Evaluation of perioperative pachymetry of thin corneas during corneal crosslinking using hypo-osmolar riboflavin and hydroxypropyl methylcellulose.

PURPOSE: This study aimed to analyze variations in intraoperative corneal thickness during corneal cross-linking in patients with keratoconus and to investigate its possible correlation with presurgical maximal keratometry (Kmax) and pachymetry. METHODS: This was a prospective case series. We used a method similar to the Dresden protocol, with the application of hydroxypropyl methylcellulose 0.1% hypo-osmolar riboflavin in corneas between 330 and 400 µm after epithelium removal. Corneal thickness was measured using portable calipers before and immediately after epithelium removal, and 30 and 60 min after the procedure. RESULTS: The 30 patients in this study were followed up for one year. A statistically significant difference was observed in pachymetry values during the intraoperative period (p<0.0001) and an increase of 3.05 µm (95%C1: 0.56-5.54) for each diopter was seen after epithelium removal (p0.019). We found an average Kmax difference of -2.12 D between men and women (p0.013). One year after treatment, there was a statistically significant reduction in pachymetry (p<0.0001) and Kmax (p0.0170) values. CONCLUSIONS: A significant increase in pachymetry measurements was seen during the procedure, and most patients showed a regression in Kmax and pachymetry values one year after surgery.

Repeatability and reproducibility of a new method for centration analysis via optical zone tangent points after corneal refractive surgery.

PURPOSE: To investigate the repeatability and reproducibility of a new method for centration analysis after small incision lenticule extraction (SMILE) and femtosecond laser-assisted LASIK (FS-LASIK). METHODS: This study comprised 29 eyes treated with SMILE and 24 with FS-LASIK. Decentrations were analyzed using tangential and pachymetry difference maps respectively. Both difference maps were generated with a Scheimpflug tomographer (Pentacam) for each eye, using preoperative and 3-month postoperative scans. Repeatability and reproducibility were evaluated by calculating the intraclass correlation coefficient (ICC), within-subject standard deviation (Sw), and coefficient of repeatability (CR). RESULTS: ICC, Sw, and CR showed good to excellent repeatability in locating the coordinates of the optical zone (OZ) center on both maps, with values ranging from 0.84 to 0.96, 0.03 to 0.13, and 0.08 to 0.36 respectively. The repeatability of the total decentration from the preoperative corneal vertex on the tangential curvature difference maps( d TC ) and the pachymetry difference maps( d PC ) were moderate and good, respectively. The ICC, Sw, and CR of d TC were 0.63, 0.09, and 0.25, respectively. The ICC, Sw, and CR of d PC were 0.77, 0.10, and 0.28, respectively. The reproducibility of the OZ center measurements was excellent for the tangential difference maps (ICC ≥ 0.97 ) and good for the pachymetry difference maps (ICC ≥ 0.86). ICC, Sw, and CR showed excellent reproducibility of d TC , with values of 0.95, 0.03, and 0.08, respectively. ICC, Sw, and CR showed good reproducibility of d PC , with values of 0.89, 0.06, and 0.17, respectively. CONCLUSION: The centration analysis method used in this study showed good to excellent repeatability and reproducibility in locating the coordinates of the center of the OZ on the tangential and pachymetry difference maps.

Combined corneal biomechanical and tomographical indices in subclinical and forme fruste keratoconus.

PURPOSE: Evaluation of combined corneal tomographic and biomechanical parameters in subclinical/forme fruste keratoconus (ScKC/FFKC). DESIGN: Cross-sectional observational case-control study. METHODS INCLUSION CRITERIA: Thirty-one eyes with ScKC (fellow eye of KC with any one sign: keratometry >47 diopters, cylinder >1.5 D, central corneal thickness <500 µm, with/without abnormal topography) or FFKC (fellow eye of KC with normal topography and slit lamp examination) >13 years (cases) and 44 eyes of age-matched 22 healthy subjects (controls). EXCLUSION CRITERIA: Clinically diagnosed KC, presence of corneal scars, and prior ocular surgery eyes. STUDY PARAMETERS: Sixteen Pentacam, 15 Corvis ST, and five Sirius parameters were analyzed using paired sample t -test, and a subsample found to be significantly different was used in receiver operating characteristic curve analysis. The Youden index was calculated, and Pearson's correlation analysis was done. RESULTS: Five Pentacam, three Corvis ST, and two Sirius parameters had an area under curve (AUC) >0.75. Tomographic and biomechanical index (TBI) (cutoff 0.59, 95% specificity, 77% sensitivity), Belin Ambrosio enhanced ecstasia display (cutoff 1.8, 81% specificity, 80% sensitivity), and symmetry index of posterior corneal curvature (cutoff 0.16, 97% specificity, 67% sensitivity) best identified early KC. TBI strongly correlated with maximum Pentacam parameters in both cases and controls. Corvis biomechanical index strongly correlated only in cases, and SP-A1-SD weakly correlated in cases. CONCLUSION: Upon combined analysis, the average sensitivity and specificity, respectively, of top three parameters (according to AUC) from Pentacam and Corvis ST were 74.1% and 95.4% for posterior elevation and TBI. TRIAL REGISTRATION: The trial was registered in Clinical Trial Registry of India on January 28, 2022. The Trial Registration Number is REF/2022/01/050638.

