Anterior Corneal Surface Research Articles

A szemnyomás változásának hatása a szaruhártya és a szem törőerejére a Liou–Brennan-modellszem alapján

It is a clinical experience that with significantly higher intraocular pressure, glass ordering may be inaccurate, therefore, it should be performed after adjustment of intraocular pressure. To analyze the effect of intraocular pressure on the refractive power of the cornea and of the eye, using geometrical properties of the Liou-Brennan model eye and finite element modeling. Using corneal parameters of the Liou-Brennan model eye, a parametric geometrical model and with these data finite element modelling, using the Ansys (Ansys, Canonsburg, PA, USA) program, has been performed. Corneal tissue properties have been defined based on trilinear material model of Wollensak and boundary conditions based on Pandolfi. The effect of changes in intraocular pressure on geometrical corneal properties with optical impact (corneal curvature at the anterior and posterior corneal surface at the optical center and axial displacement of the anterior and posterior corneal surface points at the optical center) have been analyzed. Based on the geometric characteristics obtained, using the paraxial ray tracing method, changes in the optical properties of the cornea and the eye have been calculated. With increasing intraocular pressure load, anterior and posterior central corneal radius of curvature decreased and corneal surface points at the optical center at the anterior and posterior surface moved forwards, the cornea thinned. Axial displacement of corneal volume points was maximal for all pressure load values at the optical center of the posterior corneal surface. The refractive power of the cornea decreased as eye pressure increased, while the refractive power of the entire eye increased. We verified using the Liou-Brennan model eye and finite element modelling that a change of the intraocular pressure load between 10 and 30 mmHg may result in 0.31-0.86 mm decrease of the corneal radius of curvature, in 1.5-4.8 D increase in the keratometric values and in about 1.2-3.9 D increase in the total optical power of the eye. A decrease of 0.14 D to 0.69 D has been measured in the corneal optical power in the examined eye pressure range. Orv Hetil. 2022; 163(47): 1872-1879.

Effects of rigid gas permeable contact lens on morphological parameters and vision-related quality of life in keratoconus patients.

To evaluate the effect of rigid gas permeable contact lens (RGP-CL) on corneal morphological parameters and vision-related quality of life in keratoconus (KC) patients. Totally 57 eyes of 30 KC patients who were followed-up for more than two years, including 17 RGP wearers (32 eyes) and 13 non-wearers (25 eyes) were retrospectively analyzed. Initial medical history and corneal topography were collected at baseline. Corneal topography, corneal aberration, optical coherence tomography, and vision-related quality of life questionnaires were performed at the last follow-up. According to corneal topography, increase of the flattest keratometric values was higher in RGP wearers than in non-wearers (P=0.038). The morphological parameters, including symmetry index of front corneal curvature (P=0.004) and Baiocchi-Calossi-Versaci index front (P=0.047), were lower in RGP wearers than in non-wearers. Vertical coma was smaller in RGP wearers than non-wearers in 3.0, 5.0, 6.0, and 7.0 mm pupil diameters, respectively (P<0.05). The environmental triggering domain of ocular surface disease index was worse in RGP wearers as compared to non-wearers (P=0.003). At the last follow-up, there were no significant differences in constituent ratios of KC progression, corneal thickness topography, epithelial thickness topography, morphological parameters of corneal topography, and other questionnaire scores between the two groups (all P>0.05). Long-term use of RGP does not worsen KC but may cause corneal epithelial remodeling to increase symmetry of corneal anterior surface, reduce corneal vertical coma and improve visual quality. However, RGP wearing causes a slight decrease in vision-related quality of life. The occurrence of ocular surface symptoms is mainly associated with environmental triggering factors.

