Undergone Corneal Refractive Surgery Research Articles

Visual outcomes and patient satisfaction after implantations of three types of presbyopia-correcting intraocular lenses that have undergone corneal refractive surgery

This prospective, non-randomized, comparative study aimed to compare the visual outcomes and patient satisfaction after implantations of three presbyopia-correcting intraocular lenses (IOLs) after myopic refractive surgery. It was conducted from January 2020 to December 2021 in Shanghai Heping Eye Hospital. Patients were divided into three groups based on the type of IOL implanted. The visual acuity, refractive stability, high-order aberrations, objective visual quality, spectacle independence, and visual function index 14 questionnaire scores of the three groups were compared. This study included 78 eyes of 39 patients: 26 eyes with 839MP, 26 eyes with MF30, and 26 eyes with ZXR00. Uncorrected distance visual acuity improved significantly for all three groups. For a pupil diameter of 4.0 mm, the spherical aberrations of the three groups were 0.33 ± 0.16 μ, 0.50 ± 0.08 μ, and 0.39 ± 0.10 μ, respectively. The spectacle independence for distance vision was over 90% in each group; for near vision, it was only 25% for the ZXR00 group. All three types of presbyopia-correcting IOLs improved visual quality in post-LASIK or PRK patients. However, the high incidence of photic phenomena after presbyopia-correcting IOL implantation in patients who have undergone myopic LASIK should not be neglected.

Choice of refractive surgery types for myopia assisted by machine learning based on doctors’ surgical selection data

In recent years, corneal refractive surgery has been widely used in clinics as an effective means to restore vision and improve the quality of life. When choosing myopia-refractive surgery, it is necessary to comprehensively consider the differences in equipment and technology as well as the specificity of individual patients, which heavily depend on the experience of ophthalmologists. In our study, we took advantage of machine learning to learn about the experience of ophthalmologists in decision-making and assist them in the choice of corneal refractive surgery in a new case. Our study was based on the clinical data of 7,081 patients who underwent corneal refractive surgery between 2000 and 2017 at the Department of Ophthalmology, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences. Due to the long data period, there were data losses and errors in this dataset. First, we cleaned the data and deleted the samples of key data loss. Then, patients were divided into three groups according to the type of surgery, after which we used SMOTE technology to eliminate imbalance between groups. Six statistical machine learning models, including NBM, RF, AdaBoost, XGBoost, BP neural network, and DBN were selected, and a ten-fold cross-validation and grid search were used to determine the optimal hyperparameters for better performance. When tested on the dataset, the multi-class RF model showed the best performance, with agreement with ophthalmologist decisions as high as 0.8775 and Macro F1 as high as 0.8019. Furthermore, the results of the feature importance analysis based on the SHAP technique were consistent with an ophthalmologist’s practical experience. Our research will assist ophthalmologists in choosing appropriate types of refractive surgery and will have beneficial clinical effects.

Intraocular lens power calculation after corneal refractive surgery

Challenges in IOL power calculation in eyes after corneal refractive surgery are caused by difficulties in accurately determining corneal refractive power and in predicting the effective lens position. Three factors contribute to inaccurate corneal refractive power estimation ‐ inaccurate measurement of anterior corneal curvature by standard keratometry or corneal topography, inaccurate calculation of total corneal power from the anterior corneal curvature can result from using the standardized value for the refractive index of cornea (1.3375) and finally changes in posterior corneal curvature. There are three categories of methods proposed based on the use of historical data acquired prior to the corneal refractive surgery (formulas using only historical data, no historical data or a combination of historical data and current data). The most frequently used methods of IOL power calculation in eyes after corneal refractive surgery are discussed and their accuracy are compared. The latest studies and meta‐analyses in this area are presented. Despite availability of new measurement technologies and development of new IOL calculation formulas, further advances are needed to improve outcomes of cataract surgery in eyes that have undergone corneal refractive surgery.

The impact of patient-reported visual disturbance on dynamic visual acuity in myopic patients after corneal refractive surgery.

