Agreement between invasive and noninvasive measurement of tear film breakup time.

The agreement between fluorescein breakup time (FBUT) estimates and noninvasive breakup time (NIBUT) estimates automatically acquired using two videokeratoscopes was assessed. Small-cone (E300, Medmont) and large-bowl (K5M, OCULUS) Placido-ring-based videokeratoscopes were utilized for automated NIBUT estimation and fluorescein strip method was used for FBUT estimation. 33 subjects completed the study. Clear instructions were given regarding the blink before measurements. Bland-Altman analysis was used to test the agreement between tear film breakup time estimates and repeated measure analysis of variance was used to test the differences between measurement types. In comparison to FBUT, E300 NIBUT estimate was shorter (- 0.6 ± 2.6 s), whereas K5M NIBUT estimate was longer (3.3 ± 2.4 s). Limits of agreement for FBUT vs. E300 was 29.8 s, for FBUT vs. K5M 26.4 s, and 31.4 s for E300 vs. K5M. There were significant differences between tear film breakup times (F = 3.59, df = 2, P = 0.032). E300 and K5M NIBUT measurements have poor agreement with FBUT, even when blinking is precisely clarified. Agreement was better for shorted break up times than that for longer ones but in general NIBUT measurements are not interchangeable.

Characterization of the external limbus on corneoscleral topography with ultrawide-field optical coherence tomography.

PURPOSE: To present a new method for 3-dimensional external limbal demarcation on corneoscleral topography derived from optical coherence tomography (OCT). Limbal shape is investigated and compared to other landmarks. METHODS: Images from the anterior segment were obtained with a ultrawide-field (20 mm) OCT. An automated algorithm was developed to demarcate the topographic limbus based on the transition from corneal to scleral curvature. The internal limbus was manually identified as the scleral spur on the OCT images. The external topographic limbus was fit with a circle on a plane. Ellipticity and ovality were defined by the lateral limbal deviation from the best-fit circle. Toricity was defined by the axial deviation from the best-fit plane. Repeatability was assessed by the within-subject standard deviation from two repeated measurements. For comparison, the white-to-white (WTW) diameter was obtained from Pentacam HR. RESULTS: 18 eyes from 11 subjects were analyzed. The topographic limbal diameter was 12.16 ± 0.68 mm (mean ± standard deviation) horizontally and 11.18 ± 0.65 mm vertically. The repeatability for the topographic limbal diameter was 0.054 mm. The internal and WTW horizontal limbal diameters were significantly smaller (linear mixed-effects model (GLMM), p <.017). The vertical internal limbal diameter was significantly larger (GLMM p <.05). The topographic limbus had significant ellipticity (0.25 ± 0.13 mm, wider horizontally, repeatability of 0.07 mm) and toricity (0.15 ± 0.08 mm, flatter horizontally, repeatability of 0.10 mm). Low coefficients of determination were found for the topographical limbus with the internal limbus (R2=0.021 and R2=0.039, for horizontal and vertical diameters respectively) and with the WTW (R2=0.146 for the horizontal diameter). CONCLUSION: The proposed method to demarcate the 3D external topographical limbus is repeatable. The topographic limbal shape and size cannot be accurately derived from WTW nor internal limbus measures. This new technology may improve the process of scleral lens fitting.

The efficacy of ocular surface assessment approaches in evaluating dry eye treatment with artificial tears.

This study evaluates the effectiveness of objective techniques in assessing dry eye disease (DED) treatment compared with the subjective assessment commonly used in clinical practice. Thirty subjects were recruited for two visits separated by 28(± 3) days of treatment with artificial tears. A buttery of common subjective assessment methods were accompanied by a set of objective techniques including measurement of noninvasive tear film break-up time (NIBUT), lipid layer thickness (LLT), and quantitative evaluation of tear film surface quality and dynamics (TFD). Additionally, meibography was performed. Two commercially available videokeratoscopes and a prototype of a lateral shearing interferometer were used for the measurements. Both subjective and objective techniques showed a positive effect of artificial tears in DED treatment. Statistically significant improvements were observed in subjective symptoms (from P < 0.001 for Ocular Surface Disease Index, OSDI to p = 0.019 for tearing), conjunctival redness (P = 0.022), ocular staining (P = 0.012), fluorescein tear film break-up time (P = 0.015), NIBUT (P = 0.037), LLT (P < 0.001), and TFD (P = 0.048). In general, weak or statistically insignificant correlations were observed between subjective and objective assessment methods. The apparent lack of correlation between these methods might indicate the complementary character of objective techniques that likely assess other characteristics of ocular surface health than those assessed subjectively.

