Myopic Corneal Refractive Surgery Research Articles

Bibliometric and visualized analysis of myopic corneal refractive surgery research: from 1979 to 2022.

Myopic corneal refractive surgery is one of the most prevalent ophthalmic procedures for correcting ametropia. This study aimed to perform a bibliometric analysis of research in the field of corneal refractive surgery over the past 40 years in order to describe the current international status and to identify most influential factors, while highlighting research hotspots. A bibliometric analysis based on the Web of Science Core Collection (WoSCC) was used to analyze the publication trends in research related to myopic corneal refractive surgery. VOSviewer v.1.6.10 was used to construct the knowledge map in order to visualize the publications, distribution of countries, international collaborations, author productivity, source journals, cited references, keywords, and research hotspots in this field. A total of 4,680 publications on myopic corneal refractive surgery published between 1979 and 2022 were retrieved. The United States has published the most papers, with Emory University contributing to the most citations. The Journal of Cataract and Refractive Surgery published the greatest number of articles, and the top 10 cited references mainly focused on outcomes and wound healing in refractive surgery. Previous research emphasized "radial keratotomy (RK)" and excimer laser-associated operation methods. The keywords containing femtosecond (FS) laser associated with "small incision lenticule extraction (SMILE)" and its "safety" had higher burst strength, indicating a shift of operation methods and coinciding with the global trends in refractive surgery. The document citation network was clustered into five groups: (1) outcomes of refractive surgery: (2) preoperative examinations for refractive surgery were as follows: (3) complications of myopic corneal refractive surgery; (4) corneal wound healing and cytobiology research related to photorefractive laser keratotomy; and (5) biomechanics of myopic corneal refractive surgery. The bibliometric analysis in this study may provide scholars with valuable to information and help them better understand the global trends in myopic corneal refractive surgery research frontiers. Two stages of rapid development occurred around 1991 and 2013, shortly after the innovation of PRK and SMILE surgical techniques. The most cited articles mainly focused on corneal wound healing, clinical outcomes, ocular aberration, corneal ectasia, and corneal topography, representing the safety of the new techniques.

Comparing Standard Keratometry and Total Keratometry Before and After Myopic Corneal Refractive Surgery With a Swept-Source OCT Biometer.

BackgroundMore recently, the swept-source OCT biometer-IOLMaster 700 has provided direct total corneal power measurement, named total keratometry. This study aims to evaluate whether standard keratometry (SK) and total keratometry (TK) with IOLMaster 700 can accurately reflect the corneal power changes induced by myopic corneal refractive surgery.MethodsIn this study, the biometric data measured with the swept-source OCT biometer—IOLMaster 700 before and 3 months after the myopic corneal refractive surgery were recorded. The changes of biological parameters, including SK, posterior keratometry (PK), and TK, and the difference between SK and TK were compared. In addition, the changes of SK and TK induced by the surgery were compared with the changes of spherical equivalent at the corneal plane (ΔSEco).ResultsA total of 74 eyes (74 patients) were included. The changes of SK, PK, TK, axial length, anterior chamber depth, and lens thickness after refractive surgery were all statistically significant (all p < 0.01), while the change of white-to-white was not (p = 0.075). The difference between SK and TK was −0.03 ± 0.10D before the corneal refractive surgery and increased to −0.78 ± 0.26D after surgery. The changes of SK and the changes of TK induced by the surgery had a good correlation with the changes of SEco (r = 0.97). ΔSK was significantly smaller than ΔSEco, with a difference of −0.65 ± 0.54D (p < 0.01). However, the difference between ΔTK and ΔSEco (0.10 ± 0.50D) was not statistically significant (p = 0.08).ConclusionsUsing SK to reflect the changes induced by the myopic corneal refractive surgery may lead to underestimation, while TK could generate a more accurate result. The new parameter, TK, provided by the IOLMaster 700, appeared to provide an accurate, objective measure of corneal power that closely tracked the refractive change in corneal refractive surgery.

Prediction accuracy of no-history intraocular lens formulas for a diffractive extended depth-of-focus intraocular lens after myopic corneal refractive surgery.

