Marrie Van Der Mooren - Academia.edu (original) (raw)

Papers by Marrie Van Der Mooren

Research paper thumbnail of Second harmonic generation of blue light in bulk KTP by Type 1 phase matching

In this paper measurements will be presented of the conversion efficiency for second harmonic gen... more In this paper measurements will be presented of the conversion efficiency for second harmonic generation in KTiOPO4(KTP) by type 1 phase matching for different fundamental wavelengths of a modelocked picosecond Ti:sapphire laser. At a fundamental wavelength of 797 nm and an intensity of 100 MW/sq cm the conversion efficiency is found to be 1.3% and the effective nonlinear optical coefficient d(subeff) is 0.18 pm/V.

Research paper thumbnail of Apparatus, system, and method for providing an optical filter for an implantable lens

Research paper thumbnail of Ophthalmic devices, systems, and methods for optimizing peripheral vision

Research paper thumbnail of Effect of the equivalent refractive index on intraocular lens power prediction with ray tracing after myopic laser in situ keratomileusis

Journal of cataract and refractive surgery, 2015

To determine the impact of the equivalent refractive index (ERI) on intraocular lens (IOL) power ... more To determine the impact of the equivalent refractive index (ERI) on intraocular lens (IOL) power prediction for eyes with previous myopic laser in situ keratomileusis (LASIK) using custom ray tracing. AMO B.V., Groningen, the Netherlands, and the Department of Ophthalmology, Baylor College of Medicine, Houston, Texas, USA. Retrospective data analysis. The ERI was calculated individually from the post-LASIK total corneal power. Two methods to account for the posterior corneal surface were tested; that is, calculation from pre-LASIK data or from post-LASIK data only. Four IOL power predictions were generated using a computer-based ray-tracing technique, including individual ERI results from both calculation methods, a mean ERI over the whole population, and the ERI for normal patients. For each patient, IOL power results calculated from the four predictions as well as those obtained with the Haigis-L were compared with the optimum IOL power calculated after cataract surgery. The study...

Research paper thumbnail of Visualization of the retinal image in an eye model with spherical and aspheric, diffractive, and refractive multifocal intraocular lenses

Journal of refractive surgery (Thorofare, N.J. : 1995), 2008

To present a method that visually demonstrates how spherical, aspheric, diffractive, and refracti... more To present a method that visually demonstrates how spherical, aspheric, diffractive, and refractive multifocal intraocular lenses (IOLs) process light received from the cornea. Monochromatic green light was projected through an Average Cornea Eye (ACE) Model with a cornea in front of the IOL. The model simulates a human cornea with average spherical aberration and visualizes the converging bundle of light leaving the IOL. Additionally, a US Air Force target was projected through the model, and the projected (retinal) image was captured. Various IOLs of differing designs were evaluated using this test setup. Multifocal IOLs included the aspheric diffractive Tecnis ZM900 and ZMA00 lenses; the refractive ReZoom NXG1 lens; the spherical AcrySof ReSTOR SA60D3 apodized diffractive lens; and the spherical diffractive CeeOn 811E lens. Monofocal IOLs included the spherical CeeOnEdge 911A IOL and the aspheric SofPort LI61AO, AcrySof IQ SN60WF, and Tecnis Z9000 and ZA9003 IOLs. The light paths...

Research paper thumbnail of A new intraocular lens design to reduce spherical aberration of pseudophakic eyes

Journal of refractive surgery (Thorofare, N.J. : 1995)

The aim of this study was to design and evaluate in the laboratory a new intraocular lens (IOL) i... more The aim of this study was to design and evaluate in the laboratory a new intraocular lens (IOL) intended to provide superior ocular optical quality by reducing spherical aberration. Corneal topography measurements were performed on 71 cataract patients using an Orbscan I. The measured corneal surface shapes were used to determine the wavefront aberration of each cornea. A model cornea was then designed to reproduce the measured average spherical aberration. This model cornea was used to design IOLs having a fixed amount of negative spherical aberration that partially compensates for the average positive spherical aberration of the cornea. Theoretical and physical eye models were used to assess the expected improvement in optical quality of an eye implanted with this lens. Measurements of optical quality provided evidence that if this modified prolate IOL was centered within 0.4 mm and tilted less than 7 degrees, it would exceed the optical performance of a conventional spherical IOL...

