Posters

Analysis of difference between predicted ablation depth & achieved ablation depth according to accurate corneal epithelium ablation on Trans-PRK using Amaris 1050RS Eximer Laser in patients with extremely high myopia (>-8 diopter)

Poster Details

First Author: O.Jungwoo SOUTH KOREA

Co Author(s):    J. Youngkuen                    

Abstract Details

Purpose:

To compare between Predicted Ablation Depth (PAD) and Achieved Ablation Depth (AAD) according to Accurate Corneal Epithelium Ablation System (ACEAS) on Transepithelial-PRK (Trans-PRK) using CIRRUS™ HD-OCT 5000 and Amaris 1050RS Eximer Laser in patients with extremely high myopia. If there are any statistically significant difference between these values, multiple predisposing factors will be evaluated further. Accurate Corneal Epithelium Ablation System (ACEAS) measures the corneal epithelium thickness accurately with CIRRUS™ HD-OCT 5000 and removes the corneal epithelium accurately within in the range 40 - 75um using Amaris 1050RS Eximer Laser software V 6.1.

Setting:

Real Ablation Depth is the difference between pre and postoperative Corneal Stroma Thickness without Corneal Epithelial Thickness. 〔Real Ablation Depth =(Preoperative Total Corneal Thickness - Preoperative Corneal Epithelial Thickness) – (Postoperative Total Corneal Thickness - Postoperative Corneal Epithelial Thickness)〕

Methods:

64 extremely high myopic eyes were treated with ACEAS on Trans-PRK using Amaris 1050RS Eximer Laser and their PAD and AAD were compared after postoperative 2 months later. The difference between PAD and AAD was evaluated by considering preoparative factor (corneal epithelium thickness, myopia, astigmatism, total ablation depth, Base curve and Asphericity 6, 8mm) and operative factor (optical zone, total ablation zone, the difference between pre and postoperative epithelial thickness). Total corneal thickness and corneal epithelial thickness were measured with CIRRUS™ HD-OCT 5000 (ZEISS, Germany) and Predicted Optic Zone & Effective Optic Zone were measured with SIRIUS wavefront analyser.

Results:

There was no statistically significant difference between PAD (88.58±5.98um) and AAD (89.53±7.75um). 13 patients showed AAD was smaller (over 5um) than PAD. These patients with over 5um difference between PAD and AAD were further analyzed to find out multiple factors affected in this result. Preoperative epithelial thickness (odds ratio=.546, 95% CI=[.332, .898],under 0.05) Total ablation amount (odds ratio=.848, 95% CI=[.717, 1.003], under 0.10) were statistically significant factors of the difference. But these cases did not show any under-correction on postoperative refractive outcome and there was no difference between Predicted Optic Zone and Effective Optic Zone.

Conclusions:

No difference between PAD and AAD shows improved surgical stability and safety on Trans-PRK using Amaris 1050RS Eximer Laser in patients with extremely high myopia (over -8Diopter). We predicted that Trans-PRK with thick preoperative epithelial thickness and large total ablation amount would lead to decrease of ablation amount. These results could be considered surgically advantageous in that a larger effective optical zone could be obtained on Trans-PRK with ACEAS with the same ablation amount compared to the group without ACEAS .

Financial Disclosure:

None