Comparison of newer Kane formula with Sanders Retzlaff Kraff/Theoretical and Barrett Universal II for calculation of intraocular lens power in Indian eyes

Purpose: To compare the efficacy of Kane formula with Sanders Retzlaff Kraff/Theoretical (SRK/T) and Barrett Universal II in predicting intraocular lens (IOL) power in Indian eyes. Methods: This retrospective study conducted in a tertiary care eye hospital. Data from patients having uneventful cataract surgery with Tecnis ZCB00 IOL implantation were obtained from Lenstar and electronic medical records. Eyes were divided into subgroups based on axial length (AL) as short (<22.0 mm), medium (22� mm), and long (>24 mm). The predicted refractive outcome for each patient was calculated after optimizing the lens constant. Prediction error was calculated by subtracting the predicted spherical equivalent from achieved spherical equivalent 1 week post?surgery. The mean absolute error (MAE) and median absolute error (MedAE) and percentage of eyes within 0.25, 0.5, 1, and 2 D were calculated for each formula. Friedman test, Cochrane Q test were used for statistical analysis. Results: Out of the 350 eyes included in the study, we found that without lens constant optimization, Barrett formula performed better than SRK/T and Kane (P < 0.0001). Over the entire range of axial lengths, Kane formula performed slightly inferior compared to Barrett and SRK?T, both of which performed equally well (P = 0.006). On subgroup analysis, Kane formula performed inferiorly for medium eyes as compared to the other two. No significant differences were noted between the formulae for short and long eyes. Conclusion: Kane formula did not outperform Barrett Universal II and SRK/T in Indian eyes

Theoretical and Clinical Comparison of the Hoffer Q and SRK/T Formulas

PURPOSE: To evaluate the biometric conditions causing increased disparity in the calculation of intraocular lens (IOL) power between the Hoffer Q and SRK/T formulas. METHODS: A prospective comparative study was conducted on 365 uneventful, cataract surgeries performed at a tertiary care center by one surgeon. The IOL power was calculated using both the Hoffer Q and SRK/T formulas with A-scan biometry. For a selected IOL power, the expected disparity between the 2 formulas (EDF) was measured and the EDF value was used to categorize the cases. The resultant error associated with each formula was determined at postoperative 6 weeks. KAL was defined as the product of mean corneal power (K) and axial length (AL). Postoperative errors of both formulas were calculated and their association with preoperative biometry measurements analyzed. RESULTS: In 17.8% of the cases, the EDF was larger than 0.4 D, possibly leading to different IOL diopter recommendations. The EDF value and the product of corneal curvature and axial length were significantly correlated (R2 = 0.855, p < 0.001). Multiple regression analysis of causative preoperative biometric factors on the postoperative formula errors showed that astigmatism, anterior chamber depth (ACD), and lens thickness (LT) were significantly associated with Hoffer Q error and SRK/T error. CONCLUSIONS: Overall, both formulas performed very well when recommending the correct IOL power. The cause of disparity between the predicted refraction for the 2 formulas was more associated with KAL than K or AL alone. Astigmatism, ACD, and LT were the causative factors for the postoperative errors in both formulas.

Clinical Result After Implantation of Minus Diopter Intraocular Lens in the High Myopia Patients

PURPOSE: To investigate the clinical results of 44 high myopic eyes with cataracts which had minus diopter IOLs (Intraocular lenses) implanted during cataract surgery. METHODS: A retrospective chart review was done on 44 eyes in 33 patients who had undergone cataract extraction and minus diopter posterior chamber lens implantation. The IOL power was calculated using the SRK-T formula, and ACR6D SE(R) (Corneal SA, France) IOL was implanted in all cases. We evaluated pre-operative target refraction, post-operative refraction at six months, pre-operative visual acuity with and without correction, and post-operative visual acuity with and without correction. The relationships between axial length and refractive error and between the diopter of IOLs and refractive error were analyzed. RESULTS: The mean postoperative hyperopic refractive error compared to the preoperative target refraction was +1.04+/-1.05D, which was statistically significant (p<0.01). The longer the axial length and the larger the minus diopter lens inserted, the larger the hyperopic error. However, there were no statistically significant differences between them. CONCLUSIONS: Satisfactory results in visual acuity were obtained after cataract surgery in high myopic patients. However, when choosing the IOL power in high myopic patients, the possible development of postoperative hyperopic error should be considered.

Análise da fórmula SRK/T no cálculo de lente intra-ocular em cães portadores de catarata / Analysis of the SRK/T formula for calculation of intra-ocular lens in dogs carrying cataract

Foram utilizados 20 cães de raças e idades variadas, machos e fêmeas, portadores de catarata e não diabéticos, os quais foram submetidos ao exame oftálmico. Posteriormente, realizaram-se mensurações oculares empregando-se um ecobiômetro ultra-sônico (ultra-sonografia modo-A) para o cálculo do poder dióptrico da lente intra-ocular por meio da fórmula SRK/T. O comprimento axial médio foi de 19,94±1,12mm. Todos os animais foram submetidos à facoemulsificação extracapsular. A lente calculada foi implantada no transoperatório da cirurgia de catarata, obtendo-se média de 37,33±3,05D. A avaliação pós-cirúrgica do erro refracional aos 60 dias de pós-operatório, pela retinoscopia, com a utilização da esquiascopia, foi de 5,57±1,59D. A fórmula SRK/T não ofereceu bons resultados.

Twenty males and females non-diabetic dogs of different breeds and ages underwent ophthalmic examination because they presented catarats. Ocular measurements were performed by echobiometry (A-scan ultrasound) for intraocular lens power calculation using the SRK/T formula. The obtained mean axial length was 19.94±1.12mm. All animals were submitted to extracapsular phacoemulsification; the mean intraocular lens power implanted was 37.33±3.05. At 60 days postoperative, the refractional error assessed via retinoscopy was 5.57±1.59 D. The SRK/T formula did not offer good results.