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PURPOSE: To investigate the effect of corneal shape parameters on corneal deformation responses measured with a Scheimpflug camera. METHODS: A total of 241 eyes of 241 participants were enrolled in this study. The anterior and posterior corneal curvature radii (CCR), anterior and posterior corneal Q-values, and corneal diameters of the participants were measured using the Pentacam HR. A total of 17 corneal deformation parameters including time, velocity, deflection amplitude, length, and area during ingoing applanation, highest concavity, and outgoing applanation were recorded by corneal visualization using Scheimpflug technology (Corvis ST). The effect of corneal shape parameters on corneal deformation responses was evaluated using multivariate regression models. RESULTS: Multivariate regression analyses showed that six, five, four, and three corneal deformation parameters were significantly correlated with anterior CCR, posterior CCR, anterior Q-value, and posterior Q-value, respectively. Steeper anterior corneal curvature was associated with faster velocity during ingoing applanation and greater deformation during outgoing applanation. Steeper posterior corneal curvature was correlated with faster velocity during outgoing applanation and greater deformation during ingoing applanation. Eyes that had steeper corneal curvatures were associated with less stiff corneas. More negative anterior Q-value corresponded with faster velocity and greater deformation during ingoing applanation. Eyes that had more prolate posterior corneal surfaces showed more resistance to corneal deformation at the highest concavity. However, corneal diameter was not selected in any corneal deformation parameters models. CONCLUSION: Corneal deformation response is significantly influenced by anterior and posterior corneal curvature and corneal asphericity, but not corneal diameter.

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PURPOSE: To investigate the corneal characteristics in individuals with autism spectrum disorder (ASD) and age-matched typical development (TD) participants. METHODS: This cross-sectional, clinically based study compared children with ASD to age-matched TD participants. Corneal topography was measured with a portable EyeSys Vista system. The distance visual acuity (VA) and the contrast sensitivity (CS) were determined. The refractive error (RE) was assessed using a 2WIN autorefractometer. RESULTS: A total of 31 children with ASD (mean age: 12.78 ± 4.49 years), and 60 participants with TD (mean age: 13.65 ± 3.56 years) were recruited. The two groups were similar in age (t = -2.084, p = 0.075) and VA (t = -0.35, p = 0.32). Most of the children with ASD had a significant amount of refractive errors (REs; range: +5.25 to -5.50 DS), and astigmatism was dominant (range: -0.25 to -4.50 DC). There was no statistically significant difference between both groups in terms of average corneal power (t = 1.12, p = 0.39). The children with ASD and participants with TD also did not differ significantly in terms of corneal shape descriptors (p > 0.05), such as corneal asphericity, inferior superior index, opposite sector index, and differential sector index. The spherical equivalent did not differ significantly between the ASD participants and participants with TD (t = 1.15, p = 0.15). There was a significant difference (p < 0.05) in the astigmatism component between the ASD participants and the participants with TD.

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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.

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PURPOSE: To investigate the effect of topical prostaglandin (PG) eyedrops on the biomechanics and shape of the cornea. METHODS: Consecutive patients with primary open-angle glaucoma who had been treated with the same anti-glaucoma PG (114 eyes, 57 patients) or ß-blocker (36 eyes, 18 patients) eyedrops in 1 eye alone for more than 3 months at Inouye Eye Hospital or Miyata Eye Hospital. The biomechanical properties of the cornea were measured using a Corvis ST device (Oculus, Wetzlar, Germany). Corneal tomography was measured with a Casia 1 or 2 (Tomey Corp., Nagoya, Japan). The biomechanical parameters and tomographic features of the cornea were compared between PG-treated eyes, ß-blocker-treated eyes, and contralateral eyes using a mixed-effect model adjusted for intraocular pressure and corneal thickness and a linear model adjusted for age, sex, intraocular pressure, and corneal thickness. RESULTS: The PG-treated eyes had a significantly smaller applanation 1 time, the highest concavity radius, and a larger deformation amplitude than the contralateral eyes. Also, the PG-treated eyes had a significantly smaller applanation 1 time and applanation 2 velocity but a larger peak distance than the ß-blocker-treated eyes. There were no significant differences in any of the Casia parameters between the PG-treated eyes and the contralateral eyes. CONCLUSION: The results of this study suggest that topical PG makes biochemical changes to the cornea but does not alter its shape.

