Visual Quality Assessment After FS-LASIK Using Customized Aspheric Ablation Profile for Age-Related Accommodation Deficiency Compensation.

PURPOSE: To evaluate clinical outcomes and visual quality 12 months after femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) performed with the Custom-Q algorithm for correction of myopia with or without astigmatism and compensate for age-related accommodation deficiency. METHODS: Patients who had Custom-Q FS-LASIK for myopia and myopic astigmatism with age-related accommodation deficiency were included in this retrospective study. Distance, intermediate, and near visual acuities, objective and subjective refractions, Q-factor, corneal higher order aberrations (HOAs), accommodation function, defocus curve, contrast sensitivity, and a subjective questionnaire assessing visual quality were evaluated 12 months postoperatively. RESULTS: Clinical data of 43 cases were analyzed. The mean age was 42.02 ± 1.85 years (range: 40 to 48 years). At the 12-month follow-up visit, there were 43 (100%), 42 (97%), and 33 (77%) patients who achieved a binocular uncorrected distance, intermediate, and near visual acuity, respectively, better than 20/20 separately. Defocus curves revealed better distance vision in the dominant eyes, and the nondominant eyes performed better at intermediate and near vergence (P < .001). The Q-value and corneal spherical aberration coefficient were more positive in the dominant eyes than those in the nondominant eyes (P < .001). The accommodative amplitude and relative accommodation improved binocularly (P < .001). The questionnaire demonstrated high patient satisfaction with near vision, and no one reported having severe visual disturbance. CONCLUSIONS: For myopic patients with age-related accommodation deficiency, the Custom-Q algorithm proved to be an effective way to achieve acceptable near vision without compromising distance vision. [J Refract Surg. 2024;40(4):e245-e252.].

[Comparative assessment of the accuracy of toric intraocular lens calculations]. / Sravnitel'naya otsenka tochnosti rascheta toricheskikh intraokulyarnykh linz.

PURPOSE: To compare the accuracy of toric intraocular lens (IOL) calculations on three modern toric calculators. MATERIAL AND METHODS: The study comprised 35 eyes of 35 patients who underwent phacoemulsification with toric IOL implantation (EnVista Toric). Residual postoperative refractive astigmatism was calculated on three calculators: EnVista Toric Calculator, ASSORT Toric IOL Calculator and the Kane formula. Prediction error for each calculator was determined using vector analysis. RESULTS: The mean absolute deviation of predicted postoperative refractive astigmatism over actual astigmatism in diopters was distributed in the following way: 0.82±0.58, 0.70±0.67 and 0.72±0.76 using EnVista Toric Calculator, ASSORT Toric IOL Calculator and the Kane formula, respectively. Centroid prediction error was 0.08 (EnVista Toric Calculator), 0.06 (ASSORT) and 0.10 (Kane formula). There was a significantly smaller deviation using ASSORT and the Kane formula compared to the online calculator (p<0.05). CONCLUSIONS: Toric calculators ASSORT Toric IOL Calculator and the Kane formula showed higher accuracy of toric IOL calculation than EnVista Toric Calculator.

Assessment of Refractive Outcome of Photo Refractive Keratectomy in Myopia and Myopic Astigmatism.

OBJECTIVES: To determine the refractive outcomes of wavefront optimized photo refractive keratectomy (PRK) in patients having myopia and myopic astigmatism in terms of efficacy, safety, accuracy, stability and predictability of the procedure. STUDY DESIGN: Quasi-experimental study. PLACE AND DURATION OF STUDY: Refractive Surgical Unit, Armed Forces Institute of Ophthalmology, National University of Medical Sciences, Rawalpindi, Pakistan, from October 2013 to August 2018. METHODOLOGY: Patients having myopia and myopic astigmatism, consented to be a part of the study, underwent meticulous screening consisting of detailed medical history, ocular examination and investigations. Each case was compiled and evaluated. Those who satisfied the criteria for refractive surgery were subjected to PRK procedure. Postoperative follow-up was carried out and parameters were recorded at designated intervals of 1 week, 1, 3, 6 and 12 months. RESULTS: This study included 208 eyes of 106 patients with mean age of 25.33 + 5.196 years. At the end of one year, 97% (202 out of 208) eyes had uncorrected distance visual acuity (UDVA) better than 20/25 with efficacy index of 1.009 ± 0.132 and safety index of 1.019 ± 0.126. None of the eyes lost two or more lines. In this study, 207 out of 208 eyes remained within + 0.50 diopter (D) of intended spherical equivalent (SEQ). Results showed 100% accuracy of procedure since all the study patients achieved SEQ within + 1D. CONCLUSION: PRK is an effective, predictable, and safe treatment procedure for correcting myopia and myopic astigmatism. Key Words: Photorefractive keratectomy, Myopia, Refractive surgery, Myopic astigmatism, Uncorrected distance visual acuity.

