Corneal Resistance Factor Research Articles

Corneal biomechanics and intraocular pressure changes after uneventful phacoemulsification surgery

Background Biomechanics of the cornea is represented by corneal hysteresis (CH), which is defined as the viscous damping owing to viscoelastic resistance of the cornea to deformation. Aim Assessing intraocular pressure (IOP) and corneal biomechanics alterations after phacoemulsification. Patients and methods Thirty eyes were uneventfully operated on using phacoemulsification. CH, corneal resistant factor (CRF), corneal compensated intraocular pressure (IOPcc), and Goldmann correlated intraocular pressure (IOPg) values were recorded by ocular response analyzer (ORA). Central corneal thickness (CCT) was evaluated using pentacam preoperatively and postoperatively after 1 day, 1 week, and 1 month. Results Patients comprised 22 males and 8 females, with a mean age of 63.8±6.8years. Preoperative mean CCT was 532.4±39.2 µm, mean CH was 9.4±1.7 mmHg, mean CRF was 9.5±2.0 mmHg, mean IOPg was 15.4±3.9 mmHg, and mean IOPcc was 17.1±3.6 mmHg. CCT significantly increased after 1 day and significantly decreased after 1 week, and decreased again after 1 month but remained significantly higher. CH decreased significantly after 1 day and increased to the preoperative values after 1 week and 1 month. CRF significantly increased after 1 day and then decreased significantly after 1 week and remained significantly lower. Both IOPcc and IOPg insignificantly elevated after 1 day, then significantly declined after 1 week, and insignificantly increased after 1 month but was still lower than the preoperative value. CH, CRF, and CCT correlated significantly except for 1 day after surgery. Conclusion Cataract surgery causes corneal structural alterations, changing biomechanical properties and IOP initially. CCT contributes in these parameters, as there is a correlation with CH and CRF.

Corneal Topographic and Biomechanical Changes after Small Incision Lenticule Extraction (SMILE) In Myopic Eyes

Background: Small incision lenticule extraction (SMILE) offers laser vision correction by using a less invasive technique that creates a lenticule inside the intact cornea. This procedure limits the biomechanical strength of the cornea and reduces flap-induced complications. Purpose: To evaluate outcome, post-operative corneal topographic and biomechanical changes in myopic patients who had undergone SMILE. Methods: The study included 40 eyes of 20 patients treated by SMILE for myopia and myopic astigmatism. Data included uncorrected and best corrected visual acuity (UCVA and BCVA), spherical equivalent (SE), central pachymetry Pentacam (oculus) topography to evaluate changes in keratometric readings (K1 and K2) and asphericity (Q). Corneal hysteresis (CH) and corneal resistance factor (CRF) were measured with ocular response analyzer. Patients were treated and followed for 12 months. Results: SMILE procedure for the correction of myopia and myopic astigmatism was performed on 40 eyes of 20 patients. There was highly significant difference between pre and postoperative keratometric regarding K1 and K2 was change from 42.9 ± 0.82 and 39.8 ± 1.14 to 43.9 ± 1.21 and 40.5 ± 1.18 respectively (P value <0.001).Corneal resistance factor and hysteresis were also change from 11.55 ± 1.29 mm Hg and 11.68±1.40 mm Hg to 9.47 ± 1.29 mm Hg and 8.49 ± 1.54 mm Hg, respectively) (P < .0001). At the end of follow up UDVA was 20/20 or better in 86 % of eyes. Conclusions: Biomechanical stability with small-incision lenticule extraction has been demonstrated with establishment of myopic and astigmatic corrective ability, so SMILE represents a safe and effective refractive option. The incidence of intraoperative and or postoperative complications remains minimal. Although visual recovery may be slower than LASIK in most cases.