Measuring corneal astigmatism using OCT in keratoconus.

PURPOSE: To measure net corneal astigmatism using optical coherence tomography (OCT) (Avanti) in individuals with keratoconus and compare the repeatability and accuracy with those obtained using Scheimpflug imaging (Pentacam HR). SETTING: Casey Eye Institute, Portland, Oregon. DESIGN: Prospective cross-sectional observational study. METHODS: Net corneal astigmatism was calculated in keratoconic and normal eyes using OCT and Scheimpflug imaging with 4 settings-pupil or vertex centration settings with a 3 or 4 mm circular analytical zone. Corneal elevation maps were obtained from OCT images and fitted with the Zernike polynomials to obtain net corneal astigmatism. Manifest refraction astigmatism was used to evaluate the accuracy of net corneal astigmatism measurements. The coefficient of repeatability from 2 repeated measures was calculated. RESULTS: 46 eyes with manifest or subclinical keratoconus and 52 normal control eyes were analyzed. For OCT measurements in keratoconus, better accuracy was achieved with pupil centration and 3 mm analytical zone; however, better repeatability was achieved with vertex centration and 4 mm analytical zone (coefficient of repeatability = 0.53 diopters, the Fligner-Killeen test with Bonferroni adjustment P &lt; .0017). Agreement with manifest refraction was significantly better with OCT compared with that using Pentacam HR (generalized mixed-effect model with Bonferroni adjustment P &lt; .00625). No statistically significant difference was found between instruments or settings in control eyes. CONCLUSIONS: OCT was able to measure net corneal astigmatism with better accuracy and precision in keratoconic eyes than the Pentacam HR. Measurements may be more accurate using pupil centration and a smaller analytical zone in patients with keratoconus.

Accuracy of OCT-derived net corneal astigmatism measurement.

PURPOSE: To assess the repeatability and accuracy of corneal astigmatism measurement with a spectral-domain optical coherence tomography (OCT) system (Avanti, Optovue) and compare them with Scheimpflug imaging (Pentacam HR, Oculus) and swept-source optical biometry (IOLMaster 700, Carl Zeiss Meditec AG). SETTING: Casey Eye Institute, Oregon Health & Science University, Portland, Oregon. DESIGN: Prospective cross-sectional observational study. METHODS: 60 pseudophakic eyes with monofocal nontoric intraocular lens that previously had refractive surgery were analyzed. To assess accuracy, simulated keratometry (SimK) and net corneal astigmatism, obtained from each device, were compared with subjective manifest refraction astigmatism. Repeatability for corneal astigmatism was assessed for OCT and Pentacam HR by the coefficient of repeatability from 3 repeated measures. RESULTS: Compared with manifest refraction, SimK readings produced with-the-rule astigmatic bias that was reduced for net astigmatism for the 3 devices. Except for OCT net astigmatism, all instruments significantly overestimated the magnitude of the astigmatism (linear mixed-effects model [LMM], P < .05). OCT net astigmatism showed the highest accuracy for manifest astigmatism prediction with the smaller 95% confidence ellipse for the mean difference vector. OCT net mean absolute difference was 0.57 diopters (D), significantly smaller than that of the other modalities (LMM, P < .05). Net corneal astigmatism measured with OCT showed the best repeatability (coefficient of repeatability = 0.29 D). CONCLUSIONS: OCT has the capability to measure net corneal astigmatism with higher precision and accuracy than Pentacam HR Scheimpflug imaging and IOLMaster 700 swept-source optical biometry in postrefractive subjects.

Subjective and Objective Evaluation of the Effect of Blink Type on Tear-film Breakup Time and Its Estimation.