Ratio of torus and equivalent power to refractive cylinder and spherical equivalent in phakic lenses - a Monte-Carlo simulation study.

BACKGROUND: Spherical and astigmatic powers for phakic intraocular lenses are frequently calculated using fixed ratios of phakic lens refractive power to refractive spherical equivalent, and of phakic lens astigmatism to refractive cylinder. In this study, a Monte-Carlo simulation based on biometric data was used to investigate how variations in biometrics affect these ratios, in order to improve the calculation of implantable lens parameters. METHODS: A data set of over sixteen thousand biometric measurements including axial length, phakic anterior chamber depth, and corneal equivalent and astigmatic power was used to construct a multidimensional probability density distribution. From this, we determined the axial position of the implanted lens and estimated the refractive spherical equivalent and refractive cylinder. A generic data model resampled the density distributions and interactions between variables, and the implantable lens power was determined using vergence propagation. RESULTS: 50 000 artificial data sets were used to calculate the phakic lens spherical equivalent and astigmatism required for emmetropization, and to determine the corresponding ratios for these two values. The spherical ratio ranged from 1.0640 to 1.3723 and the astigmatic ratio from 1.0501 to 1.4340. Both ratios are unaffected by the corneal spherical / astigmatic powers, or the refractive cylinder, but show strong correlation with the refractive spherical equivalent, mild correlation with the lens axial position, and moderate negative correlation with axial length. As a simplification, these ratios could be modelled using a bi-variable linear regression based on the first two of these factors. CONCLUSION: Fixed spherical and astigmatic ratios should not be used when selecting high refractive power phakic IOLs as their variation can result in refractive errors of up to ±0.3 D for a 8 D lens. Both ratios can be estimated with clinically acceptable precision using a linear regression based on the refractive spherical equivalent and the axial position.

Time-efficiency assessment of guided toric intraocular lens cataract surgery: pilot study.

PURPOSE: To compare the time spent on toric intraocular lens (IOL) implantation during cataract surgery using a manual-marking vs a digital image-guided system (t Verion) for toric IOL alignment. SETTING: Instituto Oftalmológico Quirónsalud ophthalmology clinic, A Coruña, Spain. DESIGN: Experimental and longitudinal study. METHODS: A total of 98 eyes of 65 participants (68.2 ± 12.2 years) were divided into 2 groups: 49 eyes operated with toric IOL alignment using a manual-marking technique (manual group) and another 49 eyes operated using image-guided marking (Verion group). The primary variable for comparison between both groups was cataract surgery time. Other outcomes such as toric IOL misalignment, spherical equivalent, astigmatism, uncorrected distance visual acuity, and corrected distance visual acuity were also measured. RESULTS: The total cataract surgery time was 2:09 minutes shorter (P < .001) with the Verion system (12:12 ± 2:20 in 49 eyes operated) compared with the surgical procedure performed using manual marking (15:27 ± 3:04 in 49 eyes operated). One month after surgery, there were no statistical differences in terms of toric IOL misalignment between the Verion (3.38 ± 2.95 degrees) and the manual group (4.66 ± 3.95 degrees). No statistical differences were observed between groups for refractive and visual outcomes (P ≥ .05). CONCLUSIONS: The cataract surgery time was reduced when the procedure was assisted using the Verion system to align the IOL compared with manual marking, maintaining the same efficacy in terms of toric IOL misalignment, residual refraction, and visual acuity.

Assessment of a software guided system to reduce pre-existing astigmatism in cataract surgery.