Corneal Topographic and Biomechanical Changes after Small Incision Lenticule Extraction (SMILE) In Myopic Eyes

Background: Small incision lenticule extraction (SMILE) offers laser vision correction by using a less invasive technique that creates a lenticule inside the intact cornea. This procedure limits the biomechanical strength of the cornea and reduces flap-induced complications. Purpose: To evaluate outcome, post-operative corneal topographic and biomechanical changes in myopic patients who had undergone SMILE. Methods: The study included 40 eyes of 20 patients treated by SMILE for myopia and myopic astigmatism. Data included uncorrected and best corrected visual acuity (UCVA and BCVA), spherical equivalent (SE), central pachymetry Pentacam (oculus) topography to evaluate changes in keratometric readings (K1 and K2) and asphericity (Q). Corneal hysteresis (CH) and corneal resistance factor (CRF) were measured with ocular response analyzer. Patients were treated and followed for 12 months. Results: SMILE procedure for the correction of myopia and myopic astigmatism was performed on 40 eyes of 20 patients. There was highly significant difference between pre and postoperative keratometric regarding K1 and K2 was change from 42.9 ± 0.82 and 39.8 ± 1.14 to 43.9 ± 1.21 and 40.5 ± 1.18 respectively (P value <0.001).Corneal resistance factor and hysteresis were also change from 11.55 ± 1.29 mm Hg and 11.68±1.40 mm Hg to 9.47 ± 1.29 mm Hg and 8.49 ± 1.54 mm Hg, respectively) (P < .0001). At the end of follow up UDVA was 20/20 or better in 86 % of eyes. Conclusions: Biomechanical stability with small-incision lenticule extraction has been demonstrated with establishment of myopic and astigmatic corrective ability, so SMILE represents a safe and effective refractive option. The incidence of intraoperative and or postoperative complications remains minimal. Although visual recovery may be slower than LASIK in most cases.

Effect of Intravitreal Bevacizumab Injection on Corneal in vivo Biomechanics: A Pilot Study.

Purpose:To evaluate the effect of intravitreal bevacizumab (IVB) injection on corneal biomechanical parameters as measured by the ocular response analyzer (ORA) and Corneal Visualization Scheimpflug Technology (CorVis).Methods:In this prospective pilot study, ORA and CorVis parameters were recorded before and after a three-month course of IVB injection therapy in 16 patients in the injected and the contralateral non-injected control eyes. The changes in the recorded parameters in each group and the differences between the two groups were evaluated and compared.Results:None of the changes in ORA parameters were statistically significant in the injected and non-injected groups before and three months after injection, except for corneal resistance factor (CRF) in injected eyes (paired t-test, P = 0.039). The differences in corneal hysteresis (CH) and CRF were not statistically significant between the two groups (P = 0.441 and 0.236, respectively), but significant differences were noted between corneal compensated IOP (IOPcc) and Goldmann-correlated IOP (IOPg) (P = 0.045 and 0.047, respectively). None of the changes in CorVis parameters were statistically significant in the groups before and at the end of study, except for the time of first corneal applanation (TAp1 ms) in the injected group (P = 0.040, paired t-test). Differences in TAp1, length of the second corneal applanation (LAp2 mm), velocity of the second corneal applanation (VAp2 m/s), intraocular pressure (IOP), and central corneal thickness (CCT) also showed borderline significance between the two groups.Conclusion:In this pilot study IVB injection could change CRF, IOPcc, IOPg, and TAP1 as measured by ORA and CorVis.

Does photorefractive keratectomy with mitomycin results in less weakening effect on corneal biomechanics compared to thin-flap Lasik procedure in mild to high myopia? An Ocular Response Analyzer study

Purpose To understand the changes in corneal biomechanics studied by Ocular Response Analyzer after thin-flap Lasik technique compared with photorefractive keratectomy (PRK) with mitomycin C in mild to high myopia to decrease the risk of ectasia. Patients and methods Forty eyes of 24 myopic patients with mild to severe myopia were divided into two groups; group A (included 20 eyes treated by thin-flap Lasik technique and group B (included 20 eyes treated by PRK with application of mitomycin C 0.02%). Patients were examined preoperatively and postoperatively. For the Ocular Response Analyzer, corneal hysteresis (CH), corneal resistance factor (CRF), and the keratoconus suspect (KS) were studied. Collected data were subjected to statistical analyses. Results In this study, postoperatively, a highly significant decrease (P 0.05) between both groups regarding postoperative changes in CH, CRF, and KS%. A highly significant correlation (P Conclusion Both thin-flap Lasik and PRK with mitomycin for mild to high myopia resulted in significant comparable reduction in the corneal biomechanical properties, the magnitude of which is highly dependent on the extent of correction.

