Application of Pentacam TNP in calculating the intraocular lens power after corneal refractive surgery / 国际眼科杂志(Guoji Yanke Zazhi)

AIM: To assess the accuracy of predicting intraocular lens(IOL)power after myopic refractive surgery using the Pentacam system's true net power(TNP)in the 3 mm zone combined with the SRK/T formula [i.e. TNP 3 mm(SRK/T)].METHODS: Retrospective study. This study enrolled 35 cases(50 eyes)of patients undergoing cataract surgery after laser assisted in situ keratomileusis(LASIK)or photorefractive keratectomy(PRK)from July 2019 to December 2021. Preoperatively, IOL power of 50 eyes, 34 eyes and 41 eyes was calculated by TNP 3 mm(SRK/T), Barrett True-K and Olsen 2 formulas, respectively, with at least 2 formulas used to calculate IOL power for each patient. The actual diopter was recorded 3 mo postoperatively. Prediction errors(PE)of IOL power were compared among the three calculation methods, and the proportion of eyes with PE within ±0.5 D and ±1.0 D was analyzed.RESULTS: The PE at 3 mo postoperatively for TNP 3 mm(SRK/T), Barrett True-K, and Olsen 2 was -0.02±0.63, -0.54±0.80, and 0.25±0.80 D, respectively(P<0.001). The proportions of PE within ±0.5 D were 66%(33/50), 44%(15/34)and 37%(15/41), respectively(P<0.05); the proportions of PE within ±1.0 D were 88%(44/50), 71%(24/34)and 80%(33/41), respectively(P>0.05).CONCLUSION: The Pentacam TNP 3 mm(SRK/T)method is simple to operate and provides accurate calculation of IOL power after corneal refractive surgery.

Intraocular lens formula calculation in pediatric eyes: Do we have an answer? A retrospective comparison between Sanders–Retzlaff–Kraff II and Barret’s formula

Purpose: The ideal formula for intraocular lens (IOL) power calculation following cataract surgery in pediatric eyes till date has no answer. We compared the predictability of the Sanders–Retzlaff–Kraff (SRK) II and the Barrett Universal (BU) II formula and the effect of axial length, keratometry, and age. Methods: This was a retrospective analysis of children who were under eight years of age and who underwent cataract surgery with IOL implantation under general anesthesia between September 2018 and July 2019. The prediction error of SRK II formula was calculated by subtracting the target refraction and the actual postoperative spherical equivalent. Preoperative biometry values were used to calculate the IOL power using the BU II formula with the same target refraction that was used in SRK II. The predicted spherical equivalent of the BU II formula was then back?calculated using the SRK II formula with the IOL power obtained with the BU II formula. The prediction errors of the two formulae were compared for statistical significance. Results: Seventy?two eyes of 39 patients were included in the study. The mean age at surgery was 3.8 ± 2 years. The mean axial length was 22.1 ± 1.5 mm, and the mean keratometry was 44.7 ± 1.7 D. The group with an axial length >24 mm showed a significant and strong positive correlation (r = 0.93, P = 0) on comparison mean absolute prediction errors using the SRK II formula. There was a strong negative correlation between the mean prediction error in the overall keratometry group using the BU II formula (r = ?0.72, P < 0.000). There was no significant correlation between age and refractive accuracy using the two formulae in any of the subgroups of age. Conclusion: There is no perfect answer to an ideal formula for IOL calculation in children. IOL formulae need to be chosen keeping in mind the varying ocular parameters.

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

Application of three new intraocular lens calculation formulas in patients with long axis cataract / 国际眼科杂志(Guoji Yanke Zazhi)

@#AIM: To compare the accuracy of Barrett Universal Ⅱ, Haigis and modified Wang-Koch SRK/T formulas in calculating intraocular lens(IOL)power in eyes with long axial length(AL).<p>METHODS: Eyes were divided into three AL groups as follows: 26.0 to 28.0mm(group A), 28.0 to 30.0mm(group B), and 30.0mm or more(group C). All eyes underwent phacoemulsification cataract surgery. In the 3mo after operation, IOL powers that would have resulted in emmetropia were calculated according to results of subjective refraction. The predictive error(PE)and absolute error(AE)of each formulas were calculated and compared and the factors(AL, keratometry value, the anterior chamber depth)associated with PEs were analyzed.<p>RESULTS: The average PE of Barrett Universal Ⅱ, Haigis and modified Wang-Koch SRK/T formulas were 0.37±0.78D, 0.77±0.88D and 0.36±0.82D respectively. In groups A and B, the PEs and AEs of three formulas were not statistically significant(<i>P</i>>0.05). However, in group C, the PEs and AEs of Barrett Universal Ⅱ and modified Wang-Koch SRK/T formula were significantly less than Haigis formula(<i>P</i><0.05). The PEs of Haigis formula in cataract eyes with long AL was affected by AL and keratometry value, whereas the PEs of Barrett Universal Ⅱ and modified Wang-Koch SRK/T formula was not affected by AL.<p>CONCLUSION: In eyes with an AL of 26.0 to 30.0mm, all three formulas are acceptable. In eyes with AL of 30.0mm or more, the accuracy of Barrett Universal Ⅱ and modified Wang-Koch SRK/T formula are better than Haigis formula.