Investigation of the relationship between contact lens design parameters and refractive changes in Ortho-K

PurposeTo investigate the relationship between Ortho-K contact lens design parameters and refractive power change of the eye through a parametric mathematical representation. MethodsThe current study utilises fully anonymized records of 249 eyes, 132 right eyes, and 117 left eyes from subjects aged 14.1 ± 4.0 years on average (range 9–38 years) which were selected for secondary analysis processing. The data were split into 3 groups (G1 up to 35 days wear, from 10 to 35 days, G2 up to 99 days wear, more than 35–99 days & G3 more than 100 days wear) according to the length of time, in days, that the lenses were worn. Corneal shape was measured before and after contact lens wear using the Medmont E300 topographer, from which height and distance files were read by a custom-built MATLAB code to construct the corneal anterior surface independently. Changes in refractive power pre and post-Ortho-K wear were determined using constructed tangential refractive power maps from which both centrally flattened and annular steepened zones were automatically bounded, hence used to determine the refractive power change. ResultsOn average, flat Sim-K and steep Sim-K were reduced after Ortho-K lens wear by 1.6 ± 1.3 D and 1.3 ± 1.4 D respectively. The radius of the base curve was correlated with the mean central flattened zone power change strongly in G1 (R = 0.7, p < 0.001) and moderately in G2 (R = 0.4) and G3 (R = 0.4, p < 0.001). Hence, a strong correlation with the base curve was recorded in group G1 and moderate in G2 and G3. The reverse curve was very strongly correlated to the mean central flattened zone power change in G1 (R = 0.8, p < 0.001) and strongly correlated with G2 (R = 0.6, p < 0.001) and G3 (R = 0.7, p < 0.001). The reverse curve was also strongly correlated with the mean annular steepened zone power change among all groups G1, G2, and G3 (R = 0.7, R = 0.6 and R = 0.6) respectively (p < 0.001). ConclusionsAlthough the central corneal refractive power change was strongly correlated to the Ortho-K lens base curve, it characterized only 50% of the target power change. However, the annular steepened zone refractive power change appears to be a clearer predictor of target power change, as there appears to be a one-to-one inverse relationship with the target refractive power correction. Differences between these results and the literature may be a result of the topography software smoothing effect.

Regular and irregular astigmatism of bullous keratopathy using Fourier harmonic analysis with anterior segment optical coherence tomography

Bullous keratopathy (BK) is known to present with corneal edema and Descemet's folds, which can cause corneal astigmatism. However, no report quantitatively evaluated BK astigmatism by separating it into regular and irregular astigmatism. This study investigated the regular and irregular astigmatism of the anterior and posterior corneal surface with Fourier harmonic analysis and anterior segment optical coherence tomography. Preoperative data from 43 eyes of 41 BK patients who received corneal endothelial transplantation were compared with the data from 43 eyes of 43 subjects without corneal disease. Anterior and posterior cylinder power, central corneal thickness (CCT) and thinnest corneal thickness were significantly greater in BK. With Fourier harmonic analysis, BK eyes were found to have significantly larger anterior and posterior regular astigmatism, asymmetry component and higher-order irregularity. Asymmetry component and higher-order irregularity that accounted for the posterior irregular astigmatism increased as CCT increased in BK. Higher-order irregularity in the posterior cornea also positively correlated with worsening best corrected visual acuity. Subgroup analysis found significant correlations between CCT and posterior higher-order irregularity for intraocular surgery and laser iridotomy, but not Fuchs endothelial corneal dystrophy. This study has significance in that it revealed the characteristics of the corneal posterior irregular astigmatism of BK.

Filler-based correction of tear trough depressions and eye bags in Japanese patients: A classification system and treatment algorithm.

Tear trough depressions are widely treated with fillers. However, it is questionable whether the same strategies can always be used for Caucasian and Japanese patients, owing to differences in bone and skin structures and epithelial thickness. To assess a novel classification system and treatment algorithm for correcting tear trough depressions and eye bags in Japanese patients. Tear trough depressions can be classified into three types according to the presence or absence of a "negative vector" based on retrusion of the maxilla relative to the anterior corneal surface, with or without eye-bag protrusion when smiling. Type 1 patients (without the negative vector) can be treated simply by filling the depression in the tear trough and the palpebromalar groove region. Type 2 patients (with a negative vector and no eye-bag protrusion on smiling) also require volume restoration in the mid-cheek (deep medial cheek fat, suborbicularis oculi fat, and pre-maxillary space); this not only enables volume recovery but also compensates for maxillary deficiency. Type 3 patients (with a negative vector and eye-bag protrusion on smiling) require an additional step, based on placing a filler in front of the eye bags and pushing orbital fat backward. Case presentations demonstrate the utility of the techniques involved. This system provides a simple and practical method for classifying and treating Japanese patients with tear trough depressions and eye bags. Further studies are warranted.

