgical correction between early-age and older-age groups. After ptosis correction, there was an improvement in SE and astigmatism in the ptotic eyes in both groups. However, the improvement in astigmatism did not significantly differ between the two groups. Thus, early surgical intervention might not produce significant benefits in terms of astigmatic change. Surgical correction could be delayed in cases of anisometropic amblyopic ptosis until appropriate surgical planning is done.
The limitation of our study was the small number of congenital ptosis cases,since the numbers might not have been enough to demonstrate statistical significance. Another limitation was that we did not include corneal topography, to examine the characteristics of corneal astigmatism before and after surgery because we tested children under 5 years old and because of the associated research costs.