Emmetropic Intraocular Lens Power Research Articles

Does blepharospasm effect biometric parameters and intraocular lens power calculations?

To investigate the effect of botulinum toxin-A (BTX-A) treatment on corneal topography, ocular biometry and keratometry in patients with benign essential blepharospasm (BEB) and hemifacial spasm (HFS). This study comprised 66 eyes of 33 patients with BEB and 5 eyes of 5 patients with HFS who underwent BTX-A injections consecutively. Refractive error values, tear break-up time (TBUT), corneal topography [corneal power of flat axis (K1) and steep axis (K2), mean corneal power (Km), corneal astigmatism (K2-K1)] and ocular optical biometry [axial length (AL), anterior chamber depth (ACD)] were recorded before BTX-A treatment and 1 month after BTX-A treatment. The researchers calculated the expected emmetropic intraocular lens power (emm-IOL) using the SRK-T, Holladay, Hoffer-Q and Haigis formulas at each examination. K1 (43.48 ± 2.02 vs. 43.57 ± 2.08, p = 0.036), Km (43.91 ± 1.99 vs. 43.99 ± 2.06, p = 0.024) and ACD (3.22 (2.77-3.76) vs. 3.41 (2.99-4.02), p < 0.001) values were found to be significantly higher. The expected emm-IOL according to the SRK-T (21.04 ± 1.6 vs. 20.93 ± 1.6, p = 0.048), Holladay (21.05 ± 1.6 vs. 20.91 ± 1.62, p = 0.037) and Hoffer-Q (21.08 ± 1.65 vs. 20.94 ± 1.68, p = 0.038) decreased significantly. The expected emm-IOL according to the Haigis formula slightly decreased, but it was not significant (p = 0.386). Additionally, TBUT was found to be significantly lower (p < 0.001) after BTX-A injection. Other parameters were not statistically significant (p > 0.05). Our study is the first in the literature to compare optic biometry data and intraocular lens power calculation formulas before and after BTX-A injection in eyes with BEB and HFS. BTX-A injection could play an important role in changing the keratometric and ACD values. It should be considered that IOL power calculations that might be unpredictable due to blepharospasm, so repeated measurements and especially measurements after releasing the spasm with BTX-A injections, are necessary in BEB and HFS.

Comparison of Ocular Biometric Parameters Between Hispanic and Non-Hispanic Ethnicities in White Adults Undergoing Cataract Surgery.

To compare ocular biometric parameters between Hispanic and non-Hispanic White adult patients undergoing cataract surgery. We included 433 adult patients undergoing surgery for senile cataract. Only patients with race and ethnicities of Hispanic and non-Hispanic White were included. The following parameters measured by the IOLMaster 700 were compared between Hispanic and non-Hispanic patients: mean keratometry, corneal astigmatism, anterior chamber depth (ACD), lens thickness, vitreous length, axial length, white-to-white diameter, and emmetropic intraocular lens power. There were 219 Hispanic patients and 214 non-Hispanic patients with a mean age of 70.1±7.7 years (range, 50-88 years), and 66.7% were women. Although sex distribution was similar between the two groups, Hispanic patients had a lower age compared with non-Hispanic patients (69.3±8.3 vs. 70.9±6.9 years, P=0.02). In biometric values, ACD was significantly lower in Hispanic patients (3.07±0.40 mm) than in non-Hispanic patients (3.16±0.37 mm, P=0.01). Such statistically significant difference persisted after adjustment for age and sex (P=0.01). No other significant differences were found in other ocular parameters measured. Anterior chamber depth is significantly shorter in Hispanic patients compared with non-Hispanic patients. Such ethnic difference should be considered when performing cataract and corneal surgeries because this ethnic difference may be associated with a higher risk of corneal endothelial injury.

Congenital cataract surgery: long-term refractive outcomes of a new intraocular lens power correction formula.