The aim of this pilot study was to assess the astigmatism after small incision cataract surgery by use of a novel software guided surgical technique. The software system guides the surgeon toward a hypothetical shape of the cornea. When this shape is achieved, the vertical meridian is relaxed and the incision does not produce any astigmatism. How that hypothetical shape is to be achieved by the surgeon is described. If preoperative astigmatism exists, the hypothetical shape calculated by the system takes that into account. This enables the surgeon to reduce preexisting astigmatism, without having to change the site or size of the standard 6 mm 12 o clock incision of SICS. Results: Results indicated that preoperative astigmatism reduced in 11 out of 14 cases at the end of 8 weeks, remained unchanged in one, and increased by less than 0.5D in two cases. This proves the hypothesis that the vertical corneal meridian is under higher tension and relaxing it by flattening the perpendicular meridian has a reducing effect on postoperative astigmatism.

[Monte Carlo simulation of biometric effect sizes and their influence on the translational ratio of corneal astigmatism in the cylinders of toric intraocular lenses]. / Monte-Carlo-Simulation biometrischer Effektgrößen und deren Einfluss auf das Übersetzungsverhältnis des Hornhautastigmatismus in den Zylinder torischer Intraokularlinsen.

BACKGROUND AND OBJECTIVE: Toric intraocular lenses (IOL) provide a reliable and predictable option for permanent correction of corneal astigmatism. In order to determine the lens strength necessary for achieving the desired correction, the operator can either use the calculation mode implemented in the biometry device or the calculation service offered by the lens manufacturer; however, in many cases a classical lens calculation from biometric data is not carried out but only a simplified estimation, which translates the corneal astigmatism into the torus of the toric IOL. This translational ratio, which is mostly used as an average standard value, can however show a substantial range of variation, so that in a worst case scenario an undercorrection of the refractive cylinder of up to 12.5 % or an overcorrection of up to 17 % can result. The purpose of this study was to elaborate the biometric effect sizes which determine the relationship between the corneal astigmatism to be corrected and the torus necessary for a full correction of an IOL. METHODS: A total of 16,744 datasets were extracted from the IOLCon web platform and initially the axial position of the IOL implant was derived independent of a formula, based on the preoperative biometric values and the postoperative spherical equivalent. Subsequently, based on a ray propagation strategy for spherocylindrical vergences, the corresponding refractive value of a full correcting toric IOL was calculated. The translational relationship as a ratio between lens toricity and corneal astigmatism was analyzed for potential biometric effect sizes with a Monte Carlo simulation. RESULTS: The Monte Carlo simulation showed that the ratio of lens toricity to corneal astigmatism cannot be assumed as being constant. The analyzed data revealed an average translational ratio of 1.3938 ± 0.0595 (median 1.3921) with a range from 1.2131 to 1.5974. The axial position of the IOL was found to have the greatest influence, whereby the more posterior the lens position the higher the ratio. Due to the correlation of axial eye length and axial lens position, the eye length can be assumed to be an indirect effect size. The corneal equivalent refractive strength and the corneal astigmatism have no noteworthy effect on the translational ratio. CONCLUSION: Many calculation tools on the market simplify toric IOL power calculation by assuming a constant ratio of lens toricity to corneal astigmatism; however, the present simulation study showed that such a simplification can lead to clearly incorrect results. Accordingly, an individual calculation of IOL toricity based on biometric parameters (e.g. based on vergence propagation matrices or full aperture ray tracing) is recommended.

Management of Suction Loss During SMILE in 12,057 Eyes: Incidence, Outcomes, Risk Factors, and a Novel Method of Same-Day Recutting of Refractive Lenticules.

PURPOSE: To determine the incidence, management, outcomes, and risk factors of suction loss during femtosecond laser small incision lenticule extraction (SMILE) for the treatment of myopia and myopic astigmatism. METHODS: The study reviewed 12,057 consecutive eyes treated with SMILE. Eyes that developed suction loss (study group) or underwent uneventful SMILE (control group) were analyzed. Corneal topography, manifest refractions, and measurements of uncorrected (UDVA) and corrected (CDVA) distance visual acuities were evaluated preoperatively and postoperatively after 1 day and 12 months. Risk factors were determined for suction loss development. RESULTS: Twenty-seven of 12,057 eyes (0.22%) were enrolled in the study group and 50 eyes in the control group. Suction loss occurred in 14 eyes during the cutting of the refractive lenticule, 7 eyes during the cutting of the cap, and 6 eyes during the creation of the cap small incision. There was no statistically significant difference between the two groups in logMAR UDVA (P = .52) or CDVA (P = .59). A novel method of increasing cap thickness was applied to 8 eyes when suction loss occurred after more than 10% of the lenticule was cut. The eye being operated on first (the right eye) (P = .02) and a thinner lenticule (P = .006) were associated with a significantly higher risk of developing suction loss. CONCLUSIONS: The incidence of suction loss was low. The novel method achieved visual and refractive outcomes as favorable as those of uneventful SMILE procedures. The first eye that was operated on had a higher risk for the development of suction loss. [J Refract Surg. 2020;36(5):308-316.].

