N. Szentmáry

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.

Photodynamic inactivation of multidrug-resistant Staphylococcus aureus by chlorin e6 and red light (λ = 670 nm)

Multidrug-resistant Staphylococcus aureus (MDR-SA) are a frequent cause of antibiotic treatment refractory bacterial corneal infections. Photodynamic therapy (PDT) is being discussed as a putative treatment option to cure this type of bacterial infection. Here we tested the in vitro susceptibility of a set of 12 clinically derived MDR-SA isolates with differing genetic backgrounds and antibiotic resistance profiles against photodynamic inactivation (PDI) by the porphyrin chlorin e6 (Ce6) and red light (λ=670nm). All tested clinical isolates displayed a 5-log10 reduction in viable cells by Ce6 and red light, when cells were preincubated with the photosensitizer at concentrations ≥128μM for 30min in the dark, and a subsequent irradiation with light at λ=670nm (power density: 31mW/cm(2), absorbed dose: 18,6J/cm(2)) was applied. Similarly, cells of the laboratory strain Newman required the same Ce6 pre-incubation and light dose for a 5-log10 reduction in cell viability. Inactivation of crtM in strain Newman, which interferes with pigment production in S. aureus, rendered the mutant more susceptible to this PDT procedure, indicating that the level of resistance of S. aureus to this therapy form is affected by ability of the pathogen to produce the carotenoid pigment staphyloxanthin. Incubation of freshly explanted porcine corneas with a 0.5% Ce6 gel demonstrated that the photosensitizer can diffuse into and accumulate within the stroma of the cornea in concentrations found to be sufficient to yield a 5-log10 reduction of the S. aureus cell pool in vitro. These data suggest that PDI with Ce6 and red light might be a promising new option for the treatment of MDR-SA induced corneal infections.

Gerätegestützte Diagnostikverfahren des Keratokonus im Vergleich

PURPOSE Due to the modern device-assisted diagnosis of keratoconus by topography, tomography and biomechanical properties of the cornea, a large number of parameters and indices are obtained as a result of clinical examinations. The aim of the present study was to investigate how modern screening methods support the diagnosis of keratoconus. PATIENTS AND METHODS In this prospective study, 93 eyes of 93 keratoconus patients and 107 eyes of 107 healthy subjects (control group) were included. The keratoconus group contained 85 % males, whereas the distribution in the control group was balanced. The mean age was 35 ± 12 years in the keratoconus group and 27 ± 7 years in the control group. Exclusion criteria for both groups were previous eye surgery, cross-linking therapy, glaucoma, uveitis or other inflammatory diseases of the eye. All patients with a thyroid disorder were also excluded from the control group. All eyes were examined using the TMS-5 topographer, Pentacam and Ocular Response Analyzer (ORA). Based on receiver operator characteristics (ROC), the performance of various keratoconus indices was determined by means of the area under the curve (AUC). RESULTS All parameters showed statistically highly significant differences between the keratoconus and control group (p ≤ 0.0001). The Surface Asymmetry Index (SAI) and the Keratoconus Severity Index (KSI) of TMS performed well with (mean value keratoconus group/mean value control group/AUC) SAI (2.43/0.36/0.969) and KSI (50.87/0.37/0.912). Pentacam parameters Index of Surface Variance (ISV) and Topographic Keratoconus Classification (TKC) were comparable to TMS parameters with ISV (90.05/15.77/0.969), TKC (2.23/0.00/0.940). ORA indices Corneal Hysteresis (CH), Corneal Resistance Factor (CRF) and Keratoconus Match Index (KMI) showed slightly poorer performance with CH (8.22/11.48/0.909), CRF (7.25/11.20/0.951), KMI (0.31/1.05/0.909). CONCLUSION In this study, tomography and topography was more reliable in diagnosing keratoconus than evaluating the biomechanical properties of the cornea. SAI and KSI (TMS) as well as TKC and ISV (Pentacam) showed improved recognition rates compared to the KMI (ORA). However, individual parameters alone are not sufficient for the diagnosis of keratoconus.

Confocal microscopy in acanthamoeba keratitis as an early relapse-marker

Acanthameoba keratitis is a serious ophthalmological condition with a potentially vision‐threatening prognosis. Early diagnosis and recognition of relapse, and the detection of persistent Acanthamoeba cysts, are essential for informing the prognosis and managing the condition. We suggest the use of in vivo confocal microscopy not only to identify the early signs of relapse after keratoplasty in patients with Acanthamoeba keratitis, but also as an additional follow‐up tool after antimicrobial crosslinking. This study shows that in vivo confocal microscopy is, in experienced hands, a quick and reliable diagnostic tool. Clin. Anat. 31:60–63, 2018.

