Anja Viestenz

Toric Intraocular Lenses—Theory, Matrix Calculations, and Clinical Practice

PURPOSE To describe 1) how to determine toric (posterior chamber) intraocular lenses (IOLs) with standard formulas, 2) a matrix-based calculation scheme for determining toric IOLs using 4x4 matrices, 3) a method to determine residual refraction after implantation of an arbitrary toric lens, and 4) to address clinical aspects. METHODS Formulas and metrics are reviewed for determining IOL power and residual refraction after toric IOL implantation. RESULTS From 4x4 refraction and translation matrices characterizing refractive surfaces and interspaces between refractive surfaces, a system matrix is determined characterizing the entire optical system paraxially. Toric posterior chamber IOLs are determined by solving a linear equation system. In a second step, the same methodology is used for estimation of the residual refraction at the spectacle plane after implantation of an arbitrary toric lens. The methodology is applied to working examples, and the calculation procedure is described in a step-by-step approach. CONCLUSIONS A straight-forward en bloc concept is demonstrated for determination of toric IOLs and estimation of the residual refraction. The applicability is shown in working examples, and clinical aspects such as rotation of the lens implant are addressed.

Ray tracing through a schematic eye containing second‐order (quadric) surfaces using 4 × 4 matrix notation

Ray tracing is used in ophthalmology for evaluation of the optical properties of the eye. We demonstrate an algebraic method for tracing a bundle of rays through the optical system of an eye containing aspheric surfaces. Restricting to second‐order surfaces (quadric surfaces) such as ellipsoids, paraboloids or hyperboloids, a surface is described by a 4 × 4 matrix. In this case, the normal vector can be derived analytically and the ray‐surface intersection is calculated by solving a quadratic equation. We applied this straightforward matrix‐based strategy to the spherical 4‐surface Le Grand schematic eye, and the Le Grand eye modified by Kooijman containing four aspheric surfaces. We calculated the spot diagram for the focal plane as well as a pre‐ and post‐focal plane for both model eyes, and found that the optical quality of the aspheric model characterized by the ray scatter in the spot diagram at the focal plane is much better than that of the spherical model. This calculation strategy may be helpful for evaluating the image distortion of decentred or tilted spherical or aspheric artificial intra‐ocular lenses.

Vigabatrin-assoziierte bilaterale einfache Optikusatrophie mit konzentrischer Gesichtsfeldeinengung

ZusammenfassungKasuistik. Ein 70-jähriger, vormals mit Vigabatrin behandelter Patient stellte sich mit blassen Papillen und einer bilateralen konzentrischen Gesichtsfeldeinengung auf 35° vor.Die kumulative Dosis betrug 3,7 kg. Die B-Welle war im photopischen und skotopischen ERG reduziert, die Latenzzeit im VEP war verlängert.Im HRT und GDx war die Dicke der retinalen Nervenfaserschicht pathologisch reduziert. Schlussfolgerung. Vigabatrin kann als Antikonvulsivum durch eine Hemmung der GABA-Transaminase die retinale GABA-Konzentration erhöhen und zu einer aufsteigenden einfachen Optikusatrophie führen.Vigabatrin-assoziierte Gesichtsfeldausfälle können irreversibel sein.Vor Beginn der Therapie und in 6-monatigem Intervall werden Gesichtsfeldkontrollen empfohlen.Bei Konstriktion sollte Vigabatrin abgesetzt werden.Aufgrund der Dosis-Toxizitäts-Abhängigkeit sollte ab einer kumulativen Dosis über 3 kg engmaschig kontrolliert werden.AbstractCase report. A 70-year-old male with optic disc pallor and visual field constriction up to 35° bilaterally was previously treated with vigabatrin.The cumulative dosage was 3.7 kg. The b-wave was reduced in photopic and scotopic electroretinography and the patient had delayed visual evoked potentials.The retinal nerve fiber thickness was pathologically reduced in the Heidelberg retinal tomography (HRT) and the retinal nerve fiber layer analyzer (GDx). Conclusion. Vigabatrin is an antiepileptic drug and may increase the intraretinal GABA level due to an inhibition of the enzyme GABA-transaminase and may induce an ascending simple optic nerve atrophy.Vigabatrin-associated visual field defects may be irreversible. A visual field control is recommended before starting the treatment with vigabatrin and at regular 6-month intervals thereafter. In cases of visual field constriction, the therapy should be stopped. If the cumulative dosage is more than 3 kg of vigabatrin, the visual field controls should be performed more frequently because of the dosage-toxicity relationship.