SIGNIFICANCE: While evaluating the tear-film breakup time, a careful set of precise instructions should be given to the subjects regarding the blink type because it substantially impacts the assessment of tear-film surface quality. PURPOSE: The purpose of this study was to determine to what extent the type of blink affects the tear-film breakup time and its assessment using two types of videokeratoscopes and the fluorescein test. METHODS: Thirty-three volunteers were assessed considering two different types of blinks: natural (short) and forced (unnaturally prolonged). Objective noninvasive breakup time estimation was performed using Oculus Keratograph 5M and Medmont E300, both equipped with tear-film analysis modules, followed by the fluorescein test. In addition, while overviewing videokeratoscopy recordings, noninvasive breakup time was assessed subjectively by one experienced observer marking the first noticeable distortion in the Placido-disk pattern. Statistical analyses included two-way ANOVA and paired-sample t test. The agreement between blinking and measuring modalities was assessed using Bland-Altman plots. RESULTS: Forced blink significantly shortened the tear-film breakup time in all measuring modalities (two-way ANOVA, P = .003). The mean difference between breakup time after natural and forced blink was 3.2 (P = .002), 2.4 (P = .005), and 2.1 seconds (P = .002), for Keratograph 5M, E300, and fluorescein test, respectively. The group median of differences between objective and subjective noninvasive breakup time was less than 1 second with both videokeratoscopes. The objective noninvasive breakup time measured with Keratograph 5M was significantly longer than those with E300 and fluorescein test (both P < .001). No statistically significant difference was found between E300 objective assessment and fluorescein test (P = .19). CONCLUSIONS: Forced blinks affect the assessment of tear-film stability. Hence, attention should be given in instructing the subjects before tear-film breakup time evaluation irrespectively to the method of measurement.

Meibomian glands structure in daily disposable soft contact lens wearers: a one-year follow-up study.

PURPOSE: To assess the impact of daily disposable soft contact lenses on meibomian gland morphology over a period of 12 months. METHODS: Forty-one subjects (33 experienced and 8 neophytes) were fitted with either silicone-hydrogel or hydrogel daily contact lenses. The study protocol included four visits: baseline, day-2 for contact lens fit and follow-up measurements, as well as after 6 and 12 months of lens wear. Non-contact infrared meibography images were acquired with Keratograph 5M topographer (www.oculus.de) and analysed with an automated method, which objectively estimates the area of gland atrophy, gland length and width, number of glands and gland irregularity. Protocol at follow-up visits also included symptom assessment with the Ocular Surface Disease Index and clinical assessment of tear meniscus height, bulbar and limbal redness, tear osmolarity, non-invasive fluorescein break-up time and ocular surface staining. RESULTS: Statistically significant differences were found in gland atrophy (p = 0.02) and length (p = 0.008) between experienced and novel contact lens wearers at the baseline visit. Changes over time (after 6 and 12 months) were found in gland atrophy (p = 0.02) and the number of glands (p = 0.01) in subjects fitted with hydrogel contact lenses. Changes in gland atrophy between baseline and 12 months of lens wear correlated with changes in corneal staining (r = 0.40, p = 0.03) and fluorescein break-up time in subjects fitted with silicone-hydrogel lenses (r = 1-0.43, p = 0.02). CONCLUSIONS: Contact lens wear impacts meibomian gland morphology. However, changes are either long-term or characteristic to an early phase. Subjects with no history of contact lens wear exhibit better meibomian gland condition than experienced wearers. During one year of contact lens wear, meibomian gland morphology changes in subjects wearing daily disposable hydrogel lenses.

Meibomian Gland Morphology: The Influence of Structural Variations on Gland Function and Ocular Surface Parameters.

PURPOSE: To objectively and quantitatively characterize meibomian gland morphology and to investigate the influence of morphological variations on gland function and ocular surface and tear film parameters. METHODS: One hundred fifty subjects were enrolled. The examinations included tear osmolarity, tear meniscus height, bulbar conjunctival hyperemia, noninvasive tear film breakup time, lid margin thickness, foam secretion, meibomian gland expressibility, count of functioning glands, corneal and conjunctival staining, fluorescein breakup time, lid wiper epitheliopathy, and Schirmer test. Patient symptoms were assessed using the Ocular Surface Disease Index questionnaire. Images from noncontact meibography were analyzed using an automated method that objectively estimates dropout area, number of glands, gland length and width, and gland irregularity. RESULTS: Gland irregularity highly correlated with dropout area (r = -0.4, P < 0.001) and showed significant partial correlations with fluorescein breakup time (r = 0.162, P = 0.049) and the Ocular Surface Disease Index questionnaire (r = -0.250, P = 0.002) Subjects with dropout area <32% were divided into 2 groups: high and low irregularity. Gland expressibility was statistically significantly different between the 2 groups (U = 319.5, P = 0.006). In the high irregularity group, gland irregularity correlated with the Schirmer test (r = 0.530, P = 0.001) and corneal fluorescein staining (r = -0.377, P = 0.021). CONCLUSIONS: Automated morphological analysis of meibomian gland structure provides additional quantitative and objective information regarding gland morphology. The link between dropout area and gland function is not clear. Assessment of gland irregularity might better predict gland function and its effects on ocular surface and tear film parameters.

