Preoperative Corneal Topography Research Articles

MCSTransWnet: A new deep learning process for postoperative corneal topography prediction based on raw multimodal data from the Pentacam HR system

This work provides a new multimodal fusion generative adversarial net (GAN) model, Multiple Conditions Transform W-net (MCSTransWnet), which primarily uses femtosecond laser arcuate keratotomy surgical parameters and preoperative corneal topography to predict postoperative corneal topography in astigmatism-corrected patients. The MCSTransWnet model comprises a generator and a discriminator, and the generator is composed of two sub-generators. The first sub-generator extracts features using the U-net model, vision transform (ViT) and a multi-parameter conditional module branch. ​The second sub-generator uses a U-net network for further image denoising. The discriminator uses the pixel discriminator in Pix2Pix. Currently, most GAN models are convolutional neural networks; however, due to their feature extraction locality, it is difficult to comprehend the relationships among global features. Thus, we added a vision Transform network as the model branch to extract the global features. It is normally difficult to train the transformer, and image noise and geometric information loss are likely. Hence, we adopted the standard U-net fusion scheme and transform network as the generator, so that global features, local features, and rich image details could be obtained simultaneously. Our experimental results clearly demonstrate that MCSTransWnet successfully predicts postoperative corneal topographies (structural similarity ​= ​0.765, peak signal-to-noise ratio ​= ​16.012, and Fréchet inception distance ​= ​9.264). Using this technique to obtain the rough shape of the postoperative corneal topography in advance gives clinicians more references and guides changes to surgical planning and improves the success rate of surgery.

CORNEAL TOPOGRAPHIC CHANGES AFTER PTERYGIUM EXCISION WITH CONJUNCTIVAL AUTOGRAFTING USING SUTURES VERSUS FIBRIN GLUE: A COMPARATIVE STUDY

Aim: To compare the corneal topographic changes after pterygium excision with conjunctivalautografting using sutures versus fibrin glue. Materials and Methods:A prospective study was conducted on 100 eyes of 100 patients visiting the outpatient Department of Ophthalmology,Government Medical College Srinagar over a period of two years. Patients were randomly allocated in two groups (Group S and Group FG) and underwent complete eye examination along with preoperative corneal topography where corneal astigmatism at central 3mm and total mean refractive power of cornea were noted.50 patients underwent pterygium excision with conjunctivalautografting using 10-0 nylon sutures (Group S) and other 50 underwent same procedure using fibrin glue (Group FG). Corneal topography was again repeated postoperatively in both groups at 2nd week, 1st month, 3rd month and 6th month of follow up and results were noted. Results:The mean age of study patients in suture group was41.7±8.64 years and in fibrin glue group was39.5±9.58 years. The mean corneal astigmatism at central 3mm significantly decreased from 1.95D preoperatively to 0.61D at postoperative 6thmonth following pterygium excision (p-value 0.003) in suture group. The mean preoperative corneal astigmatism in patients in fibrin glue group also decreased from 2.03D preoperatively to 0.62D at 6thmonth postoperative follow up(p value<0.001).The total mean refractive power of cornea increased significantly from 43.17D preoperatively to 44.59 D postoperatively at 6th month of follow up (p value <0.001) in suture group and in fibrin glue group it significantly increased from 43.23D preoperatively to 44.69D at 6thmonth of postoperative follow up (p value < 0.001).However no significant difference was seen in the postoperative corneal astigmatism at central 3mm or total mean refractive power of cornea between the two groups at any follow up. Conclusion:Pterygiumexcision with conjunctiva autografting causes reversal of corneal topographic changes induced by pterygium irrespective of whether fibrin glue or sutures are used for autografting.

