Photorefractive Keratectomy Group Research Articles

Early elastic and viscoelastic corneal biomechanical changes after photorefractive keratectomy and small incision lenticule extraction.

To compare early changes in the corneal biomechanical parameters after photorefractive keratectomy (PRK) and small incision lenticule extraction (SMILE) and their correlations with corneal shape parameters. One hundred twenty four eyes received myopic PRK and SMILE for similar amounts of myopia. Corneal tomography with Pentacam HR, biomechanical parameters using Corvis ST, and Ocular Response Analyzer (ORA) were evaluated before and 2weeks after surgery. The change in each parameter was compared between groups, while the difference in central corneal thickness and cornea-compensated intraocular pressure measured before and after surgery were considered as covariates. A significant reduction was seen in the corneal stiffness parameter at first applanation, and an increase in deformation amplitude ratio (DAR), and integrated inverse radius (IIR) in both groups after surgery (p < 0.001) Changes in DAR, and IIR were significantly greater in the SMILE than in the PRK group (p < 0.001) Corneal hysteresis (CH) and corneal resistance factor(CRF) decreased in both SMILE and PRK groups after surgery, (p < 0.001) with no statistically significant difference between groups (p > 0.05) Among new Corvis ST parameters, DAR showed a significant correlation with changes in Ambrosio relational thickness in both groups (p < 0.05). Both techniques caused significant changes in corneal biomechanics in the early postoperative period, with greater elastic changes in the SMILE group compared to the PRK group, likely due to lower tension in the SMILE cap and thinner residual stromal bed in SMILE. There were no differences in viscoelastic changes between them, so the lower CH may reflect the volume of tissue removed.

Does the introduction of streamlight decrease refractive surgery operating time?

The aim of the study was to analyze the time-savings associated with introduction of Streamlight™ (Alcon Laboratories, Fort Worth, TX, USA) transepithelial photorefractive keratectomy (PRK) in surface corneal ablations. All refractive surgeries were performed using the Alcon WaveLight® EX500 at the ArtLife Clinic, Gdańsk, Poland. The study included patients treated for refractive errors with transepithelial PRK between April 2019 and October 2021, who were matched with patients treated with alcohol-assisted PRK during the same period. Only results for the left eye were analyzed. One-hundred-five patients underwent transepithelial PRK (age 33.42 ± 8.67years) and were matched with 105 patients that underwent alcohol-assisted PRK (age 33.05 ± 10.16years; p = 0.11). The mean preoperative spherical equivalent refraction was - 2.04 ± 2.28 D, and - 1.9 ± 1.71 D for the transepithelial and alcohol-assisted PRK group, respectively (p = 0.20). The total surgery time was non-significantly shorter in transepithelial PRK (349.46 ± 47.83s) than in alcohol-assisted PRK (354.93 ± 137.63s; p = 0.7); however, the variance of surgical time was significantly lower in transepithelial PRK (p<0.001). The laser treatment duration was greater in transepithelial PRK (41.78 ± 17.2s) than in alcohol-assisted PRK (8.48 ± 6.12s; p < 0.001), and so was the number of breaks during the laser treatment (0.95 ± 0.63 vs. 0.53 ± 0.88, respectively; p < 0.001). The introduction of transepithelial PRK did not bring significant time-associated savings into the refractive surgery suite.

Photorefractive Keratectomy in Student Naval Aviators: Outcomes of the U.S. Navy Accessioning Study.

To present the outcomes of the U.S. Navy photorefractive keratectomy (PRK) accessioning study conducted between 2000 and 2005 that helped lead to the acceptance of laser vision correction within the U.S. aviation industry. In this prospective masked study, a total of 301 students who had PRK and underwent naval flight training were compared to 4,368 untreated peers. Three training pipelines were compared: propeller/jet transport, jet fighters, and helicopters. The evaluated metrics were flight and academic performance (assessed for the primary and advanced stage of the training as normalized Navy Standard Score [NSS]), as well as the student attrition rate from training. The attrition rate was lower in the PRK group compared to controls (15.9% vs 23.2%; P = .004). In the primary stage of training, students who had PRK outperformed controls in flight training performance in the propeller/jet transport pipeline (average NSS after PRK: 52.4 ± 7.5 vs controls: 50.7 ± 6.4, P = .02), but the flight performance in the jet fighter and helicopter pipelines was comparable between the two groups. Academic performance in the primary stage of training was approximately 7% to 13% higher in students who had PRK for all training pipelines. During the advanced training stage, there was no difference in the flight performance between the groups in any of the presented pipelines. Academic performance was significantly better for students who had PRK in the helicopter pipeline (51.2 ± 11.0 vs 46.7 ± 11.7 P < .001) but comparable between the two groups in the remaining pipelines. Refractive surgery did not have adverse effects on flight performance metrics. Pilots who had PRK had comparable or better outcomes than their untreated peers. [J Refract Surg. 2024:40(3):e173-e181.].