Comparison of Three Formulas for Intraocular Lens Power Formula Accuracy

PURPOSE: To compare the accuracy of three intraocular lens (IOL) power calculation formulas (SRK/T, Barrett Universal II, and T2) in cataract surgery patients.METHODS: In total, 73 eyes of 73 patients who underwent uneventful cataract surgery were retrospectively reviewed. IOL power was determined using SRK/T, Barrett Universal II, and T2 preoperatively. The findings were compared with the actual refractive outcome to obtain the prediction error. The mean prediction error (ME) and mean absolute error (MAE) of each formula were compared. The MAE was defined as the difference between the postoperative spherical equivalence (SE) and the preoperatively predicted SE. The ME and MAE of each formula 3 months after surgery were compared with preoperatively predicted SE. Eyes were classified into subgroups based on axial length (AL) and average keratometry (K).RESULTS: The ME and MAE for the three formulas were SRK/T [−0.08 ± 0.45 diopters (D) and 0.35 ± 0.40 D, respectively], Barrett Universal II (−0.01 ± 0.44 D and 0.33 ± 0.30 D, respectively), and T2 (0.04 ± 0.45 D and −0.34 ± 0.30 D, respectively), but no statistically significant differences were detected. Similar results were obtained in groups with a long AL or a large average K. In groups with an AL ≥ 26 mm or with an average K ≥ 47 D, the Barrett Universal II formula yielded the smallest standard deviation and a ME closest to zero, but these differences were not statistically significant.CONCLUSIONS: No significant differences were observed between the three formulas regarding ME or MAE. However, recent formulas such as the Barrett Universal II could provide certain benefits in predicting IOL power for patients with a long AL (> 26 mm) or larger average K. Further research with a larger sample size is recommended for more evaluation.

Clinical study of SRK-Ⅱ and SRK-T in the calculation of intraocular lens in cataract patients / 国际眼科杂志(Guoji Yanke Zazhi)

@#AIM: To study the SRK-II and SRK-T in clinic for calculating intraocular lens(IOL)in cataract patients, and to provide the basis for preoperative selection of IOL measurement formula and prediction of appropriate IOL diopter in cataract patients with different axial. <p>METHODS: Randomized selection of 160 cataract patients of 200 eyes with different axial from April 2013 to November 2015 admitted to the hospital were taken. There were 92 males with 120 eyes, 68 females with 80 eyes, the average age of 66.2 ± 4.36 years old. The axial length(AL)was measured by type A ultrasonography. They were divided into four groups according to AL. Patients with shorten AL were Group A, with normal AL were Group B, with lengthening AL were Group C, with extremely AL were Group D. The IOL diopter of the four groups were calculated by SRK-Ⅱ and SRK-T, and the corresponding IOL(American AMO intraocular lens)was implanted. The actual diopter at best corrected visual acuity(best corrected visual acuity, BCVA)was measured by optometry and retinoscopy at 1wk, 1, 3mo after operations. The mean absolute refractive error(MAE)was calculated.<p>RESULTS: The MAE of the SRK-Ⅱ and SRK-T at 1wk after operations was different with that at 1mo and at 3mo(<i>P</i><0.05), that at 1mo was not significantly different with that at 3mo(<i>P</i>>0.05). there was no difference between SRK-Ⅱ and SRK-T in Group A(<i>P</i>>0.05), but there were significant differences in Group B, Group C and Group D(<i>P</i><0.05). Patients of Group A more tended to become myopia at 1mo than at 1wk(<i>P</i>=0.035). Patients of Group B and C both got myopia shift at 1wk and 1mo after operation(<i>P</i> =0.84, 0.88). Patients of Group D tended to become hyperopia at 1mo than at 1wk(<i>P</i>=0.041). <p>CONCLUSION: This study shows that refraction become stable at 1mo after operations; the accuracy of the two methods are nearly same in Group A and B, while in Group C and D, SRK-Ⅱ is better than SRK-T on the comparison of MAE. SRK-T is better than SRK-Ⅱ on IOL calculation in patients with different AL.

Comparative study of various intra ocular lens formulae by IOL master.