Comparison of the repeatability and reproducibility of corneal thickness mapping using optical coherence tomography according to tear film break-up time.

BACKGROUND: To compare the repeatability and reproducibility of corneal and corneal epithelial thickness mapping using anterior segment optical coherence tomography (AS-OCT) according to tear film break-up time (TBUT). METHODS: The included eyes were divided into three subgroups according to TBUT (group 1: TBUT ≤ 5 s, group 2: 5 s < TBUT ≤ 10 s, and group 3: TBUT > 10 s). All eyes were imaged separately thrice by two operators to obtain the thickness maps (TMs) of the cornea and corneal epithelium based on spatial zones encompassing a 9-mm-diameter area. Each TM consisted of 25 areas. Intraoperator (repeatability) and interoperator (reproducibility) standard deviations (Sws), coefficients of variation (CoVs), and intraclass correlation coefficients (ICCs) among the tests were calculated and compared in all the areas. RESULTS: Altogether, 132 eyes of 67 subjects were included (50, 47, and 35 eyes in groups 1, 2, and 3; respectively). The ICCs of corneal epithelial thickness and corneal thickness were > 0.75 in most of the areas. Pairwise comparisons showed that AS-OCT exhibited lower repeatability in group 1 than in groups 2 and 3 (P < 0.05). However groups 2 and 3 showed similar results. Sws and CoVs of corneal epithelial thickness exhibited no significant interoperator differences. While no significant differences were observed in corneal thickness in most of the areas. CONCLUSIONS: TBUT significantly influences the repeatability of corneal and corneal epithelial thickness measurements. Poor tear film stability requires careful evaluation of corneal epithelial thickness.

Comparison of central corneal thickness measured by automatic and manual analysis of optical coherence tomography.

PURPOSE: To compare central corneal thickness (CCT) measured with optical coherence tomography (OCT) using an automatic algorithm (A-OCT) vs. manual measurements (M-OCT) with respect to the gold standard ultrasound pachymetry (USP). METHODS: CCT measurements were performed on both eyes of 28 healthy subjects at four times of the day. A-OCT used an automatic software analysis of the corneal image, M-OCT was performed by two operators by setting a digital calliper on the corneal borders, and USP was performed after corneal anesthesia. Measurements were compared using a three-way repeated measures ANOVA. Bland-Altman plots were used to evaluate the agreement between OCT measurements and USP. RESULTS: Both A-OCT and M-OCT significantly underestimated the USP measures, with the mean difference, i.e., the systematic error, being larger for A-OCT (- 19.0 µm) than for M-OCT (- 6.5 µm). Good reproducibility between the two operators was observed. Bland-Altman plots showed that both OCT methods suffered from proportional errors, which were not affected by time and eye. CONCLUSIONS: Measuring CCT with OCT yielded lower values than USP. Therefore, clinicians should be aware that corneal thickness values may be influenced by the measurement method and that the various devices should not be used interchangeably in following up a given patient. Intriguingly, M-OCT had less systematic error than A-OCT, an important outcome that clinicians should consider when deciding to use an OCT device.

Corneal Biomechanical Properties to Predict Prognosis of Abnormal Tomographic Corneas: A Prospective Cohort Study.

