Back-calculation of keratometer index based on OCT data and raytracing - a Monte Carlo simulation.

PURPOSE: This study aims to develop a raytracing-based strategy for calculating corneal power from anterior segment optical coherence tomography data and extracting the individual keratometer index, which converts the corneal front surface radius to corneal power. METHODS: A large OCT dataset (10,218 eyes of 8,430 patients) from the Casia 2 (Tomey, Japan) was post-processed in MATLAB (MathWorks, USA). Radius of curvature, asphericity of the corneal front and back surface, central corneal thickness and pupil size (aperture) were used to trace a bundle of rays through the cornea and derive the best focus plane. Corneal power was calculated with respect to the corneal front vertex plane, and the keratometer index was back-calculated using corneal power and front surface radius. Keratometer index was analysed in a multivariate linear model. RESULTS: The averaged resulting keratometer index was 1.3317 ± 0.0017 with a median of 1.3317 and range from 1.3233 to 1.3390. In a univariate model, only the front surface asphericity affected the keratometer index. The multivariate model for modelling the keratometer index using all 6 input parameters performed very well (RMS error: 5.54e-4, R2 : 0.90, significance vs. constant model: <0.0001). CONCLUSIONS: In the classical calculation, the keratometer index used for converting corneal radius to dioptric power uses several model assumptions. As these assumptions are not generally satisfied, corneal power cannot be calculated from corneal front surface radius alone. Considering all 6 input variables, the linear prediction model performs well and can be used if all input parameters are measured with a tomographer.

Laserinterferometric assessment of pilocarpine-induced movement of an accommodating intraocular lens: a randomized trial.

PURPOSE: To measure the axial movement of an accommodating intraocular lens (IOL) induced by ciliary muscle contraction after application of pilocarpine. DESIGN: Randomized, controlled, patient- and examiner-masked trial with intrapatient comparison. PARTICIPANTS AND CONTROLS: One hundred ten eyes of 55 patients with age-related bilateral cataract. METHODS: This study was divided into 3 parts. In the first, the accommodating IOL (1CU) was compared with a 3-piece open-loop acrylic IOL that served as the control. In the second, to assess the effect of capsule fibrosis on the potential accommodating performance of the accommodating IOL, extensive polishing of the anterior capsule with a slit cannula was compared with standard surgery. In the third, the effect of a posterior capsulorhexis was compared with that of standard surgery. Anterior chamber depth (ACD) was assessed with partial coherence interferometry, measured before and after topical application of pilocarpine 2%, and near visual acuity (VA) was evaluated 3 months after surgery. MAIN OUTCOME MEASURE: Pilocarpine-induced change in ACD. RESULTS: The accommodating IOL showed a forward movement under pilocarpine with a median amplitude of movement of -314 microm (95% confidence interval [CI]: -148 to -592), compared with the backward movement of 63 microm (95% CI: 161 to -41) for the open-loop control IOL (P = 0.001). Capsule polishing and a posterior capsulorhexis had no effect on IOL movement with the accommodating IOL. The median near VA with distance correction was 20/60. CONCLUSION: Pilocarpine induced a small but significant forward movement of the accommodating IOL. However, the amount of movement was calculated to result in a refractive change of <0.5 diopters (D) in most patients, reaching 1 D or slightly more in only single cases, with a large variability of movement. Neither polishing of the capsule bag nor a posterior capsulorhexis could enhance the accommodative ability.

Corneal endothelial cell protection with a dispersive viscoelastic material and an irrigating solution during phacoemulsification: low-cost versus expensive combination.

PURPOSE: To evaluate the protective effect on corneal endothelial cells of a low-cost and an expensive combination of a dispersive viscoelastic material and an irrigating solution during phacoemulsification. SETTING: Department of Ophthalmology, University of Vienna, Vienna, Austria. METHODS: This prospective randomized examiner- and patient-masked study comprised 90 eyes of 45 consecutive patients with age-related cataract in both eyes. For each patient, the first eye was randomly assigned to receive hydroxypropyl methylcellulose 2% (Ocucoat) and Ringer's solution (low-cost combination) or sodium chondroitin sulfate 4%-sodium hyaluronate 3% (Viscoat) and an enriched balanced salt solution (BSS Plus) (expensive combination) during phacoemulsification. The contralateral eye received the other treatment. Endothelial cell function was evaluated by measuring corneal thickness (CT) using partial coherence interferometry, morphology assessment, and endothelial cell counts. RESULTS: The acute postoperative increase in CT was +9.8 microm in the low-cost group and +10.9 microm in the expensive group; the difference between groups was not significant. After 1 month, the CT still differed significantly from baseline in the low-cost group. Three months after surgery, the CT had returned to baseline values in both groups. There was no significant between-group difference in endothelial cell counts or morphology. CONCLUSIONS: During phacoemulsification in a nonselected patient population, there was no difference in acute postoperative corneal edema and endothelial cell morphology after 3 months between a Viscoat and BSS Plus combination and an Ocucoat and Ringer's solution combination. Eyes receiving the expensive combination had marginally faster recovery of corneal swelling by 3 months. However, the cost of Viscoat and 500 mL BSS Plus is 5 times that of Ocucoat and Ringer's solution.

Assessment of anterior capsule opacification: photographic technique and quantification.

PURPOSE: To develop and evaluate a standardized slitlamp photographic technique to document and quantify anterior capsule opacification (ACO) in the pseudophakic eye. SETTING: University of Vienna, Medical School, Department of Ophthalmology, Vienna, Austria. METHODS: In this prospective study, slitlamp photographs were taken in 29 eyes of 19 patients with ACO of varying degrees and intraocular lenses of different materials. Digital slitlamp photographs were taken by 2 examiners using a standardized protocol. The intensity of anterior fibrosis was evaluated using subjective grading by 2 masked examiners and by image analysis. RESULTS: A standardized protocol was developed for documentation of ACO. The intraexaminer (or short-term) reproducibility (r = 0.96, P < .01) and interexaminer reproducibility (r = 0.93, P < .01) were excellent. The results of image analysis used to objectively quantify ACO correlated with the subjective grading (r = 0.95, P < .01). CONCLUSION: This standardized technique of slitlamp photography and image analysis provided reproducible documentation and can therefore serve as a basis for the quantification of ACO.