Intraocular lens power calculation after myopic excimer laser surgery: clinical comparison of published methods

Camellin-Calossi Formula for Intraocular Lens Power Calculation in Patients With Previous Myopic Laser Vision Correction

PURPOSE

To assess the performance of the Camellin-Calossi formula in eyes with prior myopic laser vision correction.

METHODS

This was a retrospective case series. Patients included had a history of uncomplicated myopic laser vision correction and cataract surgery. The primary outcome measures were cumulative distribution of absolute refractive prediction error, absolute refractive prediction error, and refractive prediction error. These parameters were estimated post-hoc using the Camellin-Calossi, Shammas, Haigis-L, Barrett True-K with or without history, Masket, and Modified Masket formulas and their averages starting from biometric data, clinical records, postoperative refraction, and intraocular lens power implanted.

RESULTS

Seventy-seven eyes from 77 patients were included. The Camellin-Calossi, Shammas, Haigis-L, Barrett True-K No History, Masket, Modified Masket, and Barrett True-K formulas showed a median absolute refractive error (interquartile range) of 0.25 (0.53), 0.51 (0.56), 0.44 (0.65), 0.45 (0.59), 0.40 (0.61), 0.60 (0.70), and 0.55 (0.76), respectively. The proportion of eyes with an absolute refractive error of ±0.25, 0.50, 0.75, 1.00, 1.50, and 2.00 diopters (D) for the Camellin-Calossi formula was 54.5%, 72.7%, 85.7%, 92.2%, 98.7%, and 100%, respectively. The cumulative distribution of the Camellin-Calossi formula showed the best qualitative performances when compared to the others. A statistically significant difference was identified with all of the others except the Haigis-L using a threshold of 0.25, with the Shammas, Modified Masket, and Barrett True-K at a threshold of 0.50 D and the Barrett True-K and Modified Masket at a threshold of 1.00 D.

CONCLUSIONS

The Camellin-Calossi formula is a valid option for intraocular lens power calculation in eyes with prior myopic laser vision correction. [J Refract Surg. 2024;40(3):e156-e163.].

Comparative clinical accuracy analysis of the newly developed ZZ IOL and four existing IOL formulas for post-corneal refractive surgery eyes

BACKGROUND

Intraocular lens (IOL) calculation using traditional formulas for post-corneal refractive surgery eyes can yield inaccurate results. This study aimed to compare the clinical accuracy of the newly developed Zhang & Zheng (ZZ) formula with previously reported IOL formulas.

STUDY DESIGN

Retrospective study.

METHODS

Post-corneal refractive surgery eyes were assessed for IOL power using the ZZ, Haigis-L, Shammas, Barrett True-K (no history), and ray tracing (C.S.O Sirius) IOL formulas, and their accuracy was compared. No pre-refractive surgery information was used in the calculations.

RESULTS

This study included 38 eyes in 26 patients. ZZ IOL yielded a lower arithmetic IOL prediction error (PE) compared with ray tracing (P = 0.04), whereas the other formulas had values like that of ZZ IOL (P > 0.05). The arithmetic IOL PE for the ZZ IOL formula was not significantly different from zero (P = 0.96). ZZ IOL yielded a lower absolute IOL PE compared with Shammas (P < 0.01), Haigis-L (P = 0.02), Barrett true K (P = 0.03), and ray tracing (P < 0.01). The variance of the mean arithmetic IOL PE for ZZ IOL was significantly smaller than those of Shammas (P < 0.01), Haigis-L (P = 0.03), Barrett True K (P = 0.02), and ray tracing (P < 0.01). The percentages of eyes within ± 0.5 D of the target refraction with the ZZ IOL, Shammas, Haigis-L, Barrett True-K, and ray-tracing formulas were 86.8 %, 45.5 %, 66.7 %, 73.7 %, and 50.0 %, respectively (P < 0.05 for Shammas and ray tracing vs. ZZ IOL).

CONCLUSIONS

The ZZ IOL formula might offer superior outcomes for IOL power calculation for post-corneal refractive surgery eyes without prior refractive data.

Accuracy of intraocular lens formulas using total keratometry in eyes with previous myopic laser refractive surgery

Objectives

This comparative study aimed to determine if total keratometry (TK) from IOLMaster 700 could be applied to conventional formulas to perform IOL power calculation in eyes with previous myopic laser refractive surgery, and to evaluate their accuracy with known post-laser refractive surgery formulas.