Effect of Opposite Clear Corneal Incision (CCI) on Corneal Higher-Order Aberrations after Phacoemulsification

Abstract Background: Nowadays, care of a cataractous patient greatly exceeds surgical removal of the opacified lens. In a step foreword to welfare of the elderly, phacoemulsification can perform as a refractive tool, addressing both spherical and astigmatic refractive errors. Aim of Study: The aim of that work was to evaluate safety and effectiveness of OCCIs, as an innovative procedure for correction of corneal astigmatism, during phacoemulsification. Patients and Methods: The study assessed 64 patients, who underwent phacoemulsification. Pre-operative and post-operative corneal topography was done, documented and statistically analyzed for each patient. Results: The study revealed a decrease of pre-operative corneal astigmatism from a pre-operative mean of –1.78D to a post-operative mean of 1.09D in OCCI group and a decrease of pre-operative corneal astigmatism from a pre-operative mean of –1.71D to a postoperative mean of 1.29D in single incision group. Conclusion: The present study revealed that OCCIs with appropriate pre-operative corneal topography represent a real advance in the applications of refractive lenticular surgery. OCCIs provide an innovative technique for managing pre-operative, regular, corneal astigmatism. This is simple, easy to learn technique, with no extra instrumentation. The OCCIs in this study was safe, with no wound related complications. However, OCCIs require careful early post-operative care, due to their penetrating nature. Once the wounds are sealed, risk of further complications approaches zero. Further studies on that technique, employing different incision architecture are required to help development of nomograms correlating the incision length, width, age of the patient, and the amount of pre-operative corneal astigmatism to be corrected.

Sutureless Intrascleral Posterior Chamber Intraocular Lens Fixation: Analysis of Clinical Outcomes and Postoperative Complications.

Purpose To report a technique for performing sutureless intrascleral fixation of a posterior chamber intraocular lens (PC-IOL) and analyzing the clinical outcomes and postoperative complications. Study Design. 68 eyes of 66 patients who received the technique were studied retrospectively. Methods The best-corrected visual acuity (BCVA), intraocular pressure (IOP), anterior chamber depth (ACD), IOL tilt and decentration, corneal topography (K1 and K2), and postoperative complications were determined at 3 months. Results The mean preoperative BCVA was 1.63 ± 1.24 logMAR units, and the mean postoperative BCVA was 0.74 ± 0.59 logMAR units at 3 months (P < 0.05). The mean preoperative IOP was 21.9 ± 12.6 mmHg, and the mean postoperative IOP was 16.9 ± 4.5 mmHg at 3 months (P = 0.001). The mean preoperative corneal topography (K1 and K2) was K1 = 42.14 ± 1.91 and K2 = 43.54 ± 1.51; the mean postoperative corneal topography (K1 and K2) was K1 = 43.03 ± 2.18 and K2 = 43.40 ± 1.71 at 3 months (P = 0.678 and 0.468, respectively). The mean preoperative spherical equivalent was +11.00 ± 13.19 diopters (D), and the mean postoperative spherical equivalent was +0.06 ± 0.86 D (P < 0.005). The mean IOL tilt was 2.4 ± 1.7°, and the mean decentration was 0.35 ± 0.21 mm. The mean ACD was 4.31 ± 0.29 mm. Conclusions The 27-gauge sutureless intrascleral PC-IOL implantation technique minimizes intraoperative injury, simplifies procedure, and provides good PC-IOL fixation with few postoperative complications.

Refractive and visual outcomes of small incision lenticule extraction (SMILE) in eyes with thin corneas.

To report the refractive and visual outcomes of small incision lenticule extraction (SMILE) with the thinnest corneal thickness (CCT) of less than 500 µm and evaluate it in terms of safety and efficacy. Refractive Surgery Clinic of University of Health Sciences Beyoglu Eye Training and Research Hospital, Istanbul, Turkey. Retrospective case series. The pre-and-postoperative examinations of all patients with thin corneas (preoperative CCT <500 µm) who underwent the SMILE procedure and had a minimum of 24 months of follow-up records were reviewed from medical files. The main outcome measures of the refractive and visual outcomes and the effect on corneal high order aberrations (HOAs) were evaluated. The study included 55 eyes of 39 patients. The mean preoperative uncorrected visual acuity (UDVA) was 1.3 ± 1.5 logMAR, and the mean postoperative UDVA was significantly improved to 0.05 ± 0.80 logMAR at the last visit (p < 0.001). At the last follow-up, 84% of the eyes were within ± 0.50D, and 96% of the eyes were within ±1.00D of attempted SE refraction. The HOAs of coma (p < 0.001), secondary astigmatism (p = 0.015), spherical aberration (p < 0.001), and RMS (p < 0.001) aberrations increased significantly from the baseline to the postoperative last visit. The increase in trefoil was not significant (p = 0.32). No sight threatening complications or ectasia were observed during the follow-up time. SMILE is a safe and effective technique with long-term stability for treatment of myopia in eyes with a thin cornea, and satisfactory results can be obtained if candidates for surgery are selected carefully with particular emphasis on normal preoperative corneal topography.