Alterations in Corneal Biomechanical and Topographic Features After Accelerated Crosslinking: 1-Year Results.

Objectives:To determine the biomechanical and topographic alterations within the first year after accelerated crosslinking (CXL) treatment in patients with keratoconus.Methods:In this prospective study, 52 eyes of 52 patients with progressive keratoconus underwent accelerated CXL were included. All patients had a detailed preoperative ophthalmologic examination, including slit-lamp evaluation, Goldmann tonometry, fundoscopy, topography by Scheimpflug imaging (Sirius), and corneal biomechanical evaluation with a biomechanical waveform analysis device (ORA). Alterations in visual acuity and topographic findings were evaluated before the treatment and at 12 months follow-up. Corneal biomechanical features were obtained before the treatment, and at 1st, 3rd, 6th and 12th months.Results:Uncorrected-visual acuity and best-corrected visual acuity both statistically significantly improved at 12th month (p=0.001). There were no statistically significant differences in keratometry values, whereas maximum K (AKfront) and symmetry index front (SIfront) decreased significantly (p=0.015 and p=0.009, respectively). Corneal thinnest point and volume also decreased significantly at 12th month (p=0.001 for both). Goldmann-correlated intraocular pressure (IOPg) and corneal compensated IOP (IOPcc) values transiently increased in the first three months, while corneal hysteresis (CH) and the corneal resistance factor (CRF) transiently decreased, with the difference not statistically significant (p>0.05). However, central corneal thickness significantly decreased at the end of the 12th month (p=0.001).Conclusion:Accelerated CXL seems to be effective in stopping the progression of keratoconus. Our findings showed transient alterations in biomechanical features, which will end with the preoperative values at the end of the 12th month. Further studies are needed to demonstrate the changes in corneal biomechanics in vivo.

Evaluation of the Effect of Diabetes Mellitus on Corneal Biomechanics

Background: the cornea exhibits viscoelastic properties, which give it the quality of hysteresis. Corneal hysteresis is an important indicator of the biomechanical properties of the cornea. Aim: to compare the biomechanical properties of the cornea in patients having diabetes mellitus and age matched normal individuals as regards to corneal hysteresis (CH), corneal resistance factor (CRF), Corneal compensated IOP (IOPcc) and Goldman- correlated IOP (IOPg). Patients and Methods: A total of 200 eyes of 100 patients were enrolled in our study. Patients were selected from Ophthalmology outpatient clinics in Minia Health Insurance Hospital – Ophthalmology department. The type of our study is a case-control one. Patients were divided into two equal groups: Group A: included 50 patients (100 eyes) of age matched normal individuals. Group B: included 50 patients (100 eyes) having type 2 diabetes mellitus. Results: mean CH in control group was 9.8±1.3 mm Hg in comparison to mean CH in diabetic group which was 11.9±1.4 mm Hg, which was statistically significantly higher in diabetic patients when compared to control group, (P value = 0.<001). Conclusion: the corneal biomechanics in diabetic group are significantly higher compared with those of the control group.

Comparison of the Changes in Corneal Biomechanical Properties after Photorefractive Keratectomy and Laser in Situ Keratomileusis Using Ocular Response Analyzer

AbstractBackground: Correction of vision using Photorefractive Keratectomy (PRK) or Laser In Situ Keratomileusis (LASIK) flap creation associated with ablation produces profound changes in the corneal structure and biomechanical properties secondary to central thinning and disruption of collagen lamellar continuity.Aim of Work: This study aims to compare the changes in corneal biomechanical properties after PRK and LASIK in the treatment of low and moderate myopia by Ocular Response Analyzer.Subjects and Methods: This study included 42 adult eyes divided into two groups: (1) Contain 21 eyes referred for Lasik surgery. (2) Contain 21 eyes referred for PRK surgery. Ocular Response Analyzer (ORA) was applied to each group to measure Corneal Hysteresis (CH) and Corneal Resistance Factor (CRF).Results: There was no statistically significant difference in CH and CRF, and between CCT and RSB between the two studied groups. There was statistically significant decrease in CH after both LASIK and PRK. There was statistically significant decrease in CRF after both LASIK and PRK. There was statistically significant difference in SE after LASIK and PRK. There was statistically significant difference between LASIK and PRK in CH and CRF change with more decrease after LASIK.Conclusion: PRK and LASIK substantially weaken the biomechanical strength of the cornea, depending on the amount of archived myopic correction, and that the changes in corneal biomechanics were larger after LASIK than after PRK.