PURPOSE: To analyze the corneal biomechanical properties in patients with abnormal corneal tomography (ACT) and predict their stability using the biomechanical stability index (BSI). DESIGN: Prospective cohort study. METHODS: Setting: Multicenter study. STUDY POPULATION: This study included 385 eyes of 278 patients with stable ACT (n = 70), subclinical keratoconus (SKC, n = 65), keratoconus (n = 65), normal controls (NL, n = 142). Forty-three eyes with first-visit ACT were included in a separate cohort (follow-up ACT group). OBSERVATION PROCEDURE: Tomographical and biomechanical parameters (Pentacam and Corvis ST) were recorded. MAIN OUTCOME MEASURES: Nonparametric tests were used for comparison. Logistic regression was employed to introduce BSI to separate stable ACT and SKC accurately. An independent dataset of 43 first-visit ACT eyes was followed up for 1 year to validate BSI's accuracy and positive and negative predictive values (PPV, NPV). RESULTS: The tomographical and biomechanical parameters in patients with Stable ACT remained stable over the follow-up period (12.73 ± 2.57 months, P > .05). Stable ACT had 12/14 biomechanical parameters different (P < .05) from SKC but not different from NL (P > .05). With a cut-off value of 0.585, BSI demonstrated the strongest ability to distinguish between stable ACT and SKC (area under the receiver operating characteristic curve = 0.991), with 93.85% sensitivity and 97.14% specificity. During the 1-year follow-up of 43 eyes (follow-up ACT group), 30 remained stable. The accuracy, PPV, and NPV of the BSI were 95.35%, 100%, and 93.75%, respectively. CONCLUSIONS: Biomechanical properties of patients with stable abnormal tomography corneas were stronger than SKC and close to normal corneas, which may explain the reason for tomographic stability. The BSI may be useful for predicting disease progression in patients with ACT and the possible management of corneal cross-linking at the first visit.

Advanced Corneal Imaging in Keratoconus: A Report by the American Academy of Ophthalmology.

PURPOSE: To review the published literature on the diagnostic capabilities of the newest generation of corneal imaging devices for the identification of keratoconus. METHODS: Corneal imaging devices studied included tomographic platforms (Scheimpflug photography, OCT) and functional biomechanical devices (imaging an air impulse on the cornea). A literature search in the PubMed database for English language studies was last conducted in February 2023. The search yielded 469 citations, which were reviewed in abstract form. Of these, 147 were relevant to the assessment objectives and underwent full-text review. Forty-five articles met the criteria for inclusion and were assigned a level of evidence rating by the panel methodologist. Twenty-six articles were rated level II, and 19 articles were rated level III. There were no level I evidence studies of corneal imaging for the diagnosis of keratoconus found in the literature. To provide a common cross-study outcome measure, diagnostic sensitivity, specificity, and area under the receiver operating characteristic curve (AUC) were extracted. (A perfect diagnostic test that identifies all cases properly has an AUC of 1.0.) RESULTS: For the detection of keratoconus, sensitivities for all devices and parameters (e.g., anterior or posterior corneal curvature, corneal thickness) ranged from 65% to 100%. The majority of studies and parameters had sensitivities greater than 90%. The AUCs ranged from 0.82 to 1.00, with the majority greater than 0.90. Combined indices that integrated multiple parameters had an AUC in the mid-0.90 range. Keratoconus suspect detection performance was lower with AUCs ranging from 0.66 to 0.99, but most devices and parameters had sensitivities less than 90%. CONCLUSIONS: Modern corneal imaging devices provide improved characterization of the cornea and are accurate in detecting keratoconus with high AUCs ranging from 0.82 to 1.00. The detection of keratoconus suspects is less accurate with AUCs ranging from 0.66 to 0.99. Parameters based on single anatomic locations had a wide range of AUCs. Studies with combined indices using more data and parameters consistently reported high AUCs. FINANCIAL DISCLOSURE(S): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Corneal Morphological and Biomechanical Changes in Thyroid-Associated Ophthalmopathy.

PURPOSE: This study aimed to evaluate corneal morphological and biomechanical changes in patients with thyroid-associated ophthalmopathy (TAO) and their correlations with activity and severity. METHODS: Patients diagnosed with TAO were recruited and divided into groups by activity and severity. All subjects underwent a complete ophthalmic examination, including magnetic resonance imaging. Corneal topography was measured using a Pentacam device, and biomechanical parameters were obtained using a CorVis ST tonometer. Correlations among the corneal parameters, clinical activity score, and NOSPECS score were analyzed. Areas under the receiver operating characteristic curves were calculated to evaluate the diagnostic accuracy of corneal changes for active and severe TAO. RESULTS: Fifty-three eyes with TAO and 16 healthy eyes were enrolled in our study. The back elevation, CorVis biomechanical index, tomographic and biomechanical index, stiffness parameter at the first applanation, deviation from normality in back elevation, relational thickness, and overall deviation from normality were significantly increased in patients with TAO (all P <0.05), whereas the smallest corneal thickness, maximum Ambrósio relational thickness, and deformation amplitude (DA) ratio were significantly decreased (all P <0.05). The clinical activity score was strongly positively correlated with back elevation (γ = 0.515, P <0.001). The NOSPECS score was strongly positively correlated with relational thickness and tomographic and biomechanical index (γ = 0.429 and 0.515, P <0.001) and negatively correlated with maximum Ambrósio relational thickness (γ = -0.53, P <0.001). Moreover, maximum Ambrósio relational thickness and the Ambrósio relational thickness through the horizontal meridian showed desirable diagnostic capacity in distinguishing mild TAO from moderate-severe TAO (areas under the receiver operating characteristic curve, 0.799 and 0.769). CONCLUSIONS: Corneal morphological and biomechanical changes were found in patients with TAO, which might be related to the presence of inflammation. Measurements of corneal morphological and biomechanical parameters could serve as references in evaluating TAO.