To investigate the impact of patient-reported visual disturbance on dynamic visual acuity in myopic patients after corneal refractive surgery. This is a prospective nonrandomized study. Adult myopic patients receiving bilateral laser-assisted sub-epithelial keratomileusis (LASEK), femtosecond laser-assisted in situ keratomileusis (FS-LASIK), or small incision lenticule extraction (SMILE) with Plano target were included. Eight types of patient-reported visual disturbance were evaluated regarding frequency, severity and bothersome and dynamic visual acuity (DVA) of 40 and 80 degrees per second (dps) was measured postoperatively at 3 months. The study enrolled 95 patients with an average age of 27.6 ± 6.4 years. The most frequently reported visual disturbance was the fluctuation in vision (70.5%), followed by glare (66.3%) and halo (57.4%). Postoperative DVA at 80 dps was significantly associated with the total score of haloes (p = 0.038) and difficulty in judging distance (p = 0.046). Significant worse postoperative DVA at 40 dps was observed in patients with haloes than those without (p = 0.024). The DVA at 80 dps for patients without haloes or difficulty in judging distance was significantly better than that with the symptoms (haloes, p = 0.047; difficulty in judging distance, p = 0.029). Subgroup analysis by surgical procedures demonstrated that the significant difference in DVA between patients with and without visual disturbance was only observed in patients receiving FS-LASIK. Postoperatively, myopic patients undergoing corneal refractive surgery with haloes or difficulty in judging distance have significantly worse low and high-speed DVA than those without the symptoms. The present study provided the basis for postoperative guidance in daily tasks involving dynamic vision when patients have visual disturbances.

Light adjustable lens in a post-lasik patient

The Light Adjustable Lens is a newly approved lens that can be altered in-vivo after cataract surgery to address residual refractive error. This is done through highly specific ultraviolet light applications two weeks post-operatively. Patients require 2-5 total light adjustments. The ability to adjust the lens allows patients to more confidently participate in the surgical process while customizing their refractive status. Patients who have previously undergone corneal refractive surgery can provide an added challenge to cataract surgeons. Because of induced changes in corneal structure, intraocular lens calculations can be more difficult, ultimately leading to variability in refractive outcome. The light adjustable lens is sure to change how surgeons and optometrists counsel and manage patients pre- and post-operatively. The case described below details the structure and functionality of the light adjustable lens as well as a clinical application in a post-LASIK patient.

Синдром «сухого глаза» перед кераторефракционной хирургией: частота встречаемости и патогенетически ориентированная терапия

Aim: to assess the ocular surface in patients who were planned to undergo corneal refractive surgery (CRS), using latest diagnostic tools, and to develop a differentiated approach to the preoperative preparation of the patients with confirmed dry eye disease (DED). Patients and Methods: the study included 298 patients (298 eyes), aged 18 to 36 years, with diagnosed mild and moderate myopia, who had binocular type of vision and average keratometry readings 43.0-20.0 D. The patients were planned to undergo CRS. A standardized preoperative diagnostic examination was performed in all patients according to the protocol of refraction eye testing. The diagnostic system manufactured by MediWorks (China) was used to evaluate the ocular surface and conjunctival mucous membranes. Results: based on the results of the objective methods of examination 112 (37.6%) cases of DED were detected, including 101 (33.9%) cases of evaporative and 11 (3,7%) cases of hyposecretory forms. In addition, Schirmer-1 test was performed in patients with hyposecretory DED which showed a significantly reduced aqueous tear production. Patients with DED were advised to discontinue wearing contact lenses and to use tear substitutes containing high-molecular-weight hyaluronic acid and sodium hyaluronate in a relatively low concentration (0.15%). Also, a 0.01% solution of sulfated glycosaminoglycanes was administered to the patients. To relieve the sterile inflammatory response, the patients received a course of steroids as anti-inflammatory agents followed by cyclosporin A. An eye gel was recommended for the long- lasting overnight hydration of the corneal epithelium and its faster renewal. As a result of the positive response to the treatment, after 6–8 months of therapy it was possible to perform surgical correction in 6 (54.5%) of 11 patients of this group. In post-operative period the patients demonstrated good clinical and functional outcomes and did not report any worsening of DED clinical signs. In 89 (88.1%) of 101 patients with evaporative DED the combination therapy consisting of the eyelid self-massage and two-phase cationic emulsion (oil-water), a mimic of tear film lipid layer, which contained the positively charged nanodrops of mineral oils dispersed in water, helped to normalize the ocular surface and tear production parameters, and thus enabled to perform CRS. Conclusion: in the group of examined patients, DED was found in 37.6% of cases, and the prevalence of evaporative form was almost 10-fold higher than that of secretory form. The occurrence of two DED forms dictates a need for the differentiated approach to diagnostics and treatment. In contrast to hyposecretory form, a clear trend to the regression of symptoms was demonstrated for evaporative form of DED, when patients received pathogenesis-oriented therapy. Thus, patients with evaporative DED clinical pattern are more likely to become candidates for CRS than those with tear hyposecretion. Keywords: dry eye syndrome, corneal refractive surgery, dysfunction of the meibomian glands, tear film, nanoemulsion. For citation: Maychuk N.V., Malyshev I.S., Obraztsova M.R. Dry eye syndrome before corneal refractive surgery: the prevalence and pathogenesis- oriented therapy. Russian Journal of Clinical Ophthalmology. 2023;23(1):14–20 (in Russ.). DOI: 10.32364/2311-7729-2023-23-1-14-20.