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AIM: To compare changes in the shape and astigmatism of the total and posterior cornea between eyes with a nasal clear corneal incision (CCI) and eyes with a temporal CCI in cataract surgery. METHODS: The left eyes of 100 patients undergoing phacoemulsification were randomly assigned to undergo a 2.4 mm nasal (nasal CCI group) or temporal CCI (temporal CCI group). Corneal astigmatic changes were compared between groups using power vector analysis, and corneal shape changes were compared using videokeratography maps at 2 days, and at 2, 4 and 8 weeks postoperatively. RESULTS: The mean J0 and J45 values of the total cornea were significantly greater in the nasal CCI group than in the temporal CCI group at 2 and 4 weeks postoperatively (p≤0.0392), but did not differ significantly between groups at 2 days and 8 weeks. The videokeratography maps revealed a wedge-shaped flattening in the total cornea and a steepening in the posterior cornea around the CCIs in both groups at 2 days postoperatively; those were more prominent in the nasal CCI group than in the temporal CCI group. The wound-related changes diminished by 8 weeks postoperatively in the total and posterior cornea, and were not markedly different between groups at 8 weeks postoperatively. CONCLUSION: Corneal shape and astigmatic changes were comparable between groups at 8 weeks postoperatively, although the changes were greater after nasal CCI than after temporal CCI in the early postoperative periods, indicating that nasal or temporal CCI can be selected based on the surgeon's preference.

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PURPOSE: To explore anterior segment changes with keratoconus onset and progression to determine whether structural changes are predominantly corneal, limbal or both. To investigate these changes in different corneal meridians. METHOD: Eighty-four eyes with keratoconus and 49 healthy eyes were included in the study. Eyes with keratoconus were divided in two groups according to the Amsler-Krumeich classification: stage I and stages II-IV. Scheimpflug images at three different meridians were used to evaluate the following parameters: anterior chamber depth from the endothelium (ACD_end) and corneal thickness (CT) (software provided), anterior chamber depth (ACD) and sagittal depth (SAGT) from the epithelium, and distance from the end point of SAGT to the anterior surface of the lens (DL) (measured manually), and [ACD - CT] and [SAGT - CT] (calculated). Changes in these parameters with ocular condition and meridian were analysed. RESULTS: Statistically significant larger values were found of ACD (p = 0.012) and DL (p = 0.016) with keratoconus onset and progression, with no differences in SAGT values. Besides, [ACD - CT] and [SAGT - CT] were significantly larger in keratoconus eyes (p < 0.001 and p = 0.003, respectively). Significant differences (all p < 0.001) were found in SAGT, [SAGT - CT] and DL among meridians. Changes in these parameters with keratoconus onset and progression were similar in all meridians. CONCLUSION: Considering the results from the three meridians under investigation, it may be concluded that keratoconus onset has an impact on the anterior segment as a whole and not only on corneal structures. The DL distance is a useful parameter to describe limbal changes in keratoconus.

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PURPOSE: To report a case that had a progressive decrease in the visual acuity caused by a progressive increase in the hyperopia due to a flattening of the cornea. OBSERVATIONS: A 50-year-old woman complained of decreased vision in both eyes. Her decimal best-corrected visual acuity was 1.2 in the right and 0.5 in the left eyes, and the refractive error (spherical equivalent) was +3.75 diopters (D) for the right eye and +6.5 D for the left eye. Slit-lamp examinations showed clear corneas but Descemet's folds and fine pigmentations and opacities were present beneath the corneal epithelium in both eyes. Analysis of the corneal shape by anterior segment optical coherence tomography showed that the corneas were flattened, and the corneal refractive power was decreased in both eyes. The large values of the higher-order aberration in the cornea and total eye displayed bilateral irregular astigmatism. She obtained good vision by wearing hard contact lenses but her refractive power continued to decrease for at least 1 year. CONCLUSIONS: and Importance: We report a rare case of progressive hyperopia and irregular astigmatism due to a flattening of the cornea. Folds were present in Descemet's membrane but the cornea was not edematous.

