The Cosine Law to Choose the Correct Forceps Shaft Length for Macular Surgery in Highly Myopic Eyes.

ABSTRACT

PURPOSE: To demonstrate a mathematical analogy between the Pythagorean theorem using the axial a-scan measurement, i.e., the distance between the central cornea and the sclerotomy, and the lengths of the forceps in eyes of patients with all axial lengths. METHODS: We used the Pythagorean equation (c 2 = a 2 + b 2 ) to calculate the adequate shaft length of the forceps to use in macular surgery, especially in highly myopic eyes, where c 2 represents the axial length (hypotenuse); b 2 the sum of the corneal ray and distance between the corneal limbus and the sclerotomy (base side); and a 2 the distance between the sclerotomy and the fovea (perpendicular side). RESULTS: We reproduced the cosine law to estimate the distance between the sclerotomy and the fovea. The distance between the sclerotomy and the foveal area is shorter than the axial length and can become smaller based on the distance from the sclerotomy to the corneal limbus. CONCLUSION: This simple mathematical formula is useful when performing surgery in highly myopic eyes, in which there can be difficulties reaching the macular area.