Analysis of the diagnostic accuracy of Belin/Ambrósio Enhanced Ectasia and Corvis ST parameters for subclinical keratoconus.

To investigate the diagnostic accuracy of the parameters in the Belin/Ambrósio Enhanced Ectasia Display built in Pentacam, which is designed for the screening of subclinical keratoconus (SKC) built in Pentacam, and the parameters in Corneal visualization Scheimpflug technology (Corvis ST). A retrospective study: The fellow eyes of unilateral keratoconus cases were diagnosed with SKC. Patients presented to Shanxi Eye Hospital with SKC from October 2020 to November 2021 were included as the SKC group, and myopic patients undergoing corneal refractive surgery at the Refractive Surgery Department in our hospital within the same period were included as the control group. The Belin/Ambrósio and Corvis ST parameters were extracted from the system and analyzed using independent samples t test. Receiver operating curves (ROCs) were also created to test the diagnostic accuracy of each parameter. There were 70 patients (70 eyes) in the SKC group and 137 patients (137 eyes) in the control group. For Corvis ST parameters, Radius (P = 0.021), PachySlope (P = 0.040), SP-A1 (P = 0.002), A2 Deformation Amp. (P = 0.028), A2 Deflection Length (P < 0.001), Max ICR (P = 0.005), DA Ratio Max (1mm) (P = 0.023), IR (P = 0.016), CBI (P = 0.003) and TBI (P < 0.001) were statistically different between the two groups. For Belin/Ambrósio parameters, PPI min. Axis, ART min, ART max, ART avg, Pachy min, Front K2, Astig, BAD-Df, BAD-Db, BAD-Dp, BAD-Dt, BAD-Da, BAD-D, PPI min, PPI max, PPI max. Axis, PPI avg and Dist.Apex-Thin.Loc. were significantly different between the two groups (all p < 0.001). TBI and BAD-D showed the best diagnostic accuracy, with AUCs of 0.944 and 0.965, respectively. Some Belin/Ambrósio and Corvis ST parameters differed between SKC eyes and eyes with normal cornea. TBI and BAD-D showed the ideal diagnostic performance for SKC. In clinical practice, conventional corneal topography could not be replaced by Corvis ST.

Machine learning predicting myopic regression after corneal refractive surgery using preoperative data and fundus photography.

Myopic regression after surgery is the most common long-term complication of refractive surgery, but it is difficult to identify myopic regression without long-term observation. This study aimed to develop machine learning models to identify high-risk patients for refractive regression based on preoperative data and fundus photography. This retrospective study assigned subjects to the training (n = 1606 eyes) and validation (n = 403 eyes) datasets with chronological data splitting. Machine learning models with ResNet50 (for image analysis) and XGBoost (for integration of all variables and fundus photography) were developed based on subjects who underwent corneal refractive surgery. The primary outcome was the predictive performance for the presence of myopic regression at 4years of follow-up examination postoperatively. By integrating all factors and fundus photography, the final combined machine learning model showed good performance to predict myopic regression of more than 0.5 D (area under the receiver operating characteristic curve [ROC-AUC], 0.753; 95% confidence interval [CI], 0.710-0.793). The performance of the final model was better than the single ResNet50 model only using fundus photography (ROC-AUC, 0.673; 95% CI, 0.627-0.716). The top-five most important input features were fundus photography, preoperative anterior chamber depth, planned ablation thickness, age, and preoperative central corneal thickness. Our machine learning algorithm provides an efficient strategy to identify high-risk patients with myopic regression without additional labor, cost, and time. Surgeons might benefit from preoperative risk assessment of myopic regression, patient counseling before surgery, and surgical option decisions.

