Placido-disk Corneal Topography Research Articles

Repeatability of Automatic Measurements by an Anterior Segment Swept-Source OCT Biometer in Patients With Keratoconus.

To evaluate the repeatability of automatic measurements of a new anterior segment optical coherence tomographer (ANTERION; Heidelberg Engineering) and their agreement with an anterior segment optical coherence tomography device combined with Placido disc corneal topography (MS-39; CSO) in patients affected by keratoconus. Fifty-four consecutive patients were included. Three measurements were performed with the ANTERION and one with the MS-39. Repeatability was assessed by means of within-subject standard deviation, coefficient of variation (CoV), and intraclass correlation coefficient (ICC). Agreement was investigated with the 95% limits of agreement. The paired t-test and Wilcoxon matched-pairs test were performed to compare the measurements of the different devices. Repeatability of ANTERION measurements was high, with an ICC greater than 0.98 for all parameters. Many parameters revealed a CoV of less than 1% and a CoV within 5% was obtained for astigmatism measurements. The ANTERION measured a significantly higher corneal power and the MS-39 more negative posterior keratometric values. These differences were mirrored by a moderate agreement for mean simulated keratometry and poor agreement for total corneal power and posterior keratometry. The ANTERION revealed high repeatability of automatic measurements and good agreement with the MS-39 for many parameters in patients affected by keratoconus, but for most parameters the two instruments cannot be considered interchangeable. [J Refract Surg. 2024;40(7):e445-e452.].

Estimated prevalence of keratoconus in the largest metropolitan area of Italy.

To estimate the prevalence of keratoconus in a population of subjects undergoing first eye examination in an eye clinic in Italy. A single-center, cross-sectional, study was conducted involving patients who underwent first eye examination at an eye clinic in Rome between September 2021 and June 2022. The prevalence of keratoconus was determined by Placido-disk corneal topography using the maximum keratometry (Kmax) value and the Cone Magnitude and Location Index (CLMI) for keratoconus screening. Subjective analysis was performed by two experienced corneal specialists, who classified the outcome into two groups: normal and keratoconus. Risk factors, including family history of keratoconus, allergy or atopy, thyroid disease, eye rubbing habit and gender were also examined. A total of 512 subjects between 7 and 81 years old were evaluated. The inter-observer agreement to classify subjects in normal or keratoconus group was excellent (k = 1.0); the estimated prevalence in the specific population was 2.1%. Presence of positive family history (9% of keratoconus vs 5% normal), concomitant allergy or atopy (27% vs 9%) and eye rubbing habit (18% vs 4%) were associated with a higher risk of disease. This study reported a high estimated prevalence of keratoconus in a metropolitan area of Italy, as found in recent studies in the Mediterranean and Middle East countries. Screening for keratoconus is highly recommendable and easily feasible with corneal topography under expert supervision and may be indicated primarily in young population to improve early detection and prompt therapeutic management for halting disease progression.

Epithelial Thickness Mapping in Keratoconic Corneas: Repeatability and Agreement Between CSO MS-39, Heidelberg Anterion, and Optovue Avanti OCT Devices.

To assess repeatability and agreement of corneal epithelial thickness mapping in eyes with keratoconus using three optical coherence tomography (OCT) devices featuring different technologies: spectral-domain (SD) OCT combined with Placido disk corneal topography (MS-39), swept-source OCT (Anterion), and SD-OCT (Avanti). Three consecutive measurements were acquired with the three devices in 60 eyes with keratoconus. The mean epithelial thickness was calculated in the central 2-mm zone and in 2- to 5-mm and 5- to 7-mm diameter rings. The repeatability was calculated using pooled within-subject standard deviation (Sw). The agreement was assessed by paired t tests and Bland-Altman plots. The repeatability (Sw) of the epithelial thickness for the central 2-mm zone was 0.91, 0.71, and 0.93 μm for the MS-39, Anterion, and Avanti, respectively. All thicknesses with the MS-39 were greater than those of the Anterion and Avanti, with mean differences of 4.11 ± 1.34 μm (P < .001) and 0.52 ± 1.30 μm (P = .003), respectively. The 95% limits of agreement were 1.484 to 6.736 μm for the MS-39 and Anterion, -3.068 to 2.028 μm for the Avanti and MS-39, and 1.258 to 5.922 μm for for the Avanti and Anterion. Epithelial thickness mapping results were most repeatable with the Anterion, followed by the MS-39 and Avanti. The MS-39 gave the thickest values, followed by the Avanti and Anterion. The differences were significant, making the devices not interchangeable for epithelial thickness mapping in eyes with keratoconus. [J Refract Surg. 2023;39(7):474-480.].

