The Safety of 250 µm Residual Stromal Bed in Preventing Keratectasia after Laser in situ Keratomileusis (LASIK)

Abstract

To determine if the residual corneal stromal bed of 250 µm is enough to prevent iatrogenic keratectasia in laser in situ keratomileusis (LASIK), we studied 958 patients who underwent LASIK from April 2000 to October 2003 retrospectively. The estimated probabilities of the residual stromal bed, that was less than 250 µm, were calculated using the publi- shed flap thickness data of Moria C&B microkeratome. Then we calculated the ratio of the real incidence of keratectasia to the expected the percentage of the patients with less than 250 µm residual stromal bed in our study. Using the LASIK flap thickness data of Miranda, Kezirian and Nagy, the expected probabilities that the residual stroma would be less than 250 µm were 8.8%, 4.3% and 1.5% of the 1,916 eyes respectively, while keratectasia developed in both eyes (0.1%) of 1 patient in our study. The estimated ratio of the keratectatic eyes to eyes with less than 250 µm stromal bed were 1.2-6.9%. Compared to the number of eyes with residual stromal thickness less than 250 m, the incidence of keratectasia was relatively low. The residual stromal bed thickness of more than 250 µm may possibly be safe, but further observations for long period are necessary.

Reasons for not performing keratorefractive surgery in patients seeking refractive surgery in a hospital-based cohort in "Yemen"

“…To date, the lower limit for a stable bed thickness remains uncertain. Yet, the majority of refractive surgeons consider 250 μ m as the limit 26. However, iatrogenic keratectasia has been reported in cases with residual stromal bed thickness of >275 μ m 27.…”

Pentacam HR Indices Variation in Normal Corneas with Different Corneal Thickness

“…Thinnest corneal thickness (TCT) and other pachymetric indices have been widely discussed in the literature and are frequently considered as important KC screening parameters [6], as well as major risk factors for postoperative ectasia development [7, 8]. Safe values for residual stromal bed thickness following laser in situ keratomileusis (LASIK) [9, 10], and the acceptable percentage of tissue altered [11, 12] has been previously highlighted. All these studies reflect a robust role of corneal thickness as a determinant of corneal properties and an ectasia screening parameter [13–15].…”

Stability of posterior corneal elevation one year after myopic laser in situ keratomileusis

“…Laser in situ keratomileusis (LASIK) is a successful surgical method for the correction of myopia; however, this procedure can weaken the stroma beneath and there might be increased risk for keratectasia post‐operatively 1–3 …”