SMILE With Low Energy Levels: Assessment of Early Visual and Optical Quality Recovery.

PURPOSE: To assess early visual and optical quality recovery according to preoperative refraction after small incision lenticule extraction (SMILE) at low energy level for myopia and myopic astigmatism treatment. METHODS: This prospective study included 101 eyes of 101 patients separated into three groups: low myopia (30 eyes), with a mean spherical equivalent (SE) of -2.13 ± 0.73 diopters (D); moderate myopia (33 eyes), with a mean SE of -4.53 ± 0.86 D; and high myopia (38 eyes), with a mean SE of -6.54 ± 0.78 D. Visual acuity, contrast sensitivity, refraction, corneal higher order aberrations, modulation transfer function, Strehl ratio, and Objective Scatter Index (OSI) were measured. RESULTS: All eyes had a corrected distance visual acuity of 20/20 or better at 1 day in the low myopia group and 1 month in the moderate and high myopia groups. The contrast sensitivity preoperative values recovered at 8 days in the low myopia group and 1 month in the moderate and high myopia groups. At 1 month, the low myopia group recovered the OSI preoperative values (0.61 to 0.69) and the OSI values were slightly higher than the preoperative value in the moderate and high myopia groups (0.74 to 1.00 and 0.8 to 1.14, respectively). CONCLUSIONS: The recovery time of visual and optical quality in the first month after SMILE correlated with preoperative refraction and the amount of postoperative scattering. Patients with low myopia recovered visual acuity faster and with less ocular scattering than patients with moderate or high myopia. [J Refract Surg. 2019;35(5):285-293.].

Health policy regulations pertaining to advanced surgical devices-their socio-economic effects on ophthalmology practice.

The Israel Ministry of Health enacted regulations that aim to reduce private expenditure on healthcare services and mitigate social inequality. According to the modified rules, which went into effect in the second half of 2016, patients who undergo surgery in a private hospital and are covered by their healthcare provider's supplemental insurance (SI) make only a basic co-payment.The modified regulations limited the option of self-payment for advanced devices not covered by national health basket, meaning that patients for whom such devices are indicated had to pay privately for the entire procedure. These regulations applied to all medical and surgical devices not covered by national health insurance (NHI).Toric intraocular lenses (IOLs) are a case in point. These advanced lenses are implanted during cataract surgery to correct corneal astigmatism and, in indicated cases, obviate the need for complex eyeglasses postoperatively. Toric IOL implantation has been shown to be highly cost-effective in both economic and quality-of-life terms. Limitations of the use of these advanced IOLs threatened to increase social inequality.In 2017, further adjustments of the regulations were made which enabled supplemental charges for these advanced IOLs, performed through the SI programs of the healthcare medical organizations (HMOs). Allowing additional payment for these lenses at a fixed pre-set price made it possible to apply a supplemental part of the insurance package to the surgery itself. In mid 2018 these IOLs were included without budget in the national health basket, allowing for self-payment for the additional cost in addition to the basic coverage for all patients with NHI.This case study suggests that, in their efforts to enhance health care equity, policymakers may benefit if exercising due caution when limiting the extent to which SI programs can charge co-payments. This is because, when a service or product is not available via the basic NHI benefits package, limiting SI co-payments can sometimes result in a boomerang effect - leading to an increase in inequality rather than the sought-after decrease in inequality.

Trial-based cost-effectiveness analysis of toric versus monofocal intraocular lenses in cataract patients with bilateral corneal astigmatism in the Netherlands.

