JAN 21, 2014
Cataract/Anterior Segment, Pediatric Ophth/Strabismus
This study provides guidelines for selecting an initial contact lens power in aphakic infants younger than one year who have undergone cataract surgery without primary IOL implantation. Based on this study’s results, the authors do not advocate inserting a standard +32 D lens in aphakic infants.
They write that since refraction at the conclusion of surgery in infants may be difficult, preoperative biometry can be used to estimate contact lens power. They hope that the guidelines in this study will provide better aphakic correction and decrease the need for changing contact lenses.
Subjects were 50 patients who underwent cataract surgery without primary IOL implantation before one year of age and were implanted with a SilSoft silicone eslastomer contact lens (Bausch & Lomb, Rochester, N.Y.) immediately after surgery.
Target contact lens power was calculated using postoperative refraction at the corneal plane for each eye. A regression formula was derived using the targeted contact lens power and the axial length (AL). The lens power also was estimated using various formulas. An A-constant was derived to estimate contact lens power using an IOL power calculation formula.
Within one month after surgery, refraction at the corneal plane was 29.6 ± 4.4 D. Regression analysis revealed that contact lens power was equal to 84.4 ‑ 3.2 x AL (R2 = 0.82; P < 0.001). Contact lens power could be estimated using an A-constant of 112.176 in the IOL power calculation formula. The authors say this model explains approximately 82 percent of the variation in contact lens power seen in this study and suggests change of 3.2 D per 1 mm of axial length.
Since new contact lenses are generally prescribed when the residual refractive error is more than 3 D, if a contact lens power of 32 D had been used, 22 of the 50 eyes would have needed a replacement lens.
The authors note that these results may not be applied to other types of contact lenses or age groups.