Effect of refractive surgery on Maklakov tonometry results

The study investigates the influence of changes in keratometric parameters after refractive surgery on the results of Maklakov tonometry. The study examined a total of 61 people (121 eyes). The patients were divided into a control group with no history of surgery (16 people, 31 eyes), a LASIK group (13 people, 26 eyes), a femtosecond-assisted LASIK (FS-LASIK) group (16 people, 32 eyes), and a photorefractive keratectomy (PRK) group (16 people, 32 eyes). The patients underwent standard examination, keratometry (Km), Maklakov tonometry with a 10 g weight, and elastotonometry with 5, 7.5, and 15 g weights. In the LASIK group, the indentation diameter with 5 and 7.5 g weights correlated with Km in the central and near-paracentral zone (r=0.3-0.5). Tonometry with a 10 g weight did not correlate with anything. Tonometry with a 15 g weight inversely correlated with Km in the paracentral points (4 mm) of the strong meridian (r= -0.5 ... -0.7). In the FS-LASIK group, a significant inverse correlation with Km was observed only for the indentation diameter with a 10 g weight in the paracentral (3-4 mm) zone (r= -0.4 ... -0.5). In the PRK group, weak (r<0.4) correlations were found between Km and the indentation diameter of the 7.5 and 10 g weights for the central zone (1-2 mm). No significant correlations were found for 5 and 15 g weights. Tonometry readings with the 10 g weight are the most dependent on Km in different groups, and the readings with the 5 g weight are the least dependent. LASIK is characterized by the largest scatter of dependencies for weights of different masses, FS-LASIK - by the smallest. Tonometry readings with the 5 g weight correlated with Km only in the LASIK group, and this was the only direct correlation. Considering the inverse nature of most correlations, higher Km may be associated with an overestimation of tonometry results, and lower Km - with its underestimation.

Intraocular pressure after combined photorefractive keratectomy and corneal collagen cross-linking for keratoconus

PurposeThe purpose of this prospective study was to evaluate the effect of combined photorefractive keratectomy (PRK) and corneal collagen cross-linking (CXL) on intraocular pressure (IOP) in patients with keratoconus (KC).MethodsWe included 64 eyes of 34 patients (19 males and 15 females; age: 19-40y) with stages 1–2 keratoconus which had undergone combined wavefront-optimized photorefractive keratectomy and corneal collagen cross linking. Two other groups of patients were added as controls: the PRK group including 110 eyes of 57 patients (23 males and 34 females; age: 18-44y) which had undergone wavefront-optimized photorefractive keratectomy for myopic refractive errors, and the CXL group including 36 eyes of 23 patients (14 males and 9 females; age: 12-38y) with keratoconus, not filling the inclusion criteria for combined PRK and CXL, which had undergone corneal collagen cross-linking. IOP was recorded preoperatively and postoperatively at 3, 6 and 12 months follow-up visits.ResultsPreoperative IOP in both CXL (12.1 ± 2.53 mmHg) and PRK + CXL (13.2 ± 2.50 mmHg) groups was significantly lower than PRK group (15.8 ± 3.10 mmHg) (F = 30.505, p < 0.001). At 3 months postoperatively, IOP showed no statistically significant difference between the three studied groups (F = 1.821, p = 0.164). At 6 months postoperatively, IOP in the CXL group (14.6 ± 2.64 mmHg) was significantly higher than both PRK (13.4 ± 2.27 mmHg) and PRK + CXL (13.3 ± 2.62 mmHg) groups (F = 3.721, p = 0.026). At 12 months postoperatively, IOP in the CXL group (14.3 ± 2.69 mmHg) was significantly higher than the PRK group (13.2 ± 2.23 mmHg) and was higher than PRK + CXL group (13.3 ± 2.59 mmHg) although not statistically significant (F = 3.393, p = 0.035).Regarding the percent of change from preoperative IOP, a statistically significant difference between the three studied groups was detected at 3, 6 and 12 months postoperatively (H = 117.459, 109.303, 122.694 respectively, p < 0.001). The median percent of change from preoperative IOP in the PRK group was −16.7%, −15%, and −16.7%, in the CXL group was + 14.3%, + 19.4%, and + 19.1%, while in PRK + CXL group was 0% at 3, 6 and 12 months postoperatively. (Post-hoc power analysis 75%).ConclusionsCombined PRK and CXL in patients with KC shows no significant effect on IOP, in contrast to either procedure performed separately.