Enhanced Diagnostics for Corneal Ectatic Diseases: The Whats, the Whys, and the Hows.

There are different fundamental diagnostic strategies for patients with ectatic corneal diseases (ECDs): screening, confirmation of the diagnosis, classification of the type of ECD, severity staging, prognostic assessment, and clinical follow-up. The conscious application of such strategies enables individualized treatments. The need for improved diagnostics of ECD is related to the advent of therapeutic refractive procedures that are considered prior to keratoplasty. Among such less invasive procedures, we include corneal crosslinking, customized ablations, and intracorneal ring segment implantation. Besides the paradigm shift in managing patients with ECD, enhancing the sensitivity to detect very mild forms of disease, and characterizing the inherent susceptibility for ectasia progression, became relevant for identifying patients at higher risk for progressive iatrogenic ectasia after laser vision correction (LVC). Moreover, the hypothesis that mild keratoconus is a risk factor for delivering a baby with Down's syndrome potentially augments the relevance of the diagnostics of ECD. Multimodal refractive imaging involves different technologies, including Placido-disk corneal topography, Scheimpflug 3-D tomography, segmental or layered tomography with layered epithelial thickness using OCT (optical coherence tomography), and digital very high-frequency ultrasound (VHF-US), and ocular wavefront. Corneal biomechanical assessments and genetic and molecular biology tests have translated to clinical measurements. Artificial intelligence allows for the integration of a plethora of clinical data and has proven its relevance in facilitating clinical decisions, allowing personalized or individualized treatments.

Topographic, elevation, and keratoconus indices for diagnosis of keratoconus by a combined Placido and Scheimpflug topography system.

To determine the accuracy of various corneal parameters in keratoconus diagnosis using Scheimpflug camera combined with Placido disk corneal topography (Sirius, CSO). One hundred and fifteen keratoconic eyes (group1) and a 111 normal eyes (group2) were assessed prospectively between March 2018 and July 2019 for: corneal keratometric indices (K1, K2, sim K, apex curvature) at different corneal rings of both corneal surfaces, central corneal thickness (CCT), thinnest corneal thickness (TL), corneal asphericity (Q), elevation at thinnest point, root mean square (RMS), and root mean square per area (RMS/A) in spherical, aspheric and aspherotoric reference for both corneal surfaces and keratoconus summary parameters; surface asymmetry index of front and back (SIf, SIb respectively), elevation at keratoconus vertex front and back (KVf, KVb respectively), Baiocchi Calossi Versaci front and back index (BCVf, BCVb) and its vector summation (BCV) and convergence radius and cutoff value for each was calculated. All studied indices were significantly different between the two groups. The highest predictive accuracy "Area under receiver operating characteristic curve (AUROC)" of 0.999 was observed for BCVf, KVb, RMS and RMS/A at 6 mm aspherotoric reference posterior surface. Keratoconus summary indices had high AUROC (0.986, 0.984, 0.948, 0.999, 0.999, 0.998 respectively). Curvature indices had lower AUROC than elevation indices, except for curvature of corneal apex at anterior (0.98) and posterior surface (0.99). Higher AUROC was noted with elevation at thinnest point especially at aspherotoric reference surface. Sirius topography showed high predictive accuracy in detection of keratoconus. Elevation indices and keratoconus summary parameters have the highest diagnostic ability.

Low and high order aberrations in the eyes of patients with levothyroxine treated hypothyroidism — comparison and analysis

Background: There is an increasing number of patients in optometric practices who suffer from hypothyroidism. Thyroid diseases have an impact on the ocular condition, refraction, and tear film stability, particularly when thyroid is hyperreactive. This research is focused on the optical condition of the eyes in patients with hypothyroidism treated with levothyroxine to assess its importance during refraction exams. Material and methods: A group of 43 patients was examined, their medical case history was taken, and aberrometry was performed. A research and control groups were selected for statistical analysis of the obtained results. Refractive condition, keratometry, whole eye aberrometry, and separately cornea and internal aberrometry were performed with the use of iTrace aberrometer, based on ray-tracing aberrometry and Placido disk corneal topography. Results: Statistically significant differences with a threshold of p = 0.05 were total eye horizontal coma and corneal horizontal secondary coma. Three values were slightly above the threshold — whole eye oblique tetrafoil, corneal vertical pentafoil, and internal horizontal coma. All three parameters have a p-value equal to 0.06. Conclusion: Hypothyroidism treated with levothyroxine does not have a significant impact on the ocular surface or internal eye aberrations of low order. However, in case of total eye horizontal coma and secondary corneal horizontal coma, the differences are statistically significant.