Research paper thumbnail of Methods for Measuring Light Scatter in Intraocular Lenses

Frontiers in Optics 2007/Laser Science XXIII/Organic Materials and Devices for Displays and Energy Conversion, 2007

Research paper thumbnail of Combining in vitro test methods for measuring light scatter in intraocular lenses

Biomedical Optics Express, 2011

Intraocular lenses (IOLs) are designed for implantation for vision correction following cataract ... more Intraocular lenses (IOLs) are designed for implantation for vision correction following cataract removal. The IOL typically replaces a cataractous natural lens that exhibits very high levels of light scattering. The amount of scattering is significantly reduced with an IOL, though it is rarely quantified and both the surface and the bulk of the intraocular lens may contribute to light scatter at some level, and in some cases potentially affecting patients' post-operative quality of vision. The purpose of this paper is to describe two complementary in-vitro quantitative methods for measuring light scatter caused by IOLs. The first method directly measures light scatter from the lens in one plane for angles larger than two degrees. The second method measures light scatter in an eye model including the focal point out to three degrees in the image plane. The measured amount of light scatter from an IOL is typically lower than that found in healthy donor crystalline lenses of various ages that are used as a basis for comparison.

Research paper thumbnail of Effects of glistenings in intraocular lenses

Biomedical Optics Express, 2013

Glistenings consist of multiple microvacuoles in intraocular lenses (IOLs) that cause retinal str... more Glistenings consist of multiple microvacuoles in intraocular lenses (IOLs) that cause retinal stray light and may affect quality of vision. For four IOL types, the microvacuole particle size distribution and particle volume density was measured using confocal light microscopy and dark field microscopy, and the corresponding extinction coefficient γ was determined. The light scatter contribution induced by microvacuoles was measured as function of both angle and extinction, and was verified by calculations using Mie theory. Two IOL types possessed significant glistenings having stray light levels higher than that of a healthy 20 year old crystalline lens corresponding to γ ≥ 0.08 mm −1 .

Research paper thumbnail of Impact of intraocular lens material and design on light scatter: In vitro study

Journal of cataract and refractive surgery, 2014

To determine the typical in vitro straylight levels for intraocular lenses (IOLs) of different ma... more To determine the typical in vitro straylight levels for intraocular lenses (IOLs) of different materials and designs. Abbott Medical Optics, Inc., Groningen, the Netherlands. Experimental study. Two optical bench setups were used to determine baseline straylight levels of IOLs placed in a saline-filled cuvette: one for forward scatter positions between 0.6 and 3.0 degrees and one for positions up to 22.0 degrees. Line-spread functions were measured using the small-angle setup, and scattered light intensity was measured using the wide-angle setup. From these measurements, the angular dependent straylight parameter was calculated. Ten IOLs of different materials (hydrophobic and hydrophilic) and designs (monofocal or diffractive multifocal and spheric or aspheric) were studied, and their measured straylight levels were compared with the levels in a 20-year-old and a 70-year-old healthy noncataractous human crystalline lens. Irrespective of the material or design, monofocal IOLs had st...

Research paper thumbnail of Rostock Glare Perimeter

Optometry and Vision Science, 2013

Disability glare induced by headlights of oncoming cars has been associated with reduced quality ... more Disability glare induced by headlights of oncoming cars has been associated with reduced quality of vision. This study aimed at developing the Rostock Glare Perimeter to quantify dysphotopsia effects under simulated realistic conditions. Sixty phakic subjects of different ages were dazzled by a bright light source centered at a projection screen 3.30 m away from the subject's eye. Using a projected marker moving outward from the screen center with angular steps of 0.25° in 12 directions, the area where the subject cannot distinguish the white spot from the glare effects of the light source was determined. A corresponding mean radius in a field angle relative to the subject's eye was defined as a measure for disability glare. Monocular and binocular measurements were performed, and a separate repeatability and reproducibility study was executed to determine the precision of the Rostock Glare Perimeter. A significant mean positive correlation of disability glare with age (r = 0.534, p < 0.001) was found. The disability glare ranged from 0.33° to 1.8°, and a strong (r = 0.93, p < 0.0002) binocular summation effect was found. The repeatability and reproducibility limit of the Rostock Glare Perimeter method is 0.14° for 95% confidence interval. The Rostock Glare Perimeter method is sensitive to detect age-related disability glare differences and to find binocular summation for disability glare in a healthy population for small field angles with high angular resolution. These findings suggest that the Rostock Glare Perimeter method is a helpful device to quantify symptoms of glare.