Calculation of power and field of view of keratoprostheses

To demonstrate a mathematical algorithm for calculating the refractive power of keratoprostheses and to estimate vignetting effects.

A comparison of small aperture implants providing increased depth of focus in pseudophakic eyes.

BACKGROUND AND PURPOSE Presbyopia is characterized by a decreasing ability of accommodation - the eyes ability to alter the focus between far and near distance objects. After cataract surgery, accommodation is completely lost. Several years ago, small aperture (pinhole) implants have been presented in order to increase the depth of focus providing functional vision at far and near distance without the need for spectacles. We simulated the theoretical depth of focus with three different pseudophakic eye models in order to investigate the potential benefit arising from the implantation of small aperture optical (SAO) implants. The purpose was to compare the achievable defocus range of a SAO intraocular lens with a SAO corneal inlay. MATERIAL AND METHODS We created three pseudophakic eye models with an aberration correcting intraocular lens (IOL): one with a corneal SAO implant (M1), a second one with a SAO intraocular lens (M2) and a third one with a conventional intraocular lens of the same optical design but without SAO (M0). Defocus curves were created by varying the focal length of a thin lens in front of the eye - which mimics the clinical assessment of defocus curves. RESULTS With a Strehl ratio threshold of 0.05, the reference design M0 provided a maximum defocus range of approximately 1.7D (with a 2.0mm pupil) whereas both pinhole implants (M1 and M2) showed a defocus range up to 3.0 and 3.3D, respectively. With large natural pupil diameter, where light passes outside the SAO aperture, the defocus range drops to 0.8D/0.7D for M1 and M2 compared to 0.7D with M0. CONCLUSIONS The SAO intraocular lens showed a similar defocus range as the SAO corneal inlay. Both concepts have the potential of increasing depth of focus compared to a conventional intraocular lens. In case of large physiological pupil diameters these advantages of SAO implants may be lost.

Wachstumsfaktoren und Interleukine in Amniongewebehomogenat

PURPOSE Application of amniotic membrane homogenate eye drops may be a potential treatment alternative for therapy resistant corneal epithelial defects. The purpose of this study was to determine the concentrations of epidermal growth factor (EGF), fibroblast growth factor basic (bFGF), hepatocyte growth factor (HGF), keratinocyte growth factor (KGF), interleukin-6 (IL-6) and interleukin-8 (IL-8) in amniotic membrane homogenates. METHODS Amniotic membranes of 8 placentas were prepared and thereafter stored at - 80 °C using the standard methods of the LIONS Cornea Bank Saar-Lor-Lux, Trier/Westpfalz. Following defreezing, amniotic membranes were cut in two pieces and homogenized in liquid nitrogen. One part of the homogenate was prepared in cell-lysis buffer, the other part was prepared in PBS. The tissue homogenates were stored at - 20 °C until enzyme-linked immunosorbent assay (ELISA) analysis for EGF, bFGF, HGF, KGF, IL-6 and IL-8 concentrations. RESULTS Concentrations of KGF, IL-6 and IL-8 were below the detection limit using both preparation techniques. The EGF concentration in tissue homogenates treated with cell-lysis buffer (2412 pg/g tissue) was not significantly different compared to that of tissue homogenates treated with PBS (1586 pg/g tissue, p = 0.72). bFGF release was also not significantly different using cell-lysis buffer (3606 pg/g tissue) or PBS treated tissue homogenates (4649 pg/g tissue, p = 0.35). HGF release was significantly lower using cell-lysis buffer (23,555 pg/g tissue), compared to PBS treated tissue (47,766 pg/g tissue, p = 0.007). CONCLUSION Containing EGF, bFGF and HGF, and lacking IL-6 and IL-8, the application of amniotic membrane homogenate eye drops may be a potential treatment alternative for therapy-resistant corneal epithelial defects.