Evaluation of corneal flap dimensions and cut quality using the SKBM automated microkeratome

Purpose: To evaluate flap dimensions and cut quality with repeated blade use of the automated Summit Krumeich‐Barraquer microkeratome (SKBM® [LadarVision]). Setting: Department of Ophthalmology, University Erlangen‐Nuremberg, Erlangen, Germany. Methods: The SKBM (160 &mgr;m plate, intended flap diameter 9.0 mm) was used to perform a corneal hinged flap in 35 pig cadaver eyes. Seven blades were reused 5 times each. The flap diameter was measured by planimetry, and the thickness was assessed by ultrasonic pachymetry. Scanning electron microscopy (SEM) of blades and stromal beds was performed. Results: With single use of the blade, the mean central flap thickness was 145 &mgr;m ± 25 (SD). The vertical/horizontal flap diameter was 9.0 ± 0.03 mm/8.6 ± 0.03 mm. No thickness gradient was observed from the incision (138 ± 31 &mgr;m) to the flap hinge (130 ± 30 &mgr;m). If the blade was used more than 2 times, the flap was thinner at the incision (157 ± 34 &mgr;m versus 124 ± 20 &mgr;m; P = .003) and the hinge (143 ± 24 &mgr;m versus 122 ± 31 &mgr;m; P = .04), but the central thickness remained unchanged. With multiple use of the blade, SEM analysis showed increasing cut irregularity, more tissue remnants on the blade surface, and a progression in blade irregularities (up to 9.3 &mgr;m). Conclusions: Reproducible flap size and thickness can be obtained with single use of stainless steel blades in the SKBM. With multiple use, the quality of the blades and the stromal bed deteriorates and the peripheral thickness of the flaps decreases. Thus, single use of blades is recommended.

Einfluss der Er:YAG-Laserstrahlführung auf die Schnittqualität der nichtmechanischen Hornhauttrepanation für die perforierende Keratoplastik

ZusammenfassungHintergrund. Die nichtmechanische Hornhauttrepanation für die perforierende Keratoplastik mit dem Excimerlaser ist mechanischen Trepanationsverfahren sowohl morphologisch als auch funktionell überlegen. Auf der Suche nach alternativen Laserverfahren war es unser Ziel, den Einfluss der Laserstrahlführung mit dem Er:YAG-Festkörperlaser auf die Schnittkantenqualität und die thermische Schädigungszone zu untersuchen. Methoden. Verglichen wurden A) ein manuell, B) ein halbautomatisch und C) ein unter PC-Kontrolle (“Scanning”) geführter Laserstrahl gütegeschaltet, Repetitionsrate 5 Hz, Pulsenergie 65 mJ, Fleckdurchmesser 0,7 mm) entlang von Schlitzmasken an 28 Schnitten von Kaninchenaugen. Es erfolgte die makroskopische Beurteilung der Qualität des Trepanationskanals sowie die histologische Analyse der thermischen Alterationen an PAS-Schnitten. Ergebnisse. Die am deutlichsten ausgeprägte intrastromale thermische Schädigungszone verursachte der manuelle Modus (A) mit 19,3±8,7 μm gegenüber 8,8±3,0 μm im halbautomatischen Führungsmodus (B) (p=0,03) und 7,0±3,0 μm im Scanning-Modus (C) (p=0,016). Schlussfolgerung. Die vollautomatische PC-unterstützte Scanning-Laserstrahlführung beim Er:YAG-Laser ermöglicht eine signifikante Verbesserung der Schnittqualität auch bei vorgegebener geringer Pulswiederholfrequenz und kleinem Fleckdurchmesser.AbstractBackground. Results of non-mechanical corneal trepanation using the excimer laser enhance the morphological and functional results for penetrating keratoplasty. Searching for alternative laser sources we assessed the impact of an automatic laser beam control for the Er:YAG solid-state laser on the cut performance and thermal damage zone in non-mechanical corneal trepanation. Methods. We compared the cut quality of A) a manually guided laser beam, B) a semiautomatically guided laser beam and C) a fully PC-controlled laser beam positioning system (q-switched, repetition rate 5 Hz, pulse energy 65 mJ, spot size 0.7 mm) along slit aperture masks on 28 rabbit eyes using macroscopic images and histological sections (PAS staining). Results. The manually guided laser beam control (A) induced the broadest thermal damage zone in the corneal stroma (19.3±8.7 μm) compared to the semi-automatic mode (B) (8.8±3.0 μm, p=0.03) and the PC-controlled laser beam control (C) (7.0±3.0 μm, p=0.016). Conclusion. The fully automatic PC-controlled laser beam positioning system for the Er:YAG solid-state laser with a small spot size and fixed low repetition rate allows a precise laser beam guidance and a significant enhancement of the cut performance compared to a manual laser beam control via micromanipulator in experimental nonmechanical corneal trepanation.

