Eszter Szalai

Repeatability of ocular biomechanical data measurements with a scheimpflug-based noncontact device on normal corneas

PURPOSE To analyze the repeatability of a new device measuring ocular biomechanical properties, central corneal thickness (CCT), and intraocular pressure (IOP) and to investigate these parameters and their correlations in healthy eyes. METHODS Three consecutive measurements were performed on each eye using the CorVis ST device (Oculus Optikgeräte, Inc., Wetzler, Germany). Ten specific parameters, CCT, and IOP were measured. Biometric data were recorded with IOLMaster (Carl Zeiss Meditec, Jena, Germany). RESULTS This study comprised 75 eyes of 75 healthy volunteers (mean age: 61.24 ± 15.72 years). Mean IOP was 15.02 ± 2.90 mm Hg and mean CCT was 556.33 ± 33.13 μm. Intraclass correlation coefficient (ICC) was 0.865 for IOP and 0.970 for CCT, and coefficient of variation was 0.069 for IOP and 0.008 for CCT. ICC was 0.758 for maximum amplitude at highest concavity and 0.784 for first applanation time, and less than 0.6 for all other parameters. The device-specific data showed no significant relationship with age and axial length. Flattest and steepest keratometric values and IOP showed a significant correlation with the 10 device-specific parameters. CONCLUSIONS The CorVis ST showed high repeatability for only IOP and pachymetric values. Single measurements are not reliable for the 10 device-specific parameters. The device allows for conducting clinical examinations and screening for surgeries altering ocular biomechanical properties with some form of averaging of multiple measurements.

Reliability and repeatability of swept-source Fourier-domain optical coherence tomography and Scheimpflug imaging in keratoconus

PURPOSE: To evaluate the repeatability and reliability of a recently introduced swept‐source Fourier‐domain anterior segment optical coherence tomography (AS‐OCT) system and a high‐resolution Scheimpflug camera and to assess the agreement between the 2 instruments when measuring healthy eyes and eyes with keratoconus. SETTING: Department of Ophthalmology, Medical and Health Science Center, University of Debrecen, Debrecen, Hungary. DESIGN: Evaluation of diagnostic test or technology. METHODS: Three consecutive series of anterior segment images were taken with AS‐OCT (Casia SS‐1000) followed by rotating Scheimpflug imaging (Pentacam high resolution). Axial keratometry in the steep and flat meridians and astigmatism values were recorded. Pachymetry in the apex, center, and the thinnest position and anterior chamber depth (ACD) measurements were also taken. RESULTS: This study enrolled 57 healthy volunteers (57 eyes) and 56 patients (84 eyes) with keratoconus. Significant difference was found in all measured anterior segment parameters between normal eyes and keratoconic eyes (P<.05). In keratoconic eyes, the difference between repeated measurements was less with AS‐OCT than with Scheimpflug imaging in every keratometry and astigmatism value, in apical thickness, and in ACD. For keratometry, the thinnest and central pachymetry measurement repeatability was better in healthy eyes than in keratoconic eyes with both instruments. In general, the mean difference between AS‐OCT and Scheimpflug imaging was higher in cases of keratoconus. CONCLUSIONS: Significant differences in keratometry, pachymetry, and ACD results were found between AS‐OCT and Scheimpflug imaging. However, the repeatability of the measurements was comparable. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned.

Evaluation of tear osmolarity in non-Sjögren and Sjögren syndrome dry eye patients with the tearlab system

