Cross Sectional Analysis of Impact of Seasonal Changes on Excimer Laser Ablation Performance on Polymethyl Methacrylate (PMMA).

Seasonal changes and varying degree of corneal hydration has been linked to excimer laser corneal ablation rates. The use of PMMA as a calibration material in refractive lasers is well established. However, PMMA ablation may be equally affected by seasonal variations in temperature and humidity, in turn affecting the calibration process. The aim of this work is to analyze the effect of seasonal changes in PMMA performance using SCHWIND AMARIS laser system. PET and PMMA ablations conducted in climate-controlled environment with 826 consecutive AMARIS systems manufactured over 6 years were retrospectively analyzed. Lasers were stratified depending on seasons and months of the year. Metrics like single laser pulse fluence, nominal number of laser pulses, mean performance, standard deviation, and technical performance of system were compared to global average values. Cyclic winter-summer variation was confirmed with seasons winter and summer showing statistically significant variations with respect to global values. Metric technical performance showed deeper PMMA ablation performance in summertime, with maximum seasonal deviation of 6%. Results were consistently confirmed in seasonal as well as monthly analyses. These findings could help minimize variance among laser systems by implementing compensation factors depending on seasons such that laser systems installed worldwide follow the same trend line of variation.

Excimer laser-assisted corneal epithelial pattern ablation for corneal cross-linking.

PURPOSE: To determine corneal cross-linking (CXL) efficacy and chromophore penetration after excimer laser-assisted patterned de-epithelialization. METHODS: Two-hundred-twenty porcine eyes were de-epithelialized ex vivo, either fully (mechanical; n = 88) or patterned (excimer laser; n = 132). Consecutively, corneas were impregnated with hypo- or hyperosmolar riboflavin (RF; n = 20, RF-D; n = 40, respectively) or water-soluble taurine (WST11; n = 40, and WST-D; n = 40, respectively), or kept unimpregnated (n = 80). Sixty corneas were subsequently irradiated, inducing CXL, with paired contralateral eyes serving as controls. Outcome measurements included strip extensiometry to assess CXL efficacy, and spectrophotometry and fluorescence microscopy to determine stromal chromophore penetration. RESULTS: All tested chromophores induced significant CXL (p < 0.001), ranging from 7.6% to 14.6%, with similar stiffening for all formulations (p = 0.60) and both de-epithelialization methods (p = 0.56). Light transmittance was significantly lower (p < 0.001) after full compared with patterned de-epithelialization. Stromal chromophore penetration was comparable between fully and patterned de-epithelialized samples, with full penetration in RD and RF-D samples and penetration depths measuring 591.7 ± 42.8 µm and 592.9 ± 63.5 µm for WST11 (p = 0.963) and 504.2 ± 43.2 µm and 488.8 ± 93.1 µm for WST-D (p = 0.669), respectively. CONCLUSIONS: Excimer laser-assisted patterned de-epithelialization allows for effective CXL. Stromal chromophore concentration is, however, reduced, which may have safety implications given the need for sufficient UVA attenuation in RF/UVA CXL. The different safety profile of near-infrared (NIR) may allow safe WST11/NIR CXL even with reduced stromal chromophore concentration values. In vivo studies are needed to evaluate the benefits and further assess safety of excimer laser-assisted patterned de-epithelialization for corneal CXL.

Analytical optimization of the cutting efficiency for generic cavitation bubbles.

A theoretical method to determine the optimum laser parameters for maximizing the cutting efficiency for different materials (in particular human cornea) is proposed. The model is simple and reduced to laser beam characteristics and cavitation properties. The model further provides a method to convert energy fluctuations during the cutting process to equivalent deviations in the cavitation bubbles. The proposed model can be used for calibration, verification and validation purposes of laser systems used for cutting processes at relatively low cost and may improve the quality of the results.

Three-year outcomes of mixed astigmatism correction with single-step transepithelial photorefractive keratectomy with a large ablation zone.

