Topography-Guided Photorefractive Keratectomy for Irregular Astigmatism After Penetrating Keratoplasty
Purpose
To evaluate the efficacy and safety of the Vancouver Custom Topographic Neutralization Technique (TNT) in topography-guided photorefractive keratectomy (TG PRK) for irregular astigmatism following penetrating keratoplasty (PK).
Methods
Retrospective case series. 49 eyes with post keratoplasty astigmatism underwent TG PRK with Allegretto Wavelight (AW) laser using the Vancouver Custom Topography Neutralization Technique (TNT) to modify the manifest refraction based on the refractive changes predicted from the plano TG treatment. After treatment, mitomycin C 0.02% was applied in all cases followed by standard post-PRK management. Uncorrected visual acuity (UCVA), best spectacle corrected visual acuity (BSCVA), refraction, keratometry (K), topography and haze on a 1-4 scale are evaluated at 1, 3, 6, 12, and 24 months post treatment.
Results
Sufficient data was available for analysis on 23 eyes at 12 months. 8 eyes (35%) had UCVA ≤ 20/40, none preoperatively. 11 (48%) had BSCVA improved, 8 (35%) gained 2 lines or more, while 1 (4%) lost 2 lines or more. Preoperative refractive cylinder ranged from 0.75D to 8.00D, and post-operatively ranged 0.00D to 6.00D. Average spherical equivalent improved from -2.32D to -0.87D. Mean astigmatic reduction was 2.89D. Retreatment rate was 5.76%. Delayed epithelialization beyond one week in 4 and corneal haze of greater than 2/4 in 3. 4 eyes with extreme astigmatism greater than 8D on the AW topolyzer require a second treatment for residual astigmatism, with improvement of UCVA in all. Complications include visually significant haze in 2 eyes, and delayed epithelization beyond one week in 4 eyes.
Conclusion
Topography-guided PRK for irregular astigmatism after penetrating keratoplasty using the Vancouver custom TNT ablation offers promising early results with good efficacy and safety. A third of the subjects achieved 20/40 or better UCVA compared to none preoperatively, with 43% had BSCVA improved by 1 line or more. Extreme astigmatism post keratoplasty can also be treated with TG PRK, but likely to require a second treatment.