Purpose: To evaluate tear osmolarity with the recently introduced TearLab system (TearLab Corporation, San Diego, CA) in patients with non-Sjögren syndrome dry eye (NSSDE) and Sjögren syndrome dry eye (SSDE), and in healthy subjects, and to compare the results with those from classical dry eye tests. Methods: Thirty-nine eyes of 21 patients with NSSDE, 39 eyes of 20 patients with SSDE, and 44 eyes of 22 healthy individuals were included in the study. Tear osmolarity was measured with the TearLab system, lid-parallel conjunctival folds score was examined with the slit lamp, and then the classical diagnostic tests such as Schirmer I test, tear film break-up time, and corneal staining were carried out, followed by the examination of meibomian glands and corneal transparency. Results: Mean tear osmolarity was 296.77 ± 16.48 mOsm/L in NSSDE (15% abnormal), 303.36 ± 17.22 mOsm/L in SSDE (23% abnormal), and 303.52 ± 12.92 mOsm/L in the control group (16% abnormal; P = 0.018, Kruskal–Wallis). Schirmer test, corneal staining, tear film break-up time, and meibomian gland status were significantly different in the 2 patient groups when compared with those in the control group (P < 0.0001). In the control and SSDE groups, no significant correlation was disclosed between tear osmolarity and any of the dry eye tests performed. Conclusions: Tear hyperosmolarity is considered a key factor that leads to dry eye symptoms and to the progression of clinical signs. Osmolarity measurements with the TearLab system disclosed no ability to distinguish between healthy individuals and patients with dry eye. This suggests that the TearLab device should not be used alone but in combination with classical dry eye tests.

Examination of ocular biomechanics with a new Scheimpflug technology after corneal refractive surgery

PURPOSE To analyze the early results of a new device measuring ocular biomechanics after corneal refractive surgery. PATIENTS AND METHODS Thirty nine refractive surgery patients were enrolled in the study (age: 32.6±9.9 years). Laser in situ keratomileusis (LASIK) was performed on 52 eyes of 26 patients and photorefractive keratectomy (PRK) was done on 26 eyes of 13 patients. Ten device-specific biomechanical parameters, intraocular pressure (IOP) and pachymetry were measured preoperatively and at day 1, week 1 and month 1 after the surgeries with a new technology based on Scheimpflug imaging (CorVis ST, Oculus). RESULTS In case of LASIK, the day after the procedure, radius values showed significant differences compared to preoperative data. One month after surgery, radius values, velocity of the second applanation and pachymetry showed significant differences compared to preoperative data. In case of PRK, the day after the procedure, significant differences in IOP, maximum amplitude at the apex, A1 time, A2 velocity and highest concavity time were measured. After 1 month of PRK, there were no differences in the parameters compared to preoperative data except pachymetry. CONCLUSIONS We observed that some specific biomechanical parameters changed measured with CorVis ST after LASIK and PRK, in the early postoperative time. However, most of these parameters remain unchanged after one month of LASIK and PRK compared to preoperative data.

Assessment of Tear Osmolarity and Other Dry Eye Parameters in Post-LASIK Eyes

Purposes: To assess the tear osmolarity using the TearLab device after laser in situ keratomileusis (LASIK) and to compare the values with those obtained by traditional tear film tests before and after the procedure. Methods: Thirty eyes of 15 refractive surgery candidates (5 men and 10 women of mean age: 30.55 ± 11.79 years) were examined. Using a special questionnaire (Ocular Surface Disease Index), subjective dry eye complaints were evaluated, and then, the tear osmolarity was measured with the TearLab system (TearLab Corporation) and conventional dry eye tests were carried out. Examinations were performed preoperatively and at 1, 30, and 60 days after the surgery. Results: The mean value of tear osmolarity was 303.62 ± 12.29 mOsm/L before the surgery and 303.58 ± 20.14 mOsm/L at 60 days after the treatment (P = 0.69). Mean lid parallel conjunctival folds value was 0.68 ± 0.68 before the procedure and 0.58 ± 0.65 subsequent to surgery (P = 0.25). Meibomian gland dysfunction was not detected. No significant deviation was observed in the values of Schirmer test, corneal staining, tear break-up time, and lid parallel conjunctival folds when compared with postoperatively obtained values during the follow-up period (P > 0.05). Conclusions: During LASIK flap creation, intact corneal innervation is damaged, and the ocular surface lacrimal functional unit can be impaired. In our study, no abnormal dry eye test results were observed before or after the procedure. Based on our results, LASIK treatment is safe for dry eye involving the administration of adequate artificial tears for a minimum of 3 months.