Evaluation of corneal biomechanical properties in mustard gas keratopathy

BackgroundDegenerative biomechanical factors and immunologic processes with effect on collagen and corneal reparative process are known as the main cause of ocular surface dysfunction in mustard gas keratopathy (MGK) and may cause changes in the corneal biomechanical values. Therefore, we evaluate corneal biomechanical properties of these patients. Methods and materialsThis case-control study includes 61 chemical warfare victims with MGK. After omission according to our exclusion criteria, 88 eyes of patients with MGK were enrolled as the case group and also a group of 88 normal eyes, which were matched regarding their age and sex in the control group, were enrolled. Measurements of corneal biomechanical properties which reported by ORA and Corvis ST (CST) devices were compared. The SPSS software version 23.0 was used in the statistical analysis. For comparisons between groups, if the data had a normal distribution, were analyzed by Student’s t-test and ANOVA, and if the data didn’t have a normal distribution, Mann–Whitney U test, and Kruskal-Wallis were used. Furthermore, to identify a relationship between two groups of data Spearman's rank Correlation test was used. P value < 0.05 were considered statistically significant. ResultsIn the MGK group, A1 length (A1L), A1 velocity (A1V), A2 velocity (A2V), deformation amplitude (DA) and peak distance (PD) were higher than the control group (P < 0.001). However, the corneal hysteresis (CH) (P = 0.003), corneal resistant factor (CRF), non-corrected IOP (IOPnct), corrected IOP based on corneal thickness (IOPpachy), and central corneal thickness (CCT) were lower than the control group (P < 0.001). The visual acuity according to the LogMAR scale and severity of MGK was positively associated with IOPpachy and negatively associated with CH, CRF, CCT and highest concavity radius (Radius). ConclusionMeasurement of corneal biomechanical properties may be, have a useful role in the classification, monitoring or diagnosis of MGK.

Anterior Segment Biometry and Their Correlation with Corneal Biomechanics in Caucasian Children

ABSTRACTPurpose: To assess the relationship between the corneal biomechanical parameters and the anterior segment parameters in Caucasian children.Methods: This study included 293 eyes from 293 healthy children aged between 6 and 17 years. Corneal hysteresis (CH) and corneal resistance factor (CRF) were evaluated with the Ocular Response Analyzer, axial length (AL) with IOLMaster and the anterior segment with Pentacam. Anterior segment parameters obtained were the following: central corneal thickness (CCT), corneal volume (CV), anterior chamber depth (ACD), anterior chamber volume (ACV) and mean anterior and posterior keratometry. Two multiple linear regression models were constructed to assess the association between CH and CRF with anterior segment parameters. A value of p < 0.05 was taken as the criterion for statistical significance in all analyses.Results: The mean CH and CRF were 12.12 ± 1.71 and 12.30 ± 1.89 mmHg, respectively. Multiple linear regression revealed that CH and CRF were associated negatively with AL in both models, and positively with CCT and CV in the first and second model, respectively. Meanwhile ACD, ACV or mean keratometry did not correlated with CH and CRF. Moreover, when CCT was in the model, it explained more variability for both CH (22.1%) and CRF (30.9%) than when CV was included (16.2% for CH and 16.5% for CRF).Conclusions: CH and CRF were correlated positively with CCT and CV, and negatively with AL in healthy Caucasian children. Moreover, corneal parameters were the most contributory variables to CH and CRF changes.