Validity of percentage tissue altered as a screening formula for post laser-assisted in-situ keratomileusis ectasia in Indian eyes.

Purpose:To calculate a modified percentage tissue altered (mPTA) in post laser-assisted in-situ keratomileusis (LASIK) eyes and to validate its role as an independent factor to evaluate ectasia in the Indian population.Methods:A total of 333 consecutive eyes with normal preoperative corneal topography by combined placido and scheimpflug imaging-based topography system (SIRIUS) who underwent LASIK using a microkeratome between 2011 and 2014 at a tertiary level teaching hospital in south India, were retrospectively analyzed. Preoperatively patient's refraction, flap thickness (FT), ablation depth (AD), residual stromal bed (RSB), and thinnest corneal thickness (TCT) were recorded. The formula used was mPTA = (FT + AD)/TCT. mPTA was grouped into <0.4 (low risk), 0.40 - 0.45 (moderate risk), and >0.45 (high risk). All patients were called for follow-up and underwent a topography to look for ectasia.Results:In total 60.1%, 29.1%, and 10.8% patients had mPTA of <0.4, 0.40 - 0.45 and >0.45, respectively. However, after a minimum follow-up of 2 years, none of the patients had any sign of ectasia.Conclusion:Careful selection of patients is mandatory before proceeding for LASIK. Factors like corneal thickness, RSB, degree of myopia, and AD are more important. The role of mPTA >0.4 as an independent risk factor for post LASIK ectasia is questionable in Indian eyes. Other factors or a modified formula suitable for Indian eyes needs to be investigated. A larger follow-up period is also required as ectasia has been known to develop even after 2 years.

Primary Topography-Guided LASIK: Refractive, Visual, and Subjective Quality of Vision Outcomes for Astigmatism ⩾2.00 Diopters.

To evaluate the outcomes of primary topography-guided laser in situ keratomileusis (LASIK) in eyes with subjective refractive astigmatism of 2.00 diopters (D) or greater. This was a prospective study in consecutive eyes with cylinder of 2.00 D or greater that had LASIK using the Alcon WaveLight EX500 excimer laser and T-CAT/Contoura software (Alcon Laboratories, Inc., Fort Worth, TX). The accuracy, efficacy, safety, cylinder vector analysis, higher order aberrations, and patients' subjective quality of vision were assessed. Eyes with naturally occurring topographic irregular astigmatism were not excluded. The mean cylinder was -2.55 D preoperatively and -0.34 D postoperatively; 81% and 95% of eyes were within ±0.50 and ±0.75 D of intended cylinder after LASIK, respectively. The correction index and index of success were 1.00 and 0.13, respectively. The efficacy and safety indexes were 0.98 and 1.04, respectively. The preoperative corneal topography irregularity index, anterior corneal higher order aberrations, and refractive astigmatism magnitude were mildly correlated to postoperative residual astigmatism. Mean ocular and corneal coma were not increased postoperatively. Patients had significant improvements after LASIK in both subjective uncorrected quality of vision and night vision disturbances compared to spectacle- and contact lens-corrected vision before LASIK. Topography-guided ablation using the Alcon WaveLight EX500 excimer laser and T-CAT/Contoura software results in excellent accuracy, efficacy, and safety, with improved postoperative subjective quality of vision and reduced night vision disturbances in virgin eyes with refractive astigmatism of 2.00 D or greater, including eyes with topographic naturally occurring irregular astigmatism. [J Refract Surg. 2019;35(2):78-86.].

