Keratometry using hand-held and automated keratometers with and without speculum in Indian pediatric cataract – A comparative study

To study the keratometry of Indian pediatric eyes, the effect of speculum on keratometry reading, the concordance of hand held and automated keratometry and the effect of unilateral and bilateral cataract on keratometry and IOL power calculation. This was conducted as a cross- sectional observational study on 101 eyes of children in the age range of 41 post-conceptional weeks to 144 months. All cooperative patients were subject to automated keratometry followed by keratometry using hand held keratometer with and without speculum. Hand held keratometer with and without speculum documented significantly increased average K as well as astigmatism and decreased calculated IOL power when compared to automated keratometry (p<0.01). No significant difference in K readings was observed between unilateral and bilateral cataracts and among males and females (p>0.05). As the age increased, astigmatism increased significantly (R=0.07; p=0.007) whereas no such correlation was observed for keratometry (p>0.05). Hand held keratometry offers the convenience of obtaining accurate keratometry, astigmatism and IOL power measurements in children.

Biometry in Silicone Oil Filled Eyes. A Review

The “gold standard” of modern vitreoretinal surgery is silicone oil tamponade of the vitreous cavity. The lens opacity development is in the list of complications of prolonged silicone oil eye filling (from 2 weeks to 2 years). Polydimethylsiloxanes hydrophobicity, direct contact with the front of the silicone bladder, macrophage and toxic reaction, trophic disturbances are the causes leading to the cataract initiation. This makes the problem of cataract surgery and preliminary intraocular lens calculation in silicone oil filled eyes before its removing very relevant as well as cloudy retina visualization and the necessity of minimization of number of operations through their combination. Certainly, the main error in IOL power calculation is associated with axial length measurement inaccuracy, as the most significant term of an equation. Silicone oil filled eyes biometry errors, and, consequently, postoperative refraction biases remain unresolved problem until now. To date authors report only 58 % of cases in which target refraction was achieved after combined surgery. Some researchers figure out that average calculation error after phacoemulsification with IOL implantation in avitreal eyes was 0.8 D despite of the optical biometry usage. Today it is represented by several methods: partial coherent interferometry, optical low-coherence reflectometry and optical coherence tomography, which are implemented in devices such as IOLMaster 500, Lenstar LS 900 and IOLMaster 700, which have their own characteristics and measurement accuracy. Their advantages as well as creation an accurate IOL calculation method for silicone oil filled eyes could reduce postoperative refraction error that outline significant medical and social problem.

Comparison of biometric methods in young children with congenital cataracts in their eyes

BACKGROUND: Relevant keratometric and biometric indicators are necessary for intraocular lens (IOL) power calculation, which is difficult to verify in young children. AIM: Evaluation of the accuracy of various ultrasound methods and optical biometry for axial length measurement in young children with congenital cataracts. MATERIAL AND METHODS: Forty-six children (74 eyes) with congenital cataracts (43 eyes) and pseudophakia (31 eyes) at the age of 6 months to 4 years were examined. Various methods measured the axial length: ultrasound A-scan under general anesthesia by US-4000, ultrasound B-scan without general anesthesia by Voluson E8, and optical biometry by AL-Scan in cases of transparent optics. RESULTS: The greater axial length difference was observed between A-scan and optical biometry (less by 0,78 mm) than between B-scan and optical biometry (more by 0,27 mm). The median axial length difference between A-scan and B-scan was equal for infants and young children with congenital cataracts (0,525 mm and 0,535 mm, respectively). CONCLUSION: Axial length should be measured by different methods in young children with their further comparison to obtaining more accurate biometric indicators for IOL power calculation. The decrease of 12 mm in axial length, which occurs during the A-scan, can lead to errors in the IOL calculation of 36 diopters and unplanned refraction in the long-term period.