Repeatability of automated measurements by a new anterior segment optical coherence tomographer and biometer and agreement with standard devices

We assess repeatability of automatic measurements of a new anterior segment optical coherence tomographer and biometer (ANTERION) and their agreement with those provided by an anterior segment-optical coherence tomography device combined with Placido-disk corneal topography (MS-39) and a validated optical biometer (IOLMaster 500). A consecutive series of patients underwent three measurements with ANTERION and one with MS-39. A subgroup of patients underwent biometry also with IOLMaster 500. Repeatability was assessed by means of within-subject standard deviation, coefficient of variation (COV), and intraclass correlation coefficient (ICC). Agreement was investigated with the 95% limits of agreement. Paired t-test and Wilcoxon matched-pairs test were performed to compare the measurements of the different devices. Repeatability of ANTERION measurements was high, with ICC > 0.98 for all parameters except astigmatism (0.963); all parameters apart from those related to astigmatism revealed a COV < 1%. Repeatability of astigmatism improved when only eyes whose keratometric astigmatism was higher than 1.0 D were investigated. Most measurements by ANTERION and MS-39 showed good agreement. No significant differences were found between measurements by ANTERION and IOLMaster, but for corneal diameter. ANTERION revealed high repeatability of automatic measurements and good agreement with both MS-39 and IOLMaster for most parameters.

Repeatability of anterior segment measurements by optical coherence tomography combined with Placido disk corneal topography in eyes with keratoconus

Corneal tomography is an important tool to identify and follow up eyes with keratoconus. Our study evaluate the repeatability of the automatic measurements provided in keratoconic eyes by a new anterior-segment optical coherence tomographer (AS-OCT) combined with Placido-disk topography (MS-39, CSO) and assess their agreement with the corresponding measurements taken with a rotating Scheimpflug camera combined with Placido-disk topography (Sirius, CSO). Mean simulated keratometry, posterior and total corneal power, total corneal astigmatism, corneal asphericity, thinnest corneal thickness, epithelial thickness, corneal diameter, and aqueous depth were evaluated. Repeatability was assessed using test–retest variability, the coefficient of variation, and the intraclass correlation coefficient; agreement was assessed by the 95% limits of agreement. Good repeatability was achieved for most parameters. Moderate repeatability was found for total corneal astigmatism measurements. The repeatability of mean simulated keratometry and total corneal power measurements worsened with more severe stages of keratoconus with a statistically significant relationship between the individual coefficient of variation and corneal power values. Agreement with the Scheimpflug camera was moderate for aqueous depth and thinnest corneal thickness and poor for most other measured parameters. The good repeatability of automatic measurements suggests the new AS-OCT device to be a viable option in clinical practice of eyes with keratoconus.

Anterior Chamber Angle and Volume Do Not Change after Myopic Laser-Assisted In Situ Keratomileusis in Young Patients.

Purpose We aimed to investigate whether anterior chamber angle, depth, and volume change after myopic laser-assisted in situ keratomileusis (LASIK) in young patients. Methods This retrospective study included 29 eyes of 29 patients (15 females and 14 males) between the ages of 18 and 39 years who underwent LASIK for the treatment of myopia. In addition to complete ophthalmic examination, anterior chamber angle (ACA), central anterior chamber depth (ACD), and anterior chamber volume (ACV) were measured by using a Sirius rotating Scheimpflug camera combined with Placido disc corneal topography (CSO, Florence, Italy). Preoperative and postoperative values were compared using paired t-tests. Linear regression was used to evaluate the relationship between changes in refraction and changes in ACA, ACD, and ACV as well as between attempted maximum ablation depth and changes in ACA, ACD, and ACV. Results The mean age of the study population was 25.5 ± 6.2 years. The mean preoperative and postoperative spherical equivalent values were −3.30 ± 1.92 D and −0.18 ± 0.29 D, respectively. ACV and ACA were not significantly changed after surgery; however, central ACD was significantly decreased (preoperatively = 3.366 ± 0.316 mm vs postoperatively = 3.3 ± 0.298 mm) with a mean difference of 0.066 ± 1.121 mm. There were no significant relationships between changes in refraction and anterior segment dimensions or between attempted maximum ablation depth and anterior segment dimensions. Conclusion Measurements with Sirius showed that ACA and ACV did not change; however, central ACD significantly decreased after myopic LASIK in young patients, indicating that the preoperative central ACD value should not be used interchangeably with the postoperative central ACD value.