Methods

Sixty-four eyes of 49 patients with previous myopic laser refractive surgery were evaluated 1 month after cataract surgery. A comparison of the prediction error was made between no clinical history post-laser refractive surgery formulas (Barrett True-K, Haigis-L, Shammas-PL) and conventional formulas (EVO, Haigis, Hoffer Q, Holladay I, and SRK/T) using TK values obtained with the optical biometer IOLMaster 700 (Carl Zeiss Meditec), as well as Barrett True-K with TK.

Results

The mean prediction error was statistically different from zero for Barrett True-K, Barrett True-K with TK, Haigis-L, Shammas-PL, and Holladay I with TK. The mean absolute error (MAE) was 0.424, 0.671, 0.638, 0.439, 0.408, 0.424, 0.479, 0.647, and 0.524, and median absolute error (MedAE) was 0.388, 0.586, 0.605, 0.298, 0.294, 0.324, 0.333, 0.438, and 0.377 for Barrett True-K, Haigis-L, Shammas-PL, Barrett True-K TK, EVO with TK, Haigis with TK, Hoffer Q with TK, Holladay I with TK, and SRK/T with TK, respectively. EVO TK followed by Barrett True-K TK and Haigis TK achieved the highest percentages of patients with absolute prediction error within 0.50 and 1.00 D (68.75%, 92.19%, and 64.06%, 92.19%, respectively)

Conclusions

Formulas combined with TK achieve similar or better results compared to existing no-history post-myopic laser refractive surgery formulas.

Intraocular Lens power calculation after laser refractive surgery: A Meta-Analysis

There are an increasing number of people who have had refractive surgery now developing cataract. To compare the accuracy of different intraocular lens (IOL) power calculation formulas after laser refractive surgery (photorefractive keratectomy or laser in situ keratomileusis), a comprehensive literature search of PubMed and EMBASE was conducted to identify comparative cohort studies and case series comparing different formulas: Haigis-L, Shammas-PL, SRK/T, Holladay 1 and Hoffer Q. Seven cohort studies and three observational studies including 260 eyes were identified. There were significant differences when Hoffer Q formula compared with SRK/T, Holladay 1. Holladay 1 formula produced less prediction error than SRK/T formula in double-K method. Hoffer Q formula performed best among SRK/T and Holladay 1 formulas in total and single-K method. In eyes with previous data, it is recommended to choose double-K formula except SRK/T formula. In eyes with no previous data, Haigis-L formula is recommended if available, if the fourth formula is unavailable, single-k Hoffer Q is a good choice.

Comparison of the Accuracy of Newer Intraocular Lens Power Calculation Methods in Eyes That Underwent Previous Phototherapeutic Keratectomy

PURPOSE

To evaluate the accuracy of intraocular lens (IOL) power calculations using ray tracing software in patients who had undergone phototherapeutic keratectomy (PTK).

METHODS

In this retrospective case series, 37 eyes of 22 patients (mean age: 69.4 years; range: 56 to 85 years) who underwent cataract surgery after PTK were reviewed. The prediction error, defined as the difference between the estimated postoperative spherical equivalent and the postoperative manifest refraction at the spectacle plane, was calculated using the following formulas: OKULIX (Tedics, Dortmund, Germany), PhacoOptics (IOL Innovations ApS, Aarhus, Denmark), Barrett True K No History (NH), and Camellin-Calossi. The PhacoOptics formula was used in three different ways: historical method (H), no history method (NH), and C-constant method (C). The median values of the arithmetic and absolute prediction errors among these six IOL calculation methods were compared.

RESULTS

The median arithmetic errors (in diopters [D]) and percentages of eyes within ±0.50 D of the absolute errors were as follows: OKULIX (0.33, range: -2.20 to 2.50, 30.6%), PhacoOptics (H) (-0.12, range: -3.28 to 4.85, 22.2%), PhacoOptics (NH) (-0.25, range: -2.08 to 1.70, 48.4%), PhacoOptics (C) (0.04, range: -1.40 to 2.18, 48.5%), Barrett True K (NH) (-0.35, range: -1.90 to 1.89, 48.6%), and Camellin-Calossi (-0.19, range: -1.78 to 1.47, 59.5%).