Predictability of the Achieved Lenticule Thickness in Small Incision Lenticule Extraction for Myopia Correction

To investigate the predictability of the achieved lenticule thickness in small incision lenticule extraction (SMILE) for the correction of myopia. In this prospective study, a total of 80 eyes of 45 patients who underwent the SMILE procedure were included. A Scheimpflug camera was used to measure the preoperative and postoperative corneal topography. Achieved lenticule thicknesses at the pupil center and corneal vertex were calculated by subtracting the postoperative corneal thickness at the pupil center and corneal vertex from preoperative corresponding values. Predictability between the achieved and VisuMax readout at different locations (the pupil center and corneal vertex) and postoperative visits (postoperative day 1 and 6 months) were evaluated using a general linear model. Achieved lenticule thickness at the pupil center and corneal vertex showed good correlation at both postoperative day 1 (pupil center: r=0.914, corneal vertex: r=0.903) and 6 months (pupil center: r=0.886, corneal vertex: r=0.866). The achieved lenticule thickness at postoperative day 1 was 8.5-μm thinner at the pupil center and 9.6-μm thinner at the corneal vertex than the VisuMax readout. This study suggests that the predictability between the achieved and VisuMax readout is favorable. The lenticule thickness at the pupil center is closer to the VisuMax readout than corneal vertex.

Observational study on the impact of corneal power on refractive status of patients after small incision lenticule extraction surgery

Objective: To observe the change of refractive status and possible influencing factors for patients with different corneal power who underwent small incision lenticule extraction (SMILE) surgery. Methods: Prospective cohort study was performed for patients who underwent small incision lenticule extraction (SMILE) surgery at Daping Hospital and Research Institute of Surgery of Third Military Medical University between January and August 2016. The patients were divided into 3 groups according to their corneal power: low curvature group (K(1)≤41.00 D), common curvature group (41.00 D<K(1) and K(2)< 46.00 D), and high curvature group (K(2) ≥ 46.00 D). Preoperative and postoperative (1 day, 1 week, 1, 3 and 6 month) ophthalmic examination results of the patients including uncorrected distance visual acuity (UCDVA), refractive status, intraocular pressure (IOP) and slip lamp microscope examination were recorded. Subjective refraction and Pentacam HR were detected at 6 month after operation so as to monitor the incidence of intraoperative and postoperative complications. The total corneal refractive power (TCRP) based on Ray Tracing technique was applied to evaluate the changes of corneal curvature before and after the surgery. Power vector analysis was applied to evaluate the refraction status based on preoperative and postoperative corneal topography. At 6 months postoperatively, Hotelling t(2) test was applied to compare the refractive status among the groups, and multiple linear regression was applied to analyze the potential influencing factors of under-correction/over-correction. Results: Fifty-four patients (108 eyes) were enrolled, among which 34 were male (68 eyes) and 20 were female (40 eyes). The 3 groups had the same sample size (18 patients and 36 eyes). The low curvature group was featured with youngest average age [(22±4) years, χ(2)=8.94, P<0.05], largest male patients proportion (15/18, χ(2)=11.20, P<0.01) and largest average pupil diameter [(3.26±0.36) mm, F=4.83, P<0.05], as compared to the other 2 groups. The incidence of severe OBL (25/36) was significantly higher in the high curvature group (χ(2)=65.06, P<0.01). All patients showed no diminution of vision and their UCDVA averaged 5.1 at 6 months postoperatively, however patients with low curvature were slightly "under-corrected" in 1-mm and 2-mm zones (Error values<0). The preoperative spherical equivalent (SE) and postoperative spherical aberration in 6-mm zone were the significant factors affecting the relationship between preoperative corneal curvature and postoperative refractive status (r=0.392, 2.745, P<0.05). Conclusions: SMILE is safe and effective for patients with both low and high curvature, but the incidence of intraoperative OBL is significantly higher in high curvature group. Patients with low curvature were slightly "under-corrected" in 1-mm and 2-mm zones, which may imply that the design of the lenticule may be aspheric and that the cornea reshaping process of younger patients may be of particular characteristics. (Chin J Ophthalmol, 2018, 54: 48-54).