Change Patterns in Corneal Intrinsic Aberrations and Nerve Density after Cataract Surgery in Patients with Dry Eye Disease.

This study aimed to evaluate the change patterns in corneal intrinsic aberrations and nerve density after cataract surgery in dry eye disease. The preoperative, 1- and 3-month postoperative dry eye-related parameters were obtained by the Oculus keratograph and the ocular surface disease index questionnaire. The corneal intrinsic aberrations were measured using the Pentacam HR system. In vivo confocal microscopy was performed to observe the vortical and peripheral corneal nerves. An artificial intelligence technique run by the deep learning model generated the corneal nerve parameters. Corneal aberrations on the anterior and total corneal surfaces were significantly increased at 1 month compared with the baseline (p < 0.05) but gradually returned to the baseline by 3 months (p > 0.05). However, the change in posterior corneal aberration lasted up to 3 months (p < 0.05). There was a significant decrease in the corneal vortical nerve maximum length and average density after the operation (p < 0.05), and this damage lasted approximately 3 months. The corneal vortical nerve maximum length and average density were negatively correlated with the anterior corneal surface aberrations before and 1 month after the operation (correlation coefficients, CC = −0.26, −0.25, −0.28; all p < 0.05). Corneal vortex provided a unique site to observe long-term corneal nerve injury related to eye dryness. The continuous damage to the corneal vortical nerve may be due to the continuous dry eye state.

Clinical observations of EVO-ICL implantation and changes in corneal astigmatism using a modified technique

BackgroundImplantable collamer lens (ICL) surgery techniques are constantly progressing. The purpose of this study was to investigate the application effect of the modified technique and its impact on the change in corneal astigmatism in EVO-ICL surgery.MethodsThe analysis of retrospective cohort data included 153 eyes of 81 patients with myopia from July 2018 to May 2020. An EVO-ICL was inserted by modified surgical skills, including a single 3.0 mm corneal incision and no ophthalmic viscosurgical device (OVD) before the insertion of the ICL (modified technique group: 41 cases, 80 eyes) and standard procedure (standard technique group: 40 cases, 73 eyes). Early postoperative intraocular pressure (IOP) was monitored at 2 and 24 h. IOP, corrected distance visual acuity (CDVA), uncorrected distance visual acuity (UDVA), vault, and anterior chamber depth (ACD) were measured 1, 6, and 12 months following the initial examination. The corneal endothelial cell density (ECD) was monitored at 6 and 12 months after the operation. Surgically induced astigmatism (SIA) in the total, anterior, and posterior corneal surfaces was analysed 1 month after the operation.ResultsNo serious complications were detected. The two groups had no difference in visual outcomes, ICL vaults, or ACD at any time point (P > 0.05). Two hours postoperatively, IOP was significantly lower in the modified technique group (16.22 ± 2.22 vs. 18.37 ± 1.92 mmHg, P < 0.05) than in the standard technique group. IOP decreased gradually after 24 h to preoperative levels. The postoperative IOP remained stable over a 12-month period. The ECD at 6 and 12 months was not significantly different between the groups (P > 0.05). SIA in the total, anterior, and posterior corneal surfaces were assumed to have no clinically meaningful differences between groups at one month after operation (P > 0.05).ConclusionsThe modified technique is efficient and safe, producing comparable visual and structural outcomes without adversely affecting ECD, and reduces fluctuations in IOP at the early postoperative stages. The auxiliary incision in the standard technique does not increase corneal SIA, which is also a factor to consider for inexperienced surgeons.