Corneal Biomechanical Properties and Central Corneal Thickness in Pediatric Noninfectious Uveitis: A Controlled Study

To compare the corneal biomechanics, intraocular pressure (IOP), and central corneal thickness (CCT) of 37 patients with pediatric noninfectious uveitis with 36 healthy children. Corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann-correlated and corneal-compensated IOP (IOPg and IOPcc, respectively), and CCT were measured. The mean CRF was significantly lower in the pediatric uveitic eyes than controls (9.7±1.9 vs. 10.8±1.5 mm Hg, P=0.009), whereas there was no significant difference for mean CH, IOPg, IOPcc, and CCT between the two groups (10.1±1.9 vs. 10.8±1.7, 12.9±3.3 vs. 13.9±3.1, 13.8±2.8 vs. 13.6±3.2 mm Hg, and 550.7±49.5 vs. 555.1±33.5 μm, respectively, all P>0.05). The CCT values correlated with CH and CRF, with a Pearson correlation of 0.511 and 0.670 (P=0.013 and P<0.001, respectively), whereas disease duration did not correlate with any corneal biomechanics or CCT in pediatric uveitic eyes (all P>0.05). Pediatric noninfectious uveitic eyes have lower CRF than controls but the CH, IOPg, IOPcc, and CCT values are similar.

Corneal Biomechanical Parameters With Corneoscleral Contact Lenses in Post-Laser In Situ Keratomileusis Eyes.

To evaluate corneal biomechanical parameters wearing corneoscleral contact lenses (CScL) in patients with irregular corneas after laser in situ keratomileusis (LASIK). Data from patients fitted with CScL because of corneal surface irregularities after complicated LASIK surgery were selected by two eye clinics. Previously and after 1 year of CScL fitting, corneal hysteresis (CH), corneal resistance factor (CRF), corneal-compensated intraocular pressure (IOPcc), and central corneal thickness were evaluated. In addition, visual acuity, subjective comfort, and wearing time CScL were reported. The study comprised 27 eyes. Statistically significant differences were found in visual acuity between the best spectacle-corrected vision and after CScL fitting [mean±SD, 0.16±0.03 logarithm of the minimum angle of resolution (logMAR) and 0.01±0.06 logMAR, respectively; P<0.001]. In addition, the patients reported high subjective comfort ratings (22 eyes were comfortable or very comfortable) and prolonged usage times (mean±SD, 12.67±1.98 hr of continuous wear a day). Statistically significant differences were found in the CRF between before CScL fitting and after 1 year of CScL wear (mean±SD, 7.57±0.87 and 7.68±0.84 mm Hg, respectively; P=0.015). Central corneal thickness, CH, and IOPcc showed slight differences after 1 year of CScL wear (1.78 μm, 0.04 and 0.21 mm Hg, respectively). Corneal biomechanical parameters increased slightly, although significantly for CRF, apparently without adverse clinical effects in post-LASIK eyes with irregular corneas after wearing CScL for 1 year.

Changes in corneal properties and its effect on intraocular pressure measurement following phacoemulsification with intraocular lens implantation with or without trabeculectomy

Purpose: To evaluate the changes incorneal biomechanical properties and their effect on pre and postoperative differences in IOP measurement by each tonometer&#x0D; Design: Observational study.&#x0D; Methods: The study was done in subjects who underwent phacoemulsification with intraocular lens (IOL) implantation (phaco-IOL) and combined phacoemulsification with IOL implantation and trabeculectomy (phaco-trab). IOP was measured by a single trained examiner using rebound tonometer (RBT), Ocular Response Analyzer (ORA), Goldmann applanation tonometer (GAT), dynamic contour tonometer (DCT), and Tono-Pen. Corneal hysteresis (CH) and corneal resistance factor (CRF) were measured using ORA, central corneal thickness (CCT) using ultrasonic pachymeter, and corneal curvature (CR) with manual keratometry. All measurements were done one week prior to surgery and after four weeks and six weeks of the two surgeries, respectively. Only the operated eye was included for analysis.&#x0D; Results: Twenty-nine eyes of 29 normal subjects who underwent phaco-IOL and 23 eyes of 23 glaucoma subjects who underwent phaco-trab were studied. Increase in CCT [10.2 ± 14.86 microns, p = 0.001], decrease in CH [0.82 ± 1.38 mmHg, p = 0.003] and CRF [0.97 ± 1.0 mmHg, p &lt; 0.001] were found post-phaco-IOL, whereas post-phaco-trab decrease in CCT [16.61 ± 15.22 microns, p &lt; 0.001], CRF [2.28 ± 1.93 mmHg, p &lt; 0.001] with increase in CH [0.95 ± 1.89 mmHg, p = 0.03] were noted. Multiple linear regression analysis showed significant associations for change in CH and CRF with change in IOP and not with CCT and CR postoperatively.&#x0D; Conclusion: Alterations in CH and CRF were associated with changes in IOP measured postoperatively by different tonometers. CH and CRF changes contribute to postoperative changes in measured IOP.&#x0D;

