Anterior Scleral Thickness Profile in Keratoconus.

PURPOSE: Considering that peripheral corneal thinning occurs in keratoconus (KC), the anterior scleral thickness (AST) profile was measured to compare thickness variations in healthy and KC eyes across several meridians. METHODS: This cross-sectional case-control study comprised 111 eyes of 111 patients: 61 KC eyes and 50 age- and axial-length-matched healthy eyes. The AST was explored at three scleral eccentricities (1, 2, and 3 mm from the scleral spur) across four scleral zones (nasal, temporal, superior, and inferior) by using swept-source optical coherence tomography. The AST variations among eccentricities and scleral regions within and between groups were investigated. RESULTS: The AST significantly varied with scleral eccentricity in healthy eyes over the temporal meridian (p = 0.009), whereas in KC eyes, this variation was observed over the nasal (p = 0.001), temporal (p = 0.029) and inferior (p = 0.006) meridians. The thinnest point in both groups was 2 mm posterior to the scleral spur (p < 0.001). The sclera was thickest over the inferior region (control 581 ± 52 µm, KC 577 ± 67 µm) and thinnest over the superior region (control 448 ± 48 µm, KC 468 ± 58 µm) in both populations (p < 0.001 for all eccentricities). The AST profiles were not significantly different between groups (p > 0.05). The inferior-superior thickness asymmetry was statistically different 2 mm posterior to the scleral spur between groups (p = 0.009), specifically with subclinical KC (p = 0.03). There is a trend where the asymmetry increases, although not significantly, with the KC degree (p > 0.05). CONCLUSIONS: KC eyes presented significant thickness variations among eccentricities over the paracentral sclera. Although AST profiles did not differ between groups, the inferior-superior asymmetry differences demonstrated scleral changes over the vertical meridian in KC that need further investigation.

Effects of cataract surgery on blinking.

PURPOSE: To assess the effects of cataract surgery on the spontaneous blinking pattern and blinking kinematics. SETTING: FISABIO Oftalmología Médica Eye Hospital, Valencia, Spain. DESIGN: Observational descriptive clinical study. METHOD: Patients with senile cataract were evaluated before (visit 1) and at 1 month (visit 2) and 3 months (visit 3) after undergoing phacoemulsification cataract surgery. The blinking of patients was recorded for 90 seconds using an eye-tracking device. Blinks were analyzed by means of image analysis to obtain a noninvasive detailed description of blinking including blink rate, number of complete and incomplete blinks, percentage of incomplete blinks, and kinematic parameters, including amplitude, closing, contact, opening, and total durations and closing and opening speeds. RESULTS: 50 patients were included in this study. The blink rate was significantly smaller at visit 3 compared with baseline ( P = .03) and visit 2 ( P = .001). Likewise, the number of complete blinks was significantly smaller, and the percentage of incomplete blinks was significantly higher at 3 months postoperatively compared with baseline ( P = .02 and P = .01, respectively), although no differences were observed at 1 month postoperatively ( P > .05). Conversely, no differences in the number of incomplete blinks or any kinematic parameter were observed between visits ( P = .12). CONCLUSIONS: Cataract surgery significantly altered the blinking pattern at 3 months postoperatively, although kinematic parameters remained unvaried. Clinicians should be aware of potential alterations in blinking after phacoemulsification cataract surgery and the implications this may have on the ocular surface of patients.

Chromatic Contrast Sensitivity Functions and Colour Discrimination in Smoker Patients.

In this study, effects of smoking on colour vision with the Farnsworth−Munsell 100 Hue test (FM100h) and achromatic (A), red-green (RG), and blue-yellow (BY) contrast sensitivity functions were evaluated. In total, 50 non-smoker controls and 25 smokers, divided into two groups (group 1, less than 10 cigarettes per day, with 15 patients, and group 2, >10 cigarettes per day, with 10 patients) took part in the experiments. Best-corrected visual acuity (BCVA), FM100h, and A, RG, and BY contrast sensitivity functions were measured. Total and partial RG and BY error scores (TES and PTES) and colour axis index (CA) were used in the analysis. No differences between smoker and non-smoker groups were found in BCVA, CA and A and BY contrast sensitivity, but TES and PTES values and RG contrast sensitivity at 1 cpd were statistically different. Differences between smoker groups were not significant. Error scores in smokers were positively correlated with the number of cigarettes smoked per day, and in BY also with age. Tobacco caused discrimination losses in both chromatic mechanisms but affected the red-green pathway more than the blue-yellow, and therefore, a partial RG score of FM100h test seems to be a good predictor of smoker colour deficiencies.

Evaluation of Intraocular Pressure and Other Biomechanical Parameters to Distinguish between Subclinical Keratoconus and Healthy Corneas.