Effect of Implantable Collamer Lens on Anterior Segment Measurement and Intraocular Lens Power Calculation Based on IOLMaster 700 and Sirius

Purpose. To investigate the possible effect of an implantable collamer lens (ICL) on ocular biometrics and intraocular lens (IOL) power calculation. Methods. Ocular measurements were taken preoperatively and at the two-month follow-up using IOLMaster 700 and Sirius in 85 eyes (43 patients) who had previously undergone ICL surgery. IOL power was calculated using either IOLMaster 700 (Barrett Universal II formula) or Sirius (ray-tracing). All data were compared using the paired t-test. Results. The difference between preoperative and postoperative anterior chamber depth (ACD), lens thickness (LT), and keratometry on the steep axis (K2) measured by IOLMaster 700 was statistically significant (p < 0.001). In 11 of 85 eyes, IOLMaster misjudged the anterior surface of the ICL as that of the lens, leading to an error in ACD and LT. There were no significant differences between preoperative and postoperative axial length (AL) (p = 0.223), white to white (WTW) (p = 0.100), keratometry on flat axis (K1) (p = 0.117), or central corneal thickness (CCT) (p = 0.648), measured using IOLMaster. The difference in IOL power calculated using the Barrett II formula was significant (p = 0.013). Regression analysis showed that AL and K had the greatest influence on IOL calculation (p < 0.001), and ACD and LT had less influence (p = 0.002, p = 0.218, respectively). K1 and K2 were modified to exclude the influence of K2, and modified IOLs showed no difference between pre and postoperation (p = 0.372). Preoperative and postoperative ACD measured using Sirius were significantly different (p < 0.001); however, the IOL power calculated using ray-tracing technology showed no significant differences (p > 0.05). Conclusions. The ocular biometric apparatus may misjudge the anterior surface of the lens, resulting in measurement errors of ACD and LT, which has little effect on the calculation of IOL power when using IOLMaster 700 (Barrett Universal II formula) and Sirius (ray-tracing).

Toric Intraocular Lenses for the Management of Corneal Astigmatism at the Time of Cataract Surgery

Aims/Background. To assess astigmatic outcomes with the use of toric intraocular lenses (IOLs) for patients with significant amounts of corneal astigmatism undergoing cataract surgery. Methods. This audit was conducted in a UK ophthalmology department and included 48 eyes of 42 patients. Surgery was performed during 2019 in patients with 2.50 diopters (D) or more corneal astigmatism. Anterior keratometry readings were used to determine the toric IOL power. Vector analysis using the Alpins method was used to assess changes in astigmatism pre to postoperatively. Results. There were 18 right and 26 left eyes included. In terms of gender, 61% of patients were female and 39% were male. The mean (±standard deviation (SD)) age was 70 (±11) years. The mean (±SD) axial length, K1, K2, and delta K was 23.55 (±1.4) mm, 42.71 (±1.39) D, 45.78 (±1.60) D, and 3.01 (±0.89) D, respectively. Postoperatively, the median spherical, cylinder, and spherical equivalent refraction was 0.00 D, −1.00 D, and 0.00 D, respectively. Postoperatively, 41% of the eyes had ≤0.50 D of spectacle astigmatism and 80% had ≤1.00 D. No patient required a secondary procedure to reposition the IOL from rotation. In vector analysis with the use of polar diagrams, there was a tendency for overcorrection of with-the-rule astigmatism and undercorrection of against-the-rule astigmatism. Conclusions. Significant reductions in astigmatism can be achieved with the use of toric IOLs in patients undergoing cataract surgery. Further improvements may be possible with surgeon-specific determination of their surgically induced astigmatism and flattening effect from the main corneal incision. Furthermore, the use of an optical biometer that directly measures the posterior corneal curvature and permits automatic toric IOL power determination with modern formulas avoiding the need for manual data entry may reduce the risk of human error and improve visual and refractive outcomes.

Keratometry, biometry, and prediction of intraocular lens power in adult tigers (Panthera tigris)