Customized Toric Intraocular Lens Implantation in Eyes with Cataract and Corneal Astigmatism after Deep Anterior Lamellar Keratoplasty: A Prospective Study.

Purpose To investigate the effectiveness of toric intraocular lenses (IOLs) for treating corneal astigmatism in patients with cataract and previous deep anterior lamellar keratoplasty (DALK). Setting San Giovanni-Addolorata Hospital, Rome, Italy. Design Prospective interventional case series. Methods Patients undergoing cataract surgery after DALK for keratoconus were enrolled. Total corneal astigmatism (TCA) was assessed by a rotating Scheimpflug camera combined with Placido-disk corneal topography (Sirius; CSO, Firenze, Italy). A customized toric IOL (FIL 611 T, Soleko, Rome, Italy) was implanted in all eyes. One year postoperatively, refraction was measured, the IOL position was recorded, and vectorial and nonvectorial analyses were performed to evaluate the correction of astigmatism. Results Ten eyes of 10 patients were analyzed. The mean preoperative TCA magnitude was 4.92 ± 1.99 diopters (D), and the mean cylinder of the IOL was 6.18 ± 2.44. After surgery, the difference between the planned axis of orientation of the IOL and the observed axis was ≤10° in all eyes. The mean surgically induced corneal astigmatism was 0.35 D at 20°. The mean postoperative refractive astigmatism power was 1.13 ± 0.94 D; with respect to preoperative TCA, the reduction was statistically significant (p < 0.0001). The mean change in astigmatism power was 3.80 ± 1.60 D, corresponding to a correction of 77% of preoperative TCA power. Nine eyes out of 10 had a postoperative refractive astigmatism power ≤ 2D. Conclusions Toric IOLs can effectively correct corneal astigmatism in eyes with previous DALK. The predictability of cylinder correction is partially lowered by the variability of the surgically induced changes of TCA. This trial is registered with NCT03398109.

Cornea and anterior eye assessment with placido-disc keratoscopy, slit scanning evaluation topography and scheimpflug imaging tomography.

Current corneal assessment technologies make the process of corneal evaluation extremely fast and simple and several devices and technologies allow to explore and to manage patients. The purpose of this special issue is to present and also to update in the evaluation of cornea and ocular surface and this second part, reviews a description of the corneal topography and tomography techniques, providing updated information of the clinical recommendations of these techniques in eye care practice. Placido-based topographers started an exciting anterior corneal surface analysis that allows the development of current corneal tomographers that provide a full three-dimensional reconstruction of the cornea including elevation, curvature, and pachymetry data of anterior and posterior corneal surfaces. Although, there is not an accepted reference standard technology for corneal topography description and it is not possible to determine which device produces the most accurate topographic measurements, placido-based topographers are a valuable technology to be used in primary eye care and corneal tomograhers expanding the possibilities to explore cornea and anterior eye facilitating diagnosis and follow-up in several situations, raising patient follow-up, and improving the knowledge regarding to the corneal anatomy. Main disadvantages of placido-based topographers include the absence of information about the posterior corneal surface and limited corneal surface coverage without data from the para-central and/or peripheral corneal surface. However, corneal tomographers show repeatable anterior and posterior corneal surfaces measurements, providing full corneal thickness data improving cornea, and anterior surface assessment. However, differences between devices suggest that they are not interchangeable in clinical practice.

