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Impact of tear film optics on repeatability of Pentacam AXL Wave-hybrid topographer &aberrometer

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First Author: R.Ranade INDIA

Co Author(s):    R. Shetty   G. Kundu   P. Khamar   D. Trivedi   S. Arun        

Abstract Details

Purpose:

To assess the impact of the tear film optics on the repeatability of Pentacam AXL Wave system (Oculus, Wetzlar, Germany) in measuring the mean keratometry (Km), thinnest corneal thickness (TCT),total aberrations and corneal aberrations in eyes with normal versus abnormal optical scatter index (OSI) and to compare it with the repeatability of ITrace(Tracey Technologies Corp,Houston,TX) in abnormal OSI.

Setting:

Narayana Nethralaya, Bengaluru

Methods:

30 normal and 70 post refractive surgery eyes, underwent scans on Optical quality analyzer to assess optical scatter index (OSI), three scans on the Pentacam AXL wave and Itrace. Mean keratometry(Km), thinnest corneal thickness(TCT), total and corneal aberration were analysed. Study had 3 arms- Arm1 assessed repeatability in normal vs post refractive patients on Pentacam AXL wave. Arm2 assessed repeatability of Pentacam AXL wave in normal and post refractive patients (OSI>1 vs OSI<1). Arm3 assessed repeatability of itrace in normals and post refractive patients (OSI>1 vs OSI<1) Within-subject standard deviation(Sw), test–retest repeatability(TRT),coefficient of variation(COV) were used for assessing repeatability.

Results:

Arm 1 showed no significant difference(p-0.32)between repeatability of normal & post-refractive patients.Sw for km was 0.2, COV 0.1- 0.5. Sw for TCT was 9.16, COV 0.2-3.3. Sw for HOA 0.024, COV 20.4-33.6. Arm 2 Normals&post-refractive patients were sub-divided - group 1 OSI>1; group 2 OSI<1. Group 1 Sw for km was 0.23, COV 0.2-0.4, Sw for TCT was 9.23, COV 0.4-3.5. Sw for HOA was 0.028, COV 20.9-32.3. Patients with OSI>1, Km,TCT&HOA COV was0.1-0.9,0.4-4.2,19.8-39.4 with poorer repeatability. Arm 3 assessed effect of tear-film on repeatability of iTrace with OSI>1 and OSI<1. Patients OSI>1, Km,TCT,HOA COV was 0.5-1.6,0.7-5.3,18.8-42.4 with poorer repeatability.

Conclusions:

Poor tear film optics led to poorer repeatability of both the Pentacam Wave and Itrace. Pentacam Wave however had better repeatability in patients with a poor tear film as compared to Itrace.Thus tear film optics does have an impact on repeatability of an instrument and hence its important to assess tear film prior to imaging patients which can change the way we interpret and image these patients.

Financial Disclosure:

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