PURPOSE: To evaluate the cost-effectiveness of toric versus monofocal intraocular lens (IOL) implantation in cataract patients with bilateral corneal astigmatism. SETTING: Two ophthalmology clinics in the Netherlands. DESIGN: Prospective cost-effectiveness analysis. METHODS: Resource-use data were collected over a 6-month postoperative period. Consecutive patients with bilateral age-related cataract and 1.25 diopters or more of corneal astigmatism were included in the economic evaluation. Patients were randomized to phacoemulsification with bilateral toric or monofocal IOL implantation. All relevant resources were included in the cost analysis. The base-case analysis was performed from a societal perspective based on quality-adjusted life years (QALYs). The main outcome was the incremental cost-effectiveness ratio. RESULTS: The analysis comprised 77 consecutive patients (33 toric IOL; 44 monofocal IOL). Societal costs were higher in the toric IOL group (€3203 [$3864]) than in the monofocal IOL group (€2796 [US$3373]). QALYs were slightly lower in the toric IOL group (0.30 versus 0.31; P = .75). Toric IOLs were therefore inferior to monofocal IOLs from a cost-effectiveness perspective. The cost-effectiveness probability ranged from 1% to 15%, assuming a ceiling ratio for the incremental cost-effectiveness ratio of €2500 to €20 000 per QALY. CONCLUSIONS: From a societal perspective, bilateral toric IOL implantation in cataract patients with corneal astigmatism was not cost-effective compared with monofocal IOL implantation. Copayment by patients should therefore be considered.

Incidence and management of intraoperative complications during small-incision lenticule extraction in 3004 cases.

PURPOSE: To assess the intraoperative complications during small-incision lenticule extraction (SMILE) for myopia and myopic astigmatism correction and evaluate visual outcomes 6 months postoperatively. SETTING: Tianjin Eye Hospital, Tianjin, China. DESIGN: Retrospective case series. METHODS: Patients who had small-incision lenticule extraction surgery were examined 1 day, 7 days, 1 month, 3 months, and 6 months postoperatively. Demographic characteristics, visual outcomes, and intraoperative complications were recorded. Moreover, the incidence and management of the complications and the potential factors were analyzed. RESULTS: Of the 3004 eyes (1511 patients), 134 (4.46%) had intraoperative complications, including suction loss (28 cases [0.93%]), incisional bleeding (28 cases [0.93%]), opaque bubble layer (22 cases [0.73%]), subconjunctival hemorrhage (20 cases [0.67%]), black areas (10 cases [0.33%]), unintended posterior plane dissection (10 cases [0.33%]), tearing of the lenticule (8 cases [0.27%]), abrasion at the incision (5 cases [0.17%]), and inaccurate laser pulse placement due to eye movement (3 cases [0.10%]). The complications were resolved instantaneously using appropriate management procedures; all cases had good visual outcomes. Six months postoperatively, 99.80% of cases had an uncorrected distance visual acuity better than 20/25 and the mean corrected distance visual acuity was -0.06 logarithm of the minimum angle of resolution ± 0.07 (SD). CONCLUSIONS: Although small-incision lenticule extraction shows promising outcomes for correction of myopia and myopic astigmatism, intraoperative complications still inevitably occur. However, satisfactory visual outcomes may be achieved using appropriate management techniques.

Measurement of visual function among patients undergoing corneal transplantation using the VF-14 index in Morocco.

OBJECTIVE: To validate the Moroccan version of the VF-14 in candidates for keratoplasty and to assess their quality of life using this tool before and after transplantation. METHODS: This is a longitudinal prospective study that assessed 57 patients who underwent penetrating keratoplasty, recruited in the ophthalmology service in Marrakech over 5 years. The original VF-14 questionnaire was adapted into Moroccan dialect. The questionnaire was administered before and 2 years after transplantation. The VF-12 questionnaire was also used, deleting the last two items. Data analysis was performed using SPSS 16.0 software. Comparisons of VF-14 scores before and after transplantation used the Wilcoxon test for paired samples. RESULTS: In total, 57 patients participated in the study. The most frequent indication for surgery was keratoconus (44%). All patients underwent penetrating keratoplasty. Chronbach's alpha value was 0.989 for VF-14 and 0.990 for VF-12. The two scores were negatively correlated with logMAR visual acuity. The strongest correlation was found with VA in the fellow eye. The average best-corrected visual acuity of the eye scheduled for keratoplasty was 1.1±0.16 logMAR. The average of VF-14 was 53±3. After keratoplasty, the average best-corrected visual acuity of operated eye was 0.34±0.31. The average postoperative astigmatism was 3 D. After keratoplasty, an increase in VF-14 score was observed from 53.5 to 81.92 (P<0.001). In postoperative follow-up, graft rejection was noted in two patients and maculopathy in a single patient. DISCUSSION: Graft transparency, absence of complications, minimal astigmatism, and good visual acuity have long been indicators of a successful corneal transplant. However, this does not provide information on visual quality and its impact on everyday life. It is in this sense that the VF-14 was adapted into several languages, as reliable, valid and sensitive as the original Anglo-American version, to assess objectively and subjectively the quality of life of patients after keratoplasty. CONCLUSION: With advances in techniques and availability of better materials, surgical success in performing keratoplasty is increasing. At the same time, vision-related quality of life of corneal graft recipients deserves more attention from ophthalmologists.

