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

Supplemental Digital Content is Available in the Text.Brief summary statement: Using the cosine law to estimate the distance between the sclerotomy and the fovea. This analogy between the Pythagorean theorem using the axial a-scan measurement, distance between the central cornea and the sclerotomy, and distance between the sclerotomy and the fovea can estimate the needed lengths of the forceps for 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 (c2 = a2 + b2) to calculate the adequate shaft length of the forceps to use in macular surgery, especially in highly myopic eyes, where c2 represents the axial length (hypotenuse); b2 the sum of the corneal ray and distance between the corneal limbus and the sclerotomy (base side); and a2 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.