E-ISSN:2456-6454
P-ISSN:2581-4907
RNI:MPENG/2017/74152

Research Article

IOL

Tropical Journal of Ophthalmology and Otolaryngology

2021 Volume 6 Number 1 January-February
Publisherwww.medresearch.in

Comparison of corneal power estimated by IOL master and manual keratometry

Kumar P.1, Sreevathsala T.2, Tejaswini M.3, Konda K.4*
DOI: https://doi.org/10.17511/jooo.2021.i01.04

1 P. Sanjeeva Kumar, Associate Professor, Department of Ophthalmology, Santhiram Medical College and General Hospital, Kurnool, Andhra Pradesh, India.

2 T. Sreevathsala, Assistant Professor, Department of Ophthalmology, Santhiram Medical College and General Hospital, Kurnool, Andhra Pradesh, India.

3 M. Tejaswini, MBBS, Department of Ophthalmology, Santhiram Medical College and General Hospital, Kurnool, Andhra Pradesh, India.

4* Kavya Konda, Assistant Professor, Department of Ophthalmology, Santhiram Medical College and General Hospital, Kurnool, Andhra Pradesh, India.

Aim: To compare corneal power calculated by IOL master and manual keratometry. Material & methods: A prospective, consecutive, comparative & single-centre study was done in pre cataract surgery work up patients. Manual keratometry was done using Keratometer KMS-6 (Appasamy Associates, India) while automated keratometry was done with IOL master 500 (Carl Zeiss Meditec, Jena, Germany). SPSS version 20.0 was used for statistical analysis. Results: Overall agreement between two methods was excellent for horizontal corneal diopteric power (kappa = 0.53 ) & good for vertical corneal diopteric power (kappa = 0.46) using bland-altman analysis. Conclusion: Manual keratometry is still relevant in the era of digital automated keratometry measured by IOL master.

Keywords: IOL master, keratometry, Corneal Power

Corresponding Author How to Cite this Article To Browse
Kavya Konda, Assistant Professor, Department of Ophthalmology, Santhiram Medical College and General Hospital, Kurnool, Andhra Pradesh, India.
Email: 		Kumar PS, Sreevathsala T, Tejaswini M, Konda K. Comparison of corneal power estimated by IOL master and manual keratometry. Trop J Ophthalmol Otolaryngol. 2021;6(1):18-21.
Available From
https://opthalmology.medresearch.in/index.php/jooo/article/view/180

Manuscript Received Review Round 1 Review Round 2 Review Round 3 Accepted
2021-01-04 2021-01-14 2021-01-24 2021-01-31
Conflict of Interest Funding Ethical Approval Plagiarism X-checker Note
No Nil Yes 8%

© 2021 by P. Sanjeeva Kumar, T. Sreevathsala, M. Tejaswini, Kavya Konda and Published by Siddharth Health Research and Social Welfare Society. This is an Open Access article licensed under a Creative Commons Attribution 4.0 International License https://creativecommons.org/licenses/by/4.0/ unported [CC BY 4.0].

Tropical Journal of Ophthalmology and Otolaryngology 2021;6(1)18
Kumar PS. et al: Comparison of corneal power estimated by IOL

Introduction

Accurate measurement of corneal power is essential for refractive surgery, orthokeratology, contact lens fitting, and intraocular lens (IOL) power [1,2].

Since conventional keratometers measure central corneal curvature (up to 3.25 mm in diameter), topographical systems are preferred over manual and autokeratometers for contact lens fitting and corneal refractive surgeries. In line with the digitization of various objective clinical measurements, a variety of auto-keratometers have been introduced and have rapidly gained widespread popularity among clinicians and vision scientists. Various keratometers are commercially available for clinical use. Manual (e.g. B&L and Javel-Schiotz Keratometer), automated (eg various autokeratorefractors, IOL Master) and devices for simulated keratometry (eg various corneal topographers) are the most common instruments. Since the working principles of different instruments vary, measurements are likely to differ from one to another. With an increasing trend of toric IOL implantation to correct pre-existing corneal astigmatism, precise determination of the strength and orientation of the corneal astigmatism is essential [3].

Though modern cataract surgery is a relatively simple procedure with arguably a high success rate, the refractive outcome is not always as perfect as a surgeon or a patient would like to have. The existence of significant post-operative residual spherocylindrical refractive errors is not uncommon. Along with several factors (e.g. error in axial length measurement, the inappropriate position of the implant, inaccuracy in the formula used in calculating IOL and surgically-induced refractive changes), inaccurate estimation of corneal power is one of the major sources of error [4].