PURPOSE: To evaluate refractive and visual outcomes of single-step transepithelial photorefractive keratectomy (transPRK) in the treatment of mixed astigmatism with the use of an aberration-neutral profile and large ablation zone. SETTING: Nicolaus Copernicus University and Oftalmika Eye Hospital, Bydgoszcz, Poland. DESIGN: Retrospective, observational case series. METHODS: This study included patients who underwent transPRK to correct mixed astigmatism and completed the 3-year follow-up. Procedures were performed with an Amaris 750S excimer laser using an aberration-neutral profile and optical zone of 7.2 mm or more. RESULTS: A total 48 eyes of 39 patients were included. Preoperatively, mean spherical manifest refraction was +1.37 ± 0.98 diopter (D) (0.25 to 4.00 D), and astigmatism was -4.00 ± 0.76 D (-2.25 to -6.00 D). Three years postsurgery, it was -0.17 ± 0.26 D and -0.41 ± 0.44 D, respectively. Attempted spherical equivalent correction within ±0.50 D was achieved in 45 eyes (94%) and cylindrical correction in 34 (71%). Preoperative corrected distance visual acuity (CDVA) was 20/20 or better in 38 eyes (79%), and postoperative uncorrected was 20/20 or better in 29 eyes (60.0%). No eye had lost 2 or more Snellen lines of CDVA, whereas 3 eyes (6%) gained 2 or more lines. In 4 eyes (8%), haze of low intensity was observed at the periphery, with scores between 0.5 and 1.0, and only 1 eye getting a score of 2 in 0- to 4-degree scale. CONCLUSIONS: Mixed astigmatism correction with large-ablation-zone transPRK provided good results for efficacy, safety, predictability, and visual outcomes in a 3-year follow-up.

TransPRK treatment for residual refractive error and induced aberrations in eye undergone SMILE treatment.

In this case report, we propose to correct refractive errors after SMILE a refractive lenticule surgery technique with transepithelial Photorefractive keratectomy (TransPRK).The advantage of this technique is that the measured aberrations with topography o the Cornea are also treated on the Surface of the Cornea.

Long-term Outcomes After LASIK Using a Hybrid Bi-aspheric Micro-monovision Ablation Profile for Presbyopia Correction.

PURPOSE: To evaluate visual outcomes 6 years after hybrid bi-aspheric multifocal central laser in situ keratomileusis for presbyopia correction (PresbyLASIK) treatments. METHODS: Thirty-eight eyes of 19 patients consecutively treated with central PresbyLASIK were assessed. The mean age of the patients was 51 ± 3 years at the time of treatment with a mean spherical equivalent refraction of -0.57 ± 1.98 diopters (D) and mean astigmatism of 0.58 ± 0.57 D. Monocular corrected distance visual acuity (CDVA), corrected near visual acuity (CNVA), and distance-corrected near visual acuity (DCNVA), uncorrected distance visual acuity (UDVA), uncorrected intermediate visual acuity (UIVA), distance-corrected intermediate visual acuity (DCIVA), and uncorrected near visual acuity (UNVA) were assessed preoperatively and postoperatively for the dominant eye, non-dominant eye, and binocularly. Subjective quality of vision and near vision were assessed using the 10-item, Rasch-scaled, Quality of Vision (QoV) Questionnaire and Near Activity Visual Questionnaire (NAVQ), respectively. RESULTS: At 6 years postoperatively, mean binocular UDVA was 20/18 ± 4 and mean binocular UNVA and UIVA were 0.11 ± 0.13 and -0.08 ± 0.08 logRAD, respectively. Spherical equivalent showed a slow hyperopic drift of +0.10 D per year with refractive astigmatism stable from 6 weeks postoperatively. Defocus curves showed an improvement of 0.4 Snellen lines at best focus from 1 to 6 years of follow-up, reaching preoperative levels. Compared to the preoperative status, the corneal and ocular spherical aberrations (at a 6-mm diameter) decreased and were stable from 3 months of follow-up. Questionnaires revealed a postoperative unaided QoV score comparable to preoperative scores and with an improved postoperative unaided NAVQ score compared to preoperative scores with best correction. CONCLUSIONS: Presbyopic treatment using a hybrid bi-aspheric micro-monovision ablation profile is safe and efficacious even after 6 years postoperatively. The postoperative outcomes indicate improvements in binocular vision at far, intermediate, and near distances. An 8% re-treatment rate should be considered to increase satisfaction levels, including a 3% reversal rate. [J Refract Surg. 2020;36(2):89-96.].

Analysis of Impact of Humidity and Temperature on Excimer Laser Ablation of Polyethylene Terephthalate, Polymethylmethacrylate, and Porcine Corneal Tissue.