Comparison of corneal biomechanical properties of patients with dry eye secondary to Sjögren's syndrome and healthy subjects

The goal of this study is to determine whether any difference in corneal biomechanical properties exists between Sjögren's syndrome dry eye patients and healthy subjects. Thirty-one patients diagnosed with Sjögren's syndrome and associated dry eye manifestations and 44 healthy individuals were included in the study. Ultrasonic pachymetry (UP) was used to measure central corneal thickness (CCT). Corneal biomechanical parameters were obtained using ocular response analyzer (ORA). The main parameters assessed were corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann correlated intraocular pressure (IOPg) and corneal compensated IOP (IOPcc). A Student's t-test for independent groups was performed to compare the mean of these variables between both groups. Mean CH values in Sjögren's syndrome and healthy subject eyes were 10.1mmHg and 11.18mmHg respectively, representing a statistically significant difference (P=0.003). No other variable measured differed between cases and controls (P>0.05). Mean CRF values were 9.51mmHg and 10.37mmHg respectively, and mean CCT measured by UP in cases and controls was 527.41μm and 552.51μm respectively. Sjögren's syndrome can influence corneal biomechanical properties, specifically CH. ORA measurements should be considered of interest in the evaluation of Sjögren syndrome subjects.

Corneal biomechanical properties in patients with Hashimoto's thyroiditis.

Hashimoto's thyroiditis (HT) is an autoimmune endocrine disorder that results from a dysregulation of the immune system leading to an immune attack on the thyroid gland. It has potential effects on different organs and tissues. The aim of the study was to investigate the effect of HT on corneal biomechanical properties using the ocular response analyzer (ORA). A total of 48 patients with HT and 49 healthy subjects were enrolled in the study. The mean age of the patients and healthy subjects was 42.33 ±11.96 and 40.20 ±12.60 years, respectively (p = 0.39). All of the subjects underwent a full ophthalmological examination, including visual acuity, corneal pachymetry with topography, biomicroscopy, and funduscopy. Corneal biomechanical properties, including corneal hysteresis (CH) and corneal resistance factor (CRF), Goldmann-correlated intraocular pressure (IOPg) and corneal compensated IOP (IOPcc) were measured with the ORA. Central corneal thickness (CCT) in the patient group and the control group were not significantly different (p = 0.65). Corneal hysteresis of the HT patients was significantly lower than that of the control group (p = 0.005). There were no statistically significant differences in CRF between the 2 groups (p = 0.53). Goldmann-correlated IOP and IOPcc were higher in the HT patients, but only IOPcc showed a statistically significant difference (p = 0.001). In conclusion, our data shows that HT affects corneal biomechanical properties by decreasing CH. Thus, IOPcc measured with the ORA should be taken into account when determining accurate IOP values in patients with HT.

Biomechanical Corneal Changes Post LASIK with Mechanical Microkeratome Flap versus Femtosecond Flap

Back ground: The biomechanical impact of flap creation may be important in explaining changes in the curvature of the residual stroma after flap creation which plays a critical role in the development of ectasia. OBJECTIVE: To evaluate the impact of the creation of corneal flaps with mechanical microkeratome versus femtosecond laser on the biomechanical properties of the corneas. METHOD: This study included 100 eyes of 50 patients (Microkeratome Group) Compared with 100 eyes of 52 patients (Femtosecond Group) with myopia with or without astigmatism. Corneal hysteresis (CH) and corneal resistance factor (CRF) were measured with Ocular Response Analyzer before and1, 3,6and 12 months after surgery. We also investigated the relationship between these biomechanical changes and the amount of myopic correction. RESULTS: Corneal resistance factor and hysteresis was changed significantly after flap creation in both groups. In Moria2 group, they decreased significantly from 11.55 ± 1.29 mm Hg and 11.68±1.40 mm Hg to 9.47 ± 1.29 mm Hg and 8.49 ± 1.54 mm Hg, respectively) (P <.0001). In femtosecond group, they decreased from11.51 ± 1.25 mm Hg and 11.66±1.41 mm Hg to 9.49 ± 1.30 mm Hg and 8.5 ± 1.53 mm Hg, respectively (P <.0001). The ablation depth (P=0.650), residual corneal thickness (P=0.442), and postoperative corneal curvature (P=0.354) were not significantly different between femtosecond group and Moria2 group after surgery. CONCLUSION: Both femtosecond LASIK and Moria2 LASIK can affect the biomechanical strength of the cornea depending on the amount of myopic correction. The amount of biomechanical changes is larger after LASIK with mechanical microkeratome than after femtosecond from a biomechanical viewpoint.

