Orthokeratology effect on the corneoscleral profile: Beyond the bull's eye

PURPOSE

To assess the impact of 3 months of orthokeratology (ortho-k) contact lenses (CLs) for myopia correction on the corneoscleral profile, as changes in scleral geometry could serve as indirect evidence of alteration in the corneal biomechanical properties.

METHODS

Twenty subjects (40 eyes) were recruited to wear ortho-k lenses overnight; however, after discontinuation (two CL fractures, one under-correction and two non-serious adverse events), 16 subjects (31 eyes) finished a 3-month follow-up. Corneoscleral topographies were acquired using the Eye Surface Profiler (ESP) system before and after 3 months of lens wear. Steep (SimKs) and flat (SimKf) simulated keratometry and scleral sagittal height measurements for 13-, 14- and 15-mm chord lengths were automatically calculated by the ESP software. Additionally, sagittal height and slope were calculated in polar format from 21 radii (0-10 mm from the corneal apex) at 12 angles (0-330°). Linear mixed models were fitted to determine the differences between visits.

RESULTS

SimKs and SimKf were increased significantly (p ≤ 0.02). The sagittal height in polar format increased significantly (p = 0.046) at a radius of 2.5 mm for 150°, 180°, 210° and 240° orientations and at a radius of 3.0 mm for 210°. Additionally, the slope in polar format significantly decreased (p ≤ 0.04) at radii ranges of 0.0-0.5, 0.5-1.0 and 1.0-1.5 mm for multiple angles and at a radii range of 5.0-5.5 mm for 90°. It also increased significantly (p ≤ 0.045) at a radii range of 1.5-2.0 mm for 30° and at radii ranges of 2.0-2.5, 2.5-3.0 and 3.0-3.5 mm for multiple angles. No significant changes were found for any parameter measured from the scleral area.

CONCLUSIONS

Three months of overnight ortho-k lens wear changed the central and mid-peripheral corneal geometry as expected, maintaining the peripheral cornea and the surrounding sclera stability.

Reliability and Agreement of Keratometry Measurements Obtained With Eye Surface Profilometry and Partial Coherence Interferometry

PURPOSE

The aim of this study was to assess the repeatability of keratometry parameters obtained using the Eye Surface Profiler (ESP) system and their agreement with the IOL Master 500 device.

METHODS

Seventy-one eyes of 71 healthy participants were evaluated. Three repeated measurements were performed using the ESP system. Simulated keratometry in the flat (SimKf) and steep (SimKs) meridians, astigmatism, and axis were obtained. The same parameters were measured using the IOL Master 500 device. The J0 and J45 vector components of the astigmatism were calculated. The intrasession repeatability was analyzed using within-subject SD (Sw) and intraclass correlation coefficient (ICC). Agreement was assessed using paired statistical tests and the Bland-Altman method.

RESULTS

The Sw was 0.07 mm, 0.04 mm, 0.51 D, 0.33 D, and 0.22 D, and the ICC was 0.96, 0.98, 0.74, 0.61, and 0.55 for SimKf, SimKs, astigmatism, J0, and J45, respectively. The mean difference and limits of agreement when comparing the ESP system with the IOL Master 500 device were 0.37 mm (0.08/0.66) for SimKf ( P < 0.001), 0.18 mm (0.00/0.35) for SimKs ( P < 0.001), -0.93 D (-2.42/0.56) for astigmatism ( P < 0.001), 0.51 D (-0.22/1.24) for J0 ( P < 0.001), and 0.06 D (-0.48/0.60) for J45 ( P = 0.09).

CONCLUSIONS

The ESP system provides consistent values for simulated keratometry, showing moderate consistency for astigmatism parameters. Contact lens practitioners should be aware that the ESP system and IOL Master 500 device provide different simulated keratometry from a clinically viewpoint.

The influence of soft contact lens material on the corneoscleral profile

PURPOSE

To objectively quantify changes in corneoscleral profile, as evaluated by the limbus position and corneoscleral junction (CSJ) angle, as a consequence of wearing different soft contact lens (CL) materials.

METHODS

Twenty-two healthy participants wore silicone hydrogel (SiHy, MyDay, CooperVision) and hydrogel (Hy, Biomedics 1 day extra, CooperVision) soft CLs for 8 h per lens in their left eye. In each session, corneoscleral topography was captured before and immediately after CL removal with an Eye Surface Profiler. Previously validated automatic and objective algorithms for limbal position and CSJ angle calculation were applied to 360 semi-meridians to investigate the effect of short-term CL wear on corneoscleral topography, globally and by sectors, depending on the soft CL material worn.

RESULTS

Short-term soft CL wear significantly impacted limbal position (SiHy: 120 ± 97 μm, Hy: 128 ± 85 μm) and CSJ angle (SiHy: 0.57 ± 0.36°, Hy: 0.55 ± 0.40°); all p < 0.05. A statistically significant difference was found between the sectors with regard to limbus position and CSJ angle before CL wear that remained following lens wear (all pairwise comparisons, p < 0.001). Although individual differences were observed, there was no evidence that one material caused more substantial corneoscleral alterations.

CONCLUSION

Corneoscleral profile parameters were altered significantly following 8 h of soft CL wear. The observed changes in limbus position and CSJ angle support the importance of participant-material biocompatibility.

Multi-camera optical tracking and fringe pattern analysis for eye surface profilometry in ocular proton therapy

Background and purpose

An optical tracking system for high-precision measurement of eye position and orientation during proton irradiation of intraocular tumors was designed. The system performed three-dimensional (3D) topography of the anterior eye segment using fringe pattern analysis based on Fourier Transform Method (FTM).