Corneal biomechanics in normal and subclinical keratoconus eyes.

BACKGROUND: The diagnosis of keratoconus, as the most prevalent corneal ectatic disorder, at the subclinical stage gained great attention due to the increased acceptance of refractive surgeries. This study aimed to assess the pattern of the corneal biomechanical properties derived from Corneal Visualization Scheimpflug Technology (Corvis ST) and evaluate the diagnostic value of these parameters in distinguishing subclinical keratoconus (SKC) from normal eyes. METHODS: This prospective study was conducted on 73 SKC and 69 normal eyes. Subclinical keratoconus eyes were defined as corneas with no clinical evidence of keratoconus and suspicious topographic and tomographic features. Following a complete ophthalmic examination, topographic and tomographic corneal assessment via Pentacam HR, and corneal biomechanical evaluation utilizing Corvis ST were done. RESULTS: Subclinical keratoconus eyes presented significantly higher Deformation Amplitude (DA) ratio, Tomographic Biomechanical Index (TBI), and Corvis Biomechanical Index (CBI) rates than the control group. Conversely, Ambrósio Relational Thickness to the Horizontal profile (ARTh), and Stiffness Parameter at the first Applanation (SPA1) showed significantly lower rates in SKC eyes. In diagnosing SKC from normal eyes, TBI (AUC: 0.858, Cut-off value: > 0.33, Youden index: 0.55), ARTh (AUC: 0.813, Cut-off value: ≤ 488.1, Youden index: 0.58), and CBI (AUC: 0.804, Cut-off value: > 0.47, Youden index: 0.49) appeared as good indicators. CONCLUSIONS: TBI, CBI, and ARTh parameters could be valuable in distinguishing SKC eyes from normal ones.

Parental Corneal Tomographic and Biomechanical Characteristics of Patients With Keratoconus.

PURPOSE: To investigate the hereditability of corneal tomographic and biomechanical parameters in keratoconus (KC). DESIGN: Prospective cohort study. METHODS: This study was conducted at Qingdao Eye Hospital of Shandong First Medical University in Qingdao, China. Forty-four patients with KC and their biological parents (n = 88) were recruited as the study group. The control group consisted of 84 healthy adults with matched age and gender. Both eyes of each participant underwent clinical examinations, and 1 eye was selected for statistical analysis. Exclusion criteria were as follows: individuals with glaucoma, ocular surgery, systemic diseases known to affect the eyes, or poor cooperation during examination. Subjects were asked to discontinue soft contact lens (CL) wear for 2 weeks and rigid gas permeable CL wear for 4 weeks before ocular examination. All participants underwent a comprehensive assessment including Pentacam Scheimpflug tomography, Corvis ST, visual acuity, refraction examination, axial length, and slitlamp examination for both eyes. Individuals presenting with KC manifestations in at least 1 eye were classified as having KC. A total of 9 Pentacam indices including keratometry in the flat/steep meridian (K1/K2), maximal keratometry (Kmax), thinnest point pachymetry (TP), and maximum/average Ambrósio relational thickness (ARTmax/ARTave), anterior and posterior surfaces elevation of the cornea (Ef/Eb) and total deviation value (Final D), and 21 biomechanical indices were collected. Associations of these factors with KC were evaluated using multiple comparison and binary logistics regression analyses. RESULTS: Two parents (2.27%) from 2 different families were diagnosed with KC. Parents of patients with KC had thinner corneas with altered corneal biomechanical parameters compared with healthy controls (P < .05). The combined tomographic and biomechanical index demonstrated the highest discriminatory power (area under the receiver operating characteristic curve 0.785) and strong specificity (84.5%). Parental corneal tomographic and biomechanical index, Corvis biomechanical index, and TP were identified as the major influential factors for KC in their offspring by logistic regression analysis, with a 73.3% accuracy in identifying offspring with KC. CONCLUSIONS: Parental corneal tomographic and biomechanical properties of patients with KC suggest a possible predisposition to KC. A combination of tomography and corneal biomechanics can be helpful in predicting the incidence rate of KC in the offspring of patients with subclinical KC.