Influence of Specialty Contact Lens Wear on Posterior Corneal Tomography in Keratoconus Subjects.

To evaluate the effect of specialty contact lens (CL) wear on posterior corneal tomography in keratoconus subjects. Patients with keratoconus who were wearing specialty CL were included in this retrospective cohort study. Tomographic parameters were evaluated with Scheimpflug imaging (Pentacam HR) before lens fitting and immediately after removal of CLs worn habitually for a period of several months. Subjects were divided into groups, according to type of lens (corneal, scleral, and hybrid) and keratoconus severity based on Belin/Ambrosio D (BAD-D) score, for further analysis. Thirty-four eyes of 34 subjects diagnosed with keratoconus were included. Mean duration of habitual CL wear was 7.0±0.3 months. For the entire cohort, a small increase in flat keratometric reading at the anterior corneal surface (K1F; P =0.032) and at the posterior surface (K1B; P =0.041) was found. In the corneal CL group (10 eyes; 29.4%), flattening of the anterior corneal curvature was detected (K max ; P =0.015). An increase in K1B value was seen in the scleral CL group (15 eyes; 44.1%) ( P =0.03). Combined topometric indices showed a small but significant difference in the entire cohort ( P <0.05) and in the subgroups of corneal CL wear and of moderate keratoconus (BAD-D score≥7). Various types of specialty CLs exert a differential influence on corneal parameters. A small steepening of keratometry at the posterior surface (K1B) was observed in the scleral lens group. Although corneal lens wear flattens the anterior cornea (K max ), it does not significantly alter the posterior corneal surface.

Swept-source OCT for corneal graft quantitative evaluation in the eye bank and the correlation of the measurements to pre-excision values

Quantitative evaluation of the human corneal grafts stored in the tissue banks is usually limited to endothelial cell density and central thickness. Swept-source OCT (SS-OCT) is capable of measuring the central curvatures of the corneal tissue prepared for transplantation without loss of sterileness, providing insights on its refractive state. The aim of the paper is to compare in vitro SS-OCT measurements with pre-excision values. Hand-held keratometry and ultrasound pachymetry was performed on 22 corneas before excision of corneoscleral button and insertion in the vial with Eusol-C solution (AlchimiaS.r.l, Nicolò, Italy). After 12 to 36 h of hypothermic storage the corneas were examined within the vials with custom built SS-OCT system maintaining a sterile environment. The anterior and posterior central curvatures, and central corneal thickness (CCT) were measured. Rotation of the corneoscleral button was controlled by making a 6-o'clock mark during excision. Mean pre-excision CCT was 626.45 ± 28.71 µm and 468.05 ± 52.96 µm when measured with SS OCT (r = 0.55; p < 0.001). Respective values for average keratometry were 7.74 ± 0.39 mm and 7.92 ± 0.57 mm (r = 0.6; p = 0.22). Although high differences were observed in corneal thickness, keratometric radius of curvature at the flat (r = 0.42; p < 0.001) and steep (r = 0.62; p = 0.014) meridian of the anterior corneal surface, as well as corneal anterior astigmatism (r = 0.3; p < 0.001), showed good correlation with pre-excision values. SS-OCT is capable of providing quantitative evaluation of the human corneal grafts in hypothermic storage. Good correlation between curvature measurements before excision and during banking in the vial indicates its clinical utility.

An Analytical Solution of the Hyperbolic Bioheat Model of the Cornea Subjected to Laser Irradiation

The thermal effects occurring in a cornea subjected to short-pulsed laser irradiation during laser thermokeratoplasty (LTK) are investigated. The transient bioheat transfer is described by the hyperbolic model and solved analytically using the finite Fourier transform technique and the method of variation of parameters. The computational results predicted by the hyperbolic model show that the degree of damage in the corneal tissue induced by Ho: YAG laser irradiation under LTK surgery increases linearly with time. An increase in the convection coefficient of the anterior corneal surface causes an insignificant reduction in the corneal temperature, whereas an increase in the value of phase lag in the heat flux vector causes a rise in the corneal temperature .