Materials and methods

The system consisted of four optical cameras and two projectors. The design and modifications to the FTM pipeline were optimized for the realization of a reliable measurement system. Of note, phase-to-physical coordinate mapping was achieved through the combination of stereo triangulation and fringe pattern analysis. A comprehensive pre-clinical validation was carried out. Then, the system was set to acquire the eye surface of patients undergoing proton therapy. Topographies of the eye were compared to manual contouring on MRI.

Results

Pre-clinical results demonstrated that 3D topography could achieve sub-millimetric accuracy (median:0.58 mm) and precision (RMSE:0.61 mm) in the clinical setup. The absolute median discrepancy between MRI and FTM-based anterior eye segment surface reconstruction was 0.43 mm (IQR:0.65 mm).

Conclusions

The system complied with the requirement of precision and accuracy for image guidance in ocular proton therapy radiation and is expected to be clinically tested soon to evaluate its performance against the current standard.

Dynamic topography analysis of the cornea and its application to the diagnosis of keratoconus

PROPOSE

To establish a dynamic topography analysis method which simulates the dynamic biomechanical response of the cornea and reveals the variations of such response within the corneal surface, and thereafter to propose and clinically evaluate new parameters for the definite diagnosis of keratoconus.

METHODS

58 normal (Normal) and 56 keratoconus (KC) subjects were retrospectively included. Personalized corneal air-puff model was established using corneal topography data by Pentacam for each subject, and the dynamic deformation under air-puff loading was simulated using finite element method, which then enabled calculations of corneal biomechanical parameters of the entire corneal surface along any meridian. Variations in these parameters across different meridians and between different groups were explored by two-way repeated measurement analysis of variance. New dynamic topography parameters were proposed as the range of the calculated biomechanical parameters within the entire corneal surface, and the AUC of ROC curve was used to compare the diagnostic efficiency of newly proposed and existing parameters.

RESULTS

Corneal biomechanical parameters measured in different meridians varied significantly which were more pronounced in KC group due to its irregularity in corneal morphology. Considering such between-meridian variations thus led to improved diagnostic efficiency of KC as presented by the proposed dynamic topography parameter rIR with an AUC of 0.992 (sensitivity: 91.1%, specificity: 100%), significantly better than the current topography and biomechanical parameters.

CONCLUSIONS

The diagnosis of keratoconus may be affected by the significant variations of corneal biomechanical parameters due to corneal morphology irregularity. By considering such variations, the current study established the dynamic topography analysis process which benefits from the high accuracy of (static) corneal topography measurement while improving its diagnosis capacity. The proposed dynamic topography parameters, especially the rIR parameter, showed comparable or better diagnostic efficiency for KC than existing topography and biomechanical parameters, which can be of great clinical significance for clinics without access to instrument for biomechanical evaluations.

Scheimpflug imaging for grading and measurement of corneo-scleral-profile in different quadrants

PURPOSE

The corneo-scleral-profile (CSP) describes the transition from cornea to sclera, while the corneo-scleral junction angle (CSJ), is the angle formed between the cornea and the sclera. The aims of this study were (i) to analyse the CSP and CSJ in different quadrants and (ii) to test correlation and repeatability of an established observational grading and measurement method, using Scheimpflug images.

METHODS

The nasal, temporal, superior and inferior CSP of 35 healthy eye participants (mean age 25.5 SD ± 3.1 years; 20 female) was imaged using the corneo-scleral-profile module of the Pentacam (Oculus, Wetzlar, Germany). On the captured Scheimpflug images CSP was subjectively graded into five different corneo-scleral transitions, using the Meier grading scale (profile 1 fluid-convex; profile 2 fluid-tangential; profile 3 marked-convex; profile 4 marked-tangential; profile 5 concave). The CSJ was measured on the same images using ImageJ v1.8.0. Grading and measurement was repeated at a second session. Intra-observer reliability for the CSP-grading was analysed by Cohen's Kappa. Differences between repeated CSJ-measurements and different quadrants were analysed by paired-t-test and ANOVA. The eta-coefficient was used to determine the association between subjective CSP-grading and CSJ-measurement.

RESULTS

Intra-observer reliability for the CSP grading system was poor (kappa = 0.098) whereas repeated measurements of CSJ angle showed no statistically significant difference between sessions (0.04°; 95 % CI - 0.21° to 0.29°; p = 0.77). CSJ angles ranged from 172° to 180° with no statistically significant differences between nasal, temporal, superior and inferior (p = 0.24). Eta-coefficient indicated a weak association between CSP-grading and CSJ-measurement (η = 0.27; p = 0.04).

CONCLUSIONS

The subjective CSP-grading showed poorer repeatability than the objective CSJ-measurement, which did not detect any differences in angles between the meridians. The weak association between CSP-grading and CSJ-measurement is likely caused by the limited intra-observer reliability of the Meier grading scale. Furthermore, the CSP-grading scale seems to consider other aspects beside the CSJ angle, such as scleral radius.

Comparing sagittal heights calculated using corneal parameters and those measured with profilometry

PURPOSE

To compare the sagittal height of the anterior eye (OC-SAG) calculated using corneal parameters with the OC-SAG measured by profilometry.

METHOD

Seventy right eyes of soft contact lens wearers measured with the ESP (Eaglet Eye, The Netherlands) after lens removal were retrospectively analyzed for this study. The OC-SAG of the eyes was calculated using mean k-values, eccentricity and the inner (corneal) radius obtained with the ESP for an 11-mm cord diameter. It was then extrapolated to chord diameters of 14, 14.5 and 15 mm. These values were compared with OC-SAG values obtained with the ESP for the same chord diameters. Additionally, the OC-SAG was calculated through the formula used by a lab that manufactures custom soft lenses (mark'ennovy, Madrid, Spain) and compared again with the values obtained using the ESP.