The measurement of Central Corneal Thickness.

We aimed to compare five different devices that measure Central Corneal Thickness. The Central Corneal Thickness (CCT) is an important parameter in ophthalmology. It is involved in the management of various eye conditions such as: glaucoma, keratoconus, contact lens wearing, corneal dystrophies, refractive surgery and keratoplasty. We measured the CCT using OCT, Topographer (TOPO), Ultrasonography Pachymeter (US), Specular Microscope (MS), and Non-contact Tonometer (TONO). In the analysis of the data collected from 59 patients we found the following mean values: US - 554.51 ± 29.849 µm, OCT - 548.73 ± 31.080 µm, TOPO - 553.76 ± 29.845 µm, MS - 564 ± 32.637 µm, and TONO - 538.9 ± 35.657 µm. Our results confirmed the strong correlation between techniques. Abbreviations: OCT = Optical Coherence Tomography, CCT = Central Corneal Thickness, TOPO = Topographer, US = Ultrasonography Pachymeter, MS = Specular Microscope, TONO = Non-contact Tonometer.

Comparison of corneal measurements in normal and keratoconus eyes using Anterior Segment Optical Coherence Tomography (AS-OCT) and Pentacam HR topographer.

BACKGROUND: Keratoconus (KC) is easily recognized by its unique topographic pattern, but it can be difficult to distinguish subclinical form of the disease from the normal cornea. Optovue anterior segment optical coherence tomography (AS-OCT) helps diagnose KC. AIM OF THE WORK: To assess and the level of agreement of Keratometry-readings (K), Central Corneal Thickness (CCT) and Thinnest Corneal Thickness (TCT) measurements obtained by Optovue AS-OCT and Wavelight Oculyzer Pentacam HR in two groups: KC eyes and normal eyes. PATIENTS AND METHODS: This is a prospective clinical observational study. The study included 110 eyes divided into two groups. The study group included 62 eyes with topographic evidence of KC. The control group included 48 eyes of normal subjects with no topographic evidence of KC. All of the participants underwent full cycloplegic refraction, spectacle best-corrected distance visual acuity, comprehensive slit-lamp biomicroscopy and fundoscopy. All participants underwent corneal topography by Pentacam HR and AS-OCT. RESULTS: There were highly significant differences between the studied groups as regarding BCVA, intraocular pressure and CCT measurements which were found to be lower among KC group compared to the control one. There were highly significant differences between the studied groups regarding TCT measurement detected by Pentacam HR and AS-OCT which was found to be lower among the keratoconus group compared to the control one (470.9, 455.7 versus 541.9 and 518.7 respectively). CONCLUSION: Both Scheimpflug-based imaging and AS-OCT provide comparable readings with a good agreement regarding corneal pachymetry in keratoconus group with accurate identification of KC eyes and healthy ones. However, there was a significant difference in K readings between both devices in Keratoconus and control group.

Early Visibility of Cellular Aggregates and Changes in Central Corneal Thickness as Predictors of Successful Corneal Endothelial Cell Injection Therapy.

(1) Background: Cell injection therapy is an emerging treatment for bullous keratopathy (BK). Anterior segment optical coherence tomography (AS-OCT) imaging allows the high-resolution assessment of the anterior chamber. Our study aimed to investigate the predictive value of the visibility of cellular aggregates for corneal deturgescence in an animal model of bullous keratopathy. (2) Methods: Cell injections of corneal endothelial cells were performed in 45 eyes in a rabbit model of BK. AS-OCT imaging and central corneal thickness (CCT) measurement were performed at baseline and on day 1, day 4, day 7 and day 14 following cell injection. A logistic regression was modelled to predict successful corneal deturgescence and its failure with cell aggregate visibility and CCT. Receiver-operating characteristic (ROC) curves were plotted, and areas under the curve (AUC) calculated for each time point in these models. (3) Results: Cellular aggregates were identified on days 1, 4, 7 and 14 in 86.7%, 39.5%, 20.0% and 4.4% of eyes, respectively. The positive predictive value of cellular aggregate visibility for successful corneal deturgescence was 71.8%, 64.7%, 66.7% and 100.0% at each time point, respectively. Using logistic regression modelling, the visibility of cellular aggregates on day 1 appeared to increase the likelihood of successful corneal deturgescence, but this did not reach statistical significance. An increase in pachymetry, however, resulted in a small but statistically significant decreased likelihood of success, with an odds ratio of 0.996 for days 1 (95% CI 0.993-1.000), 2 (95% CI 0.993-0.999) and 14 (95% CI 0.994-0.998) and an odds ratio of 0.994 (95% CI 0.991-0.998) for day 7. The ROC curves were plotted, and the AUC values were 0.72 (95% CI 0.55-0.89), 0.80 (95% CI 0. 62-0.98), 0.86 (95% CI 0.71-1.00) and 0.90 (95% CI 0.80-0.99) for days 1, 4, 7 and 14, respectively. (4) Conclusions: Logistic regression modelling of cell aggregate visibility and CCT was predictive of successful corneal endothelial cell injection therapy.