To compare the accuracy of intraocular lens (IOL) calculation methods for extended depth-of-focus (EDoF) IOLs in eyes with a history of myopic laser-assisted in situ keratomileusis (LASIK)/photorefractive keratectomy (PRK) surgery lacking historical data. Changsha Aier Eye Hospital, Changsha, and Wuhan Aier Eye Hospital, Wuhan, China. Retrospective case series. Patients with axial lengths (ALs) ≥25.0 mm and a history of myopic LASIK/PRK surgery who underwent cataract surgery with implantation of EDoF IOLs were enrolled. A comparison was performed of the accuracy of 10 IOL methods lacking historical data, including Barrett True-K no history (Barrett TKNH), Haigis-L, Shammas, and Potvin-Hill formulas and average, minimum, and maximum IOL power on the ASCRS online postrefractive IOL calculator; Seitz/Speicher/Savini (Triple-S) formula; and Schuster/Schanzlin-Thomas-Purcell (SToP) formulas based on Holladay 1 and SRK/T formulas. IOL power was calculated with the abovementioned methods in 2 groups according to AL (Group 1: 25.0 mm ≤ AL < 28.0 mm and Group 2: AL ≥ 28.0 mm). 64 eyes were included. Excellent outcomes were achieved with the minimum, Barrett TKNH, SToP (SRK/T), and Triple-S formulas in the whole sample and subgroups, which led to similar median absolute error, mean absolute error, and the percentage of eyes with a prediction error within ±0.5 diopters (D). In the whole sample, the Haigis-L and maximum formulas had a significantly higher absolute error than minimum, SToP (SRK/T), and Barrett TKNH formulas. The maximum formula also had a significantly lower percentage of eyes within ±0.5 D than the Barrett TKNH, and SToP (SRK/T) formulas (15.6% vs 50% and 51.5%, all P < .05 with Bonferroni adjustment). Predicting the EDoF IOL power in postmyopic refractive eyes by no-history IOL formulas remains challenging. The Barrett TKNH, Triple-S, minimum, and SToP (SRK/T) formulas achieved the best accuracy when AL ≥ 25.0 mm, while the Barrett TKNH and SToP (SRK/T) formulas were recommended when AL ≥ 28.0 mm.

Axial Length Evaluation before and after Myopic Corneal Refractive Surgery Using IOL Master

Purpose: To evaluate axial length before and after the photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK). Setting: Alhokama Eye Center, Riyadh Saudi Arabia. Design: A cross-sectional study. Methods: The study sample was comprised of 106 eyes of 54 patients. Patients were divided into 2 groups based on whether they had photorefractive surgery (PRK group) or laser in situ keratomiluesis (LASIK group). The intra-group comparison was performed of the changes in axial length before and after surgery using IOLMaster. P P < 0.00001, both intra-group comparisons). Conclusion: There was a statically significant decrease in the axial length measurements after PRK or LASIK for myopia.

Time Utilization and Refractive Prediction Enhancement Associated with Intraoperative Aberrometry Use During Cataract Surgery.

PurposeTo evaluate the time cost of intraoperative aberrometry (IA), to compare IA prediction error to the prediction error associated with conventional formulas using preoperative calculations (PC) and evaluate when IA provides clinically relevant benefit.MethodsThis is a retrospective study of eyes that underwent cataract phacoemulsification surgery with IA at an academic eye center. IA versus PC prediction error were compared amongst various preoperative and intraoperative characteristics. Additionally, a dichotomous variable indicating clinically relevant benefit of IA, where IA absolute prediction error was less than 0.5D and PC absolute prediction error greater than 0.5D, was associated with clinical factors.ResultsFive hundred eyes of 341 patients were included in the analysis. The quantitative difference between mean absolute prediction errors for IA versus PC was between 0.0D and 0.03D in most subgroups. For the 11.0% of eyes that had clinically relevant benefit to IA, the multivariable model identified the following strongest predictors: prior myopic corneal refractive surgery (Odds ratio (OR) 3.9, p<0.01 for myopic LASIK/PRK, OR 5.5, p=0.01 for radial keratotomy), toric or multifocal/EDOF lens implantation (OR 2.7, p=0.03 for toric monofocal lenses, OR 3.1, p=0.01 for EDOF/multifocal lenses), and short and long axial lengths (p<0.01). On average, IA implementation added 3.0 minutes to surgery (p<0.01).ConclusionFor greatest likelihood of a clinically meaningful improvement in outcomes despite increased surgical time, surgeons and patients should consider using IA for eyes with extremes in axial length, eyes with prior myopic corneal refractive surgery, or when implanting lenses with toric or extended-depth-of-focus/multifocal properties.