A Novel Automated Approach for Infrared-Based Assessment of Meibomian Gland Morphology.

PURPOSE: We present and validate a new methodology for analyzing, in an automated and objective fashion, infrared images of the meibomian glands (MG). METHODS: The developed algorithm consists of three main steps: selection of the region of interest, detection of MG, and analysis of MG morphometric parameters and dropout area (DOA). Additionally, a new approach to quantify the irregularity of MG is introduced. We recruited 149 adults from a general population. Infrared meibography, using Keratograph 5M, was performed. Images were assessed and graded subjectively (Meiboscore) by two experienced clinicians and objectively with the proposed automated method. RESULTS: The correlation of subjective DOA assessment between the two clinicians was poor and the average percentage of DOA estimated objectively for each Meiboscore group did not lie within their limits. The objective assessment showed lower variability of meibography grading than that obtained subjectively. Additionally, a new grading scale of MG DOA that reduces intraclass variation is proposed. Reported values of MG length and width were inversely proportional to the DOA. Gland irregularity was objectively quantified. CONCLUSIONS: The proposed automatic and objective method provides accurate estimates of the DOA as well as additional morphologic parameters that could add valuable information in MG dysfunction understanding and diagnosis. TRANSLATIONAL RELEVANCE: This approach highlights the shortcomings of currently used subjective methods, and provides the clinicians with an objective, quantitative and less variable alternative for assessing MG in a noninvasive and automated fashion. It provides a viable alternative to more time-consuming subjective methods.

Unified approach to tear film surface analysis with high-speed videokeratoscopy.

Placido disk videokeratoscopy, when used in a dynamic acquisition mode, can be utilized for noninvasive assessment of tear film quality. The different commercially available videokeratoscopes that incorporate an automatic option to evaluate tear film do not provide consistent measurements due to differences in their designs as well as differences in the algorithms used to analyze the images. Here, a standardized algorithm that can be applied to different instruments is developed. Results show that, by applying the proposed methodology in two different videokeratoscopes, the agreement among the estimated tear film parameters considerably improves. This represents a step forward in the normalization of tear film assessment.

The influence of meibomian gland loss on ocular surface clinical parameters.

PURPOSE: To assess the relationship between the meibomian gland loss (MGL) and relevant ocular surface clinical parameters as well as the influence of age in this relationship. METHODS: A total of 161 participants (mean age; 42±17 years) were enrolled in this study. Infrared meibography was performed using Keratograph 5M (K5M; Oculus GmbH, Wetzlar). Participants were divided into five groups according to total meiboscore and the ocular surface parameters of each MGL group were studied. In addition, the relationship between MGL and the ocular surface parameters was established including age as covariant. RESULTS: Both eyelids were taken into account since no association between the MGL from upper and lower eyelid was found (k value=0.2; p=0.3) despite they were significantly correlated (r= 0.3; p<0.001). No statistically significant differences were found in symptomatology among different MGL groups. Statistically significant differences were found among MGL groups in tear osmolarity (p=0.02), bulbar redness (p=0.04), corneal and conjunctival staining (p=0.01 and p=0.004, respectively). Despite this, only corneal staining showed a significant correlation with MGL when age was covariant (r=0.2; p=0.04). CONCLUSIONS: MGL higher than 50% seems to be accompanied by signs on the ocular surface. Furthermore, age demonstrated to be a relevant factor when assessing MGL. For this reason, future studies should compare age-matched groups in order to know the contribution of the MGL on the ocular surface and establish valid cut-off values for dry eye diagnosis.

Supporting Dry Eye Diagnosis with a New Method for Noninvasive Tear Film Quality Assessment.