Comparison of central corneal thickness measurements using three different imaging devices.

PURPOSE: The purpose of this study was to compare central corneal thickness (CCT) values and evaluate the agreement obtained with three different devices in healthy eyes. METHODS: A total of 120 eyes of 60 healthy individuals (36 men and 24 women) were enrolled in this retrospective study. CCT measurements were performed using an optical biometer (AL-Scan), spectral-domain optical coherence tomography (SD-OCT) (Topcon 3D) and ultrasonic pachymetry (UP) (Accupach VI), and the results were compared. Bland-Altman analysis was used to quantify the agreement between methods. MAIN RESULTS: The mean patient age was 28±5.73years (18-40years). The mean CCT values obtained by AL-Scan, UP, and SD-OCT were 532.4µm±29.7, 549µm±30.4, and 547µm±30.6, respectively. The mean differences in CCT were 15.30±9.52µm between AL-Scan and OCT (P<0.01), 17.15±8.42µm between AL-Scan and UP (P<0.01), and 1.85± 8.78µm between UP and OCT (P=0.067). All three methods of CCT measurement were closely correlated with each other. CONCLUSION: The present study results suggest that, despite good agreement between the three devices, AL-Scan significantly underestimated CCT compared to UP and OCT. Therefore, clinicians should be aware that different results can be obtained using different devices for CCT measurements. It would be a better approach not to use them as interchangeable in clinical practice. CCT examination and follow-up should be performed using the same device, especially for patients who will undergo refractive surgery.

Comparison of machine learning-based algorithms using corneal asymmetry vs. single-metric parameters for keratoconus detection.

PURPOSE: To evaluate the diagnostic performance of three different parameter sets relevant to corneal asymmetry in comparison to conventional parameters including maximum anterior corneal curvature (Kmax) and thinnest corneal thickness for diagnosis of keratoconus. METHODS: In this retrospective case control study, 290 eyes with keratoconus and 847 eyes of normal patients were included in the analyses. Corneal tomography data were acquired from Scheimpflug tomography. The sklearn and FastAI libraries were used in a Python 3 environment to create all machine learning models. The original topography metrics and derived metrics together with the clinical diagnoses were used as the dataset for model training. The data were first split to assign 20% of the data to an isolated test set. The remaining data were then split 80/20 to a training and validation group for model training. Sensitivity and specificity outcomes with standard parameters (Kmax, central curvature, and thinnest pachymetry) and ratio of asymmetry across horizontal, apex centered, and flat axis-centered axis of reflection were studied via various machine learning models. RESULTS: Thinnest corneal pachymetry and Kmax were 549.8 ± 34.3 µm and 45.3 ± 1.7 D in normal eyes and 460.5 ± 62.6 µm and 59.3 ± 11.3 D in keratoconic eyes. Use of only corneal asymmetry ratios across all 4 meridians had mean sensitivity of 99.0% and mean specificity of 94.0%, better than utilizing Kmax alone or traditional measures combined (Kmax, thinnest cornea and inferior-superior asymmetry). CONCLUSIONS: By using the ratio of asymmetry between corneal axes alone, a machine learning model could identify patients with keratoconus in our dataset with satisfactory sensitivity and specificity. Further studies on pooled/larger datasets or more borderline population can help validate or refine these parameters.

Variability of CLMI-X parameters, zonal Kmax, and single-point Kmax in keratoconus progression.