Association between corneal refractive surgery and the prevalence of glaucoma: Korea National Health and Nutrition Examination Survey 2010–2012

AimTo determine the relationship between corneal refractive surgery and the prevalence of glaucoma in the Korean population.MethodsData were obtained from the Korea National Health and Nutrition Examination Survey (KNHANES), a...

Comparison of the accuracy of intraocular lens power calculation formulas for eyes after corneal refractive surgery.

In cataract surgery, calculating intraocular lens (IOL) power in patients who have previously received corneal refractive surgery on the same eye presents a clinical challenge. This study aims to compare the accuracy of the Haigis-L, Barrett True-K, and Shammas-PL formulas in predicting the IOL power in eyes following corneal refractive surgery. This study analyzed 32 eyes belonging to 28 patients who underwent cataract surgery and IOL implantation after previously undergoing myopic corneal refractive surgery. The IOL power was calculated using the Haigis-L, Barrett True-K, and Shammas-PL formulas, and the accuracy of the three formulas was compared. The Haigis-L, Barrett True-K, and Shammas-PL formulas had a mean arithmetic IOL prediction error of -0.65, -0.39, and -0.46, respectively. The mean numerical errors of the three formulas were significantly different from zero (P<0.001). The smallest median absolute refraction prediction error (median =0.40) belonged to the Barrett True-K formula, which was significantly smaller than that of the Haigis-L formula (median =0.57, P<0.05) but similar to that of the Shammas-PL formula (median =0.49, P>0.05). There was no significant difference in the percentage of eyes within either ±0.50 D or ±1.00 D of the predicted refraction error across the three formulas. The Barrett True-K formula can predict IOL power in eyes that have previously undergone myopic corneal refractive surgery better than the Haigis-L formula.

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

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

Corneal power evaluation after myopic corneal refractive surgery using artificial neural networks.

BackgroundEfficacy and high availability of surgery techniques for refractive defect correction increase the number of patients who undergo to this type of surgery. Regardless of that, with increasing age, more and more patients must undergo cataract surgery. Accurate evaluation of corneal power is an extremely important element affecting the precision of intraocular lens (IOL) power calculation and errors in this procedure could affect quality of life of patients and satisfaction with the service provided. The available device able to measure corneal power have been tested to be not reliable after myopic refractive surgery.MethodsArtificial neural networks with error backpropagation and one hidden layer were proposed for corneal power prediction. The article analysed the features acquired from the Pentacam HR tomograph, which was necessary to measure the corneal power. Additionally, several billion iterations of artificial neural networks were conducted for several hundred simulations of different network configurations and different features derived from the Pentacam HR. The analysis was performed on a PC with Intel® Xeon® X5680 3.33 GHz CPU in Matlab® Version 7.11.0.584 (R2010b) with Signal Processing Toolbox Version 7.1 (R2010b), Neural Network Toolbox 7.0 (R2010b) and Statistics Toolbox (R2010b).Results and conclusionsA total corneal power prediction error was obtained for 172 patients (113 patients forming the training set and 59 patients in the test set) with an average age of 32 ± 9.4 years, including 67% of men. The error was at an average level of 0.16 ± 0.14 diopters and its maximum value did not exceed 0.75 dioptres. The Pentacam parameters (measurement results) providing the above result are tangential anterial/posterior. The corneal net power and equivalent k-reading power. The analysis time for a single patient (a single eye) did not exceed 0.1 s, whereas the time of network training was about 3 s for 1000 iterations (the number of neurons in the hidden layer was 400).

Q-optimized Algorithms: Theoretical Analysis of Factors Influencing Visual Quality After Myopic Corneal Refractive Surgery.

To model the effect of pupil size, optical zone, and initial myopic level on the retinal image quality after Q-optimized myopic corneal refractive surgery. Different Q-optimized and paraxial Munnerlyn algorithms were tested using a schematic myopic eye model to analyze the optical quality of the final retinal image for initial myopic errors from -1.00 to -7.00 diopters (D). Different optical zones (5.5, 6, and 6.5 mm in diameter) and two pupil diameters (5 and 7 mm, mesopic-scotopic conditions) were included in the comparison. Modulation transfer function (MTF) and area under the MTF from 0 to 60 cycles per degree (MTFa) were calculated by ray tracing to evaluate this retinal image quality. The Q-optimized algorithm with Q = -0.45 provided the highest MTF and MTFa results for myopic corrections less than -5.00 D. For refractive errors greater than -5.00 D, Q = -0.26 provided the highest MTF and MTFa results. Q-optimized algorithms improve the visual outcomes with respect to the paraxial Munnerlyn algorithm for myopic corneal surgery. The results show that the Q value that optimizes the results of the Q-optimized algorithm depends on the degree of myopia to correct and the size of the pupil. [J Refract Surg. 2016;32(9):612-617.].