Macular phototoxicity after corneal crosslinking

Introduction: Keratoconus is a progressive degenerative corneal disease of variable severity. Its management includes medical and surgical treatment. Corneal crosslinking (CXL) is being increasingly used to stabilize the condition. Macular phototoxicity is a well-known side effect of light exposure; however, its incidence after treatment with riboflavin and UV light is unknown. This study reported the clinical features of a patient with macular phototoxicity after UV-A exposure and described the structural and angiographic retinal changes observed in the patient. Patient, Clinical Findings, and Diagnosis: A 37-year-old man with keratoconus underwent corneal refractive surgery (topography-guided custom ablation with accelerated and high-fluence CXL). Postoperatively, he had decreased vision in the operated eye. Ophthalmoscopy, spectral-domain optical coherence tomography, and fluorescein angiography revealed retinal pigment epithelial changes, ellipsoid zone disruption, and window defects, respectively. The patient was diagnosed with macular phototoxicity. The corrected distance visual acuity stabilized at 20/100 after 6 months. Conclusions: Macular phototoxicity may occur after UV-A exposure during CXL. The use of accelerated and high-fluence protocols might have contributed to its occurrence in this patient.

Commentary: Aspheric intraocular lens may be the future but not always a simple solution.

Nowadays, cataract surgery is not only to achieve the vision of 20/20; rather, it demands many other qualities of vision to be fulfilled as described by Despande et al.[1] Spherical aberration is one of the varieties of higher-order aberration (HOA) in the eye. The optical design of the aspheric intraocular lens (IOLs) reduced spherical aberrations and increased contrast sensitivity as described by Despande et al.[1] As described by the authors, the crystalline lenses lose their property of negative spherical aberration to compensate for the positive spherical aberration of the eye with overall near-zero spherical aberration of the young adult eyes or very minimal spherical aberration. Wavefront technology is used nowadays more frequently by an aberrometer to map the eye before any refractive surgery to detect any aberration so that customized compensatory optical solution can be done to that eye to achieve the best possible functional vision. Patients having age-related cataracts not only suffer from a decrease in vision but also loss of contrast, especially in mesopic conditions. They did not realize it at that time due to cataracts but after cataract surgery when their contrast also improves along with their vision they are the happiest patients. Theoretically, spherical aberrations increase the depth of focus but decrease modulation transfer function at high spatial frequencies at optimum focus. Spherical aberrations, therefore, play an important role in the balance between visual acuity and depth of focus.[2] Although aspheric IOLs are replacing the spherical IOLs in our country, still PMMA rigid IOL is implanted frequently in below poverty line ( BPL) and ration cardholder patients due to the issue of affordability. Another point to be noted is that the asphericity of aspheric IOL is lost and even leads to more aberrations such as coma and coma-like effects if the IOL is slightly decentred and tilted and these aberrations occur more in aspheric IOL than in spheric IOL and monofocal IOL than multifocal IOL in such scenarios.[3] That is the reason in 1980 and 1990 there was a reluctance for aspheric IOL. However, after the evolvement of phacoemulsification, better surgery techniques such as proper rhexis size, the problems of decentration and tilt has got reduced quite a lot so more and more aspheric IOLs are implanted. The spherical aberration reduced significantly in these aspheric IOL in larger pupil aperture such as in young patients who have undergone corneal refractive surgery, especially in mesopic and scotopic conditions. Thus, the aged population with a small pupil size and having less mesopic and scotopic activity may not need the aspheric IOL. Wavefront technology is used more before corneal refractive surgery or biopics, to measure the corneal and total aberration of eyes so that customized surgery can be planned accordingly for a better functional optical outcome. The future generation of cataract surgery will not be for the recognition acuity only rather for fully functional visual outcome and aberration-free vision. With the better technique of cataract surgery, day by day such as higher competency in phacoemulsification and nowadays femto laser-assisted cataract surgery where precise capsulorhexis is done, more and more aspheric IOL will be the choice of IOL in the coming days.