BACKGROUND AND OBJECTIVES: To analyze the impact of humidity and temperature on excimer laser ablation of polyethylene terephthalate (PET), polymethylmethacrylate (PMMA) and porcine corneal tissue, and an ablation model to compensate for the temperature and humidity changes on ablation efficiency. STUDY DESIGN/MATERIALS AND METHODS: The study was conducted using an AMARIS 1050RS (Schwind eye-tech-solutions) placed inside a climate chamber at ACTS. Ablations were performed on PET, PMMA, and porcine cornea. The impact of a wide range of temperature (~18°C to ~30°C) and relative humidity (~25% to ~80%) on laser ablation outcomes was tested using nine climate test settings. For porcine eyes, change in defocus was calculated from the difference of post-ablation to pre-ablation average keratometry readings. Laser scanning deflectometry was performed to measure refractive change achieved in PMMA. Multiple linear regression was performed using the least square method with predictive factors: temperature, relative humidity, time stamp. Influence of climate settings was modeled for pulse energy, pulse fluence, ablation efficiency on PMMA and porcine cornea tissue. RESULTS: Temperature changes did not affect laser pulse energy, pulse fluence (PET), and ablation efficiency (on PMMA or porcine corneal tissue) significantly. Changes in relative humidity were critical and significantly affected laser pulse energy, high fluence and low fluence. The opposite trend was observed between the ablation performance on PMMA and porcine cornea. CONCLUSIONS: The proposed well-fitting multi-linear model can be utilized for compensation of temperature and humidity changes on ablation efficiency. Based on this model, a working window for optimum operation has been found (temperature 18°C to 28°C and relative humidity 25% to 65%) for a maximum deviation of ±2.5% in ablation efficiency in PMMA and porcine corneal tissue. Lasers Surg. Med. © 2019 The Authors. Lasers in Surgery and Medicine Published by Wiley Periodicals, Inc.

Immediate and short term visual recovery after SmartSurfACE photorefractive keratectomy / Recuperación visual inmediata y a corto plazo tras queratectomía fotorrefractiva SmartSurf ACE

PURPOSE: To investigate immediate and short-term visual recovery in a large cohort of 2093 myopic eyes (with or without astigmatism) treated with SmartSurfACE procedure, a combination of Transepithelial Photo Refractive Keratectomy (PRK) and Smart Pulse Technology (SPT, SCHWIND eye-tech-solutions GmbH, Kleinostheim, Germany). METHODS: In this retrospective case series, post-operative outcomes were evaluated immediately after the surgery (Day 0), at day 1 and 3 months postoperatively, after myopic SmartSurfACE treatment with mean pre-operative spherical equivalent -4.65 ± 2.53 D and range from -16.13D to- 0.13D. In all cases, pre and postoperative standard examinations were performed. The analysis evaluated preoperative Corrected and Uncorrected Distance Visual Acuity (CDVA and UDVA, respectively), and postoperative UDVA, monocularly and binocularly, immediately after the surgery, at day 1 and 3 month follow up. RESULTS: Sixty-two percent eyes achieved monocular UDVA 20/40 or better immediately after the surgery, while 82% patients achieved binocular UDVA 20/32 or better immediately after the surgery. At 3-month postoperatively, monocular UDVA 20/25 or better was achieved in 94% eyes. Treated eyes achieved immediately after the surgery or by the next day mean UDVA 20/41 ± 8. UDVA improved significantly from Day 1 to 3-months follow up (p < 0.0001 for both OS and OD) to mean UDVA 20/21 ± 5 (equal to preoperative CDVA 20/21 ± 8). CONCLUSION: Immediate and short-term visual recovery after SmartSurfACE PRK in our large cohort was rapid, providing functional binocular UDVA immediately after the surgery

OBJETIVO: Investigar la recuperación visual inmediata y a corto plazo en una amplia cohorte de 2.093 ojos miópicos (con o sin astigmatismo) tratados con el procedimiento SmartSurfACE, una combinación de Queratectomía Fotorrefractiva Transepitelial (PRK) y SPT (Smart Pulse Technology, SCHWIND eye-tech-solutions GmbH, Kleinostheim, Alemania). MÉTODOS: En esta serie de casos retrospectivos, se evaluaron los resultados post-operatorios inmediatamente tras la cirugía (Día 0), al día siguiente a la misma, y a los tres meses de la intervención, tras el tratamiento de la miopía con SmartSurfACE, con un equivalente esférico preoperatorio medio -4,65 ± 2,53D y rango desde -16,13D a -0,13D. En todos los casos se realizaron exámenes estándar preoperatorios y postoperatorios. El análisis evaluó preoperatoriamente la agudeza visual de lejos corregida y no corregida (CDVA y UDVA), y postoperatoriamente UDVA, monocular y binocular, inmediatamente tras la cirugía, al día siguiente, y a los tres meses de seguimiento. RESULTADOS: El 62% de los ojos logró UDVA monocular 20/40 o un valor mejor inmediatamente tras la cirugía, y el 82% de los pacientes logró UDVA binocular 20/32 o un mejor valor inmediatamente tras la cirugía. A los tres meses de la intervención, se logró UDVA monocular 20/25 o un valor mejor en el 94% de los ojos. Los ojos tratados lograron inmediatamente tras la cirugía o al día siguiente UDVA 20/41 ± 8. UDVA mejoró significativamente entre el día siguiente y los tres meses de seguimiento (p < 0,0001 para ambos ojos) a un valor medio de 20/21 ± 5 (igual a CDVA preoperatoria de 20/21 ± 8). CONCLUSIÓN: La recuperación visual inmediata y a corto plazo tras PRK con SmartSurfACE en nuestra amplia cohorte fue rápida, logrando una UDVA binocular funcional inmediatamente tras la cirugía

Immediate and short term visual recovery after SmartSurfACE photorefractive keratectomy.