CONCLUSIONS

The PhacoOptics, especially the C-constant method (C), and Camellin-Calossi formulas were good options for calculating IOL powers in eyes that underwent PTK. [J Refract Surg. 2019;35(5):310-316.].

Improving accuracy of corneal power measurement with partial coherence interferometry after corneal refractive surgery using a multivariate polynomial approach

Background

To improve accuracy of IOLMaster (Carl Zeiss, Jena, Germany) in corneal power measurement after myopic excimer corneal refractive surgery (MECRS) using multivariate polynomial analysis (MPA).

Methods

One eye of each of 403 patients (mean age 31.53 ± 8.47 years) was subjected to MECRS for a myopic defect, measured as spherical equivalent, ranging from − 9.50 to − 1 D (mean − 4.55 ± 2.20 D). Each patient underwent a complete eye examination and IOLMaster scan before surgery and at 1, 3 and 6 months follow up. Axial length (AL), flatter keratometry value (K1), steeper keratometry value (K2), mean keratometry value (KM) and anterior chamber depth measured from the corneal endothelium to the anterior surface of the lens (ACD) were used in a MPA to devise a method to improve accuracy of KM measurements.

Results

Using AL, K1, K2 and ACD measured after surgery in polynomial degree 2 analysis, mean error of corneal power evaluation after MECRS was + 0.16 ± 0.19 D.

Conclusions

MPA was found to be an effective tool in devising a method to improve precision in corneal power evaluation in eyes previously subjected to MECRS, according to our results.

Intraocular lens power calculation in eyes with previous corneal refractive surgery

Background

This review aims to explain the reasons why intraocular lens (IOL) power calculation is challenging in eyes with previous corneal refractive surgery and what solutions are currently available to obtain more accurate results.

Review

After IOL implantation in eyes with previous LASIK, PRK or RK, a refractive surprise can occur because i) the altered ratio between the anterior and posterior corneal surface makes the keratometric index invalid; ii) the corneal curvature radius is measured out of the optical zone; and iii) the effective lens position is erroneously predicted if such a prediction is based on the post-refractive surgery corneal curvature. Different methods are currently available to obtain the best refractive outcomes in these eyes, even when the perioperative data (i.e. preoperative corneal power and surgically induced refractive change) are not known. In this review, we describe the most accurate methods based on our clinical studies.

Conclusions

IOL power calculation after myopic corneal refractive surgery can be calculated with a variety of methods that lead to relatively accurate outcomes, with 60 to 70% of eyes showing a prediction error within 0.50 diopters.

Comparison of simulated keratometric changes following wavefront-guided and wavefront-optimized myopic laser-assisted in situ keratomileusis

Purpose

The aim of the study was to determine and compare the relationship between change in simulated keratometry (K) and degree of refractive correction in wavefront-guided (WFG) and wavefront-optimized (WFO) myopic laser-assisted in situ keratomileusis (LASIK).

Methods

A total of 51 patients were prospectively randomized to WFG LASIK in one eye and WFO LASIK in the contralateral eye at the Byers Eye Institute, Stanford University. Changes in simulated K and refractive error were determined at 1 year post-operatively. Linear regression was employed to calculate the slope of change in simulated K (ΔK) for change in refractive error (ΔSE). The mean ratio (ΔK/ΔSE) was also calculated.

Results

The ratio of ΔK to ΔSE was larger for WFG LASIK compared to WFO LASIK when comparing the slope (ΔK/ΔSE) as determined by linear regression (0.85 vs 0.83, p = 0.04). Upon comparing the mean ratio (ΔK/ΔSE), subgroup analysis revealed that ΔK/ΔSE was larger for WFG LASIK for refractive corrections of >3.00 D and >4.00 D (0.89 vs 0.83; p = 0.0323 and 0.88 vs 0.83; p = 0.0466, respectively). Both linear regression and direct comparison of the mean ratio (ΔK/ΔSE) for refractive corrections <4.00 D and >4.00 D revealed no difference in ΔK/ΔSE between smaller and larger refractive corrections.

Conclusion

WFO LASIK requires a smaller amount of corneal flattening compared to WFG LASIK for a given degree of refractive correction. For both, there was no significant difference in change in corneal curvature for a given degree of refractive error between smaller and larger corrections.