Evaluation of preoperative dry eye in people undergoing corneal refractive surgery to correct myopia.

To investigate the incidence of preoperative dry eye and related factors in patients undergoing corneal refractive surgery to correct myopia. A total of 141 patients with myopia who underwent corneal refractive surgery were surveyed by questionnaires, tear film break-up time (BUT) test, Schimer I test (SIt), corneal fluorescein staining (FL) test and diagnosed according to the currently recognized domestic diagnostic criteria for dry eye. Correlation analysis of factors such as age, gender, regular wearing of contact lens (CL), diopter (spherical equivalent), corneal thickness, and corneal curvature that may affect the onset of dry eye was carried out to clarify the main influencing factors. There were 64 patients (45.39%) diagnosed with dry eye. The male patients (20.31%) was significantly less than that of non-dry eye subjects (41.56%; χ 2=7.260, P=0.007); the proportion of patients with dry eye wearing CL (81.25%) was significantly higher than that of non-dry eye subjects (51.95%; χ 2=13.234, P<0.001); the median diopter level of dry eye patients was -6.59 (IQR: -8.87, -4.58) D, and the median diopter level of non-dry eye subjects was -5.69 (IQR: -7.15, -4.03) D. The diopter level of dry eye patients was significantly higher (Z=-2.086, P=0.019). However, the age, best corrected visual acuity, and intraocular pressure of dry eye patients were not statistically different from those of non-dry eye subjects (t=-0.257, -0.383 and 0.778, P=0.798, 0.702, and 0.438); the corneal thickness and corneal curvature (K1 and K2) were also not statistically different either (Z=-1.487, -1.036 and -1.707, P=0.137, 0.300, and 0.088). The research further analyzes the three significant factors in the single factor analysis (gender, CL wear, and diopter) in a multi-factor way: CL wear and diopter were the influencing factors of dry eye disease. Among them, CL wear increased the risk of dry eye by 2.934 times compared with no CL wear; for every 1 D increase in diopter, the risk of dry eye increased by 0.761 times. Preoperative dry eye is relatively common in patients who undergo corneal refractive surgery to correct myopia, especially in patients who have a history of CL wear and a high diopter level before surgery. Therefore, it is necessary to carry out preoperative screening and timely treatment of dry eye to obtain the best treatment outcome and postoperative satisfaction.

Photorefractive surgery with excimer laser and its impact on the diagnosis and follow-up of glaucoma. A review

Excimer laser refractive surgery is a procedure performed worldwide to solve refractive errors and reduce dependence on glasses or contact lenses. There has been an increase in the number of procedures performed around the world. Myopia is the most common indication for corneal photorefractive surgery. Myopic patients have a higher risk of developing some type of glaucoma in their lifetime, such as primary open-angle glaucoma and others. Refractive surgery ablates central corneal stromal tissue, altering its thickness and biomechanics, which in turn makes it difficult to accurately measure intraocular pressure (IOP), since it underestimates it. This underestimation of IOP may delay the diagnosis of de novo glaucoma in patients with a history of refractive surgery. Each patient who wishes to undergo corneal refractive surgery should undergo a thorough glaucoma examination in order to monitor and detect the possible development and / or progression of glaucoma. A very useful practical approach is to perform a series of IOP measurements before and after surgery, when the eye is already stable, and the difference between the averages of the two sets of readings can then be used as a personalised correction factor for postoperative IOP monitoring in that eye. Also, if there is any suspicion of a possible glaucoma, paraclinical tests, such as coherent optical tomography of the retinal nerve fibre layer (RNFL), visual fields and photos of the optic nerve should be requested. All this data prior to refractive surgery should be provided to these patients, so that they can save it and give it to their treating ophthalmologists in the future.