Therefore, an accurate measurement of the corneal power is as important as the entire cataract surgical procedure. Currently, different keratometers are in use with varying levels of accuracy. Studies have reported conflicting results regarding the superiority of certain keratometers or that measurements performed with the IOLMaster or Pentacam can be used with sufficient accuracy [5,6,7,8,9].

This study was planned to find agreement between two commonly used keratometers viz. manual and IOL master, for different ranges of corneal power.

Material and methods

This prospective consecutive, comparative, single centre study was conducted over 2 months ( January & February 2019). Cataract surgery posted patients requiring keratometry evaluation were included in the study after obtaining informed consent. Institutional ethics committee approval was obtained. Patients having corneal opacities, pterygium & inability to fixate the target for keratometry were excluded from the study. Manual keratometry was done using Keratometer KMS-6 (Appasamy Associates, India) while automated keratometry was done with IOL master 500 (Carl Zeiss Meditec, Jena, Germany).

Results

Total 222 eyes of 111 patients (61 females and 50 males) with a mean age of 61.6±10.3 years [Range: 24 – 88 years] were included in the study (Table 1 & 2). Table 3 shows agreement between two methods for horizontal & vertical corneal diopteric power for different diopteric ranges. Overall agreement between two methods was excellent for horizontal corneal diopteric power (kappa = 0.53 ) (Figure 1) & vertical corneal diopteric power(kappa = 0.46)(figure 2 ) using bland-altman analysis.

Table 1: Age-wise distribution

Age group (years) No. of Cases Percentage
21 – 30 01 0.9%
31 – 40 02 1.8%
41 – 50 12 10.8%
51 – 60 40 36.0%
61 – 70 39 35.2%
71 – 80 13 11.7%
>80 04 3.6%
Total 111 100%

Table 2: Gender-wise distribution

Gender No. of Patients Percentage
Male 50 45%
Female 61 55%
Total 111 100%

Table 3: Agreement between two methods for horizontal & vertical corneal diopteric power

Keratometry range (diopter) Agreement (kappa) & Standard Error (SE)
For Horizontal Diopteric Power For Vertical Diopteric Power
40.1 – 43 D 0.180 ( SE 0.057) 0.181 (SE 0.057)
43.1 – 45 D 0.259 (SE 0.046) 0.201 ( SE 0.061)

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Kumar PS. et al: Comparison of corneal power estimated by IOL
45.1 – 47 D 0.414 (SE 0.115) 0.224 (SE 0.120)
>47 D 0.333 (SE 0.0) Not available
Overall 0.531 (SE 0.041) 0.461 (SE 0.047)

Bland-Altman analysis shows excellent agreement (kappa = 0.53) between the two methods.

opthal_180_01.jpg

Fig-1: Agreement between Manual keratometry Vs IOL master for horizontal corneal diopteric power.

Bland-Altman analysis shows good agreement (kappa = 0.461) between the two methods.

opthal_180_02.jpg

Fig-2: Agreement between Manual keratometry Vs IOL master for vertical corneal diopteric power.

Discussion

We used a manual keratometer that uses two keratometry mires along the main meridians of the cornea. The corneal power is determined using the reflection from these illuminated mires from the central 3.4 mm of the cornea. The device uses a refraction index of 1.3375. In the IOL Master, six-light spots are projected onto the cornea in a hexagonal pattern, and measurement is performed in a 2.3 mm radius [10].

Our study highlights that the IOL Master and manual keratometry not only show a significant correlation but also do not show significant differences. These findings indicate the interchangeability of the results of the IOL Master and keratometry. Despite the differences in the number of data points and the axis of imaging, the estimation of corneal power between devices yields similar values. This is of importance as routinely done procedures such as IOL power calculation, toric IOL power calculation and contact lens fitting procedures which use central corneal power, can be done using a manual keratometer which is cost-effective & available at most places. The limitation of the study being, small sample size & lack of comparison in refractive surgery, keratoconus & pathological corneal disease population.

Conclusion

A very good agreement was found between manual and IOL master based corneal power calculation, underlining the importance of cost-effective manual keratometry in routine cataract surgical procedures.

What does the study add to the existing knowledge?

The current study underlines the value of economics effective of manually performed keratometry in regular cataract surgical procedures.

Author’s contribution

Dr. P. Sanjeeva Kumar: Concept, Dr. T. Sreevathsala: Manuscript preparation, Dr. M. Tejaswini: Study design, Dr. Kavya Konda: Statistical analysis

Reference

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