(1) Purpose: To assess the main corneal response differences between normal and subclinical keratoconus (SCKC) with a Corvis® ST device. (2) Material and Methods: We selected 183 eyes of normal patients, of a mean age of 33 ± 9 years and 16 eyes of patients with SCKC of a similar mean age. We measured best corrected visual acuity (BCVA) and corneal topography with a Pentacam HD device to select the SCKC group. Biomechanical measurements were performed using the Corvis® ST device. We carried out a non-parametric analysis of the data with SPSS software (Wilcoxon signed rank-test). (3) Results: We found statistically significant differences between the control and SCKC groups in some corneal biomechanical parameters: first and second applanation time (p = 0.05 and p = 0.02), maximum deformation amplitude (p = 0.016), highest concavity radius (p = 0.007), and second applanation length and corneal velocity ((p = 0.039 and p = 0.016). (4) Conclusions: Our results show that the use of normalised biomechanical parameters provided by noncontact tonometry, combined with a discriminant function theory, is a useful tool for detecting subclinical keratoconus.

Repeatability of in-vitro optical quality measurements of intraocular lenses with a deflectometry technique effect of the toricity.

AIM: To evaluate the repeatability of an optical device for measuring the Zernike coefficients of toric intraocular lenses (IOLs) and assess whether its toricity has any impact in its repeatability. METHODS: An experienced technician used the NIMO TR1504 to measure the Zernike coefficients 30 times for an aperture of 4.50 mm for all lenses included. The IOLs included were divided into two group: toric and non-toric ones. The cylindrical powers of the toric lenses included in the present study were 1.00, 1.50, 2.25, 3.00 and 3.75 D. Finally, the repeatability of the NIMO TR1504 was described in terms of within subject standard deviation (Sw) and repeatability limit. RESULTS: The Sw was smaller than 0.011 µm for both lens groups and all Zernike coefficients, and the difference between both groups was smaller than 0.004 µm for all Zernike coefficients. Regarding the repeatability limit, this value was smaller than 0.025 µm for the toric lens group, and smaller than 0.031 µm for the non-toric lens one for all Zernike coefficients. Furthermore, the maximum difference between both lens groups was 0.010 µm. CONCLUSION: The repeatability of the NIMO TR1504 to measure the optical quality is high and independent of the lens toricity. These results reflect that this system is robust and could be used to measure the in-vitro optical quality of either toric or non-toric IOLs.

A rapid method for measuring intraocular lens power in vitro with a focimeter.

In this paper we describe a new method for measuring the intraocular lens (IOL) power using a focimeter, a negative ophthalmic lens and a saline solution (0.9% NaCl). To test this we measured the power of 58 different IOLs and we compared them with the power stated by the manufacturer. Despite the limitations, the results show a good correlation.

A simple description of age-related changes in crystalline lens thickness.

PURPOSE: An increase in lens thickness is often described as a linear function of age. However, contradictory opinions exist about whether the lens thickness continues to increase after 50 years of age. Differences in slope exist between this increase in younger and older people, but these findings are inconsistent with the linear behavior of an increase in the lens thickness throughout life. We investigated among different functions, including slope variation, which would be the best to show the relation between lens thickness and age. An available model portraying lens growth could be advantageous in many practical applications. The possibility of differences between sexes in lens thickness growth is also analyzed. METHODS: We evaluated 102 eyes of patients aged between 15 and 84 years: 41 men, 61 women. The biometric measurements were performed with the aid of the OcuScan® (Alcon, USA). RESULTS: Both logarithmic and potential functions provide a good fit for the data (R2 = 0.905 and 0.906, respectively). The results do not show significant differences between men and women in any age range, nor when the data of the whole sample are considered (p = 0.29). CONCLUSIONS: The best fits for the data are both logarithmic and double logarithmic functions. According to this model, lens growth continues throughout life, but after 50 years, age-related thickness variations are lower than statistical variability. No differences were found between the sexes.

Corresponding-pair procedure: a new approach to simulation of dichromatic color perception.

The dichromatic color appearance of a chromatic stimulus T can be described if a stimulus S is found that verifies that a normal observer experiences the same sensation viewing S as a dichromat viewing T. If dichromatic and normal versions of the same color vision model are available, S can be computed by applying the inverse of the normal model to the descriptors of T obtained with the dichromatic model. We give analytical form to this algorithm, which we call the corresponding-pair procedure. The analytical form highlights the requisites that a color vision model must verify for this procedure to be used. To show the capabilities of the method, we apply the algorithm to different color vision models that verify such requisites. This algorithm avoids the need to introduce empirical information alien to the color model used, as was the case with previous methods. The relative simplicity of the procedure and its generality makes the prediction of dichromatic color appearance an additional test of the validity of color vision models.