Information sources for patients undergoing corneal refractive surgery: results from a cross-sectional patient survey from a single private center in Pola​nd.

To identify the information sources for patients undergoing laser vision correction. Individuals who underwent corneal refractive surgery at a private practice from December 2017 to August 2018 and agreed to complete an anonymous questionnaire were included. The manifest refraction and surgical method was recorded and correlated with the questionnaire results. Data collected from 126 patients (mean age, 32.8 ± 8.6 years; 55.6% women) were analyzed. Of 121 patients, 120 (99.2%) identified the Internet as a source for information on refractive surgery, and 71 of 119 (59.7%) noted that the clinic's website influenced their choice of clinic. Patients with high myopia more commonly used contact lenses and had considered undergoing refractive surgery for a longer time compared with patients with other refractive errors (P < 0.01 and P < 0.01, resp.). Patients with hyperopia were less likely to know their own refractive error (P = 0.02). In this patient cohort, the Internet was the main source of information for those undergoing refractive surgery.

Periorbital aesthetic concerns in patients seeking corneal refractive surgery.

Purpose:To report the frequency of periorbital aesthetic abnormalities in patients undergoing refractive surgery and to report the ability of the patient and the refractive surgeon in picking up these findings compared to the oculoplastic surgeon.Methods:Single-center, prospective observational case series. All patients underwent standard pre-operative work-up for refractive surgery, answered a study questionnaire, and underwent face photographs (with and without glasses). The patient, the refractive, and the oculoplastic surgeons evaluated the photographs to categorize the concerns as none, presence of ptosis, tear trough deformity, scleral show, and others. The findings of the oculoplastic surgeon were taken as the standard of reference.Results:The photographs of 121 patients were analyzed. The mean age was 25.76 ± 3.75 years and 72% were males. The main indication for surgery was to eliminate dependency on glasses in a majority (76%) followed by cosmesis in 23%. The oculoplastic surgeon noted tear trough deformity in 14 (11.5%) cases, scleral show in 51 (42.1%), ptosis in 35 (28.9%), and other findings in 45 (37.1%). When the symmetrical scleral show was excluded, the patient picked up aesthetic concerns in only 8.26%, the refractive surgeon in 14% as compared to 39% by the oculoplastic surgeon (P < 0.01).Conclusion:Periorbital aesthetic significant findings were noted in 39% of the patients undergoing corneal refractive surgery when assessed by an oculoplastic surgeon. The refractive surgeon was able to pick up less than 50% of these. We recommend a basic aesthetic initial evaluation prior to refractive surgery and photographic documentation, especially in cosmetically aware patients.

PHOTOREFRACTIVE SURGERY WITH EXCIMER LASER AND ITS IMPACT ON THE DIAGNOSIS AND FOLLOW-UP OF GLAUCOMA. A REVIEW.

Excimer laser refractive surgery is a procedure performed worldwide to solve refractive errors and reduce dependence on glasses or contact lenses. There has been an increase in the number of procedures performed around the world. Myopia is the most common indication for corneal photorefractive surgery. Myopic patients have a higher risk of developing some type of glaucoma in their lifetime, such as primary open-angle glaucoma and others. Refractive surgery ablates central corneal stromal tissue, altering its thickness and biomechanics, which in turn makes it difficult to accurately measure intraocular pressure (IOP), since it underestimates it. This underestimation of IOP may delay the diagnosis of de novo glaucoma in patients with a history of refractive surgery. Each patient who wishes to undergo corneal refractive surgery should undergo a thorough glaucoma examination in order to monitor and detect the possible development and / or progression of glaucoma. A very useful practical approach is to perform a series of IOP measurements before and after surgery, when the eye is already stable, and the difference between the averages of the two sets of readings can then be used as a personalised correction factor for postoperative IOP monitoring in that eye. Also, if there is any suspicion of a possible glaucoma, paraclinical tests, such as coherent optical tomography of the retinal nerve fibre layer (RNFL), visual fields and photos of the optic nerve should be requested. All this data prior to refractive surgery should be provided to these patients, so that they can save it and give it to their treating ophthalmologists in the future.

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...

