DR. RITIKA MULLICK

Dr. ROHIT SHETTY, Dr.Pooja Khamar

Semi Finals

Abstract

Purpose: Evaluating the performance of NXT UV-A calculator in customizing the fluence for CXL in thinner corneas.

Methods: 70 eyes with progressive KC and thinnest corneal thickness (TCT) <400 µm were included. Refraction, Corneal tomography, epithelial mapping and specular microscopy were done pre-op and post-op at 1 week, 1, 3, 6 and 12 months. TCT after de-epithelialization was fed into a custom-built web-based calculator, which provided us customized fluence time(https://jscalc.io/calc/VmanUJD6yQ13VQQ6).

Results: Post-op no patient had loss of lines. No significant haze was noted. Stability was established at 6 months where no patient showed progression. Demarcation line seen at 3 months in 64% patients at depth of 295±71µm. Cell density on specular microscopy was unchanged postoperatively(p=0.83). No other complications were seen in the study.

Conclusion: NXT calculator is a simple promising modality, wherein by titrating the energy fluence in thin cornea, CXL can be done safely.

Full Text

Introduction:

               In view of the prevailing uncertainties related to the current state of the coronavirus pandemic, the eye banking activities have been affected detrimentally. There is a paucity of donor corneas which can be used for corneal transplantation in the cases of advanced keratoconus. By expanding the scope of corneal collagen cross linking, it may be possible to delay or decrease the requirement of keratoplasty.  The purpose of our study was to evaluate the safety and efficacy of a calculator for crosslinking in corneas with thin pachymetry.

The NXT (New generation CXL for Thin Cornea) UV-A calculator customizes the fluence for cross linking (CXL) in thinner corneas. This calculator attempts to provide a technique to delay the need for keratoplasty by improving the safety of crosslinking in thin corneas.

Methods:

It was a prospective longitudinal study in which 70 eyes of 70 patients were recruited.  Before their participation in the study, a written informed consent was taken from all the patients in accordance with institutional guidelines of the Declaration of Helsinki.

The inclusion criteria was the presence of progressive keratoconus with a mean thinnest corneal thickness (TCT) <400 µm. All patients included in the study were evaluated in detail for corneal tomography, epithelial mapping (CSO MS39) & specular microscopy. These tests were done preoperatively & postoperatively at one month, three months and six months after surgery.  Lambart-Beer (LB) equation was used to build a simple calculator to decide the UV “on” time for an incident intensity of 3 and 9 mW/cm2.

The mean corneal thickness after de-epithelialization was fed into a custom-built web-based calculator, customizing fluence time based on chosen UV power. The NXT calculator provides fluence times for UV power of 9 and 3 mW/cm2. The clinicians can use the online calculator (https://jscalc.io/calc/VmanUJD6yQ13VQQ6) to calculate the fluence time at the time of surgery.

Results:

               There was an improvement in the postoperative best corrected visual acuity (p=0.14). There was no significant haze noted on densitometry using Pentacam HR (p=0.14). At 6 months postoperatively, all the patients had a stable topography, with no signs of progression.

Anterior segment optical coherence tomography showed the demarcation line at 3 months in 64% patients at a depth of 295±71µm. Postoperatively the endothelial cell density remained unchanged on specular microscopy (p=0.83). Patients were fitted with contact lenses at the end of 3 months & achieved visual acuity of 20/20 or better.

Conclusion:

The NXT (New generation CXL for Thin Cornea) UV-A calculator is a simple tool to titrate the energy fluence. It is a freely downloadable calculator and its ease of use makes the calculator an important tool in the clinician armamentarium. Using this web-based calculator crosslinking can be performed in thin corneas with no additional tools.

Keywords: Crosslinking, keratoconus, thin cornea