Intraocular Pressure Changes in Myopic Patients Undergoing Laser In-Situ Keratomileusis and Photorefractive Keratectomy.

To assess the variation in intraocular pressure measurements between Ocular Response Analyzer (ORA) and Goldmann Applanation Tonometer (GAT) in myopic patients undergoing laser assisted in-situ keratomileusis (LASIK) and photorefractive keratectomy (PRK). Quasi-experimental study. Place and Duration of the Study: Armed Forces Institute of Ophthalmology (AFIO), National University of Medical Sciences, Rawalpindi, Pakistan, between September 2020 and 2021. Myopic patients undergoing LASIK and PRK during the study period were selected. Baseline examinations and postoperative follow-ups were carried out to measure intraocular pressure at 1, 3, and 6 months after LASIK or PRK, using Goldmann Applanation Tonometer (GAT) and Ocular Response Analyzer, corneal compensated IOP (ORA IOPcc). One hundred and thirteen eyes underwent myopic refractive surgery, LASIK (n = 60) or PRK (n = 53). Mean age of patients was 23.6 ± 4.11 years in the PRK group and 24.4 ± 5.94 years in LASIK group. For the PKR group, the GAT IOP value increased at 1-month (p <0.001), decreased at 3-month (p <0.001) and further decreased at 6-month (p <0.001) follow-up postoperatively. In the LASIK group, the GAT IOP value decreased at all time points (p <0.001). In both groups, the mean ORA IOPcc value increased at 1 month (p <0.001), decreased at 3-month (p <0.001) and further decreased at 6-month (p <0.001) follow-up postoperatively. The IOP mean values were generally found to be higher when measured using ORA as compared with GAT. Corneal refractive surgery markedly decreased IOP. This decrease in IOP was observed more after LASIK than after PRK. ORA was less likely to underestimate the intraocular pressure than GAT. Myopia, Laser in-situ keratomileusis, Photorefractive keratectomy, Tonometery ocular, Intraocular pressure.

Comparison of Higher Order Aberrations between Wavefront Optimized Photorefractive Keratectomy and Laser in situ Keratomileusis in Myopic Patients.

To compare the higher order aberrations (HOA) between wavefront optimized (WFO) laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) in myopic patients. Quasi-experimental study. Place and Duration of the Study: Armed Forces Institute of Ophthalmology, Rawalpindi, Pakistan, from December 2021 to December 2022. Forty-four patients underwent wavefront optimized PRK and fifty-seven patients underwent wavefront optimized LASIK. All variables were recorded before the procedure and at 1, 3, 6, and 12 months postoperatively and included uncorrected visual acuity (UCVA), corrected distance visual acuity (CDVA), root mean square (RMS) of HOAs, spherical aberration (SA), and coma aberration (CA). A total of 101 eyes of 51 patients were considered in the final analysis. Patients were divided into two groups. Group A comprised of 44 (43.6%) eyes of 22 patients who underwent PRK while group B comprised of 57 (56.4%) eyes of 29 patients who underwent LASIK. UCVA significantly improved postoperatively at 3 and 6 months in both PRK and LASIK groups (p<0.001 for both groups). In this study, the increase in root mean square (RMS) of higher order aberrations from baseline value was 77% after PRK and 28% after LASIK, similar ratio was observed in spherical aberration (SA). The trend of rise in Coma aberrations was more in LASIK group 66.49%as compared to 46.2% in PRK group. Both Wavefront Optimized PRK and LASIK are safe and have elicited comparable results of post-procedure visual recovery. There was a marked increase in RMS of HOAs in PRK group as compared to WFO LASIK group while coma aberration increased more in LASIK as compared to PRK postoperatively. LASIK, PRK, RMSh, HOAs, Spherical aberration, Coma, Myopia.

Vector analysis of astigmatism correction after PRK, FS-LASIK, and SMILE for myopic astigmatism.