The influence of different corneal diameters on Belin/Ambrósio enhanced ectasia display of Pentacam corneal topography

Objective: To investigate the effect of corneal diameter on Belin/Ambrósio enhanced ectasia display (BAD). Methods: Retrospective case series study. The subjects were 6 744 myopic patients, including 3 341 males and 3 403 females, who had undergone corneal refractive surgery or had completed preoperative examination but had not undergone corneal refractive surgery at the Army Medical Center and Chongqing Vision Institute in Chongqing from June 2017 to June 2019. Age was (23.74±5.73) years old. No patients had keratoconus. One eye of each patient was randomly included, and the patients were divided into groups according to the corneal diameter measured by Pentacam. Group A included 630 patients (630 eyes) with corneal diameter ≤ 11.1 mm. In group B, there were 4 063 patients (4 063 eyes) with corneal diameter of 11.2 to 11.8 mm. In group C, there were 2 051 patients (2 051 eyes) with corneal diameter ≥11.9 mm. Preoperative BAD parameters of deviation of front elevation difference map (Df), deviation of back elevation difference map (Db), deviation of average pachymetric progression index (Dp), deviation of minimum thickness (Dt), deviation of Ambrósio's relational thickness maximum (Da) and overall deviation value (Do) were measured by Pentacam. One-way analysis of variance was used for preoperative BAD parameters comparison between groups. The distribution of normal, suspicious and pathological results of Df, Db, Dp, Dt, Da and Do in each group was tested by chi-square test. Results: In groups A, B and C, Df was 0.73±1.14, 0.48±1.02, and 0.11±0.91, Db was 1.09±1.07, 0.23±0.83, and-0.34±0.62, Dp was 1.57±0.91, 1.14±0.86, and 0.68±0.75, Dt was -0.11±0.84, -0.2±0.82, and 0.03±0.78, Da was 0.78±0.61, 0.64±0.64, and 0.48±0.64, and Do was 1.65±0.64, 1.24±0.60, and 0.86±0.55, respectively. The BAD parameters of Df (F=129.549), Db (F=829.491), Dp (F=344.373), Dt (F=7.249), Da (F=68.637) and Do (F=524.877) were all significantly different between groups (P<0.01). The proportion of suspicious and pathological BAD parameters [Df (χ²=161.8), Db (χ²=611.75), Dp (χ²=478.84), Da (χ²=44.636), and Do (χ²=553.11)] suggested the distribution in each group was significantly different (P<0.01). Conclusions: Corneal diameter had a significant influence on BAD. Compared with eyes with large corneas, the false positive rate of BAD was higher in eyes with small corneas.(Chin J Ophthalmol, 2020, 56: 761-767).

Intraocular Lens Power Calculations in Eyes with Previous Corneal Refractive Surgery: Review and Expert Opinion

Intraocular lens (IOL) power calculations are less accurate in eyes that have undergone corneal refractive surgery. A wide range of methods have been proposed. We reviewed the methods and outcomes of IOL power calculations in eyes with previous LASIK, excimer laser photorefractive keratectomy (PRK), or radial keratotomy (RK). The PubMed database was searched for articles that (1) discuss methods and outcomes of IOL power calculation in eyes with previous corneal refractive surgery and (2) evaluate the outcomes of toric, multifocal, or extended depth-of-focus (EDOF) IOLs in these eyes. We excluded review articles, case reports or case studies, and non-English reports. Seventy full-text articles were included in this review. Three categories of methods exist based on whether and how they use historical data acquired before the corneal refractive surgery. The American Society of Cataract and Refractive Surgery (ASCRS) postrefractive IOL calculator incorporates many commonly used methods. In eyes with previous myopic LASIK or PRK, hyperopic LASIK or PRK, and RK, 0% to 85%, 38.1% to 71.9%, and 29% to 87.5% of eyes, respectively, showed refractive prediction errors within ±0.5 diopter (D); in eyes with toric IOL implantation that met certain inclusion criteria, 80%, 84%, and 69% of eyes, respectively, achieved postoperative astigmatism of 0.50 D or less. Intraocular lenses with negative spherical aberration (SA) will reduce the positive corneal spherical aberration induced in eyes by myopic LASIK or PRK or by RK. Intraocular lenses with 0 SA on average best match corneal SA in eyes with prior hyperopic LASIK or PRK. Studies have reported excellent outcomes of postrefractive eyes implanted with multifocal or EDOF IOLs; however, corneal topographic enrollment criteria were not specified. Despite availability of new measurement technologies and development of new IOL calculation formulas, further advances are needed to improve outcomes of cataract surgery in eyes that have undergone corneal refractive surgery. Tools like the ASCRS postrefractive IOL calculator are useful for the clinician by incorporating a variety of formulas. Toric, EDOF, and multifocal IOLs may provideexcellent outcomes in selected cases that meet certain corneal topographic criteria.