RESULTS

Differences between calculated OC-SAG obviating the shape factor were 121 ± 44, 155 ± 105, 172 ± 117 and 189 ± 129 µm for chord diameters of 11, 14, 14.5 and 15 mm, respectively (p < 0.001). When the shape factor was included in the calculation, differences were 28 ± 48, 62 ± 102, 79 ± 113 and 96 ± 123 µm (p < 0.001). When the inner best fit sphere was used to estimate OC-SAG, differences were 34 ± 11, 0 ± 72, 17 ± 86 and 34 ± 99, respectively, with no significant differences for the 14 and 14.5 mm-chord diameters (p = 0.99 and 0.11, respectively). Correlation coefficients between OC-SAG calculated and measured OC-SAG ranged from 0.53 to 0.90 depending on the chord diameter used. When the mark'ennovy formula was used to calculate the OC-SAG as the lens diameter proposed by the formula, the difference was -47 ± 147 µm (p < 0.01).

CONCLUSIONS

Differences between the OC-SAG calculated using corneal parameters and that measured with a profilometer are statistically and clinically significant, especially for large chord diameters. The impact of this on contact lens fitting should be addressed in future studies.

Typical localised element-specific finite element anterior eye model

Purpose

The study presents an averaged anterior eye geometry model combined with a localised material model that is straightforward, appropriate and amenable for implementation in finite element (FE) modelling.

Methods

Both right and left eye profile data of 118 subjects (63 females and 55 males) aged 22-67 years (38.5 ± 7.6) were used to build an averaged geometry model. Parametric representation of the averaged geometry model was achieved through two polynomials dividing the eye into three smoothly connected volumes. This study utilised the collagen microstructure x-ray data of 6 ex-vivo healthy human eyes, 3 right eyes and 3 left eyes in pairs from 3 donors, 1 male and 2 females aged between 60 and 80 years, to build a localised element-specific material model for the eye.

Results

Fitting the cornea and the posterior sclera sections to a 5th-order Zernike polynomial resulted in 21 coefficients. The averaged anterior eye geometry model recorded a limbus tangent angle of 37° at a radius of 6.6 mm from the corneal apex. In terms of material models, the difference between the stresses generated in the inflation simulation up to 15 mmHg in the ring-segmented material model and localised element-specific material model were significantly different (p < 0.001) with the ring-segmented material model recording average Von-Mises stress 0.0168 ± 0.0046 MPa and the localised element-specific material model recording average Von-Mises stress 0.0144 ± 0.0025 MPa.

Conclusions

The study illustrates an averaged geometry model of the anterior human eye that is easy to generate through two parametric equations. This model is combined with a localised material model that can be used either parametrically through a Zernike fitted polynomial or non-parametrically as a function of the azimuth angle and the elevation angle of the eye globe. Both averaged geometry and localised material models were built in a way that makes them easy to implement in FE analysis without additional computation cost compared to the limbal discontinuity so-called idealised eye geometry model or ring-segmented material model.

Corneoscleral junction angle in healthy eyes assessed objectively

PURPOSE

To introduce a fully objective method to measure corneoscleral junction (CSJ) angle and evaluate the CSJ angle in healthy eyes.

METHODS

Corneoscleral topography (Eye Surface Profiler, ESP) was acquired from the right eye of 105 healthy Caucasian subjects, ranging from 18 to 59 years old. From the raw anterior eye height data, the topographic limbus was automatically demarcated in 360 semi-meridians. Further, in limbal location, the CSJ angle was automatically calculated from corneoscleral height data using neighbouring auxiliary points for angle calculation. Additionally, CSJ angle was statistically analysed regionally.

RESULTS

The mean CSJ angle was 177.5 ± 1.1°. There is a mean difference of 7.7 ± 3.7° between the steepest (smallest) and flattest (largest) CSJ angle within the same eye. There exist statistically significant differences between temporal (178.2 ± 1.4°) and nasal (176.4 ± 1.1°) regions (paired t-test, p < 0.001), and between superior (178.1 ± 1.1°) and inferior (177.9 ± 1.1°) regions (p = 0.038). CSJ angle is correlated with limbus position (r = 0.43, p < 0.001).

CONCLUSION

CSJ angle is rotationally asymmetric. CSJ varies regionally, being the smallest (steepest) in the nasal region. Significant rough changes in CSJ angle were observed for some healthy individuals.

Tear Exchange, Intraocular Pressure, and Wear Characteristics of Quadrant-specific Versus Spherical Haptic Scleral Lenses

OBJECTIVES

To compare scleral lenses (SLs) with a quadrant-specific (study lens) or a spherical (habitual lens) landing zone in a crossover study.

METHODS

Seven participants (eight eyes) wore each of two lenses for 2 weeks before measurements. We measured visual acuity, contrast sensitivity, intraocular pressure (IOP), fluid reservoir clearance, corneal thickness, tear exchange, and lens experience. Variables were compared between lenses and before and after 2 hr of wear.

RESULTS

The visual acuity was not different between the study lens, 0.12 logarithm of the minimum angle of resolution (logMAR), and habitual lens, 0.18 logMAR (median, P = 1.0). Contrast sensitivity was 1.3% under the study lens and 1.6% under the habitual lens ( P = 0.94). IOP did not change after 2 hr of wear for either lens (study lens, P = 0.33 and habitual lens, P = 0.74), and corneal thickness did not change during wear of either lens ( P = 0.44). The fluorescein concentration under the study lens did not change after 2 hr (99% of initial concentration; P = 0.84) but decreased to 46% of initial concentration under the habitual lens ( P = 0.008). Lens comfort was slightly better with the study lens (5.0 vs. 4.0, respectively; P = 0.05).