Prevalence of Glaucoma in Myopic Corneal Refractive Surgery Candidates in Hong Kong China.

To estimate the prevalence of glaucoma in myopic individuals in Hong Kong China seeking corneal refractive surgery and factors associated with the occurrence of glaucoma. Six hundred twenty-nine eyes of 315 myopic individuals seeking corneal refractive surgery in a tertiary institution in Hong Kong China, were consecutively recruited. Glaucoma was defined by the presence of abnormal retinal nerve fiber layer (RNFL) and neuroretinal rim measurements obtained with spectral-domain optical coherence tomography, as well as narrowed neuroretinal rim and optic disc excavation observed in color optic disc stereophotographs. Factors associated with glaucoma were analyzed with univariable and multivariable mixed-effects logistic regression analysis. The mean age and spherical equivalent were 36.3 ± 9.3 years (range: 21.5 to 60.1 years) and -6.59 ± 2.34 diopters (D) (range: -2.25 to -17.13 D), respectively. Twenty-three eyes of 16 myopic individuals (5.1%; 95% confidence interval [CI]: 3.2% to 8.1%) had glaucoma, of which 10 eyes of 7 myopic individuals (2.2%; 95% CI: 1.1% to 4.5%) also had visual field defects by standard automated perimetry (5 had mild and 5 had moderate visual field loss). None of the myopic individuals were aware of the diagnosis at the time of examination. The inferotemporal sector of the optic disc was the most frequent location where RNFL thinning was found and the superonasal visual field was the most common region where visual field defects were located. The only biometric factor associated with glaucoma was intraocular pressure (odds ratio: 1.77; 95% CI: 1.14 to 2.75). Glaucoma was present in 5.1% of myopic individuals seeking corneal refractive surgery in Hong Kong China. Corneal refractive surgeons should be watchful in the diagnostic evaluation of glaucoma among myopic corneal refractive surgery candidates. [J Refract Surg. 2016;32(5):298-304.].

Corneal Power Measurement With the Dual Scheimpflug-Placido Topographer After Myopic Excimer Laser Surgery

To evaluate the ability of the Sirius Scheimpflug-Placido Topographer (Costruzione Strumenti Oftalmici, Florence, Italy) in predicting corneal power in eyes with previous myopic corneal refractive surgery. The following corneal refractive power measurements were obtained with Sirius in 38 eyes with prior myopic excimer laser surgery: simulated keratometry (SimK), true net power based on the Gaussian optical formula (TNP), and the mean pupil power (MPP) calculated by ray tracing within the diameter of the entrance pupil range from 2.5 to 6 mm. These values, along with the corresponding keratometric value, which was based on the equation that converted the MPP within 4.5-mm entrance pupil diameter to a keratometric reading in 75 myopic eyes, were compared using the clinical history method. SimK significantly overestimated corneal power by 0.67 ± 0.52 diopters (D), whereas TNP significantly underestimated corneal power by -1.05 ± 0.48 D. The only measurements that showed no statistically significant difference by the clinical history method were the 5 mm MPP, 5.5 mm MPP, and KMPP4.5POST, and the 95% limits of agreement (LOA) were -1.10 to 0.62, -0.91 to 0.89, and -0.67 to 1.05 D, respectively. The Sirius Scheimpflug-Placido Topographer is an alternative method of measuring corneal power in eyes with previous corneal refractive surgery for myopia when preoperative data are not available. The best options seem to be the 5 mm MPP, 5.5 mm MPP, and the keratometric reading calculated from the regression formula.

Estimation of intraocular lens power calculation after myopic corneal refractive surgery: using corneal height in anterior segment optical coherence tomography.

