[Basic aspects of IOL calculation].

IOL calculation can now be considered a solved problem. However, the problem of sharing the knowledge of the underlying physical and mathematical basics is still unsolved. Also, the necessary hard- and software tools for an IOL calculation approximating the accuracy of prescribed glasses are not yet generally available.

Accuracy comparison of tomography devices for ray tracing-based intraocular lens calculation.

Purpose: To evaluate the interchangeability of different tomography devices used for ray tracing-based intraocular lens (IOL) calculation.

Setting: Eye clinic, Castrop-Rauxel, Germany.

Design: Retrospective analysis.

Comparison of the Automated Pattern-Noise (PANO) Glaucoma Test with the HFA, an FDT Stimulus, and the Fundus Area Cup-to-disk Ratio.

Aim And Objective: To compare the results of a new automated glaucoma test-Pattern-Noise (PANO)-to the Humphrey Visual Field Analyzer-II (HFA), the fundus area cup-to-disk ratio (CDR), and a frequency doubling technology (FDT) stimulus.

Materials And Methods: This was a prospective study performed in the West-Region of Cameroon. Two hundred and nineteen eyes of 122 adult patients were included with a clinical suspicion of normal-tension or primary open-angle glaucoma and no other major ocular pathology.

Predictability of intraocular lens power calculation after small-incision lenticule extraction for myopia.

Purpose: To evaluate and compare the predictability of intraocular lens (IOL) power calculation after small-incision lenticule extraction (SMILE) for myopia and myopic astigmatism.

Setting: Department of Ophthalmology, Philipps University of Marburg, Marburg, Germany.

Design: Retrospective comparative case series.

Pattern noise (PANO): a new automated functional glaucoma test.

Purpose: To present a newly developed visual field device (pattern noise: PANO) designed to be sensitive to glaucoma defects, cost-effective, material-practical and easy to repair and therefore particularly suited for low-income countries, where glaucoma can be highly prevalent (e.g. sub-Saharan Africa).

Impact of Posterior Corneal Surface on Toric Intraocular Lens (IOL) Calculation.

Purpose: To quantify the impact of posterior cornea on toric IOL calculation accuracy using Placido-topography of anterior corneal surface and Scheimpflug measurements of corneal thickness.

Materials And Methods: Three-hundred seventy-nine non-selected eyes undergoing cataract surgery with non-toric intraocular lens (IOL) implantation were measured with TMS-5 (Tomey, Japan), IOLMaster (Zeiss, Germany) and Lenstar (Haag-Streit, Switzerland). Anterior, posterior and total measured corneal astigmatisms were compared with astigmatisms from postoperative refraction by calculating vector differences.

Modulatory effect of different riboflavin compositions on the central corneal thickness of African keratoconus corneas during collagen crosslinking.

Purpose: A pilot investigation to transfer the established corneal collagen crosslinking (CXL) procedure in European eyes into clinically affected African eyes and to optimize the treatment by adapting the riboflavin composition.

Materials And Methods: CXL was performed in 15 eyes (11 patients) with advanced stages of keratoconus in the Eye Clinic of Bafoussam in the West Region of Cameroon. The following six riboflavin compositions with different portions of active swelling additives were applied: Solution 1 (0.

A ray tracing approach to calculate toric intraocular lenses.

Purpose: To quantify the precision of astigmatic correction in routine cataract surgery with toric intraocular lenses (IOLs) and to evaluate the predictability of keratometric and anterior/posterior topographic measurement for the improvement of the overall accuracy.

Methods: Seventy-eight eyes of 56 patients were implanted with toric IOLs. Data acquired by the Lenstar optical biometer (Haag-Streit, Bern, Switzerland) and TMS5 topography (Tomey, Nagoya, Japan) were processed with the ray tracing software Okulix (Tedics, Dortmund, Germany) to predict the residual refraction.

Accuracy of intraocular lens calculation with ray tracing.

Purpose: To quantify the current accuracy limits of ray tracing for intraocular lens (IOL) calculations, compare results for spherical vs aspheric IOLs, and determine the value of using crystalline lens thickness in IOL calculations.