Corneal topography and keratometry changes after glued intraocular lens implantation

To analyze the alterations in corneal topography and keratometry (K) after glued transscleral-fixated intraocular lens (IOL) implantation. Dr. Agarwal's Eye Hospital, Chennai, India. Prospective case series. Eyes having glued IOL implantation for aphakia or subluxated lens (>180 degrees) were included. Preoperative autorefractometer and corneal topography was performed. Intraoperative parameters, namely the type, position, and incision size, flap position, and number of sutures were noted. The mean corneal curvature in a steep meridian (maximum K), flat meridian (minimum K), simulated K, pachymetry, and surgically induced astigmatism (SIA) were analyzed. This study evaluated 16 eyes with aphakia and 15 eyes with a subluxated over a mean follow-up of 12months±6 (SD). There was a significant reduction in mean simulated K (P=.014) after surgery. The maximum K decreased significantly (P=.002), from 44.85±2.83 diopters (D) preoperatively to 44.47±2.75 D at 6months. The mean SIA was 1.0±0.7 D (range 0.16 to 3.6 D) and the postoperative astigmatism analysis by the Alpins method was negative (-1.8), showing relative flattening after surgery. Multiple regression analysis found no association between postoperative vision and preoperative maximum K, postoperative simulated K, incision size, and number of sutures. There was no correlation between the postoperative simulated K and incision position (P=.674), sutures (P=.881), and scleral flap position (P=.401). Glued transscleral fixation resulted in a reduction in mean corneal curvature in the steep meridian and there was significant change in corneal astigmatism.

Ectasia risk factors in refractive surgery

This review outlines risk factors of post-laser in situ keratomileusis (LASIK) ectasia that can be detected preoperatively and presents a new metric to be considered in the detection of ectasia risk. Relevant factors in refractive surgery screening include the analysis of intrinsic biomechanical properties (information obtained from corneal topography/tomography and patient’s age), as well as the analysis of alterable biomechanical properties (information obtained from the amount of tissue altered by surgery and the remaining load-bearing tissue). Corneal topography patterns of placido disk seem to play a pivotal role as a surrogate of corneal strength, and abnormal corneal topography remains to be the most important identifiable risk factor for ectasia. Information derived from tomography, such as pachymetric and epithelial maps as well as computational strategies, to help in the detection of keratoconus is additional and relevant. High percentage of tissue altered (PTA) is the most robust risk factor for ectasia after LASIK in patients with normal preoperative corneal topography. Compared to specific residual stromal bed (RSB) or central corneal thickness values, percentage of tissue altered likely provides a more individualized measure of biomechanical alteration because it considers the relationship between thickness, tissue altered through ablation and flap creation, and ultimate RSB thickness. Other recognized risk factors include low RSB, thin cornea, and high myopia. Age is also a very important risk factor and still remains as one of the most overlooked ones. A comprehensive screening approach with the Ectasia Risk Score System, which evaluates multiple risk factors simultaneously, is also a helpful tool in the screening strategy.

Role of Percent Tissue Altered on Ectasia After LASIK in Eyes With Suspicious Topography

To investigate the association of the percent tissue altered (PTA) with the occurrence of ectasia after LASIK in eyes with suspicious preoperative corneal topography. This retrospective comparative case-control study compared associations of reported ectasia risk factors in 129 eyes, including 57 eyes with suspicious preoperative Placido-based corneal topography that developed ectasia after LASIK (suspect ectasia group), 32 eyes with suspicious topography that remained stable for at least 3 years after LASIK (suspect control group), and 30 eyes that developed ectasia with bilateral normal topography (normal topography ectasia group). Groups were subdivided based on topographic asymmetry into high- or low-suspect groups. The PTA, preoperative central corneal thickness (CCT), residual stromal bed (RSB), and age (years) were evaluated in univariate and multivariate analyses. Average PTA values for normal topography ectasia (45), low-suspect ectasia (39), high-suspect ectasia (36), low-suspect control (32), and high-suspect control (29) were significantly different from one another in all comparisons (P < .003) except high- and low-suspect ectasia groups (P = .033), and presented the highest discriminative capability of all variables evaluated. Age was only significantly different between the high-suspect ectasia and normal topography ectasia groups, and CCT was not significantly different between any groups. Stepwise logistic regression revealed the PTA as the most significant independent variable (P < .0001), with RSB the next most significant parameter. There remains a significant correlation between PTA values and ectasia risk after LASIK, even in eyes with suspicious corneal topography. Less tissue alteration, or a lower PTA value, was necessary to induce ectasia in eyes with more remarkable signs of topographic abnormality, and PTA provided better discriminative capabilities than RSB for all study populations.

