Central islands are a very infrequent complication of LASIK and other laser vision correction procedures. The term is used to describe elevations in the central treatment zone of the cornea that can occur if the laser does not remove enough tissue in this area. The "island" is a small mound of corneal tissue that can interfere with vision.
Some researchers believe central islands are caused by evaporated corneal tissue, in a plume, interfering with the laser beam during treatment. Others believe central islands are due to pooling of water or oil pooling on the corneal surface, affecting the amount of treatment the laser beam delivers in this area.
Central islands occurred more frequently with older "broad-beam" lasers, which directed laser energy across a broad area of the cornea simultaneously. Islands rarely occur with the newer excimer lasers that use "scanning beam" or "flying spot" technologies that deliver smaller areas of laser energy in a random pattern across the surface of the cornea.
Some central islands spontaneously resolve after several months. However, patients with persisting central islands may need to wear rigid gas permeable (GP) contact lenses for a period of time to obtain acceptable vision. Eyeglasses and soft contact lenses usually cannot correct vision problems caused by central islands.
New laser vision correction procedures (LASIK and PRK) based on corneal topography have shown promise in eliminating central islands surgically to restore good vision without GP contact lenses.