Keratometry evaluations with the Pentacam high resolution in comparison with the automated keratometry and conventional corneal topography

Purpose: To determine the reliability and repeatability of keratometry (K) measurements obtained with the Pentacam high resolution (HR), automated keratometry, and corneal topography systems. Methods: The right eyes of 46 healthy subjects were examined prospectively. Keratometry measurements in the flat (Kf) and steep (Ks) meridians were taken by 2 independent investigators with the Pentacam HR (Oculus, Wetzlar, Germany) followed by automated keratorefractometry (KR-8100; Topcon, Tokyo, Japan), and corneal topography (TMS-4; Tomey, Erlangen, Germany). Results: The mean K readings of the Pentacam HR, automated keratometry, and corneal topography were 43.40/43.34 diopter (D), 43.99/43.98 D, and 43.80/43.83 D, respectively. The difference between the values was statistically significant (P < 0.0001, repeated measures analysis of variance). Strong significant correlation was observed between the Pentacam HR and keratometry (Kf: r = 0.952/0.954; Ks: r = 0.845, Spearman rank test), and Pentacam HR and corneal topography (Kf: r = 0.933/0.930; Ks: r = 0.838/0.829) (P < 0.0001). No significant difference was presented between the 2 investigators for any of the instruments (P = 0.215–0.983). Moreover, high correlation was found between the K readings of the observers (interoperator intraclass correlation coefficients ranged from 0.95 to 0.99). Conclusions: The Pentacam HR provided reliable K measurements in clinical practice in comparison with an automated keratometer and a corneal topographer. Based on the results, for patient follow-up, one keratometry device is recommended.

Analysis of surgically induced astigmatism on the posterior surface of the cornea.

PURPOSE To measure surgically induced astigmatism (SIA) on the posterior surface of the cornea using Scheimpflug-based keratometry on eyes with with-the-rule astigmatism. METHODS Repeated Scheimpflug-based keratometry was obtained preoperatively and a mean of 8.65 weeks postoperatively following superior clear corneal incisions. Differences in the keratometric values and SIA were determined on the anterior and posterior surfaces separately and the data were analyzed. RESULTS The study included 88 eyes of 88 patients (age range: 46.4 to 87.5 years), with the steepest total corneal meridian between 75° and 105°. Preoperatively, the magnitude of the anterior and posterior corneal astigmatism was 0.74 ± 0.44 and 0.29 ± 0.14 diopters (D), respectively, which was greater than 0.5 D in 10 eyes (11.36%). The difference between preoperative and postoperative keratometric data on the posterior surface was significant, as was the difference between the preoperative and postoperative posterior astigmatism. The mean magnitude of posterior corneal SIA was 0.32 ± 0.29 D, which was 0.5 D or greater in 22 eyes (25.00%). A statistically significant correlation was observed between the diopter of the preoperatively measured posterior corneal astigmatism and the postoperative SIA on the posterior surface (r = 0.34, P = .001). The correlation was not significant between SIA on the anterior and posterior surfaces (r = 0.10, P = .36). CONCLUSIONS SIA on the posterior surface of the cornea may have a significant role, especially in cases of toric intraocular lens implantation. Posterior corneal astigmatism and SIA may have a significant clinical impact on more precise planning of cataract surgeries.

