Q Value Based Ablation Profile versus Topography - Guided LASIK : A Contralateral Comparative Study

Abstract

Background: laser in situ keratomileusis (LASIK) has become the most widely used form of refractive surgery. The objective of this surgical technique was to modify the anterior corneal shape by ablating tissue from the stroma by means of the excimer laser after creating a hinged corneal flap. By this way, we were able to change the refractive status of the patient and provided better unaided vision. Continuous improvements in the original technique made the surgical procedure safer, more accurate and repeatable. These progressions are due to the development of novel technologies that are responsible for new surgical instrumentation , which makes the surgical procedure easier for the surgeon and better excimer laser ablation algorithms, which increase the optical quality of the ablation and thus the safety of the vision correction procedure. Aim of work: the aim of this study was to compare between Q value based ablation and topography-guided LASIK as regards safety, visual acuity, contrast sensitivity and high order aberration HOAs (spherical, coma and trefoil). Patients and methods: this study was conducted on 60 eyes of 30 patients, thirty eyes of them underwent topography guided LASIK and the other 30 underwent Q value based ablation. Preoperative CDVA (corrected distant visual acuity) was done. Postoperative UDVA and CDVA were measured. Postoperative high order aberrations were measured 3 months postoperatively. Results: our results showed that there was no statistically significant difference between both groups as regards UDVA, spherical equivalent, high order aberrations and Strehl ratio point spread function. Conclusion: topographic guided ablation and Q value based groups provided essentially equivalent outcomes after myopic LASIK, with statistically insignificant difference between both profiles, although both laser profiles have been found to be effective, safe and predictable. Recommendations: we recommended doing more research regarding this study with larger number of cases and doing further investigations.

Contralateral Eye Study of Topography Guided versus Q Value Adjusted Photorefractive Keratectomy in Myopia and Myopic Astigmatism

“…11 In the present study we found no significant difference between TG PRK and CQ PRK in UDVA, CDVA or MRSE at 1.3 or 6 months postoperatively, similar to the results of Hamza et al, who compared TG LASIK to CQ LASIK at 3 months. 4 In the present study, 93.8% of eyes in the TG group were within 0.5 D of emmetropia. TG ablation in virgin eyes using manifest refraction is more predictable than TG ablation using topography neutralizing techniques in post-refractive surgery eyes.…”

“…Our results were different from the findings of Hamza et al, who reported non-significant differences between TG LASK and CQ LASIK in terms of total RMS, coma, trefoil and spherical aberrations. 4 Contrast sensitivity was smaller in the CQ group, but the difference was statistically insignificant. No statistically significant difference in Strehl ratio was found between the 2 groups at any follow-up.…”

“…The only pre-operative data this treatment needs, other than the patient's refraction, is the mean corneal asphericity. 4 On the other hand, topography guided ablation reshapes the corneal irregularities into an ideal curve. Hence, it is primarily used to treat irregular astigmatism in post-LASIK eyes.…”