Ocular aberrations and contrast sensitivity after different types of excimer laser treatment
Noha Abd el sadek Aziz Hamed;
Abstract
Excimer laser refractive surgery is the most commonly used operation for correcting myopia. This refractive surgery uses excimer laser to remove corneal tissue and to reshape the cornea, changing its refractive power. These refractive procedures are divided into two main groups: laser assisted in-situ keratomileusis (LASIK) and surface treatments.
Laser in situ keratomileusis (LASIK) has become the refractive procedure of choice for moderate to high myopic corrections because of the fast visual recovery making it more practical , the painless early postoperative period, and the rare occurrence of subepithelial haze.
On the other hand, LASIK exposes the eye to intra- and postoperative flap-related complications including inadequate intraoperative flaps, flap folds, ectasia, that’s why it’s understandable why many refractive surgeons would begin tofavor surface ablation to preserve corneal tissue in the hopeof reducing the incidence of post-LASIK ectasia.Moreover, eyes with insufficient residual corneal stromal thickness are not candidates for LASIK.
Also it has been well documented that LASIK induces higher order aberrations;whereas lower order refractive errors such as hyperopia, myopia, and astigmatism are corrected successfully with highly predictable results.
Higher order aberrations induced during LASIK canbe during any of its steps either flap creation or laser ablation itself, however studies performed proved with no doubt that lots of these aberrations are induced during flap creation, however, in a study that compared flaps created using femtosecond laser and mechanical microkeratome, changes in higher order aberrations after the flap were observed only for the mechanical microkeratome and not for the femtosecond laser. This study therefore imply that aberration induction depends on factors controlling flap creation during flap formation.
Sub-Bowman keratomileusis (SBK) technique on the other hand is a laser in situ keratomileusis (LASIK) procedure in which the flap is thinner ranging between 90 µm and 110 µm in thickness.
A major advantage of creating a thin flap during SBK is leaving sufficient stromal tissue to allow safer excimer laser ablation, especially in patients with moderate or high myopia.
Recent retrospective studies evaluated the effect of thin flaps on the outcomes of LASIK one, three and six months after surgery and proposed that intended thin flaps may be advantageous over thicker flaps for myopic LASIK, studies supporting such data mentioned before as in those conducted by Prandi et al on 2004 and Cobo-Soriano et al on 2005,all in favor of SBK.
These studies paved the way to SBK, which may combine the advantages of LASIK and surface ablation.
The role of photorefractive keratectomy (PRK) has been reappraised because of insufficient preoperative corneal thickness, corneal instability, and the trend towards greater higher order aberrations in LASIK procedures.
In general, PRK with MMC eyes has showed better contrast sensitivity values than LASIK eyes. Many authors reported a decrease in contrast sensitivity and glare after conventional LASIK and PRK and some authors believe that higher order aberrations are responsible for decreased contrast sensitivity postoperatively and here comes a large part of our study importance where it’s proved here that PRK has better contrast sensitivity postoperative than preoperatively.
Laser in situ keratomileusis (LASIK) has become the refractive procedure of choice for moderate to high myopic corrections because of the fast visual recovery making it more practical , the painless early postoperative period, and the rare occurrence of subepithelial haze.
On the other hand, LASIK exposes the eye to intra- and postoperative flap-related complications including inadequate intraoperative flaps, flap folds, ectasia, that’s why it’s understandable why many refractive surgeons would begin tofavor surface ablation to preserve corneal tissue in the hopeof reducing the incidence of post-LASIK ectasia.Moreover, eyes with insufficient residual corneal stromal thickness are not candidates for LASIK.
Also it has been well documented that LASIK induces higher order aberrations;whereas lower order refractive errors such as hyperopia, myopia, and astigmatism are corrected successfully with highly predictable results.
Higher order aberrations induced during LASIK canbe during any of its steps either flap creation or laser ablation itself, however studies performed proved with no doubt that lots of these aberrations are induced during flap creation, however, in a study that compared flaps created using femtosecond laser and mechanical microkeratome, changes in higher order aberrations after the flap were observed only for the mechanical microkeratome and not for the femtosecond laser. This study therefore imply that aberration induction depends on factors controlling flap creation during flap formation.
Sub-Bowman keratomileusis (SBK) technique on the other hand is a laser in situ keratomileusis (LASIK) procedure in which the flap is thinner ranging between 90 µm and 110 µm in thickness.
A major advantage of creating a thin flap during SBK is leaving sufficient stromal tissue to allow safer excimer laser ablation, especially in patients with moderate or high myopia.
Recent retrospective studies evaluated the effect of thin flaps on the outcomes of LASIK one, three and six months after surgery and proposed that intended thin flaps may be advantageous over thicker flaps for myopic LASIK, studies supporting such data mentioned before as in those conducted by Prandi et al on 2004 and Cobo-Soriano et al on 2005,all in favor of SBK.
These studies paved the way to SBK, which may combine the advantages of LASIK and surface ablation.
The role of photorefractive keratectomy (PRK) has been reappraised because of insufficient preoperative corneal thickness, corneal instability, and the trend towards greater higher order aberrations in LASIK procedures.
In general, PRK with MMC eyes has showed better contrast sensitivity values than LASIK eyes. Many authors reported a decrease in contrast sensitivity and glare after conventional LASIK and PRK and some authors believe that higher order aberrations are responsible for decreased contrast sensitivity postoperatively and here comes a large part of our study importance where it’s proved here that PRK has better contrast sensitivity postoperative than preoperatively.
Other data
| Title | Ocular aberrations and contrast sensitivity after different types of excimer laser treatment | Other Titles | تأثير الطرق المتعددة لعمليات الإكزيمر ليزر علي كل من الانحرافات البصرية و حساسية التباين | Authors | Noha Abd el sadek Aziz Hamed | Issue Date | 2015 |
Recommend this item
Similar Items from Core Recommender Database
Items in Ain Shams Scholar are protected by copyright, with all rights reserved, unless otherwise indicated.