Surgery to correct lower lid entropion needs to address both the weakness of the lower lid muscle and the horizontal laxity of the eyelid. A very lax lid is prone to flopping in, causing an entropion, or flopping out, causing an ectropion. Tightening the eyelid is akin to tightening the guy ropes on a tent, for stability. The weak lower lid muscles can also contribute to this tendency for the lid to turn in and therefore need to be tightened. With ageing the lower lids can develop loose skin and this can be corrected at the same time as correcting the lid position.
The approach for surgical correction of upper lid entropion is different. This condition is often caused by scarring under the upper lid which pulls down the lashes so that they touch the cornea. Surgical correction involves sliding the front layer (lamellar) of the lid (skin & lashes) back over the inner layer (lamellar) of the lid. This results in the upper lid lashes being rotated away from the cornea.