PurposeTo investigate the feasibility of estimating effective lens position (ELP) and calculating intraocular lens power using corneal height (CH), as measured using anterior segment optical coherence tomography (AS-OCT), in patients who have undergone corneal refractive surgery.MethodsThis study included 23 patients (30 eyes) who have undergone myopic corneal refractive surgery and subsequent successful cataract surgery. The CH was measured with AS-OCT, and the measured ELP (ELPm) was calculated. Intraocular lens power, which could achieve actual emmetropia (Preal), was determined with medical records. Estimated ELP (ELPest) was back-calculated using Preal, axial length, and keratometric value through the SRK/T formula. After searching the best-fit regression formula between ELPm and ELPest, converted ELP and intraocular lens power (ELPconv, Pconv) were obtained and then compared to ELPest and Preal, respectively. The proportion of eyes within a defined error was investigated.ResultsMean CH, ELPest, and ELPm were 3.71 ± 0.23, 7.74 ± 1.09, 5.78 ± 0.26 mm, respectively. The ELPm and ELPest were linearly correlated (ELPest = 1.841 × ELPm - 2.018, p = 0.023, R = 0.410) and ELPconv and Pconv agreed well with ELPest and Preal, respectively. Eyes within ±0.5, ±1.0, ±1.5, and ±2.0 diopters of the calculated Pconv, were 23.3%, 66.6%, 83.3%, and 100.0%, respectively.ConclusionsIntraocular lens power calculation using CH measured with AS-OCT shows comparable accuracy to several conventional methods in eyes following corneal refractive surgery.

Diagnosis of open-angle glaucoma after myopic excimer laser corneal refractive surgery

Patients with high myopia are at high risk of glaucoma and are difficult to be discovered at early stage in the case of existing glaucoma. Myopic excimer laser corneal refractive surgery changes the structure of the eye, which makes early glaucoma diagnosis more difficult. Furthermore, refractive surgery may aggravate existing condition of glaucoma. To prevent the exacerbation of glaucoma, it is great important to perform the preoperative glaucoma risk assessment. In this paper, we presented the key diagnostic points of glaucoma assessment before and after excimer laser refractive surgery and discussed the postoperative intraocular pressure measurements and its impact on the diagnosis and treatment of glaucoma including characterization of open angle glaucoma and long-term follow up in patients with high myopia.

Refractive Results after Implantation of a Light-Adjustable Intraocular Lens in Postrefractive Surgery Cataract Patients

To evaluate whether postoperative refractive power adjustment of a light-adjustable lens (LAL; Calhoun Vision, Inc, Pasadena, CA) improves refractive outcomes in patients who have undergone prior LASIK or photorefractive keratectomy. Retrospective case series. Thirty-four eyes in 21 cataract patients with a mean age of 62.6 ± 9.7 years and a history of myopic corneal refractive surgery were implanted with the LAL during cataract surgery performed at a single clinic in Victoria, Canada. Two weeks after uncomplicated cataract surgery, we used a light delivery device to deliver a spatially resolved 365-nm beam of ultraviolet light to alter the shape of the LAL and hence its refractive power. To obtain the desired refractive change, 1, 2, or 3 adjustments were used. After adjustments, we applied 2 lock-in treatments to the LAL to consume unpolymerized macromeres in the LAL. The final manifest refraction spherical equivalent (MRSE) achieved then was compared with the initial refractive target before LAL implantation. The MRSE to target refraction, mean absolute error of cohort to target refraction, and percentage of cohort within ± 0.25 diopters (D), ± 0.50 D, ± 1.0 D, and more than ± 1.0 D relative to target refraction. The MRSE relative to target refraction after final lock-in was within ± 0.25 D in 74% of eyes, within ± 0.50 D in 97% of eyes, and within ± 1.00 D in 100% of eyes. Mean absolute error was 0.19 D with a standard deviation of ± 0.20 D. In patients with a history of laser refractive surgery, LAL implantation and postimplantation adjustment provide a precise refractive outcome. The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Emmetropization and optical aberrations in a myopic corneal refractive surgery chick model

We studied the potential of myopic corneal refractive laser surgery to induce myopia (axial elongation) and potential interactions between aberrations (generally resulting from the procedure) and myopia development in chicks (Gallus domesticus). Ten white Leghorn chicks were monolaterally treated one day post-hatching with photorefractive keratectomy (PRK), with a nominal dioptric change of −9.9 D (imposed hyperopia). Axial length was measured using an adapted ultrasonic biometer; corneal radius of curvature was measured using a custom-built videokeratometer and spherical error and high order aberrations were measured using custom-built Hartmann–Shack aberrometer post-operatively on days 9, 12, 14 and 16 after hatching. Two-weeks after surgery, there were no significant differences in corneal radius of curvature between treated and control eyes. Astigmatism increased on average by a factor of 2.6 and 3rd and higher order aberrations by a factor of 4.3 after PRK. Both treated and control eyes were close to emmetropia, and no axial elongation was found in the treated eyes. The inability of the refractive procedure to achieve significant reductions in the corneal power could be attributed to the biomechanical properties of the chick eye. High order aberrations induced significant contrast decrease (by a factor of 1.7 at 4.5 c/deg). However, reduced image quality neither produced myopic refractive error nor axial elongation in the treated eyes. Both normal and treated eyes emmetropized, indicating that increased amounts of aberrations do not appear to be a risk factor for myopia.