PURPOSE: To investigate immediate and short-term visual recovery in a large cohort of 2093 myopic eyes (with or without astigmatism) treated with SmartSurfACE procedure, a combination of Transepithelial Photo Refractive Keratectomy (PRK) and Smart Pulse Technology (SPT, SCHWIND eye-tech-solutions GmbH, Kleinostheim, Germany). METHODS: In this retrospective case series, post-operative outcomes were evaluated immediately after the surgery (Day 0), at day 1 and 3 months postoperatively, after myopic SmartSurfACE treatment with mean pre-operative spherical equivalent -4.65±2.53D and range from -16.13D to -0.13D. In all cases, pre and postoperative standard examinations were performed. The analysis evaluated preoperative Corrected and Uncorrected Distance Visual Acuity (CDVA and UDVA, respectively), and postoperative UDVA, monocularly and binocularly, immediately after the surgery, at day 1 and 3 month follow up. RESULTS: Sixty-two percent eyes achieved monocular UDVA 20/40 or better immediately after the surgery, while 82% patients achieved binocular UDVA 20/32 or better immediately after the surgery. At 3-month postoperatively, monocular UDVA 20/25 or better was achieved in 94% eyes. Treated eyes achieved immediately after the surgery or by the next day mean UDVA 20/41±8. UDVA improved significantly from Day 1 to 3-months follow up (p<0.0001 for both OS and OD) to mean UDVA 20/21±5 (equal to preoperative CDVA 20/21±8). CONCLUSION: Immediate and short-term visual recovery after SmartSurfACE PRK in our large cohort was rapid, providing functional binocular UDVA immediately after the surgery.

Varifocal Versus Monofocal LASIK in Presbyopic Hyperopic Eyes.

PURPOSE: To compare varifocal (SupraCor; Technolas Perfect Vision GmbH, Munich, Germany) to monofocal (Zyoptix TissueSaving; Bausch & Lomb, Rochester, NY) LASIK in patients with hyperopic presbyopia. METHODS: In this prospective, non-randomized, comparative case series, consecutive patients with hyperopia, presbyopia, and emmetropia as target refraction were bilaterally treated with varifocal (8 patients) or monofocal (7 patients) LASIK. The study was designed for 35 patients, but was terminated early after interim analysis. Outcomes (preoperative and 1 day, 1 week, 1 month, and 3 months postoperative) were: monocular and binocular uncorrected near visual acuity (UNVA), distance-corrected near visual acuity (DCNVA), uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), low-contrast UDVA and CDVA, efficacy, and safety. RESULTS: Preoperative data were similar in both groups. Monocular and binocular UNVA were not significantly different between both groups at any follow-up visit. At 3 months, mean monocular UNVA was 0.40 logMAR in both groups. Monocular DCNVA and binocular CDVA were not significantly different between groups. Monocular mean CDVA was 0.00 ± 0.06 logMAR after varifocal LASIK and -0.06 ± 0.04 logMAR after monofocal LASIK. The efficacy index was 0.9 after vari-focal LASIK and 0.88 after monofocal LASIK (not significant). The safety index was 1.08 after varifocal LASIK and 1.125 after monofocal LASIK (not significant). CONCLUSIONS: With emmetropia as target refraction, varifocal ablations yielded no additional benefit compared to monofocal ablations in hyperopic presbyopic LASIK. The authors speculate that epithelial remodeling masks the impact of a varifocal ablation pattern and that a myopic postoperative refraction (modified monovision) may be necessary to further improve near and intermediate vision. These results demonstrate the value of a control group in studies evaluating presbyopia corrections. [J Refract Surg. 2019;35(7):459-466.].

Three-year outcomes after high hyperopia correction using photorefractive keratectomy with a large ablation zone.

