Swetha, Ravichhandran (2020) Predictive Accuracy of Intraocular Lenspower Calculation Formulae – SRK/T Vs Haigis: A Randomised Control study. Masters thesis, Christian Medical College, Vellore.
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Abstract
INTRODUCTION: Cataract is the major cause of blindness worldwide. According to the World Health Organization, Cataract accounts for about 51 percent of blindness, that is about 20 million people in 2010. As the population grows and the life expectancy increases, the prevalence of cataract is also expected to increase Cataract is cause by the degeneration and opacification of the lens fibres accompanied by aberrant lens fibres or deposits. These ultimately result in loss of transparency and loss of a clear image from being focused on the retina. Three processes are responsible for the formation of cataract – hydration of the fibres, denaturation of the proteins and sclerosis. Patients with cataract present with symptoms of gradual, painless, progressive decrease in vision, uniocular polyopia and eventually a white reflex in the visual axis. The symptoms depend upon the stages of cataract which usually progresses from immature to mature and hyper mature. Though predominantly cataract is an age-related disease, it can also occur due other causes such as trauma, metabolic diseases, dermatological diseases, physical factors or toxic agents. No medical treatment has been proven to cure cataract. If opacification has begun, control of the general systemic condition such as diabetes which causes early lens changes, may halt the progress but the protein coagulation that has occurred remains irreversible. Therefore, the one and only treatment approved. OBJECTIVES: 1. To compare the refractive status after cataract surgery between SRK/T vs Haigis formula calculated preoperatively using IOL master. 2. To study the effect of axial length on the predictive accuracy of SRK/T and Haigis formula. 3. To study the effect of anterior chamber depth on the predictive accuracy of Haigis formula. METHODS: Patients of age >50 years, preoperative corneal cylinder value less than 2.5D , the existence of age-related cataract, consenting for the study and satisfying the inclusion, exclusion criteria were selected. All patients underwent complete ocular examination, Biometry by IOL MASTER was done by three optometrists recruited for the study after randomizing the participants into two groups (SRK/T and Haigis groups) by block randomization. Two experienced surgeons of same skill and technique performed all operation using standard phacoemulsification with in the bag IOL implantation. Patients were followed up for examination on the first post op day, after 1 week and then 6 +/- 1 weeks later. Best corrected visual acuity was done at 6 weeks (+/- 1) visit by two senior optometrists who were blinded to the formula used. The axial length and keratometry readings were also measured post-operatively at 6 weeks. RESULTS: We found similar performance of SRK/T and Haigis (Mean absolute error : 0.021 for SRK/T and -0.33 for Haigis), with a little tendency of myopic shift for both SRK/T formula (Mean error = −0.24) and the Haigis formula (ME= - 0.59). Marginally higher 103 proportion cases in the Haigis group had their refractive outcome within ± 0.50D (72.4% cases for SRK/T and 73.4% cases for Haigis formula (37.9% within ± 0.25, 34.5% within ± 0.50 for SRK/T; 36.7% ± 0.25, 36.7% ± 0.50 for Haigis). 100% cases were within ± 1.0 D in SRK/T group and 96.7% cases in Haigis group were within ± 1.0 D. There was no correlation between axial length, keratometry or anterior chamber depth to the absolute error. CONCLUSION: SRK/T and Haigis formulae are equally good in predictive accuracy of refractive outcome post cataract surgery in normal axial length eyes. The need for sophisticated and newer fourth generation formulae is disputed.
| Item Type: | Thesis (Masters) |
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| Additional Information: | 221713306 |
| Uncontrolled Keywords: | Predictive Accuracy, Intraocular Lenspower Calculation Formulae, SRK/T, Haigis. |
| Subjects: | MEDICAL > Ophthalmology |
| Depositing User: | Subramani R |
| Date Deposited: | 14 Feb 2021 14:29 |
| Last Modified: | 14 Feb 2021 14:29 |
| URI: | http://repository-tnmgrmu.ac.in/id/eprint/14194 |
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