Reverse Geometry Contact Lens Fitting After Corneal Refractive Surgery

To describe reverse geometry rigid gas permeable (RGP) contact lens fitting in eyes with irregular surface induced by complications after myopic corneal refractive surgery. Reverse geometry RGP contact lenses were fit in nine eyes that underwent myopic corneal refractive surgery and experienced a reduction in best spectacle-corrected visual acuity (BSCVA) Snellen lines postoperatively. Comparing the BSCVA with contact lenses, 5 (55.6%) eyes improved > or = 2 lines of BSCVA, 2 (22.2%) eyes improved 1 line, and 2 (22.2%) eyes maintained the same BSCVA as the one eye with spectacles (P < .004). No eye lost lines of BSCVA. All patients reported excellent tolerance and subjective visual quality with the contact lenses. The mean time of contact lens wear was 10.44 +/- 0.88 hours per day (95% confidence interval, 9.76 to 11.12). Reverse geometry RGP contact lens fitting is effective in correcting surgically induced irregular surfaces with improved visual acuity and comfortable wear. These lenses may be the best choice in cases in which surgical retreatment is unfeasible or undesirable.

Corneal power determination after previous corneal refractive surgery for intraocular lens calculation.

To assess the accuracy of different corneal power determination methods in patients who had undergone myopic laser in situ keratomileusis (LASIK), photorefractive keratectomy (PRK), and radial keratotomy (RK). The results for 208 eyes of 116 patients who had had corneal refractive surgery (LASIK, PRK, RK) for myopia were analyzed retrospectively. Keratometry measurements, i.e., autokeratometry readings (K(meas)), simulated keratotopography readings (Sim-K), and topographically measured average central corneal power in a 3-mm zone (ACP) were compared with calculated refraction-derived keratometric value. Correction factors based on the difference between measured and calculated keratometric powers were rated. Direct power measurements with standard keratometers and planokeratotopography systems overestimate corneal power after myopic PRK and LASIK. The average K(meas) and K(topo) were significantly greater than the average calculated refraction-derived keratometric values. Corneal power overestimation correlated significantly with the spherical equivalent change after refractive surgery (p < 0.001). After RK, there is no significant correlation of the difference between all measured K values and refraction-derived power with the spherical equivalent change. In these cases, the Sim-K value seems the most accurate among measured keratometric powers. The precision of measurement significantly depends on the parameters of the autokeratometer (i.e., measurement place, number of measurement points, keratometric index of refraction). To avoid underestimation of intraocular lens power after cataract surgery in the eyes that had previously undergone myopic corneal refractive surgery, the measured corneal power must be corrected. Although correction factors may be calculated for cases after PRK and LASIK, there are no universal and absolutely reliable methods to determine corneal power in these cases. More than one accessible method should be used, and the lowest, most reliable data should be used.

Higher-order wavefront aberrations induced by small ablation area and sub-clinical decentration in simulated corneal refractive surgery using a perturbed schematic eye model

The purpose was to investigate the effect of decentered ablation in myopic corneal refractive surgery by simulation. Wavefront aberrations in a small pupil area (radius: 2 mm) for photopic vision and in a large pupil area (radius: 3 mm) for mesopic vision with simulated refractive surgery were analyzed using Zernike polynomials. Radii of ablation were 3, 2.5 and 2 mm. Decentrations of ablation were 0 mm and 0.5 mm. Change of the surface shape by ablation was considered a perturbation, while Gullstrand’s schematic eye was used as un-perturbed optics. For photopic vision, wavefront aberrations were about the same as with unperturbed optics. For mesopic vision, the results were heavily dependent on the radius of ablation area. When the radius was 3 mm, wavefront aberrations did not increase very much compared to un-perturbed optics. When the radius was smaller than 3 mm, spherical aberration was induced by centered ablations, and coma was also induced by decentered ablations. In conclusion, small ablation areas or subclinical decentrations of ablations could cause serious amounts of wavefront aberrations to the optics of the eye in the simulations.