The Impact of Epithelial Remodeling on Surgical Techniques Used in Topography-guided Surface Ablation in Irregular Corneas.

To analyze the optical consequences of epithelial remodeling in irregular corneas and their impact on the choice of different surface ablation techniques. Anterior corneal and stromal surface topographies and epithelial thickness maps were analyzed in 24 eyes with irregular corneal optics. On two of the eyes, four different surface ablation techniques were simulated: (1) conventional anterior topography-guided photorefractive keratectomy (PRK), (2) transepithelial phototherapeutic keratectomy (PTK), (3) transepithelial anterior topography-guided PRK, and (4) stromal topography-guided PRK. Stromal surface topographies showed higher keratometric values, astigmatism, asphericity, and corneal higher order aberrations compared to topographies of anterior corneas covered by epithelium. Transepithelial anterior topography-guided PRK and stromal topography-guided PRK both resulted in regularized stromal surface, transepithelial PTK achieved partial regularization corresponding to the smoothing effect of the epithelial remodeling, and conventional anterior topography-guided PRK delivered after epithelial removal resulted in residual stromal surface irregularities. The difference in optical landscapes between the stromal and anterior surfaces in irregular corneas will represent a source of error when anterior topography-guided treatments are delivered on the deepithelialized stroma, as in conventional PRK. In contrast, anterior topography-guided ablations performed as transepithelial PRK and stromal topography-guided PRK delivered after epithelial removal address the full stromal irregularity, whereas transepithelial PTK alone may be used when topography-guided treatments are not possible. The authors conclude topography-guided PRK of irregular corneas should lead to significantly improved regularization only if it includes the effect of epithelial remodeling. [J Refract Surg. 2022;38(8):529-537.].

Fourier Analysis on Irregular Corneal Astigmatism Using Optical Coherence Tomography in Various Severity Stages of Keratoconus

To investigate the diagnostic capability of Fourier indices in detecting clinical or subclinical keratoconus (KC). Prospective cross-sectional study. The study included 126 eyes with clinical KC (50 KC without any corneal scar, 50 KC with anterior corneal scar, and 26 KC with posterior scar having a history of acute corneal hydrops), 50 with topographic KC (without clinical signs), 50 with pre-topographic KC (normal topography without clinical signs), and 50 controls. Corneal tomographic data were obtained using anterior segment optical coherence tomography (OCT). Fourier analysis decomposed dioptric data from both anterior and posterior corneal surface into spherical, regular astigmatism, asymmetry, and higher-order irregularity components. The discriminating ability of the Fourier indices of pre-topographic KC, topographic KC, and clinical KC from controls were assessed after quantitative Fourier analysis of irregular corneal astigmatism. Posterior asymmetry and higher-order irregularity components were significantly greater in pre-topographic KC eyes than those in controls (P < .001 for both), with the highest area under the receiver operating characteristic curve (AUROC) of 0.778 and 0.709, respectively. The same was true for anterior asymmetry, posterior asymmetry, and posterior higher-order irregularity components in topographic KC (AUROC of 0.945, 0.941, and 0.893, respectively), whereas it was >0.948 for all Fourier components in clinical KC. Fourier analysis using OCT can evaluate anterior and posterior corneal irregular astigmatism of various KC stages, from very mild to advanced, including severe cases with corneal scar. Irregular astigmatism indices from the posterior corneal surface showed the highest AUROC values in discriminating early KC stages.

Comparison of Total Corneal Astigmatism between IOLMaster and Pentacam.

