The 90-degree rule in posterior ptosis surgery.

To propose a guideline for ptosis clamp positioning to minimize the risk of globe injury during posterior ptosis surgery. Measurements of 20 consecutive patients, 40 eyelids, undergoing bilateral posterior ptosis repair surgery were taken; as a surrogate for needle tip position, measurement of the distance from the clamp base to the ocular surface was taken using a caliper with the clamp held at 90-degrees to the ocular surface and again at 45-degrees to the ocular surface. These measurements were compared to geometric predictions of the distance from the clamp base to the ocular surface. The average distance from the clamp base to the ocular surface when the clamp is held 90-degrees to the ocular surface was 7 mm, this distance decreases to 5 mm when the clamp is held 45° to the ocular surface. This coincides well with geometric predictions. Posterior ptosis surgery overall has an excellent safety profile; however, complications are possible, perhaps the most severe of which is inadvertent globe and/or corneal injury. The more acute the angle the ptosis clamp is held, the closer the clamp base, and subsequently the needle tip, is to the ocular surface as would be predicted geometrically. This coincides with closer proximity of the needle to the ocular surface during surgery. The theoretical risk of globe injury should decrease as the distance of the needle from the globe increases, and this distance is greatest when the clamp is held at a 90-degree angle to the ocular surface. This distinction becomes particularly important to consider in large eye morphology patients where the distance from the needle to the globe can approach 2 mm when the clamp is held at 45-degrees.