The final refraction after intraocular lens (IOL) implantation remains a challenge in the management of paediatric cataracts. No consensual guidelines exist for the choice of IOL power. The aim of this study was to validate a method of IOL power calculation by evaluating the final refractive error in all patients with IOL implantation operated at our institution. We retrospectively studied all children under 7 years of age who underwent cataract surgery with IOL implantation at our institution between 2010 and 2015. Intraocular lens (IOL) power was calculated as follows: After B-scan determination of the emmetropic IOL power, a reduction of 40%, 35%, 30%, 25%, 20%, 15%, 10% and 5% was applied to children 0-3, 3-6, 6-12, 12-18, 18-24, 24-30, 30-36, 36-48 months, respectively. The following data were collected: follow-up, age at surgery, uni- or bilaterality, implanted IOL power and final refraction. During this period, 81 children (125 eyes) met the inclusion criteria with a median follow-up of 60 months (36-97). The median age at surgery was 6.61 months (0.76-48). We included 52 children with bilateral cataract (96 eyes) and 29 children with unilateral cataract (29 eyes). The mean implanted IOL power was 23.3 ± 4.6 diopters (D). The mean spherical equivalent at last follow-up was 0.07 ± 3.5 D. Our undercorrection formula for IOL implantation after congenital cataract surgery leads to long-term refractive results globally close to emmetropia.

Inter-ocular and inter-visit differences in ocular biometry and refractive outcomes after cataract surgery

This study aimed to determine whether inter-ocular differences in axial length (AL), corneal power (K), and adjusted emmetropic intraocular lens power (EIOLP) and inter-visit differences in these ocular biometric values, measured on different days, are related to refractive outcomes after cataract surgery. We retrospectively reviewed 279 patients who underwent phacoemulsification. Patients underwent ocular biometry twice (1–4 weeks before and on the day of surgery). Patients were divided into three groups: group S (similar inter-ocular biometry in different measurements; n = 201), group P (inter-ocular differences persisted in the second measurement; n = 37), and group D (inter-ocular difference diminished in the second measurement; n = 41). Postoperative refractive outcomes (mean absolute errors [MAEs]) were compared among the groups. Postoperative MAE2, based on second measurement with reduced inter-ocular biometry difference, was smaller than that calculated using the first measurement (MAE1) with borderline significance in group D (MAE1, 0.49 ± 0.45 diopters vs. MAE2, 0.41 ± 0.33 diopters, p = 0.062). Postoperative MAE2 was greater in group P compared to the other two groups (p = 0.034). Large inter-ocular biometry differences were associated with poor refractive outcomes after cataract surgery. These results indicate that measurements with smaller inter-ocular differences were associated with better refractive outcomes in cases with inter-visit biometry differences.

Biometric changes in Indian pediatric cataract and postoperative refractive status.

Purpose:To prospectively evaluate the biometric changes in Indian pediatric cataract and postoperative refractive status.Methods:A total of 147 patients were recruited into three groups: age <6 months, age between 7 months and 18 months, and age between 19 and 60 months and prospectively observed for 6 months. Exclusion criteria were preterm birth, microphthalmia, microcornea, megalocornea, uveitis, glaucoma, and traumatic or complicated cataract. Axial length and keratometry, the primary outcome measures, were taken preoperatively under general anesthesia before surgery. These children were followed up for 6 months to look for refractive and biometric changes. T-test and linear regression with the logarithm of independent variables were done.Results:All unilateral cataractous eyes (n = 25) and randomly selected bilateral cases (n = 122) were included in the analysis, for a total of 147 eyes. Mean age was 17.163 ± 13.024 months; axial length growth was 0.21, 0.18, 0.06 mm/month, and keratometry decline was 0.083, 0.035, 0.001 D/month in age groups 0–6, 7–18, and 19–60 months, respectively. The visual acuity improved in log MAR from 1.020 to 0.745 at 6 months postoperatively. There was statistically significant (Spearman's correlation coefficient = –0.575, P < 0.001) between age and postoperative refraction. There were no intraocular lens (IOL)-related complications seen in the immediate postoperative period. Peripheral opacification was seen in 102 eyes and central opacification in 1 eye at a 6-month follow-up.Conclusion:Indian eyes have a lower rate of axial length growth and keratometry change in comparison with western eyes implying smaller undercorrection in emmetropic IOL power for Indian pediatric eyes to achieve a moderate amount of hyperopia.