Evaluation of Posterior Astigmatism Measured With Scheimpflug Imaging

Purpose: Our aim was to assess the corneal power, axis, and age dependence of the anterior and posterior corneal surfaces with Scheimpflug imaging. Methods: Patients older than 10 years without a history of ocular surgery, corneal diseases, contact lens wearing, or severe dry eye were enrolled. Data regarding the anterior and posterior cornea were analyzed by means of Scheimpflug imaging (Pentacam HR). Results: The median age was 46.8 years (range: 10.0–90.3), and involved 827 eyes of 827 patients. Posterior corneal astigmatism was a median of −0.30 diopters (D) and exceeded 0.50 D in 12.56%. The ratio of the anterior-to-posterior corneal radius was a median of 1.217 (range: 1.021–1.402). The correlation between this ratio and age was significant (r = −0.219; P < 0.001). The correlation between anterior and posterior corneal astigmatism and age was significant. At the anterior surface, the ratio of with-the-rule astigmatism was 80.0% for the age range 10 to 20, decreasing to 36.0% for those aged over 81 years, whereas the ratio of against-the-rule astigmatism increased from 7.1% to 44.0%. At the posterior surface, the ratio of with-the-rule astigmatism was 94.3% for the age range 10 to 20 years, decreasing to 84.0% for those aged over 81 years, whereas the ratio of against-the-rule astigmatism increased from 1.4% to 8.0%. Conclusions: The posterior cornea significantly influences corneal astigmatism. Its power value and orientation are much more stable with advancing age compared with anterior surface values.

Assessment of corneal topography indices after collagen crosslinking for keratoconus

Purpose Riboflavin UVA (collagen crosslinking [CXL]) treatment for keratoconus is a method for stabilizing or improving corneal properties. Our aim was to evaluate changes in corneal topography indices after CXL. Methods A total of 38 eyes of 25 patients (mean age 29.36 ± 9.7 years) were treated with CXL technique. The follow-up period was 36 months. Slit-lamp examination, visual acuity tests, and pachymetry measurements were performed; in order to obtain the following numerical data, corneal topography (TMS-4; Tomey) was used: simulated keratometry (K1, K2), CYL (cylinder value), SAI (surface asymmetry index), IAI (irregular astigmatism index), SRI (surface regulatory index), ACP (average corneal power), and CEI (corneal eccentricity index). Treatments were performed with In-Pro CCL-Lix (Germany) equipment. Results The values of mean K1 (p = 0.82), cylinder (p = 0.73), SAI (p = 0.99), IAI (p = 0.82), SRI (p = 0.73), ACP (p = 0.73), K2 (p = 0.8), and CEI (p = 0.99) showed no significant changes at the end of the examination period. Uncorrected visual acuity remained unchanged (p = 0.32). However, best-corrected visual acuity changed from 0.21 ± 0.17 to 0.12 ± 0.11 in logMAR scale, but this deviation was not considered significant (p = 0.08). No change was observed in intraocular pressure (p = 0.79). Cornea remained clear and during follow-up period no corneal thinning was observed (p = 0.78). Conclusions Our results suggest that corneal collagen CXL can be a successful treatment at certain stages of keratoconus, offering a way to stop progression in keratometric indices.

Reliability of the corneal thickness measurements with the Pentacam HR imaging system and ultrasound pachymetry.

Purpose: To obtain the central corneal thickness (CCT) of healthy eyes using the rotating Scheimpflug imaging system and compare these results with conventional ultrasound pachymetry values. Interoperator reliability and repeatability of the different techniques were also determined. Methods: CCT was measured on the right eye of 46 healthy subjects with the Pentacam HR (Pentacam High Resolution; Oculus, Wetzlar, Germany) and contact ultrasound pachymetry (AL-2000; Tomey, Tennenlohe, Germany) by 2 independent investigators. Results: Both observers obtained significantly higher CCT readings with the Pentacam HR imaging system (572 ± 33 and 575 ± 31 μm) than with the ultrasound device (546 ± 27 and 548 ± 28 μm) (P < 0.0001, paired Student t test). Strong and significant correlation was found between the 2 pachymetry techniques regardless of the investigator (r = 0.845 and 0.831, Spearman correlation coefficient) (P < 0.0001). For the Pentacam HR values, statistically significant difference was detected between the observers (P = 0.033). For both pachymetry methods, the degree of agreement between the investigators was reflected by the high interoperator intraclass correlation coefficient value (ICC = 0.96). No significant difference was disclosed between the 3 consecutive readings of either instrument (P > 0.05, analysis of variance). Conclusions: Significant difference in CCT values between the high-resolution Pentacam imaging system and the ultrasound pachymeter suggests that the 2 techniques cannot be used interchangeably in clinical practice.