SIGNIFICANCE: Noninvasive high-speed videokeratoscopy equipped with specific software has shown potential for assessing the homeostasis of tear film, providing clinicians with a fast and consistent tool for supporting dry eye diagnosis and management. PURPOSE: The purpose of this study was to evaluate the efficacy of a recently proposed method for characterizing tear film dynamics using noninvasive high-speed videokeratoscopy in assessing the loss of homeostasis of tear film. METHODS: Thirty subjects from a retrospective study, of which 11 were classified as dry eye and 19 as healthy, were included. High-speed videokeratoscopy measurements were performed using E300 videokeratoscope (Medmont Pty., Ltd., Melbourne, Australia). Raw data were analyzed using a recently proposed method to estimate the dynamics of the tear film based on a fractal dimension approach. This method provides three time-varying indicators related to the regularity of the reflected rings: tear film surface quality indicator, breaks feature indicator, and distortions feature indicator. From each indicator, five parameters were extracted and analyzed, including noninvasive breakup time, mean value of the indicator in the stability phase, mean value of the indicator in the whole interblink interval, mean value of the indicator in the leveling phase, and the general trend of the time series. Receiver operating characteristic curves were used to determine the sensitivity and specificity of each parameter in dry eye detection. RESULTS: The best discrimination performance between dry eye and healthy subjects was achieved with the breaks feature indicator noninvasive breakup time parameter, with an area under the curve of 0.85. For a cutoff value of 10 seconds, the sensitivity was 100% and the specificity was 84%. CONCLUSIONS: The analyzed method improves the assessment of tear film homeostasis in comparison with previous high-speed videokeratoscopy methods showing higher potential in assisting dry eye diagnosis.

Randomized crossover trial of silicone hydrogel contact lenses.

PURPOSE: The aim of the current study is to assess, using new technologies, the interaction of four monthly silicone hydrogel contact lenses on the ocular surface and the comfort over 15 days of use. METHODS: Prospective cross-over, randomized and double-masked study including four materials (lotrafilcon-B, samfilcon-A , comfilcon-A and filcom-V3). Clinical examination was performed in the following order: tear meniscus height, first break-up of the tear film, the average time of all tear film breakup incidents, bulbar redness, limbal redness (Keratograph 5M ,Oculus, Germany); central corneal thickness (Pentacam, Oculus, Germany), thermography values (FLIR A325; FLIR Systems Inc., USA), and slit-lamp evaluations, including ocular surface staining. Finally, subjective comfort was obtained from Contact Lens Dry Eye Questionnaire-8. RESULTS: The impact of contact lens wear on the ocular surface didn't show statistically significant changes over time except for corneal and conjunctival staining grades on day 15 compared to day 1 for the comfilcon A group (P = .003 and P = .01, respectively). Contact lens stability and impact on the ocular surface during contact lens wear didn't show statistically significant changes over time except in the case of the comfilcon A material with respect to the irritation item (P = .01). CONCLUSIONS: These results suggest that the impact of monthly silicone hydrogel contact lens materials on the ocular surface after and during contact lens wear, contact lens stability over time, and subjective comfort did not reveal any significant changes over 15 days of use for any of the materials.

Rotation asymmetry of the human sclera.

PURPOSE: To characterize the mean topographical shape of the human sclera of a normal eye. METHODS: Forty-five participants aged from 19 to 45 years and with no previous ocular surgeries were included in this study. Four three-dimensional (3D) corneo-scleral maps from both eyes were acquired using a corneo-scleral topographer (Eye Surface Profiler). For each 3D map, the sclera (maximum diameter of 16 mm) and cornea were automatically separated at the level of the limbus. The remaining 3D scleral ring was further fit to a quadratic function. The elevation difference between the original and fit data was calculated. For statistical analysis, sclera was divided into eight sectors: nasal, temporal, superior, inferior, supero-nasal, supero-temporal, inferior-nasal and inferior-temporal. In addition, sclera was separated as inner sclera (inner ring of 6-7-mm radius) and outer sclera (external ring of 7-8-mm radius). RESULTS: Horizontally, the nasal area of the sclera showed less elevation [mean (SD) -30 (52) µm (OD)] than the temporal area [mean (SD) 4 (47) µm (OD)], p < 0.001. Vertically, the inferior area of the sclera [mean (SD) 32 (72) µm (OD)] was slightly less elevated than the superior area (mean (SD) 36 (84) µm, but this difference was not statistically significant (p = 0.40). Besides, the asymmetry of the sclera was found to increase with radial distance from the corneal apex. No statistically significant difference was found between right and left eye. CONCLUSION: Human sclera is rotationally asymmetric, and its shape varies considerably between subjects.

Assessment of Tear Film Using Videokeratoscopy Based on Fractal Dimension.