OBJECTIVES: To compare the repeatability of Cone Location and Magnitude Index expanded (CLMI.X) parameters of 2 mm diameter zone of greatest corneal curvature (Cspot-Axi) and 1 mm diameter zone of thinnest pachmymetry (Spot-Pach) with the maximum single point keratometry (Kmax), 3 mm Zonal Kmax (Z-Kmax3), and thinnest single point pachymetry (TP) in keratoconus (KC). METHODS: In this Comparative repeatability study, data from 36 eyes of 36 normal individuals and 72 eyes of 72 KC patients (28 eyes with ≤50.0D and 44 eyes with >50.0D Z-Kmax3) were analyzed. For each enrolled eye, imaging was done 6 times (3 consecutive acquisitions with a half hour break). For each parameter, the within-subject standard deviation (Sw) was calculated from the data of the six exams. RESULTS: In the normal group, Cspot-Axi-Sw was different from Kmax-Sw (p = 0.0004). Also, Z-Kmax3-Sw was different from Kmax-Sw (p = 0.0297). The difference between Cspot-Axi-Sw and Z-Kmax3-Sw was statistically significant (p = 0.0482). In the KC group, Sw were significantly different between Cspot-Axi and Kmax (p < 0.0001), and between Z-Kmax3 and Kmax (p < 0.0001). In the Z-Kmax3 ≤ 50.0D subgroup, Sw were different between Cspot-Axi and Kmax (p = 0.0002). In the Z-Kmax3 > 50.0D subgroup, Sw were different between Cspot-Axi and Kmax (p < 0.0001), and between Z-Kmax3 and Kmax (p < 0.0001). Sw differences between Spot-Pach and TP were not significant in any of the study groups (all P > 0.05). CONCLUSIONS: In the diagnosis and follow up of KC, the zonal averages of Cspot-Axi and Z-Kmax3 are more reliable than the single point Kmax. The repeatability of Spot-Pach is similar to TP and both variables should suit the purpose equally.

Comparison of central corneal thickness measured by ultrasound pachymetry, corneal topography, spectral domain- optical coherence tomography, and non-contact specular microscopy.

BACKGROUND: This study aims to investigate the compatibility of central corneal thickness (CCT) measurements obtained with spectral-domain optical coherence tomography (SD-OCT), Scheimpflug-Placido-based corneal topography (CT), non-contact specular microscopy (NCSM), and ultrasonic pachymetry (UP). These four corneal measurement techniques have not been compared in a single study on these many subjects. METHODS: CCT was measured in 185 eyes of 185 volunteers with each of the four devices by a single observer. CCTs from Optovue® iVue SD-OCT, Sirius corneal topography, NonconRobo NCSM, and Accutom UP devices were recorded. Compatibility between devices was evaluated with intraclass correlation coefficient (ICC) and Bland-Altman plots. Pairwise comparisons were performed using the Bonferroni test. Measurement differences between devices were analyzed with the Pearson correlation coefficient. RESULTS: Of the 185 volunteers, 103 were men, and 82 were women. Their mean age was 48.55 ± 16.6 (18-70) years. Mean CCT values measured by UP, CT, OCT, and NCSM were 546.77 ± 39.2, 535.29 ± 39.2, 526.49 ± 39.05, 505.15 ± 46.1 µm, respectively. Statistically significant differences were found between the mean CCT values obtained from the paired devices (p <0.001). The highest difference between pairs was found between UP and NCSM (43.63 ± 1.8 µm; CI 38.74 to 48.5 µm; p <0.001), while the lowest difference was found between OCT and CT (7.3 ± 1.5 µm; 95%CI 3.1 to 11.6 µm; p <0.001). In pairwise comparisons of four devices, the highest ICC value was between UP and CT (ICC: 0.899, 95%CI 0.759-0.947; p <0.001). CONCLUSION: Despite the high correlation between measurements obtained from different methods, notable differences in CCT values exist, rendering devices non-interchangeable. Therefore, alternative brands of the same device may yield different outcomes.

Impact of pterygium on central corneal thickness measured by optical coherence tomography in older adults.

PURPOSE: To measure the central corneal thickness (CCT) using anterior segment optical coherence tomography (AS-OCT) in older adults with and without pterygium from the Brazilian Amazon Region Eye Survey (BARES). METHODS: BARES is a population-based epidemiological cross-sectional study conducted in Parintins city. Participants were residents ≥45 years of age identified through a door-to-door interview. Eligible participants were invited for a comprehensive eye exam. Pterygium occurrence and severity were assessed by ophthalmologists through slit-lamp examination considering its location (nasal or/and temporal) and severity (lesion with extension <3 mm, ≥3 mm not reaching the pupillary margin or ≥3 mm reaching the pupillary margin). CCTs were obtained and measurements from the more severely affected eye were included. Images were analyzed offline by masked observers. RESULTS: A total of 671 subjects, 533 (79.4%) with pterygium in at least one eye and 138 (20.6%) without pterygium in either eye, were examined. The mean CCT evaluated by multiple linear regression and adjusted for demographic variables and pterygium severity was 521 ± 34 µm (median = 521; range = 304-665). Decreased CCT was significantly associated with age and pterygium severity. Individuals aged 65-74 years had CCT 7 µm thinner than those aged 45-54 years (p = 0.044), individuals aged 75 years and older had CCT 15 µm thinner than those aged 45-54 years (p = 0.001), and eyes with severe pterygium had CCT 33 µm thinner than eyes without pterygium (p < 0.001). CONCLUSIONS: The CCT analysis in this population-based sample shows that a thinner cornea is associated with pterygium severity and older age.