Superficial corneal effects of experimental nonmechanical penetrating keratoplasty using a Q-switched Er:YAG laser.

Purpose. To assess thermal effects of Q-switched Er:YAG laser trephination to corneal epithelium and superficial stroma using different mask types and materials for experimental penetrating keratoplasty. Methods. Laser trephination was performed in 20 freshly-enucleated porcine eyes (repetition rate 5 Hz, pulse energy 65 mJ, spot size 0.7 mm). We used flat, open-metal and ceramic masks for donor and recipient trephination placed directly onto the corneal surface. Main outcome measures as assessed by light microscopy after PAS staining of 8-&mgr;m paraffin sections included: extension of tissue thermal damage at the cut edge in the superficial and basal epithelial layers, the basement membrane and subepithelial stroma, and depth and width of epithelial/stromal involvement in the area of the donor mask contact. Results. The thermal damage in the superficial epithelium was more pronounced in donor (mean extension 61.6 ± 15.6 &mgr;m) than in recipient (29.4 ± 24.9 &mgr;m, p = 0.05) trephination. In donor trephination, thermal damage zone of the superficial epithelial layer was significantly smaller with ceramic than with metal masks (21.0 ± 23.0 versus 61.6 ± 15.6 &mgr;m, p = 0.014). In contrast, differences at basal epithelial layer (p = 0.44), basement membrane (p = 0.79), and subepithelial stroma (p = 0.2) were not statistically significant. Superficial donor involvement of the cornea adjacent to the paracentral donor mask contact zone was seen neither with ceramic nor with metal masks. Conclusion. Superficial corneal alterations adjacent to the mask-cornea contact zone may be minimized by using the Er:YAG laser in a Q-switched mode. Ceramic masks, in contrast to metal masks, further reduce superficial thermal alterations at the cut edge.

Q-switched 2.94-μm Er:YAG laser trephination With convergent and divergent cut angles for penetrating keratoplasty

Purpose. To study the morphologic properties of perpendicular (P), convergent (C), and divergent (D) cut angles using different speeds of rotations during donor and recipient nonmechanical trephination for experimental penetrating keratoplasty. Methods. With a Q-switched 2.94-&mgr;m Er:YAG laser corneal trephination was performed in 150 enucleated porcine eyes using ceramic open masks with 8 “orientation teeth/notches” and an automated globe rotation device allowing different cut angles [0 degree (P), 10 and 20 degrees (C and D)] toward the optical axis and variation of the rotation speed [3, 7, and 11 rotations per minute (rpm)]. The regularity of the cut (I, regular; II, slightly irregular; III, irregular) was assessed by light microscopy. The area of thermal damage and the number and size of “spikes” in the stroma at the superficial, intermediate and deep level of the excision were analyzed using digital images and the Optimas image processing software. Results. The regularity of the cut was classified as I in 42%/22% of donor/recipient and as II in 41%/56%, respectively. The thermal damage was least expressed with D20 degree cut angle and donor mask (P < 0.01). With all cut angles and speeds of rotation, thermal damage at the deep level of excision was significantly smaller (P < 0.01). With different speeds of donor rotations, the thermal damage showed no significant difference. With recipient trephination, the thermal damage at the deep level was greatest with 7 rpm (P < 0.01). The number and size of spikes of thermal damage with donor and recipient masks were significantly smaller in the deep stroma (P < 0.01). Conclusions. Q-switched Er:YAG laser trephination with appropriate settings results in low thermal damage zones at the cut margin. Different cut angles and speeds of trephination may affect the cut performance and quality of the excision. In our study, low rotation speed and divergent donor cut angles showed the best results. The cut quality and the small thermal damage with the Q-switched 2.94-&mgr;m Er:YAG laser seem to be tolerable for corneal trephination. Therefore, this modality may be a low-cost, easy-to-handle alternative for nonmechanical corneal transplantation in humans.