Purpose To compare the total corneal astigmatism (TCA) measured by IOLMaster 700 and Pentacam and to investigate the consistency of corneal keratometry (CK) measured by IOLMaster and Pentacam. Methods Cataract patients were retrospectively enrolled in March and April, 2021. Retrospective analysis was performed on those patients with binocular and monocular CK measured by IOLMaster and Pentacam. Results A total of 102 patients (204 eyes) were included, 64 of whom were female (62.75%). The flat (K1) and steep (K2) CK of anterior corneal surface (ACS) and flat (TK1) and steep (TK2) of total cornea measured with IOLMaster 700 were 44.16 ± 1.60 D, 45.09 ± 1.68 D, 44.12 ± 1.62 D, and 45.14 ± 1.69 D, respectively. Those measured with Pentacam were 44.31 ± 1.57 D, 45.22 ± 1.65 D, 44.15 ± 1.67 D, and 45.19 ± 1.82 D, respectively. The astigmatism of ACS and TCA were −0.94 ± 0.63 D and −1.02 ± 0.69 D (p < 0.01) in the IOLMaster group and −0.90 ± 0.59 D and −1.05 ± 0.81 D in the Pentacam group, respectively (p < 0.01). TCA measurement results of IOLMaster and Pentacam were consistent (Pearson = 0.710, p < 0.01), and there was no significant difference (p = 0.591). Conclusions Total corneal astigmatism measured by IOLMaster was consistent with that measured by Pentacam. The difference between the astigmatism of anterior corneal surface and total cornea was detected in the measurement of IOLMaster and Pentacam, respectively.

Impact of rigid gas-permeable contact lens on keratometric indices and corneal thickness of keratoconus eyes examined with anterior segment optical coherence tomography.

Purpose/AimDetecting keratoconus (KC) progression helps determine the surgical indication for corneal cross-linking (CXL). This retrospective observational study aimed to examine changes in keratometric indices and corneal thickness in patients with KC who used rigid gas-permeable (RGP) contact lenses.Materials and methodsThis study involved 31 eyes (31 patients) diagnosed with KC. No patient had used RGP or any other type of contact lenses for at least 1 month. Corneal topographic data were obtained using three-dimensional anterior segment optical coherence tomography before and after >1 month of RGP lens use.ResultsThe average and maximum keratometry values changed after using an RGP lens (-1.05 ± 1.92 D, p < 0.01 and -1.65 ± 4.20 D, p = 0.04, respectively); the spherical component of the anterior corneal surface became significantly smaller (p = 0.02). No change was observed in the central or thinnest corneal thickness values. Keratometric changes were greater in eyes with severe KC than in those with moderate KC (p = 0.014).ConclusionsKeratometry and spherical components of the anterior corneal surface values decreased after RGP lens use; keratometric changes were greater in eyes with severe KC than in those with moderate KC. Corneal progression indices, including corneal thickness, posterior keratometry, and irregular astigmatism values, mostly remained unchanged. It is important to consider these findings when evaluating corneal topography of KC and preparing CXL.

Correlation and Comparison of Anterior and Posterior Corneal Surface Parameters in Healthy Eyes

Purpose: To correlate and compare anterior and posterior corneal surface parameters like Kflat, Ksteep, Kavg, R1, R2, Ravg and astigmatism in healthy eyes. Study Design: Descriptive correlational study Place and Duration of Study: This study was conducted at Mayo Hospital, Lahore from June 2020 to Dec 2020.. Methods: This study included 176 subjects (86 males and 90 females) with mean age of 28.06±9.68 and 28.13±8.24 respectively. The data was collected through non-random convenient sampling technique by self-made proforma after taking patients’ consent. Anterior and posterior corneal parameters (Kflat, Ksteep, Kavg, R1, R2, Ravg and astigmatism) were measured with GALILEI G4. Pearson correlation test was used for correlation and independent sample t-test / Mann-Whitney U test was used for comparing means of anterior and posterior corneal parameters. Data was entered and analyzed in SPSS-21. Results: Mean of anterior and posterior corneal curvatures was 44.21±1.01 D and -6.22±0.19 D[p&lt;0.001], Kflat was 43.76±0.99 D and -6.08±0.19 D [p&lt;0.001] and Ksteep was 44.66±1.08 D, -6.34±0.21 D, respectively [p&lt;0.001]. The anterior and posterior corneal curvature Ravg was 7.63±0.17 mm, 6.44±0.200 mm [p&lt;0.001], mean R1 was 7.71±0.17 mm, 6.58±0.21 mm, [p&lt;0.001] and mean R2 was 7.56±0.18 mm, 6.31±0.21 mm, respectively [p&lt;0.001]. Anterior posterior corneal astigmatism was 0.90±0.55 D and -0.25±0.11 D, respectively [p&lt;0.001].Anterior corneal parameters also show strong correlation with posterior corneal parameters. Conclusion: There are significant difference between corneal parameters of anterior and posterior surface. Strong correlation was also found in anterior and posterior corneal parameters except corneal astigmatism.