CONCLUSIONS

SLs with spherical or quadrant-specific landing zones provide good vision and do not affect IOP or corneal thickness. However, tear exchange is greater under spherical lenses than under quadrant-specific lenses. The quadrant-specific lens provides greater patient comfort.

What we know about the scleral profile and its impact on contact lens fitting

Scleral contact lens fitting has provided practitioners with one of the earliest pieces of evidence that the sclera was more often asymmetric than symmetric. Some preliminary observations such as different haptic alignment patterns over the sclera in 360 degrees, the appearance of fogging in the fluid chamber and excessive tear out-in flow through specific meridians, quadrants, or areas of the haptic provide evidence of some scleral asymmetry. The advent of technologies that allowed measurement of the scleral profile led to formal research confirming that only about 6% of scleras are symmetric, while the rest are toric, quad-specific, or irregular. This has an evident impact on how to focus scleral lens fitting. Measuring the scleral profile also provided us with true ocular sagittal height data for cord diameters beyond the cornea. Although high variability was expected in pathological eyes, healthy eyes also showed a wide range of ocular sagittal heights. Due to this variability among healthy eyes, a discussion has emerged on whether the one-size-fits-all approach to soft lens fitting is a proper strategy to fit the whole spectrum of sagittal heights. The traditional mode of selecting the parameters for custom soft lenses through corneal parameters is also questioned.

Anterior ocular surface sagittal height prediction

PURPOSE

To investigate the validity of Placido-based corneal topography parameters to predict corneoscleral sagittal heights measured by Fourier-based profilometry at various diameters.

METHODS

Minimal (Min_sag ), maximal (Max_sag ) sagittal height, toricity (Max_sag  - Min_sag ) and axis of the flattest meridian (Min_sag ) of 36 subjects (mean age 25.4 SD ± 3.2 years; 21 female) were measured using the Eye Surface Profiler and analysed for diameters (chord length) of 8 to 16 mm (in 2-mm intervals). Furthermore, corneal central radii, corneal astigmatism, eccentricity and diameter were measured using the Keratograph 5 M.

RESULTS

Using multiple linear regression analysis, the best equation for predicting the sagittal heights for 8 mm (r²  = 0.95), and 10 mm (r²  = 0.93) diameters included corneal central radii and eccentricity. The best equation for predicting sagittal heights for 12 mm (r²  = 0.86), 14 mm (r²  = 0.78) and 16 mm (r²  = 0.65) diameters included corneal central radii, eccentricity and corneal diameter. Corneal astigmatism was significantly correlated with sagittal height toricity for 8 and 10 mm diameters (r²  = 0.50 and 0.29; p < 0.01), while no correlation was observed for 12, 14 and 16 mm diameters (p = 0.18 to p = 0.76). The axis of the flattest corneal meridian measured by Placido-based topography was significantly correlated with the axis of the flattest meridian measured by Fourier-based profilometry for 8, 10 and 12 mm diameters (r²  = 0.17 to 0.44; p < 0.05), while there was no correlation for 14 and 16 mm diameters (p = 0.48 and p = 0.75). For a typical soft contact lens diameter of 14 mm, 78% of the variance could be determined with a corneal topographer and 68% with keratometry and corneal diameter measurement.

CONCLUSIONS

The combination of corneal central radii, eccentricity and corneal diameter measured by Placido-based topography is a valid predictor of the corneoscleral sagittal height in healthy eyes. Scleral toricity and axis of the flattest meridian seem to be independent from Placido-based corneal parameters and requires additional measuring tools.

Comparative Analysis of Two Clinical Diagnostic Methods of the Corneoscleral Geometry

PURPOSE

To compare the sagittal height (SH) measurements and best fit sphere (BFS) scleral curvature obtained with two different diagnostic technologies.

METHODS

Prospective, nonrandomized, and comparative study analyzing 23 healthy eyes of 23 patients (age, 14-52 years) was conducted. A complete eye examination was performed including a corneoscleral topographic analysis with the Scheimpflug camera-based system Pentacam (Oculus GmbH, Wetzlar, Germany) and afterward with the Fourier domain profilometer Eye Surface Profiler (ESP) (Eaglet-Eye, Houten, the Netherlands). Differences between devices in temporal SH (TSH), nasal SH (NSH), and mean SH (MSH) measurements at 13- and 15-mm chord length and in scleral BFS were analyzed.

RESULTS

Statistically significant differences were found in TSH, NSH, and MSH obtained with Pentacam and ESP (P≤0.017), with a range of agreement from 0.21 to 1.28 mm, and a clear trend of the Pentacam system to provide higher SH measurements. Significant differences were found between Pentacam scleral BFS and ESP outer BFS (P<0.001) (range agreement, 3.57 mm). Significant correlations were found between spherical equivalent and differences between devices in 15-mm TSH (r=0.485; P=0.048), as well as between the difference between devices for some SH measurements and the magnitude of such SH values (r≥0.504; P≤0.014).

CONCLUSION

Sagittal height and scleral BFS measurements obtained with the two devices are not interchangeable, with an increased difference in SH measures between devices in eyes with less myopic refractive error and increased SH values.

Repeatability of Anterior Eye Surface Topography Parameters from an Anterior Eye Surface Profilometer

SIGNIFICANCE

Anterior eye shape measurements are important for clinical contact lens fitting. The detailed assessment of measurement repeatability using the Eye Surface Profiler (ESP; Eaglet Eye B.V., AP Houten, the Netherlands) allows for more reliable interpretation of eye surface topography measurements.