Outcomes of the Haigis-L formula for calculating intraocular lens power in Asian eyes after refractive surgery

To report outcomes using the Haigis-L formula to calculate intraocular lens (IOL) power in Asian eyes with long axial lengths (ALs) that had previous myopic laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK). Singapore National Eye Centre, Singapore. Retrospective case series. Patients with ALs greater than 25.0 mm and previous myopic LASIK or PRK who had phacoemulsification were analyzed. The emmetropic IOL power was back-calculated using the 1-month postoperative manifest refraction and compared with the emmetropic IOL power calculated with the Haigis-L formula. The primary outcome measure was the mean arithmetic prediction error, defined as the difference between the actual postoperative refractive error and the intended formula-derived refractive target. Sixty-two eyes (52 patients) were analyzed. The mean arithmetic prediction error was -0.44 diopter (D) ± 0.98 (SD) and the mean absolute error, 0.87 ± 0.62 D. The mean arithmetic prediction error was -0.52 ± 0.96 D in eyes with an AL less than 27.0 mm and -0.36 ± 1.00 D in eyes with an AL of 27.0 mm or greater (P = .463). The predictability of being within ±0.50 D and ±1.00 D of target was 35.7% and 63.1%, respectively, overall; 31.6% and 60.5%, respectively, in eyes with an AL less than 27.0 mm; and 39.1% and 65.2%, respectively, in eyes with an AL of 27.0 mm or greater (P = .772). The Haigis-L formula was acceptably accurate in predicting and achieving target outcomes after phacoemulsification in Asian eyes with a long AL that had previous myopic LASIK or PRK. No author has a financial or proprietary interest in any material or method mentioned.

Clinical Evaluation of the Intraoperative Refraction Technique for Intraocular Lens Power Calculation

To evaluate clinically the intraoperative refraction technique for intraocular lens (IOL) power calculation using 2 existing formulas proposed by Ianchulev and Leccisotti and to derive alternative formulas for this technique. Comparative case series. One hundred eighty-two eyes from 182 patients with cataract. Recruited patients were separated into a normal cornea group and a special group that included eyes with surgically altered corneas. Phacoemulsification was carried out for all cases. Intraoperative aphakic autorefraction using a portable autorefractor was performed. An IOL with power calculated before surgery then was implanted. In each eye, postoperative refraction was obtained. The IOL power that would have achieved emmetropia was calculated retrospectively. Aphakic autorefraction readings obtained during surgery were used to calculate the aphakic spherical equivalent (SE). The 2 formulas incorporating aphakic SE were applied to calculate the target IOL power. Comparison then was made to determine the accuracy of the formulas. A difference (referred to as IOL difference) was calculated by subtracting the adjusted emmetropic IOL power determined by postoperative refraction from the emmetropic IOL power calculated by the 2 formulas using intraoperative aphakic SE. One hundred forty-four patients were in the normal cornea group and 18 were in the special group. In the normal group, the Ianchulev formula showed a relatively accurate prediction for IOL power to achieve emmetropia over almost the full range of axial length except in extremely long eyes. The Leccisotti formula tended to overestimate IOL power and worked particularly poorly in short eyes. It worked best in long eyes. In the special group, neither of the 2 formulas was able to show superiority universally. Using data from the normal group, alternative formulas for IOL power calculation were derived. These new formulas then were validated on the special group that showed good estimation. The Ianchulev formula could be applied to most eyes, with the exception of those in highly myopic subjects. The Leccisotti formula showed good performance in myopic patients. For eyes falling into the special group, an alternative formula, correction factor, or both, may be required. The new formulas reported herein may be an option. The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Intraocular lens power requirements for humanitarian missions