The assessment of the stability of the corneal structure after LASIK correction of myopia by different optical zone diameters.

BACKGROUND/AIM: Enlargement of optical zone (OZ) diameter during laser in situ keratomileusis (LASIK) correction of myopia postoperatively improves the optical outcome, however, it also leads to the increased stroma tissue consumption--progressive corneal thinning. The aim of this investigation was to present the possibility of safe OZ enlargement without impairing the structural stability of the cornea, while obtaining an improved optical outcome with LASIK treatment of short-sightedness. METHODS: Preoperative assessment of the cornea structure and prediction of the ablated stroma tissue consumption was conducted in 37 patients (74 eyes) treated for short-sightedness by means of the LASIK method. With the eyes that, according to their cornea structure, had the capacity for OZ diameter enlargement of 0.5 mm, LASIK treatment was performed within the wider OZ diameter of 7.0 mm compared to the standard 6.5 mm. The following two groups were formed, depending on the diameter of the utilized OZ: the group I (the eyes treated with the OZ 6.5 mm, n = 37) and the group II (the eyes treated with the OZ 7.0 mm, n = 37). RESULTS: No significant difference in the observed structural parameters of the cornea was detected between the groups of patients treated with different OZ diameters. The values of all the parameters were significantly bellow the threshold values for the development of postoperative ectasia. CONCLUSION: Diameter enlargement of the treated OZ, if there is a preoperative cornea capacity for such enlargement, will not impair the postoperative stability of the cornea structure, and will significantly improve the optical outcome.

Assessment of subjective intraocular forward scattering and quality of vision after posterior chamber phakic intraocular lens with a central hole (Hole ICL) implantation.

PURPOSE: To evaluate the subjective intraocular forward scattering and quality of vision after posterior chamber phakic intraocular lens with a central hole (Hole ICL, STAAR Surgical) implantation. METHODS: We prospectively examined 29 eyes of 29 consecutive patients (15 men and 14 women; ages, 37.2 ± 8.8 years) undergoing Hole ICL implantation. We assessed the values of the logarithmic straylight value [log (s)] using a straylight meter (C-Quant™ , Oculus) preoperatively and 3 months postoperatively. The patients completed a questionnaire detailing symptoms on a quantitative grading scale (National Eye Institute Refractive Error Quality of Life Instrument-42; NEI RQL-42) 3 months postoperatively. We compared the preoperative and postoperative values of the log(s) and evaluated the correlation of these values with patient subjective symptoms. RESULTS: The mean log(s) was not significantly changed, from 1.07 ± 0.20 preoperatively, to 1.06 ± 0.17 postoperatively (Wilcoxon signed-rank test, p = 0.641). There was a significant correlation between the preoperative and postoperative log(s) (Spearman's correlation coefficient r = 0.695, p < 0.001). The postoperative log(s) was significantly associated with the scores of glare in the questionnaire (Spearman's correlation coefficient r = -0.575, p = 0.017). CONCLUSIONS: According to our experience, Hole ICL implantation does not induce a significant additional change in the subjective intraocular forward scattering. The symptom of glare after Hole ICL implantation was significantly correlated with the postoperative intraocular forward scattering in relation to the preoperative one.

Correction of low levels of astigmatism.