PURPOSE

This study aimed to determine the repeatability of the ESP for anterior central corneal power and anterior eye surface height measurements.

METHODS

A Badal optometer was mounted on the ESP to provide an external fixation target with appropriate accommodation control and refractive correction. Forty-five healthy young adults underwent two sessions of anterior eye measurements, separated by 20 minutes, using the ESP. In each session, three consecutive scans were captured. Sagittal height data were obtained from 8-mm central cornea and from 8- to 14-mm diameter (encompassing the corneal periphery and anterior sclera). Anterior corneal powers were determined from the central cornea. Intersessional and intrasessional repeatability values were determined as coefficients of repeatability and root mean square error differences.

RESULTS

Sagittal height intersessional coefficients of repeatability for central nasal (5 μm) and central temporal (7 μm) were better than peripheral nasal (24 μm) and peripheral temporal (21 μm) regions. Sagittal height intrasessional coefficients of repeatability were 9, 8, 28, and 31 μm for central nasal, central temporal, peripheral nasal, and peripheral temporal regions, respectively. Intersessional coefficients of repeatability of mean sphere, 90/180° (J0) astigmatism, and oblique (J45) astigmatism were 0.67, 0.22, and 0.13 D, respectively, with corresponding intrasessional coefficients of repeatability of 1.27, 0.21, and 0.27 D.

CONCLUSIONS

The modified measuring procedure for the ESP used in this study provides highly repeatable sagittal height measurements in the central cornea but is less repeatable in the corneal periphery and scleral region. Results of the current study can be considered when using ESP in the interpretation of anterior eye surface shape measurements and in contact lens fitting and design.

The corneoscleral shape in Marfan syndrome

PURPOSE

To investigate the corneoscleral shape in Marfan syndrome (MFS) patients.

METHODS

Thirty eyes of 15 participants with molecularly proven MFS were included in this prospective, cross-sectional study. Optical biometry, Scheimpflug imaging, and corneoscleral topography (Eye Surface Profiler) were performed in all patients. Topographic data were compared to data from controls (25 emmetropes and 17 myopes). The raw three-dimensional anterior height data from MFS eyes and control eyes were exported for further analysis. Custom-made software was used to demarcate the limbal radius and to calculate the sagittal height in different concentric annuli centred at the corneal apex, placed in a pupil plane, for the central cornea (0-4 mm radius), peripheral cornea (4-6 mm radius) and sclera (6-8 mm radius) and the corneoscleral asymmetry.

RESULTS

Marfan syndrome (MFS) eyes had significantly lower values of mean sagittal height compared to non-MFS eyes in all three annuli (central cornea, corneal periphery and sclera (independent t-test, p < 0.01 except for the inferior area of the scleral radius: p > 0.05). The sclera was significantly more asymmetric in MFS eyes compared to myopes (independent t-test, p < 0.01 for both eyes), but similar to emmetropes (independent t-test, p = 0.17 and p = 0.93 for right and left eyes, respectively). In MFS eyes, scleral asymmetry was not found to be correlated with axial length (Pearson correlation coefficient, r < 0.30, p > 0.05).

CONCLUSION

The peripheral cornea and sclera of Marfan syndrome patients have a significantly different shape compared to healthy controls.

Corneoscleral Topography Measured with Fourier-based Profilometry and Scheimpflug Imaging

SIGNIFICANCE

Precise measurement of corneoscleral topography makes a valuable contribution to the understanding of anterior eye anatomy and supports the fitting process of contact lenses. Sagittal height data, determined by newer noninvasive techniques, are particularly useful for initial scleral lens selection.

PURPOSE

The purpose of this study was to investigate the agreement and repeatability of Fourier-based profilometry and Scheimpflug imaging, in the measurement of sagittal height and toricity of the corneoscleral region.

METHODS

Minimal (Minsag), maximal (Maxsag) sagittal height, toricity (Maxsag - Minsag), and the maximum possible measurement zone diameter of 38 subjects were compared using the Eye Surface Profiler (ESP; Eagle Eye, Houten, the Netherlands) and the corneoscleral profile module of the Pentacam (Oculus, Wetzlar, Germany) at two different sessions. Correlations between the instruments were analyzed using the Pearson coefficient. Differences between sessions and instruments were analyzed using Bland-Altman and paired t tests.

RESULTS

For an equal chord length, the measurement with Pentacam was significantly greater for Minsag (344 μm; 95% confidence interval [CI], 322 to 364 μm; P < .001) and significantly greater for Maxsag (280 μm; 95% CI, 256 to 305 μm; P < .001), but significantly smaller for toricity (-63 μm; 95% CI, -95 to -31 μm; P < .001). Maximum possible measurement zone diameter with ESP (16.4 ± 1.3 mm) was significantly greater than with Pentacam (14.8 ± 1.1 mm) (P < .001). Repeated measurements from session 1 and session 2 were not significantly different for Pentacam and ESP (P = .74 and P = .64, respectively). The 95% CIs around differences indicate good repeatability for Pentacam (mean difference, -0.9 μm; 95% CI, -6.7 to 4.8 μm) and ESP (4.6 μm; -22.4 to 31.6).

CONCLUSIONS

Although both instruments deliver useful data especially for the fitting of scleral and soft contact lenses, the sagittal height and the toricity measurements cannot be considered as interchangeable.