Research paper thumbnail of Single shot bulk damage threshold and conversion efficiency measurements on flux grown KTiOPO4 (KTP)

Optics Communications, 1993

ABSTRACT The single shot bulk laser damage threshold was measured on thirteen different flux grow... more ABSTRACT The single shot bulk laser damage threshold was measured on thirteen different flux grown KTP crystals. The measurements were made with the KTP oriented for type II phase matched second harmonic generation (SHG) at 1064 nm. The width of the O-switched Nd:YAG laser pulses was 8.5 ns. The crystals were grown under different experimental conditions. Some of the crystals were measured topographically in order to find possible differences in the damage thresholds between different growth sectors and to check the crystals for optical homogeneity. The measured average threshold for dielectric breakdown of KTP is 31.5±4GW/cm2. Topographic measurements showed, that the samples have a good optical homogeneity with the exception of trivalent cation doped KTP. The presence of Sc3+ and Cr3+ lowers the damage threshold of KTP and areas with preferential chromium incorporation in KTP show a lowered damage threshold in comparison with areas containing less chromium. The conversion efficiency for type II phase matching of the 1064 nm beam of a Nd:YAG laser has a maximum value of 55%. The measured deff was 3.1 pm/V.

Research paper thumbnail of Vergleich der optischen Qualität der Tecnis®-Linsen mit IOLs, die die sphärische Aberration der menschlichen Kornea teilweise kompensieren

Klinische Monatsblätter für Augenheilkunde, 2007

Research paper thumbnail of Diffraktive Multifokal Tecnis ZMB00 einteilige IOL: Optische Performance und Vergleich mit anderen asphärischen Multifokal-IOL

Klinische Monatsblätter für Augenheilkunde, 2010

Research paper thumbnail of Vergleich von Dysphotopsieeffekten bei phaken und pseudophaken Augen mit dem neuen Rostock Glare Perimeter

Klinische Monatsblätter für Augenheilkunde, 2013

Pseudophakic dysphotopsia as unwanted side effect after cataract surgery are becoming increasingl... more Pseudophakic dysphotopsia as unwanted side effect after cataract surgery are becoming increasingly important. The so-called glare perimetry allows a realistic quantification of these phenomena. The article presents the method on the example of healthy subjects and pseudophakic patients. Using glare perimetry phakic and pseudophakic subjects were examined for differences in disability glare. For this, data from 60 phakic persons of different ages (45 ± 17.1 years) were used. As pseudophakic subjects 31 carriers of monofocal lenses (70 ± 6.7 years) and 25 carriers of multifocal lenses (71 ± 8.5 years) were tested. Disability glare was significantly smaller in the phakic group (1.00 ± 0.336°) than in the pseudophakic group (1.56 ± 0.622°). Among the pseudophakic eyes those with a multifocal lens (1.69 ± 0.367°) were significantly more sensitive to glare than those with a monofocal lens (1.43 ± 0.492°). Glare perimetry allows an objective quantification of effects of dysphotopsia under realistic conditions. Pseudophakic eyes show a higher sensitivity to glare than eyes with the natural clear lens. Here, eyes with multifocal lenses prove to be particularly sensitive to glare.

Research paper thumbnail of Intraocular lens designed for the newborn infant eye

Journal of Cataract & Refractive Surgery, 2001

To evaluate the effects of an intraocular lens (IOL) designed for small eyes after clear lens ext... more To evaluate the effects of an intraocular lens (IOL) designed for small eyes after clear lens extraction in an animal model. St. Erik's Eye Hospital, Karolinska Institute, Stockholm, Sweden. Clear lens extraction was performed in both eyes in 19 3-week-old rabbits. In 1 randomly selected eye of each rabbit, a small IOL with long haptics was implanted. Axial length, corneal thickness, corneal diameter, and intraocular pressure were measured preoperatively and every month for 6 months postoperatively. Six months after surgery, the wet mass of the after-cataract was determined. The IOL remained well centered in all eyes. Four animals developed severe glaucoma in 5 eyes (3 aphakic and 2 pseudophakic) soon after surgery and were excluded. In the 15 animals completing the study, signs of glaucoma evolved in 7 animals (5 aphakic and 4 pseudophakic eyes). In aphakic eyes, significant amounts of after-cataract (median 250 mg) developed in all 15 surviving animals. In pseudophakic eyes, small amounts of after-cataract (median 30 mg) were present. During the first 2 months after surgery, ocular growth was less in pseudophakic eyes than in aphakic eyes. Results indicate that implantation of a down-sized IOL with long haptics in small eyes is safe. Considerable less after-cataract was found in eyes with the IOL than in aphakic control eyes.