To compare astigmatic correction among photorefractive keratectomy (PRK), femtosecond laser-assistedin situkeratomileusis(FS-LASIK), and small-incision lenticule extraction (SMILE). This prospective study enrolled 157 eyes that underwent three procedures (59 PRK, 47 FS-LASIK, and 51 SMILE) for the treatment of myopia with low to high astigmatism (- 0.25 to - 4.50 D). Ocular residual astigmatism (ORA) was calculated by vector analysis using refractive (RA) and corneal astigmatism. Vector analysis results were compared in different procedures in the two RA groups (low ≤ 1.00 D and high > 1.00 D) at 3 and 12months postoperatively. There were no significant between-group differences in postoperative safety and efficacy outcomes (all P > 0.05). No significant differences were found in postoperative cylinders between all surgical groups (all p > 0.05), except for 3months postoperative ORA in FS-LASIK (P = 0.004). At 12months, 77%, 59.2%, and 50% of eyes attainemmetropia in the FS-LASIK, SMILE, and PRK groups, respectively. Vector analysis showed comparable values for surgical induced astigmatism, target induced astigmatism, mean error, and angle of error between groups at 12months. Significant differences were observed only in the correction index and difference vector parameters in the astigmatic > 1.00 D group at 3months (P < 0.001), and FS-LASIK was preferable. One-year outcomes revealed that PRK, FS-LASIK, and SMILE were all equally effective in correcting myopic astigmatism. However, FS-LASIK demonstrated more favorable astigmatism correction in eyes with astigmatism > 1.00D in early postoperatively.

Long-term results of hyperopic ablations using alcohol-assisted PRK and FS-LASIK: comparative study.

To evaluate the long-term visual and refractive outcomes of hyperopic excimer ablation using alcohol-assisted photorefractive keratectomy (PRK) and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK). American University of Beirut Medical Center, Beirut, Lebanon. Retrospective, matched comparative study. Eyes that underwent alcohol-assisted PRK were compared to matched eyes that underwent FS-LASIK. All patients were followed up for at least 3 years after surgery. The refractive and visual outcomes of each group were compared at different postoperative time points. The main outcome measures were spherical equivalent deviation from target (SEDT), manifest refraction, and visual acuity. 83 eyes underwent alcohol-assisted PRK and 83 matched eyes underwent FS-LASIK. Preoperative manifest refraction spherical equivalent was 2.44 ± 1.18 diopters (D) and 2.20 ± 0.87 D ( P = .133) in the PRK and FS-LASIK groups, respectively. Preoperative manifest cylinder was -0.77 ± 0.89 D and -0.61 ± 0.59 D ( P = .175) for the PRK and LASIK groups, respectively. 3 years postoperatively, SEDT was 0.28 ± 0.66 D and 0.40 ± 0.56 D for the PRK and LASIK groups, respectively ( P = .222), whereas manifest cylinder was -0.55 ± 0.49 D and -0.30 ± 0.34 D for PRK and LASIK, respectively ( P < .001). The mean difference vector was 0.59 ± 0.46 for PRK and 0.38 ± 0.32 for LASIK ( P < .001). 13.3% of PRK eyes and 0% of LASIK eyes had >1 D of manifest cylinder ( P = .003). Both alcohol-assisted PRK and FS-LASIK are safe and effective for the treatment of hyperopia. PRK induces slightly more postoperative astigmatism than LASIK. Larger optical zones and recently introduced ablation profiles that lead to a smoother ablation surface might improve the clinical results of hyperopic PRK.

Dry Eye Disease following LASIK, PRK, and LASEK: An Observational Cross-Sectional Study.

Dry eye disease is the most frequent non-refractive postoperative complication following refractive surgery. This prospective study investigated the development of dry eye disease after three common refractive laser surgeries: laser in situ keratomileusis (LASIK), photorefractive keratectomy (PRK), and laser-assisted sub-epithelial keratectomy (LASEK). Patients who underwent uneventful refractive surgery in a single private medical center between May 2017 and September 2020 were included. Ocular surface disease was graded according to the Dry Eye Workshop severity (DEWS) classification. Patients were examined 6 months following refractive surgery. The analysis included 251 eyes of 137 patients: 64 eyes (36 patients) after LASEK, 90 eyes (48 patients) after PRK, and 97 eyes (53 patients) after LASIK. At 6 months post-surgery, the DEWS score was higher for the LASIK than the PRK and LASEK groups (p = 0.01). For the total cohort, severe DEWS score (grades 3 and 4) at 6 months post-surgery was correlated with female gender (p = 0.01) and to the amount of refractive correction (p < 0.001), but not to age (p = 0.87). In conclusion, LASIK surgery and female gender were associated with dry eye. Patients, particularly those with high myopia, should be counseled about the risk of developing dry eye after refractive surgeries.

Outcomes of Single-Step Transepithelial Photorefractive Keratectomy Compared With Alcohol-Assisted Photorefractive Keratectomy Using Wave-Light EX500 Platform.