Comparison of Corneal Thickness Measurements After Customized Corneal Crosslinking Using High-Resolution Optical Coherence Tomography and Scheimpflug Tomography.

PURPOSE: The aim of this study was to compare the evolution of corneal pachymetry after customized corneal crosslinking (CXL) between Scheimpflug-based and optical coherence-based corneal tomography (OCT). METHODS: In this retrospective study, central corneal thickness (CCT), thinnest corneal thickness, and epithelial thickness of 33 eyes of 33 patients with keratoconus were measured preoperatively and 1, 3, and 12 months after customized CXL using the Pentacam HR and the MS-39. The mean pachymetry values of measurements were compared with a paired sample t test. Bland-Altman plots and 95% limits of agreement (LoA) were used to assess the agreement between the measurements of the 2 devices. RESULTS: The mean age of the participants was 29.7 ± 11.4 years. At baseline, the mean CCT measurements were equal with Pentacam HR (478.30 ± 36.77 µm) and MS-39 (478.46 ± 38.01 µm). After CXL, CCT obtained by Pentacam HR was 460.65 ± 38.69 µm, 464.65 ± 44.45 µm, and 476.77 ± 39.85 µm, and by MS-39 was 478.18 ± 39.50 µm, 472.89 ± 40.92 µm, and 479.51 ± 39.20 µm at 1, 3, and 12 months, respectively. Pentacam HR measured significantly lower CCT ( P < 0.05) at months 1 and 3 after CXL. The agreement was smallest between both devices at month 1 (95% LoA -59 to 24 µm) followed by month 3 (95% LoA: -41 to 23 µm). Epithelial thickness, measured with OCT alone, increased significantly at 1 month and regained preoperative levels at 3 months and thereafter. CONCLUSIONS: After CXL, corneal pachymetry significantly differs between OCT-based and Scheimpflug-based corneal tomography. Pentacam HR seems to underestimate pachymetry when haze is present.

Corneal thickness measurements with the RTVue, Casia-2, and Pentacam devices in patients with mild-to-moderate keratoconus: a comparative study.

BACKGROUND: To compare the characteristics of corneal thickness measurements among the RTVue, Casia-2, and Pentacam in patients with mild-to-moderate keratoconus. METHODS: We recruited 46 eyes of 46 patients diagnosed with mild-to-moderate keratoconus at our hospital between January and March 2022. The central corneal thickness (CCT) and thinnest corneal thickness (TCT) were measured using two optical coherence tomography (OCT) instruments (RTVue and Casia-2) and the more conventional Pentacam. Differences and correlations between the CCTs and TCTs, based on the device and influencing factors, were explored. RESULTS: The CCTs were highly consistent among the groups (p = 0.434) and correlated with one another (p < 0.001). The TCTs measured by OCTs were thinner than those measured by the Pentacam (p < 0.001); however, all three devices were highly correlated (p < 0.001). The thinnest point location measurements with RTVue and Casia-2 differed significantly from the measurements with the Pentacam. Bland-Altman plots demonstrated a significant agreement between Pentacam and OCTs in TCT measurement (p < 0.001); the 95% limits of agreement were - 3.1 µm to + 33.1 µm for Pentacam and RTVue and - 8.6 µm to + 36.5 µm for Pentacam and Casia-2. RTVue and Casia-2 showed no difference in corneal thickness (p = 0.633) and thinnest point location measurement (p > 0.05). Multivariate analysis identified that the TCT measurement difference between the RTVue and Pentacam was related to the difference between the CCT and TCT (b = 0.490, 95% confidence interval [CI]: 0.033 to 0.948, p = 0.036), whereas the difference between the Casia-2 and Pentacam was related to the anterior radius for curvature (A) grade (b = 3.9, 95% CI: 1.753 to 6.074, p = 0.001), corneal pachymetry at the thinnest (C) grade (b = - 7.875, 95% CI: - 11.404 to - 4.346, p < 0.001), and the difference between the CCT and TCT (b = 0.425, 95% CI: 0.1 to 0.751, p = 0.012). CONCLUSIONS: CCTs in patients with mild-to-moderate keratoconus were similar among all three devices, but the TCTs and the thinnest point locations were not. Furthermore, the TCT measurement differences between the OCT devices and the Pentacam were more pronounced in keratoconus cases with a steeper anterior surface, thicker TCTs, and a larger difference between the CCT and TCT. TRIAL REGISTRATION: Number: 2021118-1. Retrospectively registered: September 01, 2021.