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Title:	Deriving a newly modified equation of contact lens method for corneal power determination in post myopic laser refractive surgery
Authors:	Md Muziman Syah Md Mustafa (P65538)
Supervisor:	Haliza Abdul Mutalib, Assoc. Prof. Dr.
Keywords:	Contact lens method (CLM) Rigid gas permeable (RGP) Eye Contact lens Dissertations, Academic -- Malaysia Universiti Kebangsaan Malaysia -- Dissertations Ophthalmology
Issue Date:	7-Jan-2016
Description:	The aims of this study were to evaluate the accuracy of contact lens method (CLM) and subsequently to modify the CLM equation in calculating corneal power after myopic laser refractive surgery. This study also assessed the reliability of five keratometry instruments (Topcon OM-4 manual keratometer, Grand Seiko WR-5100K autokeratometer, Shin Nippon CT-1000 topographer, Pentacam high resolution single Scheimpflug tomographer and IOLMaster 500 optical biometer) and their agreement in measuring corneal power, and determined the best type of rigid gas permeable (RGP) lens for CLM. This study was conducted at IIUM Optometry Clinic and IIUM Eye Specialist Clinic. A total of 40 and 45 normal eyes were involved in Phase I and II studies respectively. Phase III was conducted on 93 eyes of post myopic laser refractive surgery from January 2013 to June 2014. Phase I demonstrated IOLMaster having the lowest within-subject standard deviation (0.02; 0.02 D), coefficient of variation (0.06; 0.05 %) and strongest intraclass correlation (0.999; 0.999) in both intra-examiner repeatability and inter-examiner reproducibility. All comparisons between instruments provided excellent correlation (r > 0.90) and acceptable 95% limit of agreement, (LOA < 1.00 D) except for the comparison which involved Shin Nippon topographer. In Phase II, corneal power measurements were determined by CLM using spherical Boston ES® and aspheric Boston Envision® RGPs. IOLMaster was set as the reference method for comparison. Phase II study found that the aspheric RGP provided a lower mean arithmetic difference (0.04 ± 0.09 D), mean absolute difference (0.08 ± 0.05 D) and 95% LOA (-0.14 to +0.21 D) to the IOLMaster value. In Phase III, the accuracy of postoperative corneal power using the original CLM and newly-derived contact lens modified method (CLMmod) were compared to the standard reference method; historical method (HM). The CLMmod equation was derived by adjusting postoperative corneal power of the CLM according to amount of refractive change induced by laser refractive surgery. There was a significant difference between the mean postoperative corneal power using the original CLM and HM (mean arithmetic difference: -0.24, p < 0.001). Fifty seven percent (n = 53 eyes) of the original CLM results were within ±0.50 D of HM results. The difference between postoperative corneal power using the original CLM and HM increased significantly with the amount of refractive change (r = 0.835, p < 0.001). The mean postoperative corneal power of the CLMmod showed that there was no statistical significant difference compared to the HM results (mean arithmetic difference: 0.00, p > 0.01). Eighty eight percent (n = 82 eyes) of the CLMmod results were within ±0.50 D of HM results with improvement of 31% from the original CLM results. In conclusion, the IOLMaster is the most reliable keratometry instrument. For CLM, the aspheric RGP design is suggested for measuring corneal power hence deriving CLMmod equation more accurately in determining post myopic laser refractive surgery corneal power. In near future, this modified equation can be used as an alternative equation to calculate postoperative corneal power when the preoperative data is unavailable.,Ph.D.
Pages:	245
Call Number:	WW20.M478d 2016 9 tesis
Publisher:	UKM, Kuala Lumpur
Appears in Collections:	Faculty of Health Sciences / Fakulti Sains Kesihatan

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