Biomechanical Corneal Changes Post LASIK with Mechanical Microkeratome Flap versus Femtosecond Flap

Back ground: The biomechanical impact of flap creation may be important in explaining changes in the curvature of the residual stroma after flap creation which plays a critical role in the development of ectasia. OBJECTIVE: To evaluate the impact of the creation of corneal flaps with mechanical microkeratome versus femtosecond laser on the biomechanical properties of the corneas. METHOD: This study included 100 eyes of 50 patients (Microkeratome Group) Compared with 100 eyes of 52 patients (Femtosecond Group) with myopia with or without astigmatism. Corneal hysteresis (CH) and corneal resistance factor (CRF) were measured with Ocular Response Analyzer before and1, 3,6and 12 months after surgery. We also investigated the relationship between these biomechanical changes and the amount of myopic correction. RESULTS: Corneal resistance factor and hysteresis was changed significantly after flap creation in both groups. In Moria2 group, they decreased significantly from 11.55 ± 1.29 mm Hg and 11.68±1.40 mm Hg to 9.47 ± 1.29 mm Hg and 8.49 ± 1.54 mm Hg, respectively) (P <.0001). In femtosecond group, they decreased from11.51 ± 1.25 mm Hg and 11.66±1.41 mm Hg to 9.49 ± 1.30 mm Hg and 8.5 ± 1.53 mm Hg, respectively (P <.0001). The ablation depth (P=0.650), residual corneal thickness (P=0.442), and postoperative corneal curvature (P=0.354) were not significantly different between femtosecond group and Moria2 group after surgery. CONCLUSION: Both femtosecond LASIK and Moria2 LASIK can affect the biomechanical strength of the cornea depending on the amount of myopic correction. The amount of biomechanical changes is larger after LASIK with mechanical microkeratome than after femtosecond from a biomechanical viewpoint.

Outcome of PRK in Management of Post LISIK Residual Myopia and Myopic Astigmatism

Background: Different retreatment options are available for management of post LASIK residual myopia and myopic astigmatism, however PRK reduces the risk of ectasia by preserving the corneal stroma as much as possible and avoids the flap-related complications. Purpose: To evaluate the outcome as regards the safety, efficacy, and predictability of photorefractive keratectomy (PRK) for correction of residual myopia and myopic astigmatism after laser in situ keratomileusis (LASIK). Patients and Methods: The study included 30 eyes of 15 patients retreated by PRK for residual myopia and myopic astigmatism after laser in situ keratomileusis (LASIK).Data included uncorrected and best corrected visual acuity (UCVA and BCVA), spherical equivalent (SE), central pachymetry, corneal higher order aberrations (HOAs), corneal hysteresis (CH), corneal resistance factor (CRF), and corneal haze. Results: This study was performed on 30 eyes of 15patients. The mean age was 25.27±3.70 SD years old (9 women and 6 men). The average interval between procedures was 13.35 ± 5.51 months. The mean follow-up was 16.58 ± 3.06 months. Before PRK, the mean UCVA and BCVA were 0.35 ± 0.18 and 0.91 ± 0.07, respectively. The mean central pachymetry was 400.21 ± 7.8 μm, the mean SE was −1.74 ± 0.51 D. 12 months postoperatively. The mean UCVA and BCVA were 0.78 ± 0.14 (P = 0.01) and 0.92 ± 0.13 (P > 0.5), respectively. The mean central corneal thickness was 382.41 ± 2.61 μm, the mean SE was −0.18 ± 0.32 D (P < 0.01). Two eyes gained 1 line of best spectacle-corrected visual acuity; one eye lost 1 line because of corneal ectasia. No other sight-threatening complications was occurred postoperatively. Conclusions: Photorefractive keratectomy and mitomycin C was an effective, predictable, and safe procedure for correcting residual myopia and myopic astigmatism less than 3 D after LASIK. This decrease postoperative ectasia and avoids the flap related complications but has no significant effect on HOAs.