Precision of a new ocular biometer in eyes with cataract using swept source optical coherence tomography combined with Placido-disk corneal topography

The present study was to assess the precision (repeatability and reproducibility) of a new optical biometer (OA-2000, Tomey, Japan) based on swept-source optical coherence tomography (SS-OCT) and Placido disk topography in eyes with cataracts. Seventy-eight eyes from seventy-eight patients with cataracts were evaluated. Axial length (AL), anterior chamber depth (ACD), keratometry (K) over a 2.5 mm and 3.0 mm diameter, lens thickness (LT), central corneal thickness (CCT) and white-to-white (WTW) distance were measured by 2 skilled operators. OA-2000 measurements were highly repeatable and reproducible for all parameters (intraclass correlation, 0.925 to 1.000). OA-2000 derived K-values with a diameter of 3.0mm showed narrower 95% limits of agreement (LoA) (SRK/T: −0.18 to 0.16D; Holladay 1: −0.20 to 0.19D; Hoffer Q: −0.22 to 0.20D) than those with a diameter of 2.5 mm for IOL power calculations (SRK/T: −0.20 to 0.20D; Holladay 1: −0.23 to 0.23D; Hoffer Q: −0.25 to 0.25D). The precision (repeatability and reproducibility) of the OA-2000 was excellent for all parameters. The 3.0mm diameter K-readings appear to be the most reliable choice for calculation of IOL power with the OA-2000. In addition, the average values determined from each operator’s 3 consecutive readings were more reproducible.

Accuracy of optical biometry combined with Placido disc corneal topography for intraocular lens power calculation.

PurposeTo investigate the accuracy of a new optical biometer for intraocular lens (IOL) power calculation in eyes undergoing cataract surgery.MethodsConsecutive eyes of patients undergoing cataract surgery with the same IOL model were enrolled in a prospective cohort study.Axial length (AL) and corneal power were measured with an optical biometer based on optical low-coherence interferometry and Placido-disc corneal topography. IOL power was calculated with the Hoffer Q, Holladay 1 and SRK/T formulas. For each formula the lens constant was optimized in retrospect in order to achieve a mean prediction error (PE) of zero (difference between the predicted and the postoperative refraction). Median absolute error (MedAE) and percentage of eyes with PE ±0.50 D were calculated.ResultsSeventy-four eyes of 74 cataract patients were enrolled. The MedAE was 0.25 D with all formulas. A PE within ±0.50 D was obtained in 89.04% of cases with the Hoffer Q and SRK/T formulas, and in 87.67% of cases with the Holladay 1 formula.ConclusionsThe optical biometer investigated in the present study provides accurate measurements for IOL power calculation.

Scheimpflug camera combined with placido-disk corneal topography and optical biometry for intraocular lens power calculation

The purpose of this study was to compare the keratometry (K) values obtained by the Scheimpflug camera combined with placido-disk corneal topography (Sirius) and optical biometry (Lenstar) for intraocular lens (IOL) power calculation before the cataract surgery, and to evaluate the accuracy of postoperative refraction. 50 eyes of 40 patients were scheduled to have phacoemulsification with the implantation of a posterior chamber intraocular lens. The IOL power was calculated using the SRK/T formula with Lenstar K and K readings from Sirius. Simulated K (SimK), K at 3-, 5-, and 7-mm zones from Sirius were compared with Lenstar K readings. The accuracy of these parameters was determined by calculating the mean absolute error (MAE). The mean Lenstar K value was 44.05 diopters (D) ±1.93 (SD) and SimK, K at 3-, 5-, and 7-mm zones were 43.85±1.91, 43.88±1.9, 43.84±1.9, 43.66±1.85D, respectively. There was no statistically significant difference between the K readings (P=0.901). When Lenstar was used for the corneal power measurements, MAE was 0.42±0.33D, but when simK of Sirius was used, it was 0.37±0.32D (the lowest MAE (0.36±0.32D) was achieved as a result of 5mmK measurement), but it was not statistically significant (P=0.892). Of all the K readings of Sirius and Lenstar, Sirius 5-mm zone K readings were the best in predicting a more precise IOL power. The corneal power measurements with the Scheimpflug camera combined with placido-disk corneal topography can be safely used for IOL power calculation.

Anterior segment characteristics in normal and keratoconus eyes evaluated with a combined Scheimpflug/Placido corneal imaging device