CLEAR - Scleral lenses

Scleral lenses were the first type of contact lens, developed in the late nineteenth century to restore vision and protect the ocular surface. With the advent of rigid corneal lenses in the middle of the twentieth century and soft lenses in the 1970's, the use of scleral lenses diminished; in recent times there has been a resurgence in their use driven by advances in manufacturing and ocular imaging technology. Scleral lenses are often the only viable form of contact lens wear across a range of clinical indications and can potentially delay the need for corneal surgery. This report provides a brief historical review of scleral lenses and a detailed account of contemporary scleral lens practice including common indications and recommended terminology. Recent research on ocular surface shape is presented, in addition to a comprehensive account of modern scleral lens fitting and on-eye evaluation. A range of optical and physiological challenges associated with scleral lenses are presented, including options for the clinical management of a range of ocular conditions. Future applications which take advantage of the stability of scleral lenses are also discussed. In summary, this report presents evidence-based recommendations to optimise patient outcomes in modern scleral lens practice.

Anterior scleral thickness and shape changes with different levels of simulated convergence

PURPOSE

Convergence plays a fundamental role in the performance of near visual tasks. We measured the effect of two levels of convergence on anterior scleral thickness and shape in emmetropes, low to moderate myopes and high myopes.

METHODS

Forty-five healthy young adults aged between 18 and 35 years including 15 emmetropes, 15 low/moderate myopes, and 15 high myopes were recruited. Anterior segment optical coherence tomography and eye surface profilometry were used to evaluate the anterior scleral thickness (nasal only, n = 42) and shape (n = 40), before and during two visual tasks involving 9° and 18° convergence, in those participants with complete and reliable data.

RESULTS

Convergence led to a thickening of the total anterior eye wall (5.9 ± 1.4 μm) and forward movement (10 ± 2 μm) of the nasal anterior scleral surface (both p < 0.001). Larger changes were found at 18° than at 9° convergence and in more peripheral nasal scleral regions. There was a significant association between total wall thickening and forward movement of the scleral surface. Refractive group was not a significant main effect, but there were significant interactions between refractive group and the thickness changes with convergence in different scleral regions.

CONCLUSION

During convergence, the biomechanical forces acting on the eye lead to nasal anterior scleral thickening and forward movement of the nasal scleral surface.

Intrasession repeatability of corneal, limbal and scleral measurements obtained with a fourier transform profilometer

PURPOSE

To evaluate the intrasession repeatability of corneal, limbal and scleral measurements obtained by an experienced operator with a Fourier transform profilometer in healthy eyes.

METHODS

Prospective, single-center study including 35 eyes of 35 participants with ages ranging from 13 to 52 years. All patients underwent three consecutive corneoscleral topographic evaluations with the Eye Surface Profiler (ESP) system (Eaglet Eye b.v.). Intrasession repeatability was analyzed for different geometric and sagittal height variables using the following parameters: the within-subject standard deviation (S_w) of the three consecutive measurements, intrasubject precision (1.96 × S_w), coefficient of variation (CV) and the intraclass correlation coefficient (ICC).

RESULTS

Inner best fit sphere (BFS) showed good repeatability, with ICC of 0.844. Higher variability was observed for the repeated measurements of limbus and outer BFS, with ICCs of 0.636 and 0.739, respectively. For mean corneal and scleral radius, ICCs were 0.933 and 0.888, respectively. The repeatability of all sagittal height data was good for all chords evaluated (11-15 mm), with Sw values from 0.02 to 0.11 mm, and ICCs from 0.568 to 0.909. A significant positive correlation was found between the magnitude of temporal-nasal sagittal height difference for all measured chords and its S_w associated.

CONCLUSION

The ESP system can provide consistent measurements of sagittal height data for different chord diameters as well as for mean corneal and scleral radius in healthy eyes. Best fit approaches for limbal and scleral areas were less repeatable, although within a clinically acceptable range.

Anterior Scleral Regional Variation between Asian and Caucasian Populations

Purpose: To evaluate the anterior scleral shape regional differences between Asian and Caucasian populations. Methods: The study included 250 Asian eyes and 235 Caucasian eyes from participants aged 22 to 67 years (38.5 ± 7.6). Three-dimensional (3D) corneo-scleral maps were acquired using a corneo-scleral topographer (Eye Surface Profiler, Eaglet Eye BV) and used to calculate sagittal height. For each 3D map, the sclera (maximum diameter of 18 mm) and cornea were separated at the limbus using an automated technique. Advanced data processing steps were applied to ensure levelled artefact-free datasets to build an average scleral shape map for each population. Results: Statistically, Asian and Caucasian sclerae are significantly different from each other in sagittal height (overall sclera, p = 0.001). The largest difference in sagittal height between groups was found in the inferior-temporal region (271 ± 203 µm, p = 0.03), whereas the smallest difference was found in the superior-temporal region (84 ± 105 µm, p = 0.17). The difference in sagittal height between Caucasian and Asian sclera increases with the distance from the limbus. Conclusions: Asian anterior sclera was found to be less elevated than Caucasian anterior sclera. However, the nasal area of the sclera is less elevated than the temporal area, independently of race. Gaining knowledge in race-related scleral topography differences could assist contact lens manufacturers in the process of lens design and practitioners during the process of contact lens fitting.

Limbus misrepresentation in parametric eye models

Purpose

To assess the axial, radial and tangential limbus position misrepresentation when parametric models are used to represent the cornea and the sclera.

Methods

This retrospective study included 135 subjects aged 22 to 65 years (36.5 mean ±9.8 STD), 71 females and 64 males. Topography measurements were taken using an Eye Surface Profiler topographer and processed by a custom-built MATLAB code. Eye surfaces were freed from edge-effect artefacts and fitted to spherical, conic and biconic models.