Intraocular Lens Power Calculation in Eyes After Laser In Situ Keratomileusis or Photorefractive Keratectomy for Myopia

Intraocular power calculation is challenging for patients who have previously undergone corneal refractive surgery. The sources of prediction errors for these eyes are well known; however, the numerous formulas and methods available for calculating intraocular lens power in these cases are eloquent testimony to the absence of a definitive solution. This review discusses some of the available methods for improving the accuracy for predicting the refractive outcome for these patients. It focuses mainly on the methods available on the American Society of Cataract and Refractive Surgery (ASCRS) online calculator and provides some practical guidelines for cataract surgeons who encounter these challenging cases.

A pilot study of intraocular lens explantation in 69 eyes in Chinese patients

AIM

To study the effects of intraocular lens (IOL) explantation and demographic characteristics.

METHODS

Retrospective non-comparative case series. Clinical data recorded from patient charts included the following: demographic, preoperative and postoperative characteristics; complications; surgical methods, and changes in visual acuity.

RESULTS

A total of 69 eyes in 67 Chinese patients who received IOL explants were studied. The patients' mean age at the time of explantation was 46.1 years old [SD 22.5 (6-85)], and 37 patients were female (55.2%). Regarding employment, 47.8% were farmers, 23.9% were retired, 16.4% were students, 4.5% were unemployed, 3% were workers, and 4.5% were other (including staff members, teachers and officers). The main reasons for explantation were dislocation/decentration in 41 cases (59.4%) and retinal detachment in 10 cases (14.5%). The third most prevalent cause was incorrect lens power in 7 eyes (10.1%). The remaining reasons were endophthalmitis in 6 cases (8.7%), posterior capsular opacity in 3 eyes (4.3%), and impacting retinal surgery operation in 2 cases (2.9%). The main comorbidities were high myopia in 18 eyes (26.1%), trauma in 8 eyes (11.6%), retinal detachment in 6 eyes (8.7%), congenital cataracts in 8 eyes (11.6%), and Marfan's syndrome in 2 eyes (2.9%). The mean time from implantation to explantation was 4.0y [SD 4.2 (0.005-15)]. Treatment after explantation included posterior chamber IOL implantation in 44 eyes (63.8%) and aphakia in 25 eyes (36.2%). After surgery, the best corrected visual ability (BCVA) was improved in 50 cases (72.5%), including 28 patients (40.6%) in whom visual ability was improved by more than two lines.

CONCLUSION

Dislocation/decentration is the main cause for explantation, and high myopia is a main risk factor. Posterior chamber IOL implantation remains the most elected treatment after explantation.

Cataract surgery on the previous corneal refractive surgery patient

Cataract surgery in cases with previous corneal refractive surgery may be a major challenge for the ophthalmologist. The refractive outcome of the case deserves special attention in the preoperative planning process, which should be tailored for the type of prior refractive procedure: incisional, ablative under a flap, or on the corneal surface. Avoiding refractive surprise after cataract surgery in these cases is principally dependent on the accuracy of the intraocular lens calculation, together with the selection of the appropriate biometric formula for each case. Modern techniques for cataract surgery help surgeons to move toward the goal of cataract surgery as a refractive procedure free from refractive error. We give practical guidelines for the cataract surgeon in the management of these challenging cases.

Clinical Validation of Adjusted Corneal Power in Patients with Previous Myopic Lasik Surgery

Purpose. To validate clinically a new method for estimating the corneal power (P_c) using a variable keratometric index (n_kadj) in eyes with previous laser refractive surgery. Setting. University of Alicante and Medimar International Hospital (Oftalmar), Alicante, (Spain). Design. Retrospective case series. Methods. This retrospective study comprised 62 eyes of 62 patients that had undergone myopic LASIK surgery. An algorithm for the calculation of n_kadj was used for the estimation of the adjusted keratometric corneal power (P_kadj). This value was compared with the classical keratometric corneal power (P_k), the True Net Power (TNP), and the Gaussian corneal power (P_cGauss). Likewise, P_kadj was compared with other previously described methods. Results. Differences between P_cGauss and P_c values obtained with all methods evaluated were statistically significant (p < 0.01). Differences between P_kadj and P_cGauss were in the limit of clinical significance (p < 0.01, loA [−0.33,0.60] D). Differences between P_kadj and TNP were not statistically and clinically significant (p = 0.319, loA [−0.50,0.44] D). Differences between P_kadj and previously described methods were statistically significant (p < 0.01), except with P_cHaigisL (p = 0.09, loA [−0.37,0.29] D). Conclusion. The use of the adjusted keratometric index (n_kadj) is a valid method to estimate the central corneal power in corneas with previous myopic laser refractive surgery, providing results comparable to P_cHaigisL.