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PURPOSE: To compare corneal tomography and its statistical uncertainty for measurements obtained by three clinically used corneal tomographers: A Scheimpflug camera (Pentacam HR), a swept source optical coherence tomography system (CASIA SS-1000), and Placido ring imaging (TMS-5). MATERIAL AND METHODS: Repeated measurements with all three devices on 34 normal eyes were used to estimate the repeatability, precision, and mean values of corneal elevation and pachymetry within 8 mm diameter. The repeatability (standard deviation) was calculated for each data point of the corneal elevation data-maps of anterior and posterior cornea as well as for the pachymetry data-maps. Uncertainty on the position of the eye at each measurement might contribute to the differences between elevation data-maps. To take this into account, we defined the precision as the standard deviation for the elevation data-maps of anterior and posterior cornea after correction of misalignment-effects (rotation, translation). The mean elevation and pachymetry data-maps were fitted with Zernike polynomials for interdevice-comparison. RESULTS: Pentacam HR offered the best repeatability and precision for the anterior corneal elevation (<3 and <1.6 µm, respectively). CASIA SS-1000 offered good repeatability and precision with high resolution for posterior corneal elevation, and the best repeatability for pachymetry (<3 µm). TMS-5 measured anterior elevation with similar repeatability to CASIA SS-1000 (<6 µm). The data-maps of the three tomographers could not be used interchangeably. The largest differences were observed for pachymetry and posterior corneal elevation data-maps. CONCLUSIONS: Misalignment limited the repeatability of TMS-5 and Pentacam HR, but had little influence on the repeatability of CASIA SS-1000.

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PURPOSE: Whether cycloplegics affect standard keratorefractometric and tomographic measurements is unknown. The purpose of our study was to compare the effects of cycloplegics (cyclopentolate and atropine) on corneal shape and refractive power of the eye. METHODS: This study was performed on 84 eyes of 49 study participants. Patients were randomized into two groups: atropine 1% (32 eyes) and cyclopentolate 1% (52 eyes). Corneal tomography was performed with the Orbscan IIz. To evaluate the corneal shape, simulated keratometry values, anterior and posterior best-fit sphere, white-to-white and tangential and axial corneal power were performed for the anterior and posterior corneal surfaces before and during cycloplegia. Pupil diameter, anterior chamber depth, corneal thickness at the 3, 5 and 7mm optical zones, thinnest area of the cornea and corneal thickness at the visual axis were examined. Data were analyzed using an SPSS statistical package. RESULTS: The anterior and posterior BFS (in the atropine 1% group, anterior BFS was P=0.188; anterior BFS in the cyclopentolate group was P=0.227) and tangential and axial corneal power showed no change during cycloplegia in either group. SimK showed no statistical significance. The ACD was deeper when using atropine than cyclopentolate. Corneal thickness remained unchanged during cycloplegia in both groups. Pupil diameter was larger in light-colored irides in the cyclopentolate group than the atropine group. There was no change in W to W before (P=0.473) and during cycloplegia (P=0.287) in either group. CONCLUSIONS: Our results suggest that usage of atropine or cyclopentolate does not alter corneal shape.

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PURPOSE: To analyse, describe and test diverse corneal and anterior segment parameters in normal and keratoconic eyes to better understand the geometry of the keratoconic cornea. METHOD: 44 eyes from 44 keratoconic patients and 44 eyes from 44 healthy patients were included in the study. The Pentacam System was used for the analysis of the anterior segment parameters. New ad-hoc parameters were defined by measuring the distances on the Scheimpflug image at the horizontal diameter, with chamber depth now comprising of two distinctive distances: corneal sagittal depth and the distance from the endpoint of this segment to the anterior surface of the lens (DL). RESULTS: Statistically significant differences (p<0.05) between normal and keratoconic eyes were found in all of the analysed corneal parameters. Anterior chamber depth presented statistical differences between normal and keratoconic eyes (3.06±0.43mm versus 3.34±0.45mm, respectively; p=0.004). This difference was found to originate in an increase of the DL distance (0.40±0.33mm in normal eyes against 0.61±0.45mm in keratoconic eyes; p=0.014), rather than in the changes in corneal sagittal depth. CONCLUSION: These findings indicate that keratoconus results in central and peripheral corneal manifestations, as well as changes in the shape of the scleral limbus. The DL parameter was useful in describing the forward elongation and advance of the scleral tissue in keratoconic eyes. This finding may help in the monitoring of disease progression and contact lens design and fitting.

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