Background: The aim and objective of the study was to calculate intraocular lens power with IOL master in 100 eyes of 100 patients with long axial lengths between 25mm to 32mm.To analyse and compare the results of various formulae by postoperative auto refractometry and corrected distance visual acuity and to know the most accurate formula for highly myopic eyes (Axial length more than 25.00 mm). Methods: Patients coming to Sarojini Devi Eye Hospital from December 2012-September 2014 for cataract surgery were considered in this study. All patients with visually significant cataract having fundus findings within normal limits were included in this study and patients of complicated cataract due to trauma, uveitis, Glaucoma and any corneal pathology were excluded from the study. Results: The Mean AL was 27.25 ± 1.25 mm, the Mean keratometric value was 43.62 ± 1.45 D, and the Mean Absolute Error (MAE) calculated by the Haigis was 0.07 DD. Compared to the MAEs generated by the other formulae, the MAE generated by the Haigis was comparable to that by the SRK/T (0.231 D), and significantly lower than those by the Hoffer Q (0.481 D) and Holladay (0.864 D). Conclusions: The Mean post-operative refractive error (spherical equivalent) was found to be the least with Haigis formula followed by SRK/T for eyes with long axial length. The HAIGIS formula has a better predictability and accuracy. The postoperative hyperopic shift was comparable between HAIGIS and SRK-T formulae the least postoperative hyperopic shift with Haigis formula compared to other formulae.

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.

The Analysis of Refractive Errors of AMO Array(R) Multifocal Intraocular Lens with SRK II Formula

PURPOSE: To evaluate the accuracy of the SRK II formula for the AMO Array(R) multifocal intraocular lens (Array lens) power calculation according to axial length. In case of refractive error more than +/- 1.0 diopter (D), we compared the accuracy of the SRK II with that of other formulas. METHODS: Participants were 178 eyes (142 patients) received the Array lens. These were divided into 3 subgroups based on axial length. Group I had 21 eyes of short axial length (less than 22.0 mm). Group II had 133 eyes of average axial length (more than 22.0mm below 24.5mm). Group III had 24 eyes of long axial length (more than 24.5mm). The difference between preoperative predicted refractive value and postoperative manifest refractive value were calculated. We compared the accuracy of the SRK II and that of SRK/T, Holladay formulas in case of refractive error more than +/- 1.0D. RESULTS: Three eyes (14.2%) in Group I, 14 eyes (10.5%) in group II and 15 eyes (62.5%) in Group III showed refractive errors more than +/- 1.0D. Fifteen eyes (62.5%) in Group III were significantly reduced to 7 eyes (29.1%) with using SRK/T, Holladay formulas. CONCLUSIONS: SRK II formula had better predictive accuracy in axial length less than 24.5mm with Array lens. But it is better to apply SRK/T or Holladay formulas when axial length is more than 24.5mm.

Accuracy of Intraocular Lens Power in Cataract Patients Underwent Excimer Laser PRK

We retrospectively evaluated postoperative refraction of four patients(five eyes)who received intraocular lens implantation after excimer laser photorefractive keratectomy (PRK).The mean age of the patients was 44.8 years and 3 patients were female and 1 patient was male.The mean interval between PRK and cataract operation was 20.2 months (1 to 45 months)and the mean follow-up time after cataract operation was 16.2 months(2~43months).Phacoemulsification and PMMA-PCL(6.0~6.5 mm)implantation were made in all cases.SRK-II formula,the most popular empirical formula was used in first 3 cases(group I),but Idem-lens formula,a primitive theoretical formula was used in another 2 cases (group II)after occurrence postoperative refraction errors in group I .In group I and II,the mean postoperative refraction error was +3.00 diopters and +0.50 diopters and uncorrected visual acuity at postoperative 2 months was 20/60 and 20/24 respectively.The mean of calculated IOL-power was -3.75 diopter in group I and -0.625 diopter in group II.From these results,the empirical formula is definitely unsuitable for the calculation of IOL power in the cataract operation following excimer laser PRK. Moreover,although a primitive one,Idem-lens theory could be temporally useful for the IOL-power calculation in such cases.In conclusion,new formula is required for the cataract operation following excimer laser PRK.

Prediction of the Refractive Power after Cataract Surgery on Myopic Eyes

After extracapsular cataract extraction and posterior chamber intraocular lens implantation on 62 high myopic patients(79 eyes) whose axial lengths were more than 26.0mm, the authors investigated the differences between the calcualted, predicted, peroperative values and measured postoperative values retrospectively. The patients were divided into 2 groups according to their axial lengths; Group C is 35 patients (44 eyes) with 26.0-28.4mm. Group D is 27 patients(35 eyes) with more than 28.4mm. Group A, as control group, is 70 patients(81 eyes) with 22.0-24.4mm and group B, as control group, is 37 patients(44 eyes) with 24.5-25.9mm. Autorefractive examination and manifest refraction was done at 1week, 1month, 3 months postoperatively. Preoperative intraocular lens diopter was calculated by SRK-II and SRK/T formula. After the scleral incision, continuous circumlinear capsulorhexis, and phacoemulsification, one-piece PMMA lens was implanted in the bag. At postoperative 3 months, all patients had the tendency of myopic shift and the shift calculated by SRK-II was much more than that by SRK/T. The difference was statistically significant. In conclusion, it is better to apply SRK/T formula when axial length is more than 26.0mm, in order to acheive goal diopter postoperatively.