Effect of intracorneal ring segments on posterior corneal topography in eyes with keratoconus

PurposeTo analyze the changes in the anterior and posterior corneal surfaces measured with a Scheimpflug imaging device in keratoconus patients implanted with intracorneal ring segments (ICRS) and to correlate those changes with the visual outcomes. MethodsThis prospective interventional case series study included 92 eyes of 60 patients with keratoconus who underwent Kerarings (Mediphacos, Belo Horizonte, Brazil) ICRS implantation. Keratometric (K) readings, corneal asphericity (Q value) and elevations of both anterior and posterior corneal surfaces were evaluated using a Scheimpflug imaging device preoperatively and at 1, 3, 6 and 12 months after surgery. ResultsThe mean best corrected visual acuity (BCVA) improved from 0.61 to 0.19 logMAR at 12 months after surgery. Both anterior and posterior corneal surfaces showed significant flattening with statistically significant reduction of the mean anterior K reading by 3.39 D and the mean posterior K reading by 0.39 D (p<0.001) at 12 months. Statistically significant change of the anterior Q to a less negative value (from -1.05 to -0.36) was observed (p<0.001) with no significant change of the posterior Q value. Improvement of the anterior Q was significantly correlated to better postoperative BCVA (p=0.03). Better postoperative BCVA significantly correlated to better preoperative BCVA, flatter preoperative anterior and posterior K, less prolate anterior Q value and lower anterior elevations. ConclusionsICRS implantation has a significant flattening effect on both anterior and posterior corneal surfaces. Improvement of corneal asphericity is correlated to better visual outcome. Certain preoperative parameters were predictive factors of the postoperative visual improvement.

Comparison of keratometry versions in patients with corneal astigmatism

Purpose: to compare the corneal power at main meridians, the magnitude and the axis of corneal astigmatism and the reproducibility of measurements taken three times with different types of biometers.Material and methods. 22 subjects (24 eyes) with regular corneal astigmatism 1.89–8.02 D were given three biometry tests using IOL Master 500, Lenstar LS 900, IOL Master 700, Pentacam and Galilei G6.Results. The data were divided into groups depending on the principle of mathematical modeling of the corneal surface: group I involved the material processed by IOL Master 500, Lenstar LS 900, IOL Master 700; group II contained maps of the anterior corneal surface; and group III, those of the posterior surface. In group I, Lenstar showed the highest values of keratometry. In group II, the values of K1 , Kave in the 6 mm area were lower than in the pupil diameter area and than any values of K in the 4 mm area; the lowest values of K in this area were obtained on the Pentacam SimK. In group III, in the pupil diameter area (4.0–4.5 mm), all K values obtained with diverse equipment were different whilst in the 6 mm area the values differed only in the flat meridian. Astigmatism within groups I, III showed no difference while in group II the SimK data were different. The astigmatism axes obtained on IOLMaster 500 differed from the respective data provided by other devices. The devices of group I, 6 mm area, were the most stable.Conclusions. The highest values of keratometry are obtained when only the anterior surface of the cornea is taken into account, the lowest values are characteristic of the posterior surface. The stability of the parameter registered grew with the increase of the measured zone diameters. The biometers of group 1 showed the highest values of astigmatism with the maximum repeatability of the measurements

Wavefront aberrations caused by biomechanical effects after Small Incision Lenticule Extraction (SMILE) based on finite element analysis