SIGNIFICANCE: The proposed automated approach for estimating the quality of the tear film closes the gap between the manual and automated assessment, translating the high-speed videokeratoscopy technology from scientific laboratories to a clinical practice. PURPOSE: To develop and test a new method for characterizing Tear Film Surface Quality with high-speed videokeratoscopy utilizing a fractal dimension approach. METHODS: The regularity of the reflected pattern in high-speed videokeratoscopy (E300; Medmont) depends on tear film stability. Thus, determining tear film stability can be addressed by estimating the fractal dimension of the reflected pattern. The method is tested on 39 normal subjects. The results of the fractal dimension approach are compared with those obtained using previously proposed automated method, based on a gray-level co-occurrence matrix approach, and with subjective results obtained by two operators that were assessing the video recordings in ideal conditions. RESULTS: Fractal dimension method was less affected by eye movements and changes in the videokeratoscopic image background than gray-level co-occurrence matrix method. Median difference of the noninvasive break-up time between manual and automated methods was 0.03 s (IQR = 4.47 s) and 0.0 s (IQR = 2.22 s) for gray-level co-occurrence matrix and fractal dimension approaches, respectively. Correlation coefficient with manual noninvasive break-up time was r = 0.86 (P < 0.001) for gray-level co-occurrence matrix approach, and r = 0.82 (P < 0.001) for fractal dimension approach. Significant statistical difference was found between noninvasive break-up measurements of manual and gray-level co-occurrence matrix method (P = 0.008). CONCLUSIONS: The proposed method has the potential to characterize tear film dynamics in more detail compared to previous methods based on high-speed videokeratoscopy. It showed good correlation with manual assessment of tear film.

Non-invasive pre-lens tear film assessment with high-speed videokeratoscopy.

PURPOSE: To evaluate the effect of two types of daily contact lenses (delefilcon A and omafilcon A) on the tear film and establish whether it is dependent on pre-corneal tear film characteristics using a new method to analyse high-speed videokeratoscopy recordings, as well as to determine the sensitivity of the method in differentiating between contact lens materials on eye. METHODS: High-speed videokeratoscopy recordings were analysed using a custom made automated algorithm based on a fractal dimension approach that provides a set of parameters directly related to tear film stability. Fifty-four subjects participated in the study. Baseline measurements, in suppressed and natural blinking conditions, were taken before subjects were fitted with two different daily contact lenses and after four hours of contact lens wear. RESULTS: The method for analysing the stability of the tear film provides alternative parameters to the non-invasive break up time to assess the quality of the pre-corneal and pre-lens tear film. Both contact lenses significantly decreased the quality of the tear film in suppressed and natural blinking conditions (p<0.001). The utilised method was able to distinguish between contact lens materials on eye in suppressed blinking conditions. The pre-corneal tear film characteristics were not correlated with the decrease in pre-lens tear film quality. CONCLUSION: High-speed videokeratoscopy equipped with an automated method to analyse the dynamics of the tear film is able to distinguish between contact lens materials in vivo. Incorporating the assessment of pre-lens tear film to the clinical practice could aid improving contact lens fitting and understand contact lens comfort.

Mean shape of the human limbus.

PURPOSE: To characterize the mean topographic shape of the limbus of a normal human eye and determine whether it depends on age or refractive power. SETTING: University of Manchester, Manchester, United Kingdom. DESIGN: Prospective case series. METHODS: Participants with no previous ocular surgeries were included in this study. The left eye was measured with a corneoscleral topographer (Eye Surface Profiler). From the raw anterior eye height data, the topographic limbus was demarcated and fitted in 3 dimensions to a circle, an ellipse, and a Fourier series. The root mean square error was calculated to evaluate the goodness of fit. In addition, the white-to-white (WTW) corneal diameter was taken from the readings of the measuring device. For statistical analysis, participants were grouped according to their age and their spherical equivalent correction. RESULTS: The study comprised 74 participants aged 20 to 84 years. From the considered models, the 2nd-order Fourier series was the most accurate model to describe the shape of the human limbus. The mean difference between the topographic limbus diameter and the WTW corneal diameter was 0.33 mm ± 0.24 (SD). There were statistically significant differences between eye quadrants (P < .001); however, there were no statistically significant differences in the horizontal and vertical meridians between age groups (P = .71 and P = .082, respectively) or between eyes with myopia and eyes with emmetropia (P = .78 and P = .68, respectively). CONCLUSION: The human limbus is not symmetrical and although its shape is person-dependent, it is not related to age or the eye's refractive power.