Importance of Performing Corneal Topography Before Cataract Surgery

Corneal topography assessment has become increasingly important for surgical planning in patients scheduled for cataract surgery. One of the main reasons is the increased expectations for reduced spectacle dependence following cataract surgery, whether patients are selecting an advanced technology intraocular lens (ATIOL), such as a toric or multifocal IOL, or even when choosing a monofocal IOL Preoperative topography enables surgeons to determine whether a patient is an appropriate candidate for an ATIOL, and also enables surgeons to identify corneal conditions that are contraindications to certain types of IOLs, especially as many corneal conditions are not visible on slit lamp exam. This article will focus on the value provided by preoperative corneal topography prior to cataract surgery and discuss clinical situations where it has been critical in guiding IOL selection.

Association Between the Percent Tissue Altered and Post–Laser In Situ Keratomileusis Ectasia in Eyes With Normal Preoperative Topography

To investigate the association of a novel metric, percent tissue altered, with the occurrence of ectasia after laser in situ keratomileusis (LASIK) in eyes with normal corneal topography and to compare this metric with other recognized risk factors. Retrospective case-control study. The study included 30 eyes from 16 patients with bilateral normal preoperative Placido-based corneal topography that developed ectasia after LASIK (ectasia group) and 174 eyes from 88 consecutive patients with uncomplicated LASIK and at least 3 years of postoperative follow-up. The following metrics were evaluated: age, preoperative central corneal thickness, residual stromal bed, Ectasia Risk Score System scores, and percent tissue altered, derived from [PTA = (FT + AD)/CCT], where FT = flap thickness, AD = ablation depth, and CCT = preoperative central corneal thickness. In the ectasia group, percent tissue altered ≥40 was the most prevalent factor (97%), followed by age <30 years (63%), residual stromal bed ≤300 μm (57%), and ectasia risk score ≥ 3 (43%) (P < .001 for all). Percent tissue altered ≥ 40 had the highest odds ratio (223), followed by residual stromal bed ≤ 300 μm (74) and ectasia risk score ≥ 4 (8). Stepwise logistic regression revealed percent tissue altered ≥ 40 as the single most significant independent variable (P < .0001). Percent tissue altered at the time of LASIK was significantly associated with the development of ectasia in eyes with normal preoperative topography and was a more robust indicator of risk than all other variables in this patient population.

Transepithelial Photorefractive Keratectomy with Crosslinking for Keratoconus

Purpose:To analyse visual, refractive and topographic outcomes of combining transepithelial photorefractive keratectomy (tPRK) with simultaneous corneal crosslinking for the visual rehabilitation of contact lens intolerant keratoconus patients.Methods:Patients with topographically significant keratoconus, limited corrected vision and intolerant of contact lenses were prospectively recruited, subject to ethical approval and consent. All patients underwent single step aspheric tPRK and sequential crosslinking. Preoperative vision, refraction, corneal topography and wavefront were assessed, with postoperative assessment at 1, 3, 6, and 12 months.Results:22 eyes of 14 patients were included in the pilot study. Mean age was 32 years (SD 6.8, range 24 to 43). Mean preoperative unaided vision was 1.39 LogMAR (SD 0.5) best corrected 0.31 LogMAR (SD 0.2). Mean preoperative spherical equivalent was -2.74 Diopters (D) (SD 4.1 range -12.25 to +7.75), and mean cylinder -2.9 D (SD 1.2, range 0 to -5.5). Mean central corneal thickness was 461um (SD 29, range 411 to 516). Vision improved postoperatively; unaided 0.32 LogMAR (SD 0.4), best corrected 0.11 (SD 0.13) (P=<0.005). Mean postoperative cylinder was -1.4D (SD1.2), significantly reduced (p<0.005). Maximum keratometry (Kmax) was stable throughout postoperative follow up. (p<0.05).Conclusions:Non topographic transepithelial PRK with simultaneous crosslinking improves vision, and may offer an alternative to keratoplasty in contact lens intolerant keratoconus. Further comparative studies to topographic PRK techniques are indicated.

