Overcorrection may occur if significant stromal dehydration develops prior to initiation of the excimer treatment, as more stromal tissue will be ablated per pulse. This overcorrection may occur if there is a long delay prior to beginning the ablation, following either removal of the epithelium in surface ablation or lifting the flap in LASIK. Controlling the humidity and temperature in the laser suite within the recommended excimer laser guidelines may decrease variability and ideally improve refractive outcomes. Overcorrection tends to occur more often in older individuals, as their wound-healing response is less vigorous and their corneas ablate more rapidly for reasons not fully understood.
Myopic or hyperopic surface ablation typically undergoes some degree of refractive regression for at least 3–6 months. In general, patients with higher degrees of myopia and any degree of hyperopia require more time to attain refractive stability, which must be achieved before any decision is made regarding possible re-treatment of the overcorrection.
Various modalities are available for treating small amounts of overcorrection. Myopic regression can be induced after surface ablation by abrupt discontinuation of corticosteroids. Patients with consecutive hyperopia (ie, hyperopia due to overcorrection of myopia) or consecutive myopia (ie, myopia due to overcorrection of hyperopia) require less treatment to achieve emmetropia compared with previously untreated eyes, as both are considered to have over-responded to the initial treatment. When re-treating such patients, the surgeon should take care not to overcorrect a second time. With conventional ablation, most surgeons will reduce the ablation by 20%–25% for consecutive treatments. For wavefront procedures, review of the depth of the ablation and the amount of higher-order aberration helps titrate the re-treatment.
Excerpted from BCSC 2020-2021 series: Section 13 - Refractive Surgery. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.