PURPOSE: To reevaluate the analysis of the correction of astigmatism. SETTING: Academia, industry, and private practice. DESIGN: Evaluation of diagnostic test or technology. METHODS: Astigmatic refractive surgery outcomes are based on vector methods, including the correction index (also known as the correction ratio), which is the ratio of the surgically induced astigmatism to the target induced astigmatism (TIA). Mean correction indices substantially greater than 1 have been reported for astigmatic corrections less than 1.00 diopter (D) and as representing systematic overcorrection. We hypothesize that this reflects a limitation of the correction index rather than systematic flaws in treatments. The theoretical mathematic behavior of the correction index was analyzed, accounting for variability in astigmatism measurement. Then, the impact of cylinder measurement variability on the mean correction index was modeled. A Monte Carlo simulation was performed and calculated 10 000 values of correction index for various values of TIA. Finally, correction indices from published and unpublished studies of refractive lasers were compared with the simulations. RESULTS: The mean correction index is always greater than 1 for the case of a perfect refractive correction; however, for astigmatic corrections less than 1.00 D, the mean correction index increases sharply because the measurement variability is similar in magnitude to TIA. Almost all previous studies show the predicted increase in the correction index for low astigmatic corrections. CONCLUSION: The correction index is a useful vector-based metric for the evaluation of refractive procedures, but mean values greater than 1 should be anticipated for lower astigmatic treatments and do not necessarily represent systematic overcorrection. FINANCIAL DISCLOSURE: Dr. Bullimore is a consultant to Alcon Surgical, Inc., Carl Zeiss Meditec AG, Digital Vision Systems, Essilor, Innovega, Inc., and Paragon Vision Sciences, Inc. Dr. Spooner is a consultant to Alcon Surgical, Inc., Carl Zeiss Meditec AG, Digital Vision Systems, Thru-Focus Optics LLC, and i2eyediagnostics, Ltd. Dr. Dishler is a consultant to Carl Zeiss Meditec AG and Revision Optics, Inc. Dr. Sluyterman is an employee of Carl Zeiss Meditec AG.

Comparison of 3 marking techniques in preoperative assessment of toric intraocular lenses using a wavefront aberrometer.

PURPOSE: To assess the accuracy of 3 corneal horizontal meridian marking techniques using the iTrace Surgical Workstation in preoperative assessment for toric intraocular lens (IOL) implantation. SETTING: Department of Ophthalmology, Yonsei University College of Medicine, Seoul, South Korea. DESIGN: Prospective comparative observational study. METHODS: Patients were allocated into 3 groups. Three techniques-marking with a nonpendular marker with a surgeon's direct visualization, slitlamp-assisted marking with a pendulum-attached marker, and slitlamp-assisted marking with a horizontal slit beam-were used to perform the horizontal meridian marking. The marks were immediately documented and aligned with the Zaldivar toric caliper transparent topographic map. Using a horizontal reference meridian determined by the toric caliper, the accuracy of corneal horizontal marking techniques was quantitatively evaluated by determining the rotational deviation and vertical misalignment. RESULTS: For rotational deviation, the pendular marking showed the fewest errors to the horizontal reference meridian (mean error -0.66 degrees; mean absolute error [MAE] 3.77 degrees). There was a significant difference between the pendular marking and the surgeon's direct visual marking. For the MAE, the pendular marking showed less deviation than the surgeon's direct visual marking and the horizontal slit-beam marking. With vertical misalignment, there was no significant difference between the 3 different corneal horizontal meridian marking techniques. CONCLUSION: The slitlamp-assisted technique with the pendulum-attached marker was more precise than marking with a nonpendular marker with a surgeon's direct visualization and marking with a horizontal slit beam in preoperative assessment for toric IOLs. FINANCIAL DISCLOSURE: No author has a financial or proprietary interest in any material or method mentioned.

Macroeconomic landscape of refractive surgery in the United States.

PURPOSE OF REVIEW: This review examines the economic history of refractive surgery and the decline of laser-assisted in-situ keratomileusis (LASIK) in the USA, and the emergence of refractive cataract surgery as an area of growth. RECENT FINDINGS: Since it peaked in 2007 at 1.4 million procedures per year, LASIK has declined 50% in the USA, whereas refractive cataract surgery, including presbyopia-correcting intraocular lenses (IOLs), astigmatism-correcting IOLs, and femtosecond laser-assisted cataract surgery, has grown to 350 000 procedures per year, beginning in 2003. SUMMARY: Patients are price-sensitive and responsive to publicity (good or bad) about refractive surgery and refractive cataract surgery. LASIK's decline has been partially offset by the emergence of refractive cataract surgery. About 11% of all cataract surgery in the USA involves presbyopia-correcting IOLs, astigmatism-correcting IOLs, or a femtosecond laser. From the surgeon's perspective, there are high barriers to entry into the marketplace for refractive surgery and refractive cataract surgery due to the high capital cost of excimer and femtosecond lasers, the high skill level required to deliver spectacular results to demanding patients who pay out of pocket, and the necessity to perform a high volume of surgeries to satisfy both of these requirements. Probably, less than 7% of US cataract surgeons can readily meet all of these requirements.