Results

When comparing the radial position of the limbus, average errors of -0.83±0.19mm, -0.76±0.20mm and -0.69±0.20mm were observed within the right eye population for the spherical, conic and biconic models fitted up to 5mm. For the same fitting radius, the average fitting errors were -0.86±0.23mm, -0.78±0.23mm and -0.73±0.23mm for the spherical, conic and biconic models respectively within the left eye population. For the whole cornea fit, the average errors were -0.27±0.12mm and -0.28±0.13mm for the spherical models, -0.02±0.29mm and -0.05±0.27mm for the conic models, and -0.22±0.16mm and 0.24±0.17mm for the biconic models in the right and left eye populations respectively.

Conclusions

Through the use of spherical, conic and biconic parametric modelling methods, the eye’s limbus is being mislocated. Additionally, it is evident that the magnitude of fitting error associated with the sclera may be propagating through the other components of the eye. This suggests that a corneal nonparametric model may be necessary to improve the representation of the limbus.

Characterization of the geometric properties of the sclero-conjunctival structure: a review

To revise the peer-reviewed literature on geometric properties of the scleral-conjunctival structure in order to define their clinical relevance and the potential relationship between their changes and myopia development or progression. A bibliographic search focused on the study of the geometry of conjunctiva and/or sclera as well as those studies evaluating the relationship between geometric changes in the scleral-conjunctival structure and myopia was carried out. Several studies have been performed with different diagnostic technologies, including optical coherence tomography, profilometry and Scheimpflug imaging, to detect geometric changes of the scleral-conjunctival tissue in different physiological conditions of the eye, after use of contact lenses and in different ocular pathologies. Likewise, these technologies have been shown to be a valuable clinical tool to optimize scleral contact lens fitting. Future studies should investigate new potential clinical applications of such technologies, including the evaluation of anterior scleral changes related to myopia, as well as to define standardized clinical standard operating procedures for obtaining accurate and reproducible clinical measurement of the scleral-conjunctival morphology.

Biometric Measurement of Anterior Segment: A Review

Biometric measurement of the anterior segment is of great importance for the ophthalmology, human eye modeling, contact lens fitting, intraocular lens design, etc. This paper serves as a comprehensive review on the historical development and basic principles of the technologies for measuring the geometric profiles of the anterior segment. Both the advantages and drawbacks of the current technologies are illustrated. For in vivo measurement of the anterior segment, there are two main challenges that need to be addressed to achieve high speed, fine resolution, and large range imaging. One is the motion artefacts caused by the inevitable and random human eye movement. The other is the serious multiple scattering effects in intraocular turbid media. The future research perspectives are also outlined in this paper.

Anatomical and physiological considerations in scleral lens wear: Conjunctiva and sclera

While scleral lenses have been fitted using diagnostic lenses or impression moulding techniques for over a century, recent advances in anterior segment imaging such as optical coherence tomography and corneo-scleral profilometry have significantly improved the current understanding of the anatomy of the anterior eye including the morphometry of the conjunctiva, sclera, and corneo-scleral junction, as well as the ocular surface shape and elevation. These technological advances in ocular imaging along with continual improvements and innovations in scleral lens design and manufacturing have led to a global increase in scleral lens prescribing. This review provides a comprehensive overview of the conjunctiva and sclera in the context of modern scleral lens practice, including anatomical variations in healthy and diseased eyes, the physiological impact of scleral lens wear, potential fitting challenges, and current approaches to lens modifications in order to minimise lens-induced complications and adverse ocular effects. Specific topics requiring further research are also discussed.

The effect of sodium fluorescein on anterior eye surface measurements

PURPOSE

During image acquisition, certain topographers require the addition of sodium fluorescein (NaFl) dye to the tear film. This study investigates the effect of NaFl dye on corneal topography and tear surface quality.

METHOD

The E300 corneal topographer (Medmont International Pty Ltd., Victoria, Australia) was used to measure ocular surface topography and quality of 57 eyes of 57 healthy individuals without dry eye symptoms, age 35.1 ± 15.2 years (mean ± standard deviation) ranging between 19 and 65 years. The mean of three simulated keratometry values, a variety of corneal shape descriptors, and Tear Film Surface Quality (TFSQ) were measured under three different conditions; without NaFl (baseline), with the addition of a single dose NaFl, and using a double dose of NaFl.

RESULTS

Compared to baseline, the Inferior-Superior (IS) index decreased significantly after a single dose (P = 0.034) or double dose of NaFl (P = 0.030). The corneal surface was significantly more regular without NaFl (P = 0.003) or one insertion of NaFl (P = 0.024) when compared to two doses of NaFl. There was no association with age, or dry eye signs or symptoms on the variance observed in any of the indices between baseline, intervention I, and intervention II (P > 0.05). Agreement between corneal surface indices reduced following the addition of NaFl.

CONCLUSION

In comparison to measurements taken without an ocular dye, one dose of NaFl resulted in increased reliability and consistency in corneal topography measurements using the E300 topographer, but 2 doses decreased reliability and consistency. Practitioners ought to be aware that tear film surface regularity and inferior-superior corneal power changed significantly following the addition of NaFl in those with healthy corneas. Its effect in diseased corneas is unknown.

Artefact-free topography based scleral-asymmetry

PURPOSE

To present a three-dimensional non-parametric method for detecting scleral asymmetry using corneoscleral topography data that are free of edge-effect artefacts.

METHODS

The study included 88 participants aged 23 to 65 years (37.7±9.7), 47 women and 41 men. The eye topography data were exported from the Eye Surface Profiler software in MATLAB binary data container format then processed by custom built MATLAB codes entirely independent from the profiler software. Scleral asymmetry was determined initially from the unprocessed topography before being determined again after removing the edge-effect noise. Topography data were levelled around the limbus, then edge-effect was eliminated using a robust statistical moving median technique. In addition to comparing raw elevation data, scleral elevation was also compared through fitting a sphere to every single scleral surface and determining the relative elevation from the best-fit sphere reference surface.