Comparison of Corrected Intraocular Pressure Methods after Corneal Refractive Surgery according to Corneal Ablation Amounts

Purpose : The purpose of this study was to evaluate the intraocular pressure (IOP) that would be underestimated after corneal refractive surgery according to corneal ablation amounts, and was to suggest the most appropriate corrected IOP method for each group. Methods : The subjects were 1,002 eyes of 501 people (237 men, 264 women) who underwent corneal refractive surgery. The mean age was 26.89±5.18 years. IOP was measured with a non-contact tonometer and 4 correction methods, and was used to correct the underestimated IOP. IOP in three groups with low, moderate and high myopia according to ablation amounts was analyzed postoperative corrected IOP to compare correction methods. Results : The preoperative IOP was 15.67±2.39 mmHg and postoperative IOP was 10.12±2.11 mmHg, which was significantly lower than the mean 5.55±2.09 mmHg. The postoperative IOP calculated by Ehlers' correction method was 14.53±2.47 mmHg, which was 1.14±2.83 mmHg different from the preoperative IOP, showing the most similar to preoperative IOP. In addition, the IOP corrected by the Ehlers equation showed the smallest difference from preoperative IOP in all groups. Conclusion : The Ehlers correction method is shown the most accurate among the four correction methods in low, moderate, and high myopia groups after corneal refractive surgery. It would be a useful method for preventing the late diagnosis and treatment of glaucoma.

Study on the Corneal Higher-Order Aberrations and Correlation in Patients with Different Degrees of Myopia Suitable for Wavefront-Guided FS-LASIK

Background: Individualized corneal refractive surgery requires an understanding of the basis of higher-order aberrations before surgery. To investigate the characteristics and distribution of anterior surface wavefront aberrations in patients suitable for corneal refractive surgery. Methods: A total of 121 myopic patients (121 eyes, 18 - 45 years old) who underwent corneal refractive surgery were recruited from January to May 2016 at Affiliated Hospital, Yanbian University. Patients were randomly selected by the Pentacam anterior segment analysis system with a spherical equivalent (SE) of -0.25 to -10.00 D. The corneal anterior aberrations (total higher-order aberration; spherical aberration; Coma; Trefoil) and Q and K values were detected, and a correlation analysis of the relevant parameters was carried out. Results: The root-mean-square (RMS) of the third to sixth order aberrations of the corneal anterior wavefront aberrations at a 6 mm analysis diameter showed a decreasing trend in patients suitable for the corneal refractive surgery, and the RMS of the third order aberrations accounted for 62.92% of the total HOAs. The coma ratio (coma/total cornea higher-order aberrations) was increased with the increasing diopters, while the spherical aberration ratio (spherical aberration/total cornea higher-order aberrations) was not changed. In addition, the spherical aberration was 0.203 ± 0.082 μm (range: 0.061 to 0.503 μm), and the Q30 was -0.19 ± 0.03 (range: -0.58 to 0.31). There were significant differences in the coma aberrations of preoperative corneal anterior surface (3, 1) between the low, middle and high myopia groups (P = 0.013). The spherical equivalent was positively correlated with the corneal coma of the anterior corneal surfaces (R = -0.241, P = 0.009), and the Q value was positively correlated with the total higher-order aberrations (R = 0.326, P Conclusions: Individual wavefront aberrations on the anterior surfaces of the cornea are comparatively different, and the Zernike coefficients are related to the degree of myopia. Spherical aberrations are the most overriding aberrations of the cornea.