Purpose To compare the visual outcome of transepithelial photorefractive keratectomy (PRK) against alcohol-assisted PRK in treating low-to-moderate myopia with or without astigmatism. Setting Dhahran Eye Specialist Hospital, Dhahran, Saudi Arabia. Design This is a retrospective study. Methods Forty eyes of 22 patients with myopia from -0.75 to -6.00 diopters (D) with or without astigmatism from 0 to -3D were included in this study. Preoperative and postoperative data of 20 eyes from 11 patients who underwent transepithelial PRK were compared with 20 eyes from 11 patients who underwent alcohol-assisted PRK were collected and analyzed. The uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), manifest spherical equivalence (SE), manifest cylinder, vector analysis of astigmatism, and efficacy and safety indices were compared between the groups at a mean follow-up of one year postoperatively. Results Baseline characteristics were similar between groups, except the transepithelial PRK group had lower cylinder values than the alcohol-assisted PRK group by 0.69D. Regression analysis was used to control for the difference in the cylinder in all outcome parameters. Both groups had similar mean UDVA (p=0.73), CDVA (p=0.98), the proportion of eyes in either group achieved (20/20, 20/25, and 20/30) UDVA (p=0.72, 0.68 and 0.31 respectively) and percentage of eyes lost two lines of CDVA (p=1.0). There was no statistically significant difference between the two groups in regard to both efficacy and safety indices (p=0.55 and 0.67, respectively). Both groups had similar residual SE (p=0.72), the proportion of eyes within ±0.5D of SE (p=0.29), and residual refractive astigmatism (p=0.87). Both groups had similar difference vectors, surgically induced astigmatism, and correction index (p=0.82, 0.10, and 0.26, respectively). However, the transepithelial PRK group had lower target-induced astigmatism (TIA; p=0.01), higher magnitude of error (ME; p=0.05), and higher angle of error (AE; p=0.02) than the alcohol-assisted PRK group. Conclusion Transepithelial PRK had similar visual and refractive outcomes as alcohol-assisted PRK. This approach was considered as safe and effective as alcohol-assisted PRK in treating patients with low-to-moderate myopia with or without astigmatism.

Prolonged Inflammation and Infectious Changes in the Corneal Epithelium Are Associated with Persistent Epithelial Defect (PED).

Purpose: Failure of rapid re-epithelialization within 10-14 days after corneal injury, even with standard supportive treatment, is referred to as persistent corneal epithelial (CE) defect (PED). Though an array of genes regulates reepithelization, their mechanisms are poorly understood. We sought to understand the network of genes driving the re-epithelialization in PED. Method: After obtaining informed consent, patients underwent an ophthalmic examination. Epithelial scrapes and tears samples of six PED patients and six individuals (control) undergoing photorefractive keratectomy (PRK) were collected. RNA isolation and quantification were performed using either the epithelial scrape taken from PED patients or from HCLE cells treated with control tears or tears of PED patients. Quantitative real-time polymerase chain reaction (qRT-PCR) was performed to detect the expression of a few important genes in CE homeostasis, inflammation, and cell-cell communication, viz., Kruppel-like factor 4 (KLF4), GPX4, IL6, TNFα, STING, IL8, desmoglein, and E-cadherin, among others. Their expressions were normalized with their respective housekeeping genes and fold changes were recorded. KLF4 localization and MMPs activity was carried out via immunofluorescence and zymography, respectively. Results: KLF4, a transcription factor important for CE homeostasis, was upregulated in tears-treated HCLE cells and downregulated in PED patients compared to the healthy PRK group. Cell-cell communication genes were also upregulated in tears-treated cells, whereas they were downregulated in the PED tissue group. Genes involved in proinflammation (IL6, 282-fold; TNFα, 43-fold; IL8, 4.2-fold) were highly upregulated in both conditions. MMP9 activity increased upon tears treatment. Conclusions: This study suggests that tears create an acute proinflammatory milieu driving the PED disease pathology, whereas the PED patients scrapes are an indicator of the chronic stage of the disease. Interferons, pro-inflammatory genes, and their pathways are involved in PED, which can be a potential target for inducing epithelialization of the cornea.

Comparison of objective and subjective visual quality after flapless laser vision correction for mild to moderate myopia: SMILE vs PRK.