Phototherapeutic Keratectomy in Salzmann Nodular Degeneration With "Optical Cornea Plana".

Purpose: Typically, we observe an unintended hyperopic shift after phototherapeutic keratectomy (PTK). Despite a clear optical axis, elevations of the mid-peripheral cornea often lead to remarkable visual impairment in Salzmann nodular degeneration (SND). The aim of this study was to analyze the effect of mechanical pannus removal and PTK on the corneal curvature in SND. Methods: Fifteen eyes of 10 patients with visual impairment caused by SND were treated with combined pannus removal and PTK using a masking fluid. Mean age was 53 years. We analyzed best-corrected visual acuity, central corneal power (in diopters, D), spherical equivalent (in D), and irregularity of corneal topography (Index of Surface Variance, Pentacam). Results: Best corrected visual acuity before PTK was 0.64 (median) and improved to 0.85 (median) after the surgical procedure. Mean spherical equivalent was reduced by 1.82 ± 1.4 D from +2.53 D preoperatively to +0.75 D postoperatively (P = 0.001). Mean central corneal power increased by 3.18 ± 3.5 D from 39.8 ± 4.6 D preoperatively to 43 ± 1.7 D postoperatively (P = 0.013). Topographic irregularity normalized from 83.9 ± 53.7 (27–204) to 33.3 ± 14.3 (20–56; Index of Surface Variance) (P = 0.016). Conclusions: In SND, asymmetric tear film pooling caused by nodules located in the mid-periphery of the cornea may lead to an “optical cornea plana,” which results in a marked hyperopic shift accompanied with high irregular astigmatism. Pannus removal combined with excimer laser PTK may restore visual performance, at least in part, because of a myopic shift and regularization of the corneal curvature.

Torische Intraokularlinsen und Astigmatismuskorrektur@@@Toric intraocular lenses and correction of astigmatism

ZusammenfassungTorische Intraokularlinsen (tIOLs) können den kornealen Astigmatismus korrigieren. Der Hintergrund dieser Übersicht ist1.die biometrischen, keratometrischen und topographischen Konditionen für eine tIOL-Implantation zu beschreiben,2.Vor- und Nachteile von tIOLs aufzuzeigen,3.Indikationen und Kontraindikationen für tIOLs zu definieren,4.klinische Empfehlungen für die Implantation von tIOLs anzubieten und5.die Spezifikationen der derzeit kommerziell erhältlichen tIOLs aufzuzeigen.AbstractToric intraocular lenses (tIOLs) have the potential to correct corneal astigmatism. The purpose of this review paper is1.to describe the biometric, keratometric and topographic conditions for implantion of tIOLs,2.to highlight the advantages and disadvantages of tIOLs,3.to define indications for and contraindications to tIOL implantation,4.to provide clinical recommendations for the implantation of toric lenses, and5.to report the specifications of all tIOLs that are currently available commercially.Toric intraocular lenses (tIOLs) have the potential to correct corneal astigmatism. The purpose of this review paper is: 1. to describe the biometric, keratometric and topographic conditions for implantion of tIOLs, 2. to highlight the advantages and disadvantages of tIOLs, 3. to define indications for and contraindications to tIOL implantation, 4. to provide clinical recommendations for the implantation of toric lenses, and 5. to report the specifications of all tIOLs that are currently available commercially.