AIM: To evaluate refractive and visual outcomes of photorefractive keratectomy (PRK) to treat high hyperopia using an aberration-neutral profile and large ablation zone. METHODS: This was a retrospective, consecutive observational case series at the Oftalmika Eye Hospital, Bydgoszcz, Poland. We included 51 consecutive eyes of 34 patients who underwent alcohol-assisted PRK to correct hyperopia within the range of +3.6 to +6.15 D (mean+4.61±0.67 D). Procedures were performed with an Amaris 750S excimer laser (Schwind eye-tech-solutions GmbH, Kleinostheim, Germany) using an aberration-neutral profile and a 10 mm total ablation zone. Refractive results, predictability, safety and efficacy were evaluated 3 years postoperatively. RESULTS: At 1-year postsurgery, the mean manifest refraction spherical equivalent (MRSE) was -0.002±0.43 D and mean cylinder was -0.181±0.31 D, while the values were +0.09±0.46 D and -0.15±0.26 D, respectively, at 2 years (MRSE p<0.001) and +0.15±0.44 D and -0.15±0.26 D, respectively, at 3 years (MRSE p<0.001). 78% of eyes were within ±0.50 D of the attempted spherical equivalent correction. Three years postoperatively, 22% of eyes lost one line of corrected distance visual acuity and 27% gained a line or two. The change in the mean corneal spherical aberrations for the 6 mm zone was from 0.27±0.07 to 0.08±0.13 µm. CONCLUSIONS: High hyperopia correction with PRK using an aberration-neutral profile and large ablation zone provides good efficacy, safety, predictability and visual outcomes. Relatively low change of corneal spherical aberrations and low increase of hyperopia in the first three postoperative years were observed.

Transepithelial Photorefractive Keratectomy in Moderate to High Astigmatism With a Non-wavefront-Guided Aberration-Neutral Ablation Profile.

PURPOSE: To evaluate the outcomes of transepithelial photorefractive keratectomy (PRK) in moderate to high astigmatism with a non-wavefront-guided aberration-neutral ablation profile using SmartPulse allocation. METHODS: In this retrospective study, myopic patients with a preoperative cylinder of 2.00 diopters (D) or greater were analyzed at 3 months of follow-up. Transepithelial PRK treatments were performed in each patient with the Amaris 1050RS laser (SCHWIND eye-tech-solutions, Kleinostheim, Germany) creating aspheric ablation profiles by applying a SmartPulse allocation. Standard examinations and wavefront analyses were included for low and high ocular residual astigmatism subgroups. RESULTS: Fifty-eight eyes (44 patients) were included in the cohort. The eyes were divided into separate ocular residual astigmatism subgroups: 17 eyes presented with less than 0.50 D (low ocular residual astigmatism) and 24 eyes with greater than 0.75 D (high ocular residual astigmatism). The mean refractive cylinder in the entire cohort was 2.84 ± 0.86 D preoperatively and 0.40 ± 0.39 D postoperatively, with 81% of the eyes within 0.75 D of the target astigmatism. At 3 months of follow-up, significant improvement (P < .05) was seen in terms of sphere, cylinder, spherical equivalent, and uncorrected (UDVA) and corrected (CDVA) distance visual acuity. CDVA improved in 40% of eyes and 3% of eyes lost one line of CDVA. No clinically relevant changes were seen in higher order aberrations. The refractive changes showed an excellent match with the keratometric changes. The difference between the low and high ocular residual astigmatism subgroups was not significant except for the change of Snellen lines of CDVA (P < .05). CONCLUSIONS: Transepithelial PRK using a non-wavefront-guided aberration-neutral ablation profile performed by applying SmartPulse allocation yielded excellent visual outcomes. The preoperative astigmatism was reduced to subclinical values. Both subgroups were effective in terms of UDVA, CDVA, spherical and astigmatic correction, and preserving higher order aberrations. However, the low ocular residual astigmatism subgroup was slightly more prone to gain lines of CDVA. [J Refract Surg. 2018;34(7):466-474.].

An alternative application of Rasch analysis to assess data from ophthalmic patient-reported outcome instruments.

PURPOSE: To highlight the potential shortcomings associated with the current use Rasch analysis for validation of ophthalmic questionnaires, and to present an alternative application of Rasch analysis to derive insights specific to the cohort of patients under investigation. METHODS: An alternative application of Rasch analysis was used to investigate the quality of vision (QoV) for a cohort of 481 patients. Patients received multifocal intraocular lenses and completed a QoV questionnaire one and twelve months post-operatively. The rating scale variant of the polytomous Rasch model was utilized. The parameters of the model were estimated using the joint maximum likelihood estimation. Analysis was performed on data at both post-operative assessments, and the outcomes were compared. RESULTS: The distribution of the location of symptoms altered between assessments with the most annoyed patients completely differing. One month post-operatively, the most prevalent symptom was starbursts compared to glare at twelve months. The visual discomfort from the most annoyed patients is substantially higher at twelve months. The current most advocated approach for validating questionnaires using Rasch analysis found that the questionnaire was "Rasch-valid" one month post-operatively and "Rasch-invalid" twelve months post-operatively. CONCLUSION: The proposed alternative application of Rasch analysis to questionnaires can be used as an effective decision support tool at population and individual level. At population level, this new approach enables one to investigate the prevalence of symptoms across different cohorts of patients. At individual level, the new approach enables one to identify patients with poor QoV over time. This study highlights some of the potential shortcomings associated with the current use of Rasch analysis to validate questionnaires.