To investigate the differences in surgical results and the objective and subjective quality of vision (QoV) of patients after small incision lenticule extraction (SMILE) versus alcohol-assisted photorefractive keratectomy (PRK). Medical records of patients treated with SMILE and PRK were retrospectively examined. Visual quality, biometric parameters, Strehl ratio (SR), and corneal higher-order aberrations (HOAs) within a 6.0mm area were recorded. The effective optical zone (EOZ) and decentration were measured using a tangential pre-post operation difference map. Subjective QoV and operation satisfaction were evaluated 6months postoperatively using the Quality of Vision questionnaire. The study comprised 100 eyes treated with SMILE (preoperative mean spherical equivalent (SE), - 4.52 ± 0.81 dioptres (D)) and 69 eyes with PRK (mean SE, - 4.21 ± 1.25 D). Six months postoperatively, the EOZ reduction was significantly larger in the PRK group (P < 0.001). Decentrations were comparable between the groups. Regarding visual symptoms, monocular diplopia was more common following PRK (P = 0.02), and 98 (98.00%) SMILE-treated and 67 (97.10%) PRK-treated patients were satisfied with the QoV. Both groups demonstrated significant increases in total HOAs, coma, and spherical aberration (SA) at 6months postoperatively compared to preoperatively (P < 0.001); these values were significantly higher in the PRK (P < 0.05) compared to the SMILE group. SR increased significantly only in the PRK group (P < 0.05). Although EOZ was more consistent with anticipated treatment and HOAs were fewer in SMILE, high patient-reported satisfaction and good corneal optical quality were achieved in both groups, indicating that both SMILE and alcohol-assisted PRK are excellent options for mild to moderate myopia correction.

Analysis of corneal biomechanical properties 25years after myopic photorefractive keratectomy.

To evaluate corneal biomechanical changes using Corvis ST in patients treated with photorefractive keratectomy (PRK) 25years ago. In this study, 32 post-PRK and 38 normal eyes underwent Corvis ST (CST) assessments. The measured CST factors were: time of highest concavity (HC), time of applanation 1 (AT1), time of applanation 2 (AT2), length of applanation 1 (AL1), length of applanation 2 (AL2), velocity of applanation 1 (AV1), velocity of applanation 2 (AV2), deformation amplitude (DA), peak distance (PD), integrated radius (IR), Ambrosio relational thickness horizontal (ARTh), stiffness parameter at first applanation (SP-A1), DA ratio (2mm), Belin/Ambrosio enhanced ectasia display (BAD) and corneal biomechanical index (CBI). The mean [± standard deviation (SD)] age was 51.4 ± 7.36years in PRK, 51.4 ± 3.62 in control group. PRK was performed 24.69 ± 1.78years ago. ARTh, SP-A1, AT1, AL1, and AL2 were lower in PRK. PD, AT2, DA ratio (2mm), and IR were statistically higher in PRK (P < 0.01). In PRK and control group the mean value of CBI was 0.91 ± 0.11 and 0.50 ± 0.27 (P < 0.001), and mean value of BAD was 3.34 ± 1.53 and 1.1 ± 0.70 (P < 0.001). In PRK 71.9% of eyes were classed "high risk CBI plus diseased BAD" and 25% remained in the "high risk CBI and normal BAD" group. In this study, most of the post-PRK eyes which were clinically and topographically normal were classified as "high risk CBI plus diseased BAD" and had significantly worse CBI and BAD values than the control group. This leads to the conclusion that CBI and BAD alone are not appropriate to evaluate post-PRK ectasia.

Clinical outcomes after alcohol assisted photorefractive keratectomy versus excimer laser assisted epithelial removal photorefractive keratectomy

Background: Surface ablation methods as a method of refractive surgery is making a comeback considering its safety, efficacy and the ease of doing the surgery. Various techniques of epithelial debridement in photorefractive keratectomy were described, like mechanical debridement, using 20% alcohol, using excimer laser or using a rotating brush. This study compares two methods of epithelial removal, namely alcohol assisted and excimer laser assisted in patients undergoing photorefractive keratectomy. Material and methods: A prospective, randomized, interventional study in a tertiary care centre. A total of 50 patients were enrolled, after subjecting them to various test including a detailed history, ocular examination and pentacam. The patients selected were then divided into 2 groups using a randomization software, and the surgery was performed on the de novo eyes. Analysis was done using descriptive statistics namely mean, standard deviation, percentage. Student t test and chi square test was used for the analysis of the data, wherever applicable. Results: The baseline best corrected visual acuity was 0.03 ± 0.0 in the alcohol assisted photorefractive keratectomy group and 0.03 ± 0.08 in the excimer laser assisted epithelial removal photorefractive keratectomy group. At the end of 6 months, all the patients had a visual acuity of 0.00 on logmar scale. Corneal haze noticed on post-operative day one was 0.98 ± 0.09 in the alcohol assisted photorefractive keratectomy group and 0.94 ± 0.1 in the excimer laser assisted group. No corneal haze was found at the end of one week. Pain scale analysis showed that it was 3.08 ± 0.80 in the alcohol assisted photorefractive keratectomy group and 2.9 ± 0.1 in the excimer laser assisted epithelial removal photorefractive keratectomy group which was not statistically significant. There was no pain at the end of one week. Conclusion: Various modes of epithelium removal have evolved over time. The two methods of epithelial removal here have similar outcomes in visual outcome, corneal haze and pain, with a good safety margin.