To develop a generalized method to determine an optimum set of intraocular lens (IOL) powers for humanitarian missions. Humanitarian missions to Central America, South America, and Southeast Asia. Biometric data of adults who had cataract surgery on 2 humanitarian missions were reviewed, and the ideal emmetropic IOL power for each eye was calculated. Using statistical modeling, the number of extra IOLs required at each power to account for natural variation inherent in random population samples was calculated. To limit the total number of IOLs and maximize availability of suitable IOLs for each patient, a tolerance strategy for choosing IOL powers was developed and the ideal proportion of extra IOLs required at each power was empirically determined. Data of 103 patients were reviewed. The mean IOL power was 20.38 diopters (D) +/- 2.32 (SD). Applying a tolerance strategy to accept IOLs with powers 0.5 D below or 1.0 D above the emmetropic IOL power, the number of extra IOLs required at each power was decreased to a fraction of the fourth root of the number of eyes anticipated to require that IOL power. The model predicted that with this strategy, fewer than 2% of all patients would be rejected due to lack of an IOL with a suitable power. The spreadsheet-based IOL power prediction model calculated an ideal distribution of IOLs to order for humanitarian cataract surgery. It is generalizable to missions of any size and should help planners minimize costs while ensuring excellent refractive outcomes.

Estimation of Posterior Corneal Power for IOL Calculation After Myopic LASIK

To estimate the posterior corneal power for intraocular lens (IOL) calculation after myopic LASIK. A retrospective study of 50 patients (92 eyes) who underwent uneventful myopic LASIK was conducted. Pre- and postoperative data (12 months) were collected including refraction and Orbscan II (Bausch & Lomb) for simulated keratometry (Sim K), central corneal thickness, and posterior corneal power. Statistical analysis was performed to determine the correlation between the postoperative posterior corneal power and other variables. An empirical formula was generated to predict the postoperative posterior corneal power. The net corneal power was calculated based on the new formula and Gaussian optics formula in an additional 31 eyes that underwent myopic LASIK and compared to the Orbscan total optical power map. The net corneal power was retrospectively applied to calculate the IOL power in an additional 10 patients who underwent cataract extraction after myopic LASIK. The back-calculation for emmetropic IOL power was performed and compared to the IOL power derived from the net corneal power. By using multiple linear regression, a formula to predict postoperative posterior corneal power can be computed from postoperative Sim K, central corneal thickness, and the amount of myopia treated with R2 of 0.63 (standard error =0.25) (P<.05). The net corneal power was highly correlated to the total optical power (R2=0.96); no statistically significant difference (paired t test) was noted (P>.05). The error of the IOL power derived from the net corneal power was -0.30+/-0.20 diopters. Corneal power after myopic LASIK can be estimated using postoperative Sim K, central corneal thickness, and the amount of myopia treated, which can be used for the assessment of IOL power after myopic LASIK.

Intraoperative optical refractive biometry for intraocular lens power estimation without axial length and keratometry measurements

To correlate intraoperative aphakic autorefraction to conventional emmetropic intraocular lens (IOL) calculations and derive an empiric predictive model for IOL estimation based on optical refractive biometry without axial length and keratometry measurements. Institutional Review Board of the University of Southern California, Los Angeles County General Hospital, Los Angeles, California, USA. A pilot group of 22 eyes of 22 patients scheduled for cataract surgery were enrolled in a prospective trial. All patients had a standard preoperative workup with subsequent cataract extraction and IOL implantation according to conventional biometric measurements and IOL calculations. Intraoperative autorefractive retinoscopy was used to obtain aphakic autorefraction and to measure the aphakic spherical equivalent before lens implantation. A linear regression analysis was used to correlate the aphakic spherical equivalent to the final adjusted emmetropic IOL power to empirically derive a refractive formula for IOL calculation (optical refractive biometry method). A second validation series of 16 eyes was used in a head-to-head comparison between the optical refractive biometry and the conventional IOL formulas. A subset of 6 eyes from the validation series were post-refractive cases having subsequent cataract surgery. Intraoperative retinoscopic autorefraction was successfully obtained in all 22 patients in the pilot group and all 16 patients in the validation group. The spherical equivalent of the aphakic autorefraction correlated linearly with the final adjusted emmetropic IOL power (P<.0001, with adjusted r(2)=.9985). The relationship was sustained over an axial length range of 21.43 to 25.25 mm and an IOL power range of 12.0 to 25.5 diopters (D). In a subsequent validation series of 10 standard and 6 post-laser in situ keratomileusis (LASIK) cataract cases, the optical refractive biometry method proved to be a better predictive model for IOL estimation than conventional formulas; 83% of the LASIK eyes and 100% of the normal eyes were within +/-1.0 D of the final IOL power when aphakic autorefraction was used, compared with 67% of LASIK eyes and 100% of the normal eyes, using the conventional methodology. A new model for IOL power calculation was derived based on an optical refractive methodology that breaks away from the conventional art introduced by Fyodorov in the 1960s. A purely refractive algorithm is used to predict the power of the IOL at the time of surgery without the need for axial length and keratometry measurements. This method bypasses some limitations of conventional biometry and shows promise in the post-refractive cataract cases.