Research paper thumbnail of Determination of type I phase matching angles and conversion efficiency in KTP

Applied Optics, 1995

Measurements of the conversion efficiency of second-harmonic generation in KTP 1KTiOPO 4 2 by the... more Measurements of the conversion efficiency of second-harmonic generation in KTP 1KTiOPO 4 2 by the use of type I phase matching for different fundamental wavelengths of a mode-locked picosecond Ti:sapphire laser are presented. The observed phase matching angles are in agreement with the calculated phase matching curves. At a fundamental wavelength of 834 nm and an intensity of 100 MW@cm 2 the conversion efficiency is 4% at maximum, and the corresponding effective nonlinear coefficient d eff is equal to 0.32 pm@V. The experimental values of d eff are related to d 11 15 0.46 pm@V2 of quartz and are in line with the predictions.

Research paper thumbnail of Model eyes for evaluation of intraocular lenses

Applied Optics, 2007

In accordance with the present international standard for intraocular lenses (IOLs), their imagin... more In accordance with the present international standard for intraocular lenses (IOLs), their imaging performance should be measured in a model eye having an aberration-free cornea. This was an acceptable setup when IOLs had all surfaces spherical and hence the measured result reflected the spherical aberration of the IOL. With newer IOLs designed to compensate for the spherical aberration of the cornea there is a need for a model eye with a physiological level of spherical aberration in the cornea. A literature review of recent studies indicated a fairly high amount of spherical aberration in human corneas. Two model eyes are proposed. One is a modification of the present ISO standard, replacing the current achromat doublet with an aspheric singlet cut in poly(methyl methacrylate) (PMMA). The other also has an aspheric singlet cut in PMMA, but the dimensions of it and the entire model eye are close to the physiological dimensions of the eye. They give equivalent results when the object is at infinity, but for finite object distances only the latter is correct. The two models are analyzed by calculation assuming IOLs with different degrees of asphericity to elucidate their sensitivity to variation and propose tolerances. Measured results in a variant of the modified ISO model eye are presented.

Research paper thumbnail of Explanted multifocal intraocular lenses

Journal of cataract and refractive surgery, 2015

We report 2 cases in which single-piece multifocal acrylic intraocular lenses (IOLs) were explant... more We report 2 cases in which single-piece multifocal acrylic intraocular lenses (IOLs) were explanted because of complications related to the presence of glistenings in the bulk of the IOL optic. In both cases, the patients complained about blurry or hazy vision. In vivo slitlamp examinations prior to IOL explantation confirmed the presence of severe glistenings in the IOL optic in 1 case and moderate glistenings in the second case. In the first case, the symptoms resolved and both corrected and uncorrected distance visual acuities improved by 4 lines following IOL exchange with a monofocal IOL. In the second case, the visual symptoms persisted with a hard contact lens. Symptoms resolved following an exchange with a monofocal IOL that was free of glistenings. These findings indicate that straylight caused by IOLs with glistenings may be clinically significant in cases in which multifocal IOLs are implanted and patients require optimized retinal sensitivity. Mr. van der Mooren, Ms. Lan...

Research paper thumbnail of Second harmonic generation of blue light in bulk KTP by Type 1 phase matching

In this paper measurements will be presented of the conversion efficiency for second harmonic gen... more In this paper measurements will be presented of the conversion efficiency for second harmonic generation in KTiOPO4(KTP) by type 1 phase matching for different fundamental wavelengths of a modelocked picosecond Ti:sapphire laser. At a fundamental wavelength of 797 nm and an intensity of 100 MW/sq cm the conversion efficiency is found to be 1.3% and the effective nonlinear optical coefficient d(subeff) is 0.18 pm/V.