Comparison of Three Tonometers in Measuring Intraocular Pressure in Eyes That Underwent Myopic Laser in situ Keratomileusis and Photorefractive Keratectomy.

ObjectiveTo compare the intraocular pressure (IOP) obtained by Goldmann applanation tonometer (GAT), correcting applanation tonometer surface (CATS) and biomechanically corrected IOP (bIOP) of Corvis ST tonometer (CVS); and to determine the effects of manifest refraction spherical equivalent (MRSE), central corneal thickness (CCT) and mean corneal curvature (Km) on the IOP measurements of corneal refractive patients.MethodsThis was a single-center, retrospective, cross-sectional study of 120 eyes of 64 patients from May 1, 2020 to June 1, 2021 who underwent laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK). The level of agreement between the three tonometers was evaluated, and correlation between parameters was calculated using Pearson correlation.ResultsMean preoperative to postoperative IOP in LASIK and PRK was 15.1 ± 3 to 11.3 ± 2.1 and 14.4 ± 2.6 to 12.1 ± 3 using GAT, 16.4 ± 2.8 to 13.1 ± 2.3 and 15.9 ± 2.6 to 13.7 ± 3 using CATS and 14.8 ± 2.4 to 12.9 ± 1.5 and 14.2 ± 2.4 to 12.6 ± 1.9 using CVS-bIOP. Preoperative IOP correlation between each tonometer pair showed that the lowest mean difference was between GAT and CVS-bIOP (0.32 in LASIK, 0.15 in PRK). Preoperative to postoperative IOP correlation of each tonometer resulted in a difference of 3.77, 2.30 in GAT; 3.32, 2.28 in CATS and 1.88, 1.62 in CVS-bIOP in the LASIK and PRK groups, respectively. Percentage change in CCT and Km was not correlated while change in MRSE had a weak relationship with percentage change in CVS-bIOP.ConclusionPreoperatively, GAT and CVS-bIOP had the best agreement in IOP measurements. CATS recorded the highest IOP preoperatively and postoperatively. IOP decreased in the three tonometers after LASIK and PRK with GAT having the largest decrease. CVS-bIOP had the lowest change between preoperative and postoperative IOP measurements. Only percentage change in MRSE was correlated with percentage change in CVS-bIOP in the LASIK group.

Changes of high order aberrations after photorefractive keratectomy (PRK) and FemtoLASIK

Purpose: a comparative study of corneal and total wavefront aberration changes after traditional PRK and FemtoLASIK.Material and methods. Corneal and total wavefront aberrations were studied on OPD-Scan III aberrometer (Nidek) in 63 patients (126 eyes) with moderate and high myopia before and after FemtoLASIK (Ziemer + Nidek-Quest, Japan) (44 patients, 88 eyes) and PRK (Nidek-Quest, Japan) (19 patients, 38 eyes). Spherical aberration (SA) was considered as the sum Z4 + Z8 + Z12.Results. The corneal asphericity coefficient Q changed to positive values after both types of intervention. Corneal RMS HOA increased in both Femto and PRK groups. Corneal Tilt 1 increased after FemtoLASIK and moved to negative values after PRK, corneal tilt 2 moved to negative values after Femto and to positive values after PRK. The vertical trefoil showed no significant change in the Femto group and dropped in the PRK group. The vertical and horizontal coma (coma 7, coma 8) changed synchronously. Corneal SA increased after Femtolasic, and became negative after PRK. The total aberrations showed a lesser change and the changes were not synchronized with the corneal ones: in particular, the RMS HOA fell from 0.28 ± 0.05 to 0.19 ± 0.05 in the Femto group, while the corneal RMS increased significantly. In the PRK group, the corneal RMS HOA showed some increase, but it was much less than corneal RMS: from 0.25 ± 0.07 to 0.62 ± 0.02 μm. The total SA increased from 0.11±0.03 to 0.27±0.02 in the Femto group and showed an insignificant drop from 0.09±0.03 to 0.03 ± 0.01, while remaining positive in the PRK group.Conclusions. The changes of the wavefront after FemtoLASIK and PRK are both significant and different. The revealed differences in the changes of corneal aberrations correspond to different profiles of the anterior surface of the cornea formed after FemtoLASIC and PRK. The internal optics of the eye partially compensates the corneal aberrations induced by excimer laser surgery.