Surgical identification of posterior lenticonus

A 79-year-old patient was referred for cataract and high myopia. His optometrist noted difficult refraction. Biometry predicted an emmetropic intraocular lens power of +22.0 diopters. During cataract extraction, the typical features of posterior lenticonus were noted. A careful look for posterior lenticonus is suggested in cases in which there is a discrepancy between the biometry and refraction and no significant nuclear sclerosis to account for the high myopia. Surgeons should be aware of dehiscence or thinning of the posterior capsule while doing cataract extraction in these patients.

Intraocular lens power prediction in a Vietnamese population A study to establish a limited set of intraocular lens powers that could be used in a Vietnamese population

AIM: To determine a range of dioptric powers for Intraocular Lenses (IOLs) that would cover at least 95% of the Vietnamese population attending hospital for cataract removal and IOL implantation. OBJECTIVE: To determine the ocular axial lengths and keratometric powers of people attending for cataract surgery at a hospital in Vietnam and hence predict the intraocular lens powers required for emmetropia for this population. HYPOTHESIS: 95% of the population attending a Vietnamese hospital for cataract and intraocular lens surgery would be within ± 4.5 dioptres of the mean predicted emmetropic intraocular lens power. STUDY DESIGN: A case series. STUDY FACTORS: Axial length, keratometric power, age, sex, preoperative refractive status, preoperative vision, ethnicity. OUTCOME: Intraocular lens power for emmetropia. RESULTS: 346 adults attending for cataract surgery at the Hue Central Hospital, Vietnam were examined. The mean axial length was found to be 22.96 mm ± 0.99 (range 20.37–27.25), median 23.01 mm. The mean corneal power was 44.24 dioptres ± 1.53 (range 39.50–49.00), median 44.5 dioptres. Using the SRK/T formula, with an "A" constant of 118.3, the mean predicted intraocular lens power required for emmetropia was 21.44 dioptres ± 2.77 (range 10.87–27.25), median 21.56 dioptres. The mean predicted IOL power for females was 21.94 dioptres ± 2.60 (range 13.84–29.68), median 22.13 dioptres. The mean predicted IOL power for males was 20.72 dioptres ± 2.84 (range 10.87–28.95), median 20.66 dioptres. conclusion 95% of the population attending for cataract surgery were within 5.5 dioptres of the mean predicted emmetropic IOL power.

Calculation of intraocular lens power with the SRK II formula for axial high myopia.

The SRK II formula has been widely used for intraocular lens (IOL) power calculations. The predictability of this formula is evaluated in axial myopic patients. Planned extracapsular cataract extraction and posterior chamber IOL implantation (PECCE + IOL) were performed on 98 eyes of 98 patients with axial length > 24.5 mm. Cases had no preoperative complications and postoperative visual acuity was at least 0.5 (Snellen). Corneal refractive power and axial length were measured preoperatively and emmetropic IOL power calculations were made using the SRK II formula. Long-term (mean 4.7 months) visual acuities and refractions were noted postoperatively. The absolute refractive error was < 1.00 Diopters (D) in 57 eyes (58.2%) and < 2.00 D in 83 eyes (84.7%). The mean absolute error of the SRK II formula in axial myopia was 1.16 D +/- 0.78 SD. The SRK II formula is not very accurate in axial myopic patients.