Flap thickness in eyes with ectasia after laser in situ keratomileusis

To measure central flap thickness in eyes with ectasia after laser in situ keratomileusis (LASIK) and to compare these values with estimated anticipated flap thickness based on mean published values for each device used for flap creation. Emory Vision at Emory University, Atlanta, Georgia, USA. Retrospective comparative case series, using published data for controls. Confocal microscopic analysis was performed using the Confoscan 3 device to measure central flap thickness in eyes with ectasia after LASIK. Pre-LASIK records were evaluated for information, including basic patient demographics, preoperative corneal topographies, estimated anticipated flap thickness based on the mean average thickness values, and residual stromal bed (RSB) thickness calculations using measured and estimated flap thicknesses. Fifty eyes of 29 patients were evaluated. The mean measured flap thickness was 138 μm ± 26 (SD) (range 90 to 220 μm). There were no significant differences between measured and estimated flap thicknesses (138 μm versus 135 μm; P=.5) or RSB thickness (329 μm versus 332 μm; P=.7), nor were there differences in flap thickness between eyes developing ectasia with normal corneal topographies and eyes with abnormal corneal topographies. One eye had a measured flap resulting in an unintended RSB thickness less than 250 μm; this eye also had abnormal topography. Measured central flap thickness was not thicker than estimated in most eyes developing ectasia after LASIK. Thus, excessively thick flaps do not appear to be a major contributing factor to the pathogenesis of ectasia after LASIK. No author has a financial or proprietary interest in any material or method mentioned.

Astigmatism management at the time of cataract surgery

Patients expect their vision to improve after cataract surgery and, increasingly, they expect to be free of the encumbrance of glasses and contact lenses. These expectations are driven by technological advancements throughout the ophthalmic industry and the experiences of family and friends. To meet or exceed patient expectations, cataract surgeons must pay increasing attention to the management of pre-existing corneal astigmatism at the time of cataract surgery. Pre-existing corneal astigmatism is a significant component of preoperative ametropia. To achieve satisfactory postoperative refractive results, it is important to correct pre-existing spherical errors by accurate biometry and intraocular lens (IOL) power calculation, and to manage preoperative corneal cylinder errors by a suitable method. Guided by preoperative corneal topography, patients with varying degrees of corneal astigmatism can be placed into a variety of dioptric categories. These categories dictate a systematic ‘stepladder’ approach to guide the optimum approach to surgical correction. For patients with less than 1 D of corneal astigmatism, the preferred approach is to place the phacoemulsification incision on the steep corneal meridian. For 1–3 D of corneal astigmatism, single or paired peripheral corneal-relaxing incisions may be used. Alternately, for astigmatic errors of 1–4 D, toric IOLs can be implanted. Astigmatism of 4.5–7 D may be addressed using a combined approach of toric IOL implantation and peripheral corneal relaxing incision placement in the steep meridian of corneal cylinder. Moreover, high-powered toric IOLs, currently available in select European and Asian markets and not currently approved by the US FDA, may be implanted in the USA if an ophthalmologist obtains a compassionate use exemption from the FDA and local Institutional Review Board approval. If visually significant refractive errors are present after cataract surgery, surgical management options include piggyback IOL implantation, IOL exchange, toric IOL rotation, photorefractive keratectomy and laser-assisted in situ keratomileusis. Of these options, photorefractive keratectomy and laser-assisted in situ keratomileusis usually provide the most simple solution to manage suboptimal refractive outcomes. This simple stepladder approach to astigmatism management, which is based on preoperative corneal topography, enables cataract surgeons to achieve excellent unaided visual acuity in the absence of vision-limiting ocular comorbidities.