Intraocular lens power calculation following laser refractive surgery

Refractive outcomes following cataract surgery in patients that have previously undergone laser refractive surgery have traditionally been underwhelming. This is related to several key issues including the preoperative assessment (keratometry) and intraocular lens power calculations. Peer-reviewed literature is overwhelmed by the influx of methodology to manipulate the corneal or intraocular lens (IOL) powers following refractive surgery. This would suggest that the optimal derivative formula has yet been introduced. This review discusses the problems facing surgeons approaching IOL calculations in these post-refractive laser patients, the existing formulae and programs to address these concerns. Prior published outcomes will be reviewed.

New Scheimpflug camera device in measuring corneal power changes after myopic laser refractive surgery

PURPOSE

To assess the accuracy of a combined Scheimpflug camera-Placido disk device (Sirius, CSO, Italy) in evaluating corneal power changes after myopic photorefractive keratectomy (PRK).

METHODS

Two hundred and thirty-seven eyes of 237 patients that underwent myopic PRK with a refractive error, measured as spherical equivalent, ranging from -10.75 D to -0.5D (mean -4.63 ± 2.21D), were enrolled in this study. Corneal power evaluation using Sirius were performed before, 1, 3 and 6 months after myopic PRK. Mean simulated keratometry (SimK) and mean pupil power (MPP) were measured. Correlations between changes in corneal power, measured with SimK and MPP, and variations in subjective refraction, calculated at corneal plane, were evaluated using Pearson test at every follow up; differences between preoperative and postoperative data were evaluated with the Student paired t-test.

RESULTS

A good correlation has been detected between the variations in subjective refraction measured at corneal plane 1, 3 and 6 months after myopic PRK and both SimK (R(2) = 0.8463; R(2) = 0.8643; R(2) = 0.7102, respectively) and MPP (R(2) = 0.6622; R(2) = 0.5561; R(2) = 0.5522, respectively) but corneal power changes are statistically undervalued for both parameters (p < 0.001).

CONCLUSIONS

Even if our data should be confirmed in further studies, SimK and MPP provided by this new device do not seem to accurately reflect the changes in corneal power after myopic PRK.

Intraocular lens power calculation by ray-tracing after myopic excimer laser surgery

PURPOSE

To investigate the refractive outcomes of intraocular lens (IOL) power calculation by ray-tracing after myopic excimer laser surgery.

DESIGN

Prospective, interventional case series.

METHODS

setting: Multicenter study. participants: Twenty-one eyes of 21 patients undergoing phacoemulsification and IOL implantation after myopic laser in situ keratomileusis or photorefractive keratectomy were enrolled. intervention: IOL power calculation was performed using internal software of a Scheimpflug camera combined with a Placido disc corneal topographer (Sirius; CSO). Exact ray-tracing was carried out after the axial length (measured either by immersion ultrasound biometry or partial coherence interferometry), target refraction, and pupil size had been entered. main outcome measures: Median absolute error, mean absolute error, and mean arithmetic error in refraction prediction, that is, the difference between the expected refraction (as calculated by the software) and the actual refraction 1 month after surgery.

RESULTS

The mean postoperative refraction was -0.43 ± 1.08 diopters (D), with a range between -1.28 and 0.85 D. The mean arithmetic error was -0.13 ± 0.49 D. The median and mean absolute errors were +0.25 D and 0.36 D, respectively. Also, 71.4% of the eyes were within ± 0.50 D of the predicted refraction, 85.7% were within ± 1.00 D, and 100% within ± 1.50 D.

CONCLUSIONS

Ray-tracing can calculate IOL power accurately in eyes with prior myopic laser in situ keratomileusis and photorefractive keratectomy, with no need for preoperative data.

Scheimpflug analysis of corneal power changes after myopic excimer laser surgery

PURPOSE

To assess the ability of corneal power measurements by a rotating Scheimpflug camera to measure the refractive change induced by myopic excimer laser surgery.