To examine wavefront aberrations induced by biomechanical effects after Small Incision Lenticule Extraction (SMILE) surgery. The three-dimensional (3D) finite element models of the human eye were established. By loading the intraocular pressure (IOP), the displacement of the anterior and posterior surface of the cornea was calculated. Then the displacement was converted into the wavefront aberrations by wave-surface fitting. The results showed that the induced wavefront aberrations were noticeable from biomechanical effects after SMILE surgery. The induced higher-order aberrations from the anterior corneal surface included spherical aberration, y-Trefoil, and x-Tetrafoil. Spherical aberration was positively correlated with corrected diopter (D), but x-Tetrafoil and y-Trefoil remained stable. The induced wavefront aberrations from the posterior corneal surface were smaller than those from the anterior corneal surface, and some of the aberrations compensated each other. With IOP increased, defocus and x-Tetrafoil from the anterior corneal surface increased, while y-Trefoil and spherical aberration decreased. The IOP only affected defocus from the posterior corneal surface. In addition, the incision size also had a distinct impact on primary x-astigmatism and x-Trefoil from the anterior corneal surface, and it had a smaller effect on the aberrations from the posterior corneal surface. Therefore, the biomechanical effects increased residual wavefront aberrations after SMILE refractive surgery.

Assessment of corneal topographic patterns and densitometric parameters in patients with severe delayed-onset mustard gas keratopathy and patients suffered from corneal scarring

Purpose: This study was performed to evaluate the densitometric values and the type of corneal topographic pattern extracted from Pentacam HR (OCULUS, Wetzlar, Germany) in two groups of severe delayed-onset mustard gas keratopathy (DMGK) and old herpes simplex corneal scarring. Materials and methods: Twenty eyes of each group were enrolled to the study and were examined using the Pentacam HR. Total corneal densitometry was measured over a 12 mm diameter area, divided by annular concentric regions and depths. Also, the corneal topographic pattern from the axial curvature map of the anterior corneal surface was determined in all patients. Results: The most common observed patterns in severe DMGK and old corneal scarring were superior steepening and irregular pattern, respectively. Densitometry measurement in 10 to 12 mm in diameter in DMGK was significantly higher than old corneal scarring. There were not any significant differences in other densitometry values between the groups. Conclusion: It seems that clinical evaluation of corneal structure using Pentacam can improve our knowledge about this rare mustard gas keratopathy. Keywords: Delayed-onset mustard gas keratopathy; Corneal scarring; Pentacam HR; Densitometry; Corneal pattern.

Changes in asphericity of anterior and posterior corneal surfaces for mild-moderate and high myopia after topography-guided FS-LASIK.

To compare changes in asphericity of anterior and posterior corneal surfaces for different myopia patients after corneal topography-guided femtosecond-assisted laser in situ keratomileuses (FS-LASIK), and to analyze correlations between asphericity of corneal surfaces and preoperative spherical equivalence (SEQ). In this prospective study, 59 patients who underwent corneal topography-guided FS-LASIK surgery were enrolled and divided into the mild-moderate myopia group (67 eyes) and the high myopia group (44 eyes). Postoperative follow-ups were performed at 1, 3, and 6months. Postoperative changes in aspherical coefficient (Q values), corneal higher-order aberrations (HOAs), and spherical aberrations (Z40) were compared between the two groups. Relevance between Q value changes and SEQ, HOAs, and Z40 as well as between SEQ and changes of HOAs and Z40 was analyzed. There was a significant increase in Q values of the anterior (each diameter) and posterior (6-8mm) corneal surface in both groups than before surgery (P < 0.001). Q values of corneal anterior (each diameter) and posterior (7-9mm) surface in the high group were considerably larger than the mild-moderate group (P < 0.05). Corneal anterior surface HOAs and Z40 values in the high group largely exceeded those of the mild-moderate group (P < 0.001). The preoperative SEQ was linearly correlated with postoperative anterior Q change (ΔQ), HOAs change (ΔHOAs), and spherical aberration change (ΔZ40). The changes of corneal asphericity in patients with high myopia were greater than mild-moderate myopia, with more corneal HOAs and Z40 introduced when corneal topography-guided FS-LASIK was conducted.