Sains Malaysiana 49(6)(2020): 1431-1437

http://dx.doi.org/10.17576/jsm-2020-4906-21

Accuracy of Contact Lens Method by Spherical and Aspheric Rigid Gas Permeable Lenses on Corneal Power Determination in Normal Eyes

(Ketepatan Kaedah Kanta Sentuh dengan Kanta Sfera dan Asferik Gas Tegar Boleh Telap ke atas Penentuan Daya Kornea pada Mata Normal)

MD MUZIMAN SYAH MD MUSTAFA¹*, HALIZA ABDUL MUTALIB², NOORHAZAYTI AB. HALIM³ & MOHD RADZI HILMI¹

¹Department of Optometry and Visual Science, Kulliyyah of Allied Health Sciences, International Islamic University Malaysia, Bandar Indera Mahkota, 25200 Kuantan, Pahang Darul Makmur, Malaysia

²Optometry and Visual Science Programme, School of Healthcare Sciences, Faculty of Health Sciences, Universiti Kebangsaan Malaysia, Jalan Raja Muda Abdul Aziz, 50300 UKM Kuala Lumpur, Federal Territory, Malaysia

³Department of Paediatric Dentistry and Dental Public Health, Kulliyyah of Dentistry, International Islamic University Malaysia, Bandar Indera Mahkota, 25200 Kuantan, Pahang Darul Makmur, Malaysia

Received: 8 October 2019/Accepted: 2 February 2020

ABSTRACT

Contact lens method (CLM) is an alternative option to measure corneal power by evaluating the difference of patient’s over-refraction with rigid gas permeable (RGP) lens to manifest refraction. The purpose of this study was to evaluate the accuracy of CLM using spherical (CLM_spherical) and aspheric (CLM_aspheric) RGP lenses in measuring corneal refractive power of normal corneas. This prospective study recruited 45 normal eyes of 45 healthy subjects. The corneal power measurements were determined by CLM_spherical using Boston ES RGP and CLM_aspheric using Boston Envision RGP based on alignment fitting strategy. Manifest refraction and over-refraction were determined using a standard procedure of objective and subjective refraction methods. IOLMaster was set as the reference method for comparison. The mean arithmetic difference, mean absolute difference and 95% limits of agreement (LOA) of corneal powers obtained from CLM_spherical and CLM_aspheric to IOLMaster value were evaluated for the accuracy assessment. The mean arithmetic difference and mean absolute difference of corneal power s obtained from CLM_spherical and CLM_aspheric to IOLMaster values were 0.10 ± 0.21 D and 0.20 ± 0.11 D, and 0.04 ± 0.09 D and 0.08 ± 0.05 D, respectively. The 95% LOA between CLM_spherical and IOLMaster ranged from -0.30 to 0.51 D, whereas between CLM_aspheric and IOLMaster was ranging from -0.14 to 0.21 D. CLM in estimating corneal power is more accurate with application of aspheric RGP compared to spherical RGP. Hence, aspheric RGP is suggested for CLM when determining corneal power in normal eyes. 

Keywords: Aspheric RGP; contact lens design; contact lens method; corneal power; rigid gas permeable

ABSTRAK

Kaedah kantah sentuh (CLM) merupakan satu pilihan alternatif untuk menentukan kuasa kornea dengan menilai perbezaan atas-pembiasan dengan kanta sentuh separa keras (RGP) kepada refraksi nyata. Tujuan kajian ini adalah untuk menilai ketepatan CLM menggunakan kanta sentuh sfera (CLM_spherical) dan asferik (CLM_aspheric) dalam pengukuran kuasa refraksi kornea normal. Kajian prospektif ini merekrut 45 mata normal daripada 45 subjek sihat. Pengukuran kuasa kornea ditentukan oleh CLM_spherical menggunakan RGP Boston ES dan CLM_aspheric menggunakan RGP Boston Envision berdasarkan strategi pemasangan optimum. Refraksi nyata dan atas-pembiasan ditentukan menggunakan keadah refraksi objektif dan subjektif yang piawai. IOLMaster ditetapkan sebagai kaedah rujukan untuk perbandingan. Min perbezaan aritmetik, min perbezaan mutlak dan 95% had-had persetujuan (LOA) kuasa kornea yang diperoleh daripada CLM_spherical dan CLM_aspheric kepada nilai IOLMaster dinilai untuk perbandingan ketepatan. Min perbezaan aritmetik dan min perbezaan mutlak kuasa kornea yang diperoleh CLM_spherical dan CLM_aspheric kepada nilai IOLMaster adalah masing-masing 0.10 ± 0.21 D dan 0.20 ± 0.11 D dan 0.04 ± 0.09 D dan 0.08 ± 0.05 D. Julat 95% LOA antara CLM_spherical dan IOLMaster adalah -0.30 ke 0.51 D, manakala antara CLM_aspheric dan IOLMaster adalah -0.14 ke 0.21 D. CLM dalam menganggar kuasa kornea adalah lebih tepat dengan menggunakan RGP asferik berbanding RGP sfera. Oleh demikian, penggunaan RGP asferik dicadangkan untuk CLM bagi menentukan kuasa kornea pada mata normal. 

Kata kunci: Kaedah kanta sentuh; kanta sentuh separa keras; kuasa kornea; reka bentuk kanta sentuh; RGP asferik

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*Corresponding author; email: syah@iium.edu.my