Results of excimer laser penetrating keratoplasty in aphakic eyes

BackgroundCorneal grafting in aphakic eyes is often challenging. We report about the outcome of excimer laser trephination in aphakic eyes.MethodsWe examined 17 eyes of 17 patients. Diagnosis in 11 eyes was endothelial decompensation and in six, corneal scars. We performed an excimer laser keratoplasty with intraoperative “Flieringa ring” suturing. Follow-up ranged between 3 and 41 (17.6 ± 11.7) months. Main outcome measures included: best-corrected visual acuity (BCVA), intraocular pressure (IOP), topographic astigmatism, corneal refractive power (CRP), central corneal thickness (CCT) and endothelial cell density (ECD).ResultsPreoperative BCVA was light perception in two eyes, hand motion in seven, finger counting in one eye, under 20/400 in six eyes and 20/200 in one eye. IOP ranged between 4 and 28 (13.6 ± 5.1) mmHg. Topographic astigmatism ranged from 0.5 to 18.5 (7.0 ± 6.9) dioptres. CRP was between 38 and 59 (46 ± 9) dioptres. CCT was between 404 and 1069 (748 ± 181) μm. Postoperative BCVA was hand motion in five eyes, under 20/400 in two and ranged between 20/200 and 20/20 in ten eyes. IOP ranged between 10 and 40 (18.3 ± 8.5) mmHg. Topographic astigmatism ranged from 0.9 to 13 (5.5 ± 3.2) dioptres. CRP was between 31.9 and 46.7 (42 ± 4.1) dioptres. CCT was between 349 and 820 (552 ± 115.57) μm. ECD was between 592 and 2319 (1674 ± 553) cells/mm2.ConclusionsExcimer laser trephination can deliver beneficial visual outcomes in most of the aphakic eyes.

Anatomy-Based DMEK-Wetlab in Homburg/Saar – Novel aspects of donor preparation and host maneuvers to teach Descemet Membrane Endothelial Keratoplasty

Use of Descemet Membrane Endothelial Keratoplasty (DMEK) has been limited because of problems with donor preparation, i.e. tearing of the Descemet membrane and difficulties in unfolding the Endothelium‐Descemet‐Membrane‐Layer (EDML) in the anterior chamber (AC). The purpose of this work was to describe a novel approach to teaching anatomy‐based donor and recipient preparation in a DMEK‐Wetlab. We teach successful mono‐manual donor preparation of human corneas in organ culture not suitable for transplantation, including peripheral markers for orientation. We also teach safe recipient preparation in a freshly‐enucleated pig eye in organ culture preservation medium for atraumatic introduction of the EDML roll into the AC, reliable orientation of the EDML during surgery, and stepwise unfolding within the AC. Twenty‐two candidates in the 1. Homburg Cornea Curriculum HCC 2015 who practiced both preparations using three human donor corneas and three pig eyes assessed the procedure as follows: (1) overall grade of the Wetlab 1.4 (median 1, range 1 to 2 ‐ on a scale from 1 (excellent) to 6 (terrible); (2) most participants and tutors stated that the Wetlab is most effective for colleagues who have some previous experience with corneal microsurgery. Our novel anatomy‐based approach to simulating donor preparation and graft implantation for DMEK seems to meet the expectations and requirements of colleagues with previous experience in corneal microsurgery and will help to reduce the rate of complications for incipient DMEK surgeons in the future. Clin. Anat. 31:16–27, 2018.

Calculation of Pseudophakic and Phakic Toric Lenses for Correction of Corneal Astigmatism - Theory and Clinical Aspects

BACKGROUND In the last decades the implantation of pseudophakic and phakic toric lenses has become wide-spread for the correction of corneal astigmatism in cases of classical cataract surgery with implantation of a posterior chamber lens or in cases of refractive surgery with implantation of a piggyback lens. The purpose of this review article is to present an en bloc mathematical strategy for calculating pseudophakic and phakic toric lenses and for deriving the spectacle refraction after implantation of an arbitrary lens. METHODS We restrict ourselves to a centred coaxial optical system containing spherocylindrical surfaces and interspaces with a homogeneous optical medium. All calculations are done in the paraxial space according to linear Gaussian optics. We define an optical model for the pseudophakic and phakic eye and characterise all known refractive surfaces and interspaces between the surfaces with 4 x 4 refraction and translation matrices, respectively. The entire optical system is described with a 4 x 4 system matrix, which relates the impinging beam (slope angle and height, both in x and y directions) with the exiting beam (slope angle and height, both in x and y directions) and extract the required parameters from the matrix representation. RESULTS In example 1, we describe step-by-step how to derive a pseudophakic toric lens implant from the biometric parameters and in example 2 we estimate the residual refraction at spectacle plane after implantation of a pseudophakic lens. In example 3, we describe step-by-step how to derive a phakic toric lens implant from the initial refraction and biometric measurements and in example 4 we estimate the residual refraction at spectacle plane after implantation of a phakic lens. CONCLUSIONS The calculation scheme presents a strategy for calculating toric lenses and residual refractions based on a thin lens model of the spectacle correction, the cornea and the lens implant. This model can be generalised easily to a thick lens model, if the appropriate geometric parameters of both lens surfaces are known. The phakic lens calculation can directly be transferred to the case of pseudophakic piggyback lenses.