The art of nomograms.

BACKGROUND: To retrospectively analyse strategies for adjusting refractive surgery plans with reference to the preoperative manifest refraction. METHODS: We constructed seven nomograms based on the refractive outcomes (sphere, cylinder, axis [SCA]) of 150 consecutive eyes treated with laser in situ keratomileusis for myopic astigmatism. We limited the initial data to the SCA of the manifest refraction. All nomograms were based on the strategy: if for x diopters (D) of attempted metric, y D is achieved; we can reverse this sentence and state for achieving y D of change in the metric, x D will be planned. The effects of the use of plus or minus astigmatism notation, spherical equivalent, sphere, principal meridians notation, cardinal and oblique astigmatism, and astigmatic axis were incorporated. RESULTS: All nomograms detected subtle differences in the spherical component (p < 0.0001). Nomograms 5 and 7 (using power vectors) and 6 (considering axis shifts) detected significant astigmatic differences (nomogram 5, p < 0.001; nomogram 6, p < 0.05; nomogram 7, p < 0.005 for cardinal astigmatism, p = 0.1 for oblique astigmatism). We observed mild clinically relevant differences (~ 0.5 D) in sphere or astigmatism among the nomograms; differences of ~ 0.25 D in the proposals for sphere or cylinder were not uncommon. All nomograms suggested minor improvements versus actual observed outcomes, with no clinically relevant differences among them. CONCLUSIONS: All nomograms anticipated minor improvements versus actual observed outcomes without clinically relevant differences among them. The minimal uncertainties in determining the manifest refraction (~ 0.6 D) are the major limitation to improving the accuracy of refractive surgery nomograms.

Review of technological advancements in calibration systems for laser vision correction.

Using PubMed and our internal database, we extensively reviewed the literature on the technological advancements in calibration systems, with a motive to present an account of the development history, and latest developments in calibration systems used in refractive surgery laser systems. As a second motive, we explored the clinical impact of the error introduced due to the roughness in ablation and its corresponding effect on system calibration. The inclusion criterion for this review was strict relevance to the clinical questions under research. The existing calibration methods, including various plastic models, are highly affected by various factors involved in refractive surgery, such as temperature, airflow, and hydration. Surface roughness plays an important role in accurate measurement of ablation performance on calibration materials. The ratio of ablation efficiency between the human cornea and calibration material is very critical and highly dependent on the laser beam characteristics and test conditions. Objective evaluation of the calibration data and corresponding adjustment of the laser systems at regular intervals are essential for the continuing success and further improvements in outcomes of laser vision correction procedures.

Corneal functional optical zone under monocular and binocular assessment.

BACKGROUND: In this retrospective randomized case series, we compared bilateral symmetry between OD and OS eyes, intercorneal differences and Functional Optical Zone (FOZ) of the corneal aberrations. METHODS: Sixty-seven normal subjects (with no ocular pathology) who never had any ocular surgery were bilaterally evaluated at Augenzentrum Recklinghausen (Germany). In all cases, standard examinations and corneal wavefront topography (OPTIKON Scout) were performed. The OD/OS bilateral symmetry was evaluated for corneal wavefront aberrations, and FOZ-values were evaluated from the Root-Mean-Square (RMS) of High-Order Wavefront-Aberration (HOWAb). Moreover, correlations of FOZ, spherical equivalent (SE), astigmatism power, and cardinal and oblique astigmatism for binocular vs. monocular, and binocular vs. intercorneal differences were analyzed. RESULTS: Mean FOZ was 6.56 ± 1.13 mm monocularly, 6.97 ± 1.34 mm binocularly, and 7.64 ± 1.30 mm intercorneal difference, with all strongly positively correlated, showing that the diameter of glare-free vision is larger in binocular than monocular conditions. Mean SE was 0.78 ± 1.30 D, and the mean astigmatism power (magnitude) was 0.46 ± 0.52 D binocularly. The corresponding monocular values for these metrics were 0.78 ± 1.30 D and 0.53 ± 0.53 D respectively. SE, astigmatism magnitude, cardinal astigmatism component, and FOZ showed a strong correlation and even symmetry; and oblique astigmatism component showed odd symmetry indicating Enantiomorphism between the left and right eye. CONCLUSIONS: These results confirm OD-vs.-OS bilateral symmetry (which influences binocular summation) of HOWAb, FOZ, defocus, astigmatism power, and cardinal and oblique astigmatism. Binocular Functional Optical Zone calculated from corneal wavefront aberrations can be used to optimize refractive surgery design.