SETTING

G.B. Bietti Foundation-IRCCS, Rome, Italy.

DESIGN

Evaluation of diagnostic test.

METHODS

The following corneal power measurements by the Pentacam Scheimpflug camera were analyzed: average keratometry (K), true net power (calculated by Gaussian optics formula), and total corneal refractive power (TCRP) at 2.0 mm, 3.0 mm, and 4.0 mm, calculated by ray tracing on a ring and as the average of the zone inside the ring. The difference between the preoperative and postoperative values was compared with the subjective surgically induced refractive change (SIRC) and with the difference between the preoperative and the postoperative anterior corneal power measured by Placido corneal topography (Keratron).

RESULTS

In 36 consecutive eyes, the average K significantly underestimated the SIRC as determined by subjective refraction (-4.47 diopters [D] ± 1.81 [SD]) and corneal topography (-4.38 ± 1.81 D). The 3.0 mm and 4.0 mm ring total corneal refractive power significantly overestimated the SIRC. The remaining values did not show statistically significant differences with respect to the SIRC. The 3.0 mm zone TCRP and the 2.0 mm ring TCRP provided the lowest median difference compared with the SIRC (-0.07 D and -0.17 D, respectively) and the closest agreement.

CONCLUSIONS

The corneal power values provided by the Scheimpflug camera accurately reflected the SIRC after myopic excimer laser surgery. The best options seem to be the 3.0 mm zone TCRP and the 2.0 mm ring TCRP.

Comparison of methods to measure corneal power for intraocular lens power calculation using a rotating Scheimpflug camera

PURPOSE

To assess the accuracy of corneal power measurements provided by a Scheimpflug camera (Pentacam HR) for intraocular lens (IOL) power calculation in unoperated eyes and compare the results with those of simulated keratometry (SimK) performed with a Placido-disk corneal topographer (Keratron).

SETTING

Private practice.

DESIGN

Evaluation of diagnostic test.

METHODS

Eight Scheimpflug camera corneal power measurements were analyzed: (1) average K, (2) true net power calculated using the Gaussian optics formula, (3) total corneal refractive power at 2.0 mm calculated by ray tracing on a ring and (4) as the average of the zone inside the ring, (5) total corneal refractive power at 3.0 mm on a ring and (6) as the average of the zone inside the ring, (7) the equivalent K reading at 3.0 mm and (8) at 4.5 mm. The IOL power was calculated using the Hoffer Q, Holladay 1, and SRK/T formulas.

RESULTS

No statistically significant differences were observed between any corneal power measurements, including simulated K, in 41 consecutive patients. The latter showed slightly lower mean absolute errors with all 3 formulas (range 0.26 to 0.27 diopter [D]). The Scheimpflug camera gave the lowest median absolute errors with all formulas; that is, the 3.0 mm equivalent K reading with the Hoffer Q formula (0.18 D) and Holladay 1 formula (0.17 D) and the 2.0 mm total corneal refractive power ring with the SRK/T formula (0.18 D).

CONCLUSION

Corneal power measurements provided by the Scheimpflug camera and Placido disk corneal topographer displayed comparable accuracy in IOL power calculation.

Intraocular lens explantation technique for one-piece acrylic lenses

PURPOSE

To present a simple technique to remove a one-piece, acrylic AcrySof (Alcon Laboratories Inc) intraocular lens (IOL) via the original incision.

METHODS

The AcrySof IOL is removed via the original (2.75-mm) incision, without cutting or folding the IOL or widening the incision. After the IOL is viscodissected from the capsular bag and brought into the anterior chamber, toothed forceps hold the optic through the incision while the manipulator enters the side-port incision and hooks onto the optic 180° away.

RESULTS

With the forceps pulling and the lens manipulator pushing the IOL toward the incision, the IOL will fold and be delivered.

CONCLUSIONS

A one-piece, acrylic (Acrysof) IOL can be removed without cutting or folding the lens and without widening the original 2.75-mm incision.

Intraocular lens power calculation after previous myopic laser vision correction based on corneal power measured by Fourier-domain optical coherence tomography

PURPOSE

To use Fourier-domain optical coherence tomography (OCT) to measure corneal power and calculate intraocular lens (IOL) power in cataract surgeries after laser vision correction.