Comparison of visual and refractive outcomes between femtosecond laser-assisted in situ keratomileusis (FS-LASIK) and photorefractive keratectomy (PRK): a long-term outcomes analysis

Aim: We aimed to compare the results of photorefractive keratectomy (PRK) and femtosecond-assisted laser in situ keratomileusis (FS-LASIK) procedures in the treatment of myopia and myopic astigmatism.&#x0D; Material and Method: Seventy eyes of 35 patients with myopia and/or myopic astigmatism who had undergone PRK procedure were compared retrospectively with 70 eyes of 35 patients with myopia and/or myopic astigmatism who had undergone FS-LASIK procedure. &#x0D; Results: All patients completed the 2-year follow-up period. With respect to age and sex, PRK and FS-LASIK groups were comparable. The differences in uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), and spherical equivalent were significantly better with PRK than with FS-LASIK at 6- and 24-month visits. FS-LASIK and PRK had similar values of safety index, efficacy index, and predictability at 6 and 24 months postoperatively. No significant complications were observed in neither of the procedures during the follow-up period. &#x0D; Conclusion: Both PRK and FS-LASIK seem equally effective options for the correction of myopia and myopic astigmatism. However, PRK provided slightly better visual and refractive outcomes than FS-LASIK at 6 and 24 months postoperatively.

Comparative study of refractive outcomes after photorefractive keratectomy and small-incision lenticule extraction in moderate myopia

ObjectivesTo compare the refractive outcomes after photorefractive keratectomy (PRK) and small-incision lenticule extraction (SMILE) in moderate myopia.BackgroundPRK and SMILE are two flapless procedures for the correction of myopia and astigmatism. In PRK, an excimer laser is used for photoablation, whereas in SMILE, a femtosecond laser is used to create the lenticule.Patients and methodsA retrospective study was conducted on 80 patients (160 eyes) who were classified into two groups: PRK and SMILE. A total of 40 patients (80 eyes) were included in each group. Assessment was between 6 months and 3 years postoperatively comparing the uncorrected distance visual acuity, best-corrected distance visual acuity, and manifest refraction spherical equivalent with the preoperative data in addition to assessing the efficacy, safety, and predictability in each procedure.ResultsThe two groups were matched for age, sex, and preoperative characteristics. The mean postoperative uncorrected distance visual acuity in the PRK group was 0.96 ± 0.06 and in the SMILE group was 0.95 ± 0.08 (P = 0.621). The mean postoperative best-corrected distance visual acuity in the PRK group was 0.96 ± 0.06 and in the SMILE group was 0.97 ± 0.07 (P = 0.735). The mean postoperative manifest refraction spherical equivalent in the PRK group was − 0.24 ± 0.34 and in the SMILE group was − 0.30 ± 0.20 (P = 0.186). The mean efficacy index in the PRK group was 0.99 ± 0.05 and in the SMILE group was 0.99 ± 0.07 (P = 0.456). The mean safety index in the PRK group of all eyes was 1.00 ± 0.03 and in the SMILE group was 1.00 ± 0.04 (P = 0.704). In the PRK group, 90% of all eyes were within ± 0.50 D of intended refraction and 100% were within ± 1.00 D. In the SMILE group, 95% of all eyes are within ± 0.50 D of intended refraction and 100% were within ± 1.00 D.ConclusionPRK and SMILE procedures showed excellent efficacy, safety, and predictability in moderate myopia, whereas SMILE was noticed to be better in predictability than PRK.

Angle Kappa measurement pre-keratorefractive and post-keratorefractive surgery using Orbscan 3

Aim of the study Measurement of the mean angle Kappa pre-keratorefractive and post-keratorefractive surgery utilizing Orbscan 3.Patients and methods This retrospective study was conducted on patients who had refractive surgeries, group A included patients who underwent Lasik and group B included patients who underwent Photo Refractive Keratectomy (PRK). Mean age from 18 to 45 years. Preoperative, 1-week, and 1-month postoperative assessments included detailed ocular examination, slit-scanning topography done by Orbscan 3, and total ocular aberrations by Zywave 3 were done.Results The study comprised 146 eyes of 75 individuals. Preoperative data demonstrated that angle Kappa mean in Lasik group (group A) was 2.38±1.54 at 147.05±96.94, in PRK group (group B) was 2.31±1.17 at 137.67±85.7. Paired mean differences of the two groups between preoperative data and 1-week postoperative show no statistically significant difference in central corneal thickness (CCT) nor angle Kappa values. Paired mean differences of the two groups between preoperative data and 1-month postoperative show no statistically significant difference regarding CCT nor angle Kappa values. Preoperative, 1-week postoperative, and 1-month postoperative correlation of angle Kappa to refractive error, spherical equivalent, average K-reading, CCT and axial length, showed that both groups had a positive correlation with axial length.Conclusion Keratorefractive surgeries do not affect angle Kappa or its intercept measurements.