OBJECTIVE To calculate the necessary pseudophakic intraocular lens (IOL) power to approximate emmetropia in adult tigers. ANIMALS 17 clinically normal adult tigers. PROCEDURES 33 eyes of 17 clinically normal adult tigers underwent routine ophthalmic examination and B-scan ultrasonography while anesthetized for unrelated procedures. Specific ultrasound data (globe measurements and corneal curvature) and estimated postoperative IOL positions were utilized to calculate predicted IOL power by use of Retzlaff and Binkhorst theoretical formulas. Applanation tonometry and refraction were also performed. RESULTS Mean ± SD axial globe length was 29.36 ± 0.82 mm, preoperative anterior chamber depth was 7.00 ± 0.74 mm, and crystalline lens thickness was 8.72 ± 0.56 mm. Mean net refractive error (n = 33 eyes) was +0.27 ± 0.30 diopters (D). By use of the Retzlaff formula, mean predicted IOL power for the postoperative anterior chamber depth (PACD), PACD – 2 mm, and PACD + 2 mm was 43.72 ± 4.84 D, 37.62 ± 4.19 D, and 51.57 ± 5.72 D, respectively. By use of the Binkhorst equation, these values were 45.11 ± 4.91 D, 38.84 ± 4.25 D, and 53.18 ± 5.81 D, respectively. Mean intraocular pressure for all eyes was 14.7 ± 2.69 mm Hg. CLINICAL RELEVANCE The calculated tiger IOL was lower than reported values for adult domestic felids. Further studies evaluating actual PACD and pseudophakic refraction would help determine the appropriate IOL power to achieve emmetropia in this species.

Accuracy of Intraocular Lens Power Calculation Formulas in Pediatric Cataract Patients: A Systematic Review and Meta-Analysis

Background: Among the various intraocular lens (IOL) power calculation formulas available in clinical settings, which one can yield more accurate results is still inconclusive. We performed a meta-analysis to compare the accuracy of the IOL power calculation formulas used for pediatric cataract patients.Methods: Observational cohort studies published through April 2021 were systematically searched in PubMed, Web of Science, and EMBASE databases. For each included study, the mean differences of the mean prediction error and mean absolute prediction error (APE) were analyzed and compared using the random-effects model.Results: Twelve studies involving 1,647 eyes were enrolled in the meta-analysis, and five formulas were compared: Holladay 1, Holladay 2, Hoffer Q, SRK/T, and SRK II. Holladay 1 exhibited the smallest APE (0.97; 95% confidence interval [CI]: 0.92–1.03). For the patients with an axial length (AL) less than 22 mm, SRK/T showed a significantly smaller APE than SRK II (mean difference [MD]: −0.37; 95% CI: −0.63 to −0.12). For the patients younger than 24 months, SRK/T had a significantly smaller APE than Hoffer Q (MD: −0.28; 95% CI: −0.51 to −0.06). For the patients aged 24–60 months, SRK/T presented a significantly smaller APE than Holladay 2 (MD: −0.60; 95% CI: −0.93 to −0.26).Conclusion: Due to the rapid growth and high variability of pediatric eyes, the formulas for IOL calculation should be considered according to clinical parameters such as age and AL. The evidence obtained supported the accuracy and reliability of SRK/T under certain conditions.Systematic Review Registration: PROSPERO, identifier: INPLASY202190077.

An ensemble-based approach for estimating personalized intraocular lens power

The fundamental difference between modern formulae for intraocular lens (IOL) power calculation lies on the single ad hoc regression model they use to estimate the effective lens position (ELP). The ELP is very difficult to predict and its estimation is considered critical for an accurate prediction of the required IOL power of the lens to be implanted during cataract surgery. Hence, more advanced prediction techniques, which improve the prediction accuracy of the ELP, could play a decisive role in improving patient refractive outcomes. This study introduced a new approach for the calculation of personalized IOL power, which used an ensemble of regression models to devise a more accurate and robust prediction of the ELP. The concept of cross-validation was used to rigorously assess the performance of the devised formula against the most commonly used and published formulae. The results from this study show that overall, the proposed approach outperforms the most commonly used modern formulae (namely, Haigis, Holladay I, Hoffer Q and SRK/T) in terms of mean absolute prediction errors and prediction accuracy i.e., the percentage of eyes within ± 0.5D and ± 1 D ranges of prediction, for various ranges of axial lengths of the eyes. The new formula proposed in this study exhibited some promising features in terms of robustness. This enables the new formula to cope with variations in the axial length, the pre-operative anterior chamber depth and the keratometry readings of the corneal power; hence mitigating the impact of their measurement accuracy. Furthermore, the new formula performed well for both monofocal and multifocal lenses.