Compartive Accuracy of the SRK II, SRK/T and Holladay Formulas for Intraocular Lens Power Calculation in Severe Myopic Eyes

The predictive accuracy of the SRK II, SRK/T and Holladay formulas was evaluated in 22 eyes with sever myopia who had phacoemulsification and implantaton of posterior chamber IOL without suture. These patients were followed up for at least 6 months postoperatively. Correlation coefficient between the predicted refraction and actual refraction was 0.57(P0.05). The percentage of the eye with hyperopic shift(more hyperopic actual refraction than the predicted refraction) was 77% in the SRK II, 77% in the SRK/T and 86% in the Holladay, but there was no statistically significant difference between each formula(p>0.05). In conclusion, the SRK/T has the better predictive accuracy than the SRK II and Holladay in severe myopia and hyperopic shift tends to occur with the application of all three formulas.

Evaluation for the Accuracy of the SRK/T Formula in PCL Implanted Patients(II): Optimizing, A-Constant

To evaluate the efficacy of optimizing of A-constant, the error in prediction was analyzed in three groups of eyes after posterior chamber lens implantation ; 102 eyes with bag placed, 66 eyes with simple sulcus places, and 25 eyes with sulcus placed with transscleral fixation suture. We compared the predictive accuracy of the SRK/T formula using optimized A-constant (bag-placed, sulcus-placed) derived from the 300 eyes with Holladay and SRK/T using original surgeon factor and A-constant. The SRK/T formula with optimized A-constant has a better mean relative, absolut, and standard error and has a better range of IOL prediction error, which was more accurate than other formulas without optimizing. In this study it is our recommendation that each surgeon use a different optimized A-constants for sulcus or bag placement to enhance the predictability of the postoperative refraction.

Comparison of the Hoffer Q and SRK-II fomulas in IOL Power Calculation

Although most available IOL power calculation formulas perform accurately for eyes of average axial length, they have been shown to be inaccurate for eyes that have unusually short and long axial length. To compare the prediction accuracy of new Hoffer Q with SRK-II formula, we reviewed, retrospectively, a series of 225 ECCE with PCL implantation cases, including 106 Hoffer Q group and 119 SRK-II group, each of which was further divided into subgroups based on axial length. The Hoffer Q formula overestimated the refraction and resulted in more myopic shift and was less accurate than SRK-II in all length eyes, except short length eyes. In short length eyes, both formulas had similar mean error and mean absolute error but Hoffer Q formula was more accurate than the SRK-II in +/- 0.5D prediction proportion.

Comparison of the SRK and SRKII Formulas with Revision of Constant A in Intraocular Lens Power Calculation

The predictive accuracy of the SRK and SRKII formulas were compared in 113 pseudophakic eyes who had extracapsular cataract extraction with implantation of same type of posterior chamber IOL from Feburary 1990 to March 1991. These patients were folio we red up for at least 2 months postoperatively. Their best corrected visual acuities were above 0.5 and their astigmatisms were below 3 diopters by spectacles correction at the time of the last refraction. The results were as follows. 1. Overall, there were no significant differences in predictive accuracy between SRK and SRKII formulas. 2. The revised constant A for same type of implatnts, which constant A was 118.8. was 117.4 The SRK and SRKII formulas with revised constant A were more accurate than conventional formulas(p<0.001). 3. Our results suggested the constant A was to be revised appropriately according to the surgeon's individual regression analysis when using SRK or SRKII formulas for the calculation of intraocular lens power in Koreans.

Evaluation for the Accuracy of the SRK/T Formula in PCL Implanted Patients(I)

The 1224 cataractous patients who had extracapsular cataract extraction and posterior chamber lens implantations were evaluated retrospectively irrespective of style, postoperative position of intraocular lens and surgeon. The 100 cataractous patients who had extracapsular cataract extraction and posterior chamber lens implantations in the bag accurately using single lens style by one surgeon(E.H.L) were evaluated prospectively. And then the predictive accuracy of the SRK/T intraocular lens power calculation formula was compared with other formulas (SRK, SRKII and Holladay) without consideration of individual A constant. The SRK/T formula was more accurate than other 3 formulas in all axial length, but there were no significant differences statistically. Especially for short and long eyes, SRK/T formula was more accurate than other 3 formulas.