Postoperative Corneal Asphericity in Low, Moderate, and High Myopic Eyes After Transepithelial PRK Using a New Pulse Allocation.

PURPOSE: To evaluate the postoperative asphericity in low, moderate, and high myopic eyes after combined transepithelial photorefractive keratectomy and SmartSurfACE treatment (SCHWIND eye-tech-solutions GmbH, Kleinostheim, Germany). METHODS: In this retrospective case series, the outcomes of myopic SmartSurfACE were evaluated at 3 months postoperatively in 106 eyes and divided into low (less than -4.125 diopters [D]), moderate (-4.125 to -6.25 D), and high (more than -6.25 D) myopia groups. In all cases, standard examinations and preoperative and postoperative corneal topography (SCHWIND Sirius) were performed. The analysis comprised evaluating the change in asphericity versus planned correction, comparing expected and achieved postoperative asphericity for all eyes, and comparison of the three groups in terms of the preoperative and postoperatively expected and achieved asphericity. RESULTS At 3 months postoperatively, the low myopia group (n = 33) improved average negative asphericity (Q = -0.04 ± 0.17 preoperative vs -0.19 ± 0.20 postoperative, P < .05). The moderate myopia group (n = 35) maintained or slightly improved average negative asphericity (Q = -0.07 ± 0.14 preoperative vs -0.05 ± 0.24 postoperative, P = .35). For the high myopia group (n = 38), the eyes became more oblate compared to the preoperative status (Q = -0.09 ± 0.15 preoperative vs 0.62 ± 0.70 postoperative, P < .05). In terms of asphericity, the difference between the three groups was not statistically significant preoperatively (P > .10), but showed significant differences postoperatively (P < .007). The cohort's average preoperative corrected distance visual acuity was 0.01 ± 0.04 logMAR (range: 0.0 to 0.18 logMAR) and uncorrected distance visual acuity was 0.03 ± 0.08 logMAR (range: -0.12 to 0.40 logMAR) 3 months postoperatively. CONCLUSIONS: SmartSurfACE maintained or slightly improved preoperative corneal asphericity for low to moderate myopic corrections (up to -6.00 D). This may provide advantages in the quality of vision and the onset of presbyopic symptoms after laser refractive surgery in myopic patients. [J Refract Surg. 2017;33(12):820-826.].

Optimum Laser Beam Characteristics for Achieving Smoother Ablations in Laser Vision Correction.

Purpose: Controversial opinions exist regarding optimum laser beam characteristics for achieving smoother ablations in laser-based vision correction. The purpose of the study was to outline a rigorous simulation model for simulating shot-by-shot ablation process. The impact of laser beam characteristics like super Gaussian order, truncation radius, spot geometry, spot overlap, and lattice geometry were tested on ablation smoothness. Methods: Given the super Gaussian order, the theoretical beam profile was determined following Lambert-Beer model. The intensity beam profile originating from an excimer laser was measured with a beam profiler camera. For both, the measured and theoretical beam profiles, two spot geometries (round and square spots) were considered, and two types of lattices (reticular and triangular) were simulated with varying spot overlaps and ablated material (cornea or polymethylmethacrylate [PMMA]). The roughness in ablation was determined by the root-mean-square per square root of layer depth. Results: Truncating the beam profile increases the roughness in ablation, Gaussian profiles theoretically result in smoother ablations, round spot geometries produce lower roughness in ablation compared to square geometry, triangular lattices theoretically produce lower roughness in ablation compared to the reticular lattice, theoretically modeled beam profiles show lower roughness in ablation compared to the measured beam profile, and the simulated roughness in ablation on PMMA tends to be lower than on human cornea. For given input parameters, proper optimum parameters for minimizing the roughness have been found. Conclusions: Theoretically, the proposed model can be used for achieving smoothness with laser systems used for ablation processes at relatively low cost. This model may improve the quality of results and could be directly applied for improving postoperative surface quality.

Clinical outcomes of laser in situ keratomileusis with an aberration-neutral profile centered on the corneal vertex comparing vector planning with manifest refraction planning for the treatment of myopic astigmatism.