SETTING

Doheny Eye Institute, Los Angeles, California, and Cullen Eye Institute, Houston, Texas, USA.

DESIGN

Prospective comparative case series.

METHODS

Patients with previous myopic laser vision correction who had monofocal IOL implantation were enrolled. A Fourier-domain OCT system was used to measure corneal power and pachymetry. Axial length and anterior chamber depth were measured with partial coherence biometry. An OCT-based IOL formula was developed, and the mean absolution error (MAE) of postoperative refraction was compared with that for the Haigis-L formula. At Doheny, corneal power was also measured using the clinical history method, the contact lens overrefraction method, and slit-scanning tomography total optical power.

RESULTS

Sixteen eyes of 16 patients were enrolled at the 2 sites. Previous laser vision correction ranged from -9.81 to -0.88 diopter (D). The MAE was 0.50 D for OCT-based IOL calculation and 0.76 D for the Haigis-L formula (P=.14). In the 6 eyes enrolled at Doheny, the MAE of OCT-based IOL calculation was 0.60 D. In comparison, the contact lens overrefraction (MAE = 1.46 D, P<.05) and clinical history (MAE = 1.78 D, P<.05) methods were worse. Slit-scanning tomography gave an MAE of 1.28 D (P>.05).

CONCLUSION

The predictive accuracy of OCT-based IOL power calculation was equal to or better than current standards in post-laser vision correction eyes.

Clinically relevant biometry

PURPOSE OF REVIEW

Obtaining precise postoperative target refraction is of utmost importance in today's modern cataract and refractive surgery. Given the growing number of patients undergoing premium intraocular lens (IOL) implantations, patient expectation continues to rise. In order to meet heightened patient expectations, it is crucial to pay utmost attention to patient selection, accurate keratometry and biometry readings, as well as to the application of correct IOL power formula with optimized lens constants. This article reviews recent advances in the field of clinical biometry and IOL power calculations.

RECENT FINDINGS

Recently developed low-coherence reflectometry optical biometry is comparable to older ultrasonic biometric and keratometric techniques. In addition, the new IOLMaster software upgrade has improved reproducibility and enhanced signal acquisition. Further, the modern lens power formulas currently determine the effective lens position and the shape of the intraocular lens power prediction curve more accurately.

SUMMARY

In order to reach target refraction, precise biometric measurements are imperative. Understanding the strengths and limitations of the currently available biometry devices allows prevention of high variability and inaccuracy, ultimately determining the refractive outcomes.

Intraocular lens power calculation after myopic and hyperopic laser vision correction using optical coherence tomography

PURPOSE

To use optical coherence tomography (OCT) to measure corneal power and calculate intraocular lens (IOL) power in cataract surgeries after myopic and hyperopic laser vision correction (LVC).

METHODS

Patients with previous LVC were enrolled in this prospective study at two centers (Doheny Eye Institute, Los Angeles, CA, USA and Cullen Eye Institute, Houston, TX, USA). Corneal power was measured with a Fourier-domain OCT system. The intravisit repeatability of OCT corneal power measurement was evaluated by the pooled standard deviation of repeat scans. Axial length, anterior chamber depth, and automated keratometry were measured with the IOLMaster. An OCT-based IOL formula was developed. The mean absolute error (MAE) of refractive prediction for OCT-based IOL formula was calculated. The results were compared with the MAE for Haigis-L formula.

RESULTS

A total of 31 eyes of 24 subjects who had uncomplicated cataract surgery with monofocal IOL implantation were enrolled in the two sites. Twenty-two eyes of 16 subjects had previous myopic LVC that ranged from -12.46 D to -0.88 D. Nine eyes of 8 subjects had previous hyperopic LVC that ranged from 0.66 D to 5.52 D. The intravisit repeatability of OCT corneal power measurement was 0.24 D. For the myopic LVC group, the OCT formula had a MAE of 0.57 D compared to an MAE of 0.73 D for the Haigis-L formula (p = 0.19). For the hyperopic LVC group, the MAE for OCT and Haigis-L formula was 0.26 D and 0.54 D, respectively (p > 0.05).

CONCLUSIONS

Corneal power can be precisely measured with OCT. The predictive accuracy of OCT-based IOL power calculation is equal to current standards for post-LVC eyes.