Factors influencing the accuracy of the SRK formula in the intraocular less power calculation.

Several intraocular lens (IOL) power calculation formulas (either theoretical or empirical) are used to determine the emmetropic IOL power) The Sanders-Retzlaff-Kraff (SRK) linear regression formula is among the most widely recognized empirical ones. In the present study intraocular lens power calculation aiming at emmetropia was performed, using SRK formula, in 145 cataractous eyes undergoing lens implantation. The final refraction was evaluated at 8 to 12 months after surgery. The purpose of this study was the identification and quantitative evaluation of the factors which influence significantly the accuracy of SRK in the intraocular lens power calculation. The following factors were studied: (1) the error in preoperative biometry with regard to the difference between post and preoperative axial length measurements, (2) the position of the implantation of the intraocular lens (anterior versus posterior chamber), (3) the intraocular lens style, (4) the intraocular lens power level, (5) the preoperative corneal astigmatism, (6) the surgically induced corneal astigmatism, and (7) the postoperative astigmatism. Multiple regression and stepwise regression analysis showed a strong correlation (R2 = 0.65; p < 0.001) between postoperative refractive error (Rf) and error in preoperative biometry (delta AL), surgically induced corneal astigmatism (SIA) and postoperative astigmatism (Ap) only. This correlation is expressed by the following equation: Rf = 0.07 -2.55 delta AL -0.42 SIA + 0.34 Ap. This equation indicates the quantitative effect of each factor on the accuracy of the SRK formula, by defining the pattern of the fluctuations of the amount or state (myopic or hyperopic) of refractive error induced by changes of variables delta AL, SIA and Ap.

Clinical variability in keratometry, ultrasound biometry measurements, and emmetropic intraocular lens power calculation

We calculated inter-examiner and intea-examiner variability in keratometry and ultrasound biometry when performed by two different examiners. The potential effect on intraocular lens power calculation was also considered. Intra-examiner variability was statistically and clinically significant for axial measurements, particularly in eyes with axial length greater than 24 mm. Thus, variability in biometric examination affected the emmetropic intraocular lens power, especially in myopic eyes.

Effectiveness of intraocular lens calculation in high ametropia

The error in prediction of emmetropic intraocular lens power or postoperative refractive error after lens implantation was analyzed in three groups of eyes after posterior chamber lens implantation. Regression line calculation with the SRK equation or with a groupspecific regression was compared with theoretical calculations in unselected, long myopic and short hyperopic eyes. The cut-off length was below 22.0 mm for the short eyes and above 25.9 mm for the long eyes. In the unselected and hyperopic group, there was only a small difference in mean error and error variance when the three calculation methods were compared. In the high myopic group, the range of error increased in all methods. The worst results were obtained with the standard SRK equation because the slope of the regression line in myopic eyes differs from the classical regression line calculated on an average population of implants. Lens calculation in high myopic eyes should therefore be performed with a specific regression line or by theoretical calculation.

Secondary IOL power calculations: A comparison of regression formula and refractionmethod in accurate prediction of emmetropia

A retrospective review of 51 secondary intraocular lens (IOL) implantationswas made to determine the relative accuracy of the SRKTM regression formula and the refraction method described by Holladay in preoperative prediction of emmetropic IOL power. The regression formula accurately predicted emmetropia within 1 diopter (D) in 63% of patients; the refraction method accurately predicted within 1 D in only 26% of cases. The emmetropic power predicted by the two formulas differed by at least 1 D in 76% of patients. Precise measurement of preoperative variables is imperative to ensure accurate prediction of emmetropic IOL power in the patient considered for secondary implantation.