PURPOSE: To evaluate clinical outcomes of laser in situ keratomileusis (LASIK) with an aberration-neutral profile centered on the estimated visual axis (considering 70% of the pupil offset toward the corneal vertex) comparing vector planning with manifest refraction planning for the treatment of myopic astigmatism. SETTING: Muscat Eye Laser Center, Muscat, Sultanate of Oman, Muscat, Oman. DESIGN: Retrospective case series. METHODS: The outcomes were evaluated at a 6-month follow-up in eyes showing ocular residual astigmatism (ORA) over 0.75 diopters (D) preoperatively. RESULTS: Eighty-five treatments were based on manifest astigmatism (preoperative sphere -2.11 D ± 1.3 [SD], cylinder -0.90 ± 1.0 D), and 79 treatments were based on vector planning (preoperative sphere -2.46 ± 1.5 D, cylinder -0.78 ± 0.79 D). At a 6-month follow-up, 128 patients (164 eyes) were evaluated and no significant differences were observed between the 2 groups in terms of difference between corrected distance visual acuity and uncorrected distance visual acuity (UDVA) (P = .1, t test and Fisher exact test Snellen lines 1 or better, P = .4) and postoperative UDVA (P = .05, t test and Fisher exact test for UDVA 20/16 or better, P = .3). Significant differences were observed between the 2 groups in terms of achieved spherical equivalent (P = .04), corneal toricity, and ORA (P < .001, t test and Fisher exact test for ORA ≤0.75 D, P < .001). CONCLUSION: Performing LASIK for myopic astigmatism with the vector planning approach resulted in comparable visual outcomes to manifest refraction planning.

Bilateral symmetry in vision and influence of ocular surgical procedures on binocular vision: A topical review / Simetría bilateral en la visión e influencia de los procedimientos quirúrgicos oculares sobre la visión binocular: Revisión de actualidad

We analyze the role of bilateral symmetry in enhancing binocular visual ability in human eyes, and further explore how efficiently bilateral symmetry is preserved in different ocular surgical procedures. The inclusion criterion for this review was strict relevance to the clinical questions under research. Enantiomorphism has been reported in lower order aberrations, higher order aberrations and cone directionality. When contrast differs in the two eyes, binocular acuity is better than monocular acuity of the eye that receives higher contrast. Anisometropia has an uncommon occurrence in large populations. Anisometropia seen in infancy and childhood is transitory and of little consequence for the visual acuity. Binocular summation of contrast signals declines with age, independent of inter-ocular differences. The symmetric associations between the right and left eye could be explained by the symmetry in pupil offset and visual axis which is always nasal in both eyes. Binocular summation mitigates poor visual performance under low luminance conditions and strong inter-ocular disparity detrimentally affects binocular summation. Considerable symmetry of response exists in fellow eyes of patients undergoing myopic PRK and LASIK, however the method to determine whether or not symmetry is maintained consist of comparing individual terms in a variety of ad hoc ways both before and after the refractive surgery, ignoring the fact that retinal image quality for any individual is based on the sum of all terms. The analysis of bilateral symmetry should be related to the patients’ binocular vision status. The role of aberrations in monocular and binocular vision needs further investigation (AU)

Analizamos el papel de la simetría bilateral para mejorar la capacidad visual binocular en ojos humanos, y exploramos adicionalmente el modo en que la simetría bilateral se conserva en diferentes procedimientos quirúrgicos oculares. Los criterios de inclusión para esta revisión fueron la relevancia estricta ante las cuestiones clínicas en estudio. El enantiomorfismo se ha reportado en aberraciones de bajo orden, aberraciones de alto orden, y direccionalidad de los conos. Cuando el contraste difiere en ambos ojos, la agudeza binocular es mejor que la agudeza monocular del ojo con mejor contraste. La anisometropía es una situación infrecuente en las grandes poblaciones. La anisometropía observada en la infancia y la juventud es transitoria, y de consecuencia menor para la agudeza visual. La sumación binocular de las señales de contraste declina con la edad, independientemente de las diferencias inter-oculares. Las asociaciones simétricas entre el ojo derecho y el izquierdo podrían explicarse mediante la simetría del offset pupilar y el eje visual, que es siempre nasal en ambos ojos. La sumación binocular mitiga el empeoramiento de la función visual en situaciones de baja luminosidad, y la fuerte disparidad inter-ocular afecta de manera perjudicial a la sumación binocular. Existe una simetría considerable de la respuesta en los ojos de los pacientes que se someten a PRK y LASIK para la corrección de la miopía, pero sin embargo el método para determinar si la simetría se mantiene o no consiste en comparar los términos aberrométricos individuales en una serie de modos ad hoc, con anterioridad y posterioridad a la cirugía refractiva, ignorando el hecho de que la calidad de la imagen de la retina para cualquier individuo se basa en la suma de todos los términos. El análisis de la simetría bilateral podría relacionarse con la situación de la visión binocular de los pacientes. El papel de las aberraciones en la visión monocular y binocular precisa una mayor investigación (AU)