PurposeTo assess the anterior segment parameters of keratoconus (KC) eyes at different stages of the disease by a new Scheimpflug camera combined with Placido disk corneal topography (Sirius, CSO, Italy) in a sample of the Iranian population. MethodsA total of 225 eyes of 225 individuals comprising 41 suspect KC, 40 mild KC, 71 moderate KC, 48 severe KC and 25 normal eyes were assessed for the following parameters: corneal thickness at the apex (CTA), thinnest corneal thickness (TCT), anterior chamber depth (ACD), corneal volume (CV), corneal keratometry (K), corneal asphericity (Q), and corneal elevation in the anterior and posterior surface. Also, the Zernike coefficients for the corneal aberrations including total root mean square (RMS), RMS Coma, RMS spherical aberration (SA), RMS Astigmatism, Baiocchi Calossi Versaci front index (BCVf), and BCV back index (BCVb) were noted for all eyes. Data was analyzed using analysis of variance (ANOVA) and post hoc Bonferroni test for comparison of the means of the five groups. P-value was considered significant if it was <0.05. ResultsThe TCT, CTA and posterior corneal elevation were significantly different between all comparison groups (P < 0.05). ACD values showed inconsistent differences between groups. Mean value of CV in comparing normal eyes vs suspect KC group, normal eyes vs mild KC, and normal eyes vs moderate KC revealed statistically significant change (P < 0.05). Also, weak non-significant positive correlation was demonstrated between K and CV (r = 0.08). There were statistically significant differences in total RMS, RMS coma, BCVf, and BCVb for most groups (P < 0.05). ConclusionPosterior corneal elevation, corneal thickness and high order aberrations are important indices that need to be considered to diagnose different grades of keratoconus.

Precision of pachymetric measurements with Scheimpflug –Placido disc cornealTopography and comparison of these measurements with ultrasonic pachymetry

Back ground: Several devices with different physical bases have been developed for the clinical measurement of corneal thickness, they classified into 4 categories: Scheimpflug photography based, Slit –Scanning topography, optical coherence tomography (OCT) based and ultrasound (US) based.Objective:To evaluatethe precision of the new Scheimpflug –Placido disc corneal topography in measurement of corneal thickness and to compare the measured values with that obtained by US pachymetry.Methods: Setting of this study is Lasik center in Eye Specialty Private Hospital. Baghdad. Iraq.Eyes of healthy subjects were examined with the Sirius topography.3 consecutive measurements of central (CCT)and thinnest (TCT) corneal thicknesses were obtainedand the measurements repeated within 1 week. The within –subject standard deviation (Sw),test-retest repeatability ,coefficient of variation (CoV),and interclass correlation coefficient (ICC) were calculated to evaluate intra session repeatability and intersession reproducibility. For US pachymetry (Tomey-SP 100) only CCT was measured. Comparison ofthe measurements that obtained by the 2 devices done by paired t-test.Results: The topography provides high intrasession repeatability with test-retest and CoV close to 6μm and0.4%, respectively for both CCT and TCT. The inter session reproducibility also high with test-retest and CoV close to 8μm and 0.5%, respectively.ICC was higher than 0.97 for repeatability and reproducibility . Anarrow 95% limit of agreement was found between the pachymetry obtained by topography and US pachymetry measurements.Conclusions :The topography has been used showed high intrasession repeatability and intersession reproducibility of CCT and TCT measurements in healthy eyes .Absence of statistically significant differences suggest that the topography -TCT and the US pachymetry - CCT can be used interchangeably in subject with normal cornea.Financial Disclosure: No financial or proprietary interest in any material or method mentioned.

Options for a young patient with considerably high, topographically stable, astigmatism: December consultation #1

A 21-year-old woman was referred for a refractive surgery evaluation. She has no relevant allergies or medical or family history of keratoconus or corneal transplantation. Spectacle dependence is her chief complaint. She occasionally wears contact lenses but wants to have surgery performed. The corrected near visual acuity and the corrected distance visual acuity (CDVA) are 20/20 in both eyes. The manifest refraction is 5.75 3.25 178 in the right eye and 5.00 3.50 170 in the left eye. The intraocular pressure and the results from a slitlamp examination and a fundus retinoscopy are normal. The ultrasound pachymetry shows the central corneal thickness (CCT) to be 505 mm in the right eye and 508 mm in the left eye. Among all devices used tomeasure the CCT, the thinnest measured point is 504 mm in the right eye and 503 mm in the left eye. Placido-disk corneal topography shows a high regular symmetric astigmatism that was stable over 1 year of follow up, with an insignificant change in keratometry (K) values (Figure 1). The 5 topographies were obtained at 3-month intervals. Scheimpflug and dual Scheimpflug tomography (Figures 2, 3, and 4) are normal with no suspicious pattern except a high regular astigmatism. The pachymetry maps show corneas that, although slightly thin, are within normal limits across the diameter. An excimer laser system predicts a stromal ablation of approximately 127 mm in the right eye and 121 mm in the left eye. For laser in situ keratomileusis (LASIK) with a 110 mm flap thickness, the percentage of tissue altered (PTA) would be 47% in the right eye and 46% in the left eye. The residual stromal bed (RSB) would be 267 mm in the right eye and 272 mm in the left eye. For photorefractive keratectomy (PRK), the PTA would be 25% in the right eye and 24% in the left. What kind of refractive surgery (if any) would you recommend to this patient? If none, why? Would you consider LASIK with a thin, predictable LASIK flap? What data helped you most in making your decision? Did the stability shown by the Placido disk–based corneal topography over 1 year significantly affect your surgery decision?What are your limits for treating a cornea with high regular symmetric astigmatism? If you recommend proceeding with surgery, was age a significant factor in that decision?