Methods: Of 591 eyes, 363 eyes were implanted with spherical IOLs (320 SA60AT [Alcon Laboratories Inc] and 43 Y-60H [Hoya Corp]) and 228 eyes had aspheric, aberration-correcting IOLs (57 SN60WF [Alcon Laboratories Inc], 112 Tecnis ZCB00 [Abbott Medical Optics], 21 CTAsphina404 [Carl Zeiss Meditec], and 38 iMics1 [Hoya Corp]), all calculated with OKULIX ray tracing (Tedics), based on Lenstar (Haag-Streit) measurements of axial length, corneal radii, and position and thickness of the crystalline lens. The measure of accuracy was the prediction error, ie, the difference between calculated refraction and manifest refraction (spherical equivalent) 1 month after surgery calculated as mean absolute error (MAE).

Controlled cyclophotocoagulation with the 940 nm laser for primary open angle glaucoma in African eyes.

Background: "Controlled cyclophotocoagulation" is a real-time dosage control which reduces the complications of transscleral cyclophotocoagulation to a negligible amount in European eyes. Applied to a few African eyes, however, the method failed. Obviously, the physical parameters of the laser procedure need adjustment to African eyes.

Glaucoma screening in Western Cameroon.

Purpose: To quantify glaucoma-related parameters in a rural African region.

Material And Method: In a population-based investigation, 635 persons in six villages underwent slit-lamp examination including investigation of the optic nerve head with a 90D lens and Goldmann applanation tonometry. The mean age of the persons was 49.

Is gaze-dependent tonometry a useful tool in the differential diagnosis of Graves' ophthalmopathy?

Background: A rise in intraocular pressure (IOP) in upgaze is regarded as a diagnostic sign in Graves' ophthalmopathy (GO). However, the question of erroneous IOP measurement due to applanation carried out on the peripheral cornea has never been addressed.

Methods: In 22 healthy volunteers, as well as in 51 GO patients, applanation tonometry was performed in the primary position of gaze and at 20 degrees of upgaze.

Intraocular lens calculation accuracy limits in normal eyes.

Purpose: To quantify the current accuracy limits, analyze the residual errors, and propose the next steps for prediction accuracy improvements.

Setting: Eye hospitals in Germany, Denmark, and Austria.

Method: Numerical ray tracing using manufacturer's intraocular lens (IOL) data (vertex radii, central thickness, refractive index) was used for all calculations.

Topography-based intraocular lens power selection.

Purpose: To provide mathematical tools for selecting intraocular lens (IOL) power for normal eyes and for "odd" eyes, particularly after corneal refractive surgery.

Setting: Universitats-Augenklinik, Mainz, Germany.

Methods: First, IOL power is selected based on the radii and numerical eccentricity of the cornea, extracted from corneal topography in a consistent numerical model of the cornea.

Predicting postoperative intraocular lens position and refraction.

Purpose: To predict the postoperative IOL position and refraction as accurately as possible independent of individualization of the parameters.

Setting: Universitats-Augenklinik, Mainz, Germany, and Vienna, Austria.

Methods: One patient cohort (189 eyes, Vienna) was used to calibrate the prediction method, which was then applied to a second cohort (65 eyes, Mainz).

Determining postoperative anterior chamber depth.

Purpose: To compare measured and calculated postoperative anterior chamber depths (ACDs).

Setting: Department of Ophthalmology and Institute of Medical Physics, University of Vienna, Vienna, Austria, and Department of Ophthalmology, University of Mainz, Mainz, Germany.

Methods: The postoperative ACD was measured in 189 pseudophakic eyes using a laboratory prototype of partial coherence interferometry (PCI).

Corneal model.

Purpose: To describe the optical region of the cornea with as few parameters as possible and to compare this approach to commonly used mathematical models for the cornea.

Setting: University eye hospital, Mainz, Germany.

Methods: Corneal surface is approximated by a simple model (SM) that is defined by 2 perpendicular vertex radii, their angle to the horizontal, and a unique numerical eccentricity.

Simplified mathematics for customized refractive surgery.

Purpose: To describe a simple mathematical approach to customized corneal refractive surgery or customized intraocular lens (IOL) design that allows "hypervision" and to investigate the accuracy limits.

Setting: University eye hospital, Mainz, Germany.

Methods: Corneal shape and at least 1 IOL surface are approximated by the well-known Cartesian conic section curves (ellipsoid, paraboloid, or hyperboloid).

Ray tracing for intraocular lens calculation.

Purpose: To improve accuracy in intraocular lens (IOL) calculations and clarify the effect of various errors.

Setting: University eye hospitals, Mainz, Germany, and Vienna, Austria.

Methods: A numerical ray-tracing calculation has been developed for the pseudophakic eye.