CATz for Highly Irregular Corneas after Keratorefractive Surgery Hamed M. Anwar, MD, FRCS Alaa El-Danasoury, MD, FRCS 1 Institutional affiliation: Magrabi Eye Hospital, Jeddah, Saudi Arabia. 1. Dr. Alaa El-Danasoury is a consultant to Nidek Co. Ltd, Gamagori, Japan.

Introduction Keratorefractive surgery such as LASIK and radial keratotomy can reduce visual acuity due to induction of higher order aberrations. Keratorefractive surgery such as LASIK and radial keratotomy can reduce visual acuity due to induction of higher order aberrations. Decreased visual acuity in such cases is due to an irregular corneal surface. Decreased visual acuity in such cases is due to an irregular corneal surface. Management modalities include: Management modalities include: Extensive postoperative counseling, Extensive postoperative counseling, Pharmacologic intervention Pharmacologic intervention Contact lens therapy Contact lens therapy Topography-guided retreatment Topography-guided retreatment

Topography guided retreatments may be a better option compared to wavefront guided treatments in such patients as: Quality of topographic images can be checked Data isn’t limited to pupillary area. Data limited to pupillary area. Questionable reliability of data in highly aberrated eyes Shack-Hartmaann aberrometry

CATz Key concepts Uses scanning spot for irregular ablation Uses scanning spot for irregular ablation Uses scanning slit for sphere & Cylinder Uses scanning slit for sphere & Cylinder Corneal topography guided ablation Corneal topography guided ablation The basic treatment in CATz is the aspheric ablation Oblate cornea: Conventional ablation CATz The “red ring” indicating the transition zone (TZ) is more peripheral and less pronounced in the CATz ablation Prolate cornea: Aspheric ablation

Demographics and patients n 8 eyes of 7 patients Mean age 34 years (23y – 47y) Gender Males – 100% VASC >20/30 in all cases Mean SE: D ± 2.03 D Range (-4.38 to 2.50) Mean Cyl: D ± 0.38 D ( Range (-1.25 to -0.25) Corneal irregularities 20-33um Night vision complaints in all patients

6 Ablation centered midway between corneal vertex and pupil center (50% PDist on FinalFit) No treatment of spherical or cylindrical error due to the high degree of corneal irregularity 100% treatment rate of all irregularities Corneal wavefront mode used Methods Corneal topography, wavefront data, and pupillometry were acquired using the OPD-Scan IICorneal topography, wavefront data, and pupillometry were acquired using the OPD-Scan II All surgeries were planned using Nidek Final Fit 1.13 softwareAll surgeries were planned using Nidek Final Fit 1.13 software Ablation performed with Nidek EC-5000 CXIII excimer laserAblation performed with Nidek EC-5000 CXIII excimer laser

Mean HO MTF over time Results – 8 eyes at 1 year Postoperatively 50% of all eyes saw  20/20 All eyes saw better than 20/30 Improvement in modulation transfer frequency values postoperatively Cumulative BSCVA of patients before and after CATz treatment The higher order MTF plots the effect on visual performance of the higher order aberrations, not sphere and cylinder.

Coma RMS over time [  m] Spherical aberration (Z12) over time (  m) Results (cont) 0.45  m decrease in the mean coma postoperatively 0.45  m decrease in the mean higher order spherical aberration postoperatively

MTF: Poor quality of vision A/B = H/B = PSF: Poor quality WF error: 1.28 Strehl Ratio: 0.01 OPD HO: Coma RMS = 1.83 Topography: Small EOZ = 4 mm Well centered ablation Case example 1 year after LASIK (2006 Flying spot laser): Night Vision symptoms (Starbursts ) UCVA: 20/20 MR: x 20 BSCVA: 20/16 Pachymetry 450 Mesopic pupil 6.7 mm

Enlargement of functional optical zone from 4mm to 6mm Difference map shows the targeted area of localised ablation Decrease in OPD HO coma RMS from 2.07D to 1.2D

Point spread function (PSF) improvement shown by the Strehl ratio increase from 0.01 to 0.04 and WF error decrease from 1.28  m to 0.6  m Modulation transfer function (MTF) shows an improvement on the higher spatial frequencies. A/B and H/B ratios increase.

Conclusion  Customized Topography Guided Ablation using Final Fit 1.13 & the CATz profile is safe and effective in the treatment of corneas with high irregularities after keratorefractive procedure.