Options for an eye with a thin cornea: June consultation #1

Journal of Cataract & Refractive Surgery: June 2015 - Volume 41 - Issue 6 - p 1324-1327 doi: 10.1016/j.jcrs.2015.06.006

Influence of corneal asphericity on the refractive outcome of intraocular lens implantation in cataract surgery

To evaluate the possible influence of anterior corneal surface asphericity on the refractive outcomes in eyes having intraocular lens (IOL) implantation after cataract surgery. Fondazione G.B. Bietti IRCCS, Rome, Italy. Retrospective comparative case series. Intraocular lens power was calculated using the Haigis, Hoffer Q, Holladay 1, and SRK/T formulas. Asphericity (Q-value) was measured at 8.0 mm with a Placido-disk corneal topographer (Keratron), a rotating Scheimpflug camera (Pentacam), and a rotating Scheimpflug camera combined with Placido-disk corneal topography (Sirius). The relationship between the error in refraction prediction (ie, difference between expected refraction and refraction measured 1 month after surgery) and the Q-value was assessed by linear regression. The same IOL model (Acrysof SA60AT) was implanted in 115 eyes of 115 consecutive patients. Regression analysis showed a statistically significant relationship between the error in refraction prediction and the Q-value with all formulas and all devices. In all cases, a more negative Q-value (prolate cornea) was associated with a myopic outcome, whereas a more positive Q-value (oblate cornea) was associated with a hyperopic outcome. The highest coefficient of determination was detected between the Hoffer Q formula and the Placido-disk corneal topographer (R(2) = 0.2630), for which the error in refraction prediction (y) was related to the Q-value (x) according to the formula y = -0.2641 + 1.4589 × x. Corneal asphericity influences the refractive outcomes of IOL implantation and should be taken into consideration when using third-generation IOL power formulas. Dr. Hoffer receives book royalties from Slack, Inc., Thorofare, New Jersey, and formula royalties from all manufacturers using the Hoffer Q formula. No other author has a financial or proprietary interest in any material or method mentioned.

Effect of religious fasting on tear osmolarity and ocular surface.

To evaluate the effects of religious fasting on tear secretion, tear osmolarity, corneal topography, and ocular aberrations. This prospective controlled study comprised 29 eyes of 29 healthy men. Before ophthalmologic examination, all subjects underwent corneal topography by a placido disc corneal topography and aberrometry device (OPD Scan II). Tear osmolarity was measured using OcuSense TearLab osmometer. Ocular surface disease index (OSDI) scores, tear break-up time (BUT), Schirmer I test, and lissamine green staining were evaluated. The measurements taken before and during Ramadan at the same hours between 4.00 and 5.00 PM were compared using paired sample t test, and a P value less than 0.05 was accepted as statistically significant. The mean age of the study group was 27.8 ± 5.9 years (range, 20-47 years). The mean tear osmolarity values were measured as 285.6 ± 8.2 mOsm/L and 293.3 ± 16.0 mOsm/L, whereas the mean Schirmer I values were 14.8 ± 6.0 mm and 10.6 ± 5.3 mm in nonfasting and fasting periods, respectively. Tear osmolarity, OSDI, and Oxford grading scores significantly increased (P=0.02, P=0.002, P=0.003, respectively), whereas Schirmer I values and intraocular pressure decreased (both, P<0.001) during the fasting period compared with the nonfasting period. There were no significant differences in tear BUT, keratometry values, and corneal aberration measurements between nonfasting and fasting periods (P>0.05, for all). Fasting significantly decreases tear production and increases tear osmolarity; however, it does not deteriorate corneal topographic parameters and ocular aberrations in healthy subjects.