Refractive surgery in anisometropic adult patients induce plastic changes in primary visual cortex

To prospectively study the effect of refractive surgery in the primary visual cortex of adult anisometropic and isometropic myopic patients. Two anisometropic and two isometropic myopic patients were examined with multifocal functional magnetic resonance imaging technique (mffMRI) before refractive surgery and at 3, 6, 9 and 12 months postoperatively. Two controls without refractive surgery were also examined with mffMRI in the beginning and in the end of the study. Anisometropic patients had only their more myopic eye operated to correct the anisometropia. The myopic isometropic patients had their both eyes operated. Operated anisometropic eyes showed 65% reduced amount of active voxels in foveal data at 12 months postoperatively compared with the preoperative situation. In unoperated anisometropic eyes, the corresponding value was 86% and in myopic patients and controls 31% and 1%, respectively. To confirm this finding, the number of activated voxels representing the innermost ring of the stimulus was also calculated, and an exactly similar phenomenon was encountered in the anisometropic patients. Both anisometropic patients improved the best-spectacle-corrected visual acuity in the operated eye after refractive surgery. Our results suggest that plastic changes may take place in the primary visual cortex of anisometropic adult patients after refractive surgery.

Minor Influence of Myopic Laser In Situ Keratomileusis on the Posterior Corneal Surface

To check whether myopic LASIK induces changes on the posterior corneal surface. A Scheimpflug system (Pentacam; Oculus, GmbH, Wetzlar, Germany) was used to measure preoperative and postoperative posterior corneal topography in 27 eyes (of 14 subjects) that had undergone standard myopic LASIK surgery (attempted corrections between -1.25 and -8.50 D) and on 18 nonoperated eyes (9 subjects). A hybrid porcine-plastic eye model was developed to validate the measurement technique. Longitudinal displacement of the posterior corneal apex and changes of the apical radius of curvature and asphericity were computed. Measurements on a hybrid model eye of known posterior corneal geometry showed that the measured posterior corneal radius of curvature was minimally affected by the geometry of the anterior surface. The measurements on patients showed that, on average, the only relevant (though clinically unimportant) change in radius of curvature and asphericity occurred the first day after surgery (DeltaR = -28 +/- 34 microm and DeltaQ = -0.06 +/- 0.06). No statistically significant change was observed afterward. The change in radius was more pronounced in the vertical direction than in the horizontal direction. On average, there was no significant displacement of the posterior corneal apex. Individual changes over time did not show a systematic trend across patients, and control subjects experienced changes of the same order of magnitude. The Pentacam Scheimpflug system can be used reliably to assess changes in the posterior corneal radius of curvature after LASIK. There is no evidence of surgically induced changes in the corneal posterior surface beyond 1 week after surgery.

High myopia as a risk factor for post-LASIK ectasia: a case report.

To describe the case of a patient developing corneal ectasia following LASIK for the correction of myopic astigmatism. A 39-year-old man underwent bilateral uneventful LASIK for myopic astigmatism of -10.25 -1.75 ×040 OD and -8.00 -2.50 ×005 OS. Preoperative corneal pachymetry was 542 micrometers OD and 543 micrometers OS. Preoperative corneal topography showed bilateral oblique bow-tie patterns. Central keratometry measurements were 45.12 D @ 124 / 43.87 D @ 34 OD and 44.87 D @ 78 / 43.12 D @ 168 OS. Keratoconus or forme fruste keratoconus were not present preoperatively. The residual stromal bed was 314 micrometers OD and 295 micrometers OS. Increasing astigmatism was documented progressively after LASIK. Central keratometry and topography were performed with evidence of ectasia OD at 17 months post-operatively and early evidence of ectasia OS at last follow-up of 58 months. High myopia appears to be a predisposing factor in this patient. High myopia may need to be considered as an ectasia risk factor independent of amount of ablation or residual stromal bed thickness and in the absence of forme fruste keratoconus. The possibility remains that ectasia was due to an unidentified risk factor or an intrinsic corneal problem with this patient's right eye.