Outcome of PRK in Management of Post LISIK Residual Myopia and Myopic Astigmatism

Background: Different retreatment options are available for management of post LASIK residual myopia and myopic astigmatism, however PRK reduces the risk of ectasia by preserving the corneal stroma as much as possible and avoids the flap-related complications. Purpose: To evaluate the outcome as regards the safety, efficacy, and predictability of photorefractive keratectomy (PRK) for correction of residual myopia and myopic astigmatism after laser in situ keratomileusis (LASIK). Patients and Methods: The study included 30 eyes of 15 patients retreated by PRK for residual myopia and myopic astigmatism after laser in situ keratomileusis (LASIK).Data included uncorrected and best corrected visual acuity (UCVA and BCVA), spherical equivalent (SE), central pachymetry, corneal higher order aberrations (HOAs), corneal hysteresis (CH), corneal resistance factor (CRF), and corneal haze. Results: This study was performed on 30 eyes of 15patients. The mean age was 25.27±3.70 SD years old (9 women and 6 men). The average interval between procedures was 13.35 ± 5.51 months. The mean follow-up was 16.58 ± 3.06 months. Before PRK, the mean UCVA and BCVA were 0.35 ± 0.18 and 0.91 ± 0.07, respectively. The mean central pachymetry was 400.21 ± 7.8 μm, the mean SE was −1.74 ± 0.51 D. 12 months postoperatively. The mean UCVA and BCVA were 0.78 ± 0.14 (P = 0.01) and 0.92 ± 0.13 (P > 0.5), respectively. The mean central corneal thickness was 382.41 ± 2.61 μm, the mean SE was −0.18 ± 0.32 D (P < 0.01). Two eyes gained 1 line of best spectacle-corrected visual acuity; one eye lost 1 line because of corneal ectasia. No other sight-threatening complications was occurred postoperatively. Conclusions: Photorefractive keratectomy and mitomycin C was an effective, predictable, and safe procedure for correcting residual myopia and myopic astigmatism less than 3 D after LASIK. This decrease postoperative ectasia and avoids the flap related complications but has no significant effect on HOAs.

Factors associated with lamina cribrosa displacement after trabeculectomy measured by optical coherence tomography in advanced primary open-angle glaucoma

To investigate the relationship of lamina cribrosa displacement to corneal biomechanical properties and visual function after mitomycin C-augmented trabeculectomy. Eighty-one primary open-angle eyes were imaged before and after trabeculectomy using an enhanced depth spectral domain optical coherence tomography (SDOCT). Corneal biomechanical properties were measured with the ocular response analyzer before the surgery. The anterior lamina cribrosa (LC) was marked at several points in each of the six radial scans to evaluate LC displacement in response to intraocular pressure (IOP) reduction. A Humphrey visual field test (HVF) was performed before the surgery as well as 3 and 6months, postoperatively. Factors associated with a deeper baseline anterior lamina cribrosa depth (ALD) were cup-disc ratio (P= 0.04), baseline IOP (P= 0.01), corneal hysteresis (P= 0.001), and corneal resistance factor (P= 0.001). After the surgery, the position of LC became more anterior (negative), posterior (positive), or remained unchanged. The mean LC displacement was - 42μm (P= 0.001) and was positively correlated with the magnitude of IOP reduction (regression coefficient = 0.251, P= 0.02) and negatively correlated with age (regression coefficient = - 0.224, P= 0.04) as well as baseline cup-disk ratio (Regression coefficient = - 0.212, P= 0.05). Eyes with a larger negative LC displacement were more likely to experience an HVF improvement of more than a 3dB gain in mean deviation (P= 0.002). A larger IOP reduction and younger age was correlated with a larger negative LC displacement and improving HVF. The correlation between lower SDOCT cup-disc ratio and postoperative negative LC displacement was borderline (P = 0.05). Corneal biomechanics did not predict LC displacement.