RESULTS

When considering the averaged raw topography elevation data in the scleral section of the eye at radius 8 mm, the average raw elevations of the right eyes' sclera were -1.5±1.77, -1.87±2.12, -1.36±1.82 and -1.57±1.87 mm. In the left eyes at the same radius the average raw elevations were -1.62±1.78, -1.82±2.07, -1.28±1.76 and -1.68±1.93 mm. While, when considering the average raw elevation of the sclera after removing the edge effect, the average raw elevations of the right eyes were -3.71±0.25, -4.06±0.23, -3.95±0.19 and -3.95±0.23 mm. In the left eyes at the same radius the average raw elevations were -3.71±0.19, -3.97±0.22, -3.96±0.19 and -3.96±0.18 mm in the nasal, temporal, superior and inferior sides respectively. Maximum raw elevation asymmetry in the averaged scleral raw elevation was 1.6647±0.9015 mm in right eyes and 1.0358±0.6842 mm in left eyes, both detected at -38° to the nasal side. Best-fit sphere-based relative elevation showed that sclera is more elevated in three main meridians at angles -40°, 76°, and 170° in right eyes and -40°, 76°, and 170° in left eyes, all measured from the nasal meridian. Maximum recorded relative elevation asymmetries were 0.0844±0.0355 mm and 0.068±0.0607 mm at angular positions 76° and 63.5° for right and left eyes in turn.

CONCLUSIONS

It is not possible to use corneoscleral topography data to predict the scleral shape without considering a method of removing the edge-effect from the topography data. The nasal side of the sclera is higher than the temporal side, therefore, rotationally symmetric scleral contact lenses are more likely to be translated towards the temporal side. The scleral shape is best described by levelled raw elevation rather than relative elevation.

In vivo assessment of the anterior scleral contour assisted by automatic profilometry and changes in conjunctival shape after miniscleral contact lens fitting

PURPOSE

To compare the shape of the anterior sclera of candidates to scleral lens (ScCL) fitting with regular and irregular corneas and analyze the changes induced in the shape of the sclero-conjunctiva after ScCL wear.

METHODS

Thirty-five eyes of 18 subjects (19 eyes with irregular corneas and 16 with regular corneas) were consecutively recruited. Three measures of sclero-conjunctival shape were taken with Eye Surface Profiler (ESP, Eaglet Eye, Houten, The Netherlands). Tangent angles and ocular sagittal heights (OC-SAG) were analyzed at different chords from 13 to 17mm in the nasal, temporal, superior and inferior regions. The 19 eyes with irregular cornea were selected to wear ScCL and the changes in their sclero-conjunctival surface parameters were compared before and after 3h of lens wear.

RESULTS

Irregular corneas showed higher OC-SAG values than regular corneas in all the chords analyzed, with statistical significant differences in the temporal region. Regarding tangent angles, regular corneas showed lower values (flatter surface), with statistical significant differences at 8 and 8.50mm on the nasal and 8.50mm on the temporal region. Some changes were seen in sclero-conjuctival shape after short-term ScCL wear. There was an augment in OC-SAG after 3h of scleral lens wear and a reduction on tangent angles, namely on the nasal region at 7.5mm and 8.00mm chord lengths, which is coincidental with the landing zone of ScCL.

CONCLUSIONS

ESP shows mild differences in scleral shape between eyes with regular and irregular corneas. ESP might be valuable in quantifying the mechanical impact of the ScCL on the anterior eye surface.

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.

Optical coherence tomography and scleral contact lenses: clinical and research applications

Anterior segment optical coherence tomography (OCT) provides a wealth of opportunities for modern contact lens practice. OCT imaging has numerous clinical and research applications related to the tear film, cornea, conjunctiva, sclera and ocular adnexae, in addition to soft, rigid, and hybrid contact lenses. This review summarises the potential use of OCT imaging in modern scleral contact lens practice including initial lens selection, assessing the scleral contact lens fit with respect to the cornea and sclera, and accurately quantifying the ocular response to lens wear. Recent advances in the understanding of anterior segment metrics including scleral thickness, curvature, toricity, and the anatomy of the corneoscleral limbal junction are also discussed.

Corneo-scleral limbal changes following short-term soft contact lens wear

PURPOSE

To assess whether short-term soft contact lens wear alters the anterior eye surface.

METHODS

Twenty-two neophyte subjects wore soft contact lenses for a period of five hours. Topography based corneo-scleral limbal radius estimates were derived from height measurements acquired with a corneo-scleral profilometer. Additionally, central corneal thickness (CCT), anterior chamber depth (ACD), corneal curvature radius (R) and white-to-white (WTW) diameter were acquired with an OCT-assisted biometer. Measurements were obtained without lens wear (baseline), immediately after lens removal following five hours of wear and three hours after lens removal.

RESULTS

Short-term soft contact lens wear significantly modifies corneo-scleral limbal radius (mean±SD: 130±74μm, p << 0.001) and the changes are repeatable. In contrast, the WTW diameter and R were not modified. ACD and CCT were significantly affected but no significant correlations were found between the increment of the limbal radius and the decrease in ACD and CCT. Limbal radius increment was reversed three hours after lens removal for 68% of the subjects but the time course of this reversal was not uniform.

CONCLUSIONS

It is possible to accurately quantify limbal radius changes as a consequence of soft contact lens wear. The increment in the limbal diameter could reach over 0.5mm but that alteration does not correspond to changes in WTW diameter and it was not observable to the examiner using a slit lamp. Assessing topographical limbus after contact lens wear could be a tool to optimize the selection of the contact lens, from the perspective of anterior eye surface changes.