Research paper thumbnail of Apparatus, system, and method for providing an optical filter for an implantable lens

Research paper thumbnail of Ophthalmic devices, systems, and methods for optimizing peripheral vision

Research paper thumbnail of Effect of the equivalent refractive index on intraocular lens power prediction with ray tracing after myopic laser in situ keratomileusis

Journal of cataract and refractive surgery, 2015

To determine the impact of the equivalent refractive index (ERI) on intraocular lens (IOL) power ... more To determine the impact of the equivalent refractive index (ERI) on intraocular lens (IOL) power prediction for eyes with previous myopic laser in situ keratomileusis (LASIK) using custom ray tracing. AMO B.V., Groningen, the Netherlands, and the Department of Ophthalmology, Baylor College of Medicine, Houston, Texas, USA. Retrospective data analysis. The ERI was calculated individually from the post-LASIK total corneal power. Two methods to account for the posterior corneal surface were tested; that is, calculation from pre-LASIK data or from post-LASIK data only. Four IOL power predictions were generated using a computer-based ray-tracing technique, including individual ERI results from both calculation methods, a mean ERI over the whole population, and the ERI for normal patients. For each patient, IOL power results calculated from the four predictions as well as those obtained with the Haigis-L were compared with the optimum IOL power calculated after cataract surgery. The study...

Research paper thumbnail of Visualization of the retinal image in an eye model with spherical and aspheric, diffractive, and refractive multifocal intraocular lenses

Journal of refractive surgery (Thorofare, N.J. : 1995), 2008

To present a method that visually demonstrates how spherical, aspheric, diffractive, and refracti... more To present a method that visually demonstrates how spherical, aspheric, diffractive, and refractive multifocal intraocular lenses (IOLs) process light received from the cornea. Monochromatic green light was projected through an Average Cornea Eye (ACE) Model with a cornea in front of the IOL. The model simulates a human cornea with average spherical aberration and visualizes the converging bundle of light leaving the IOL. Additionally, a US Air Force target was projected through the model, and the projected (retinal) image was captured. Various IOLs of differing designs were evaluated using this test setup. Multifocal IOLs included the aspheric diffractive Tecnis ZM900 and ZMA00 lenses; the refractive ReZoom NXG1 lens; the spherical AcrySof ReSTOR SA60D3 apodized diffractive lens; and the spherical diffractive CeeOn 811E lens. Monofocal IOLs included the spherical CeeOnEdge 911A IOL and the aspheric SofPort LI61AO, AcrySof IQ SN60WF, and Tecnis Z9000 and ZA9003 IOLs. The light paths...

Research paper thumbnail of A new intraocular lens design to reduce spherical aberration of pseudophakic eyes

Journal of refractive surgery (Thorofare, N.J. : 1995)

The aim of this study was to design and evaluate in the laboratory a new intraocular lens (IOL) i... more The aim of this study was to design and evaluate in the laboratory a new intraocular lens (IOL) intended to provide superior ocular optical quality by reducing spherical aberration. Corneal topography measurements were performed on 71 cataract patients using an Orbscan I. The measured corneal surface shapes were used to determine the wavefront aberration of each cornea. A model cornea was then designed to reproduce the measured average spherical aberration. This model cornea was used to design IOLs having a fixed amount of negative spherical aberration that partially compensates for the average positive spherical aberration of the cornea. Theoretical and physical eye models were used to assess the expected improvement in optical quality of an eye implanted with this lens. Measurements of optical quality provided evidence that if this modified prolate IOL was centered within 0.4 mm and tilted less than 7 degrees, it would exceed the optical performance of a conventional spherical IOL...

Research paper thumbnail of Methods for Measuring Light Scatter in Intraocular Lenses

Frontiers in Optics 2007/Laser Science XXIII/Organic Materials and Devices for Displays and Energy Conversion, 2007

Research paper thumbnail of Combining in vitro test methods for measuring light scatter in intraocular lenses

Biomedical Optics Express, 2011

Intraocular lenses (IOLs) are designed for implantation for vision correction following cataract ... more Intraocular lenses (IOLs) are designed for implantation for vision correction following cataract removal. The IOL typically replaces a cataractous natural lens that exhibits very high levels of light scattering. The amount of scattering is significantly reduced with an IOL, though it is rarely quantified and both the surface and the bulk of the intraocular lens may contribute to light scatter at some level, and in some cases potentially affecting patients' post-operative quality of vision. The purpose of this paper is to describe two complementary in-vitro quantitative methods for measuring light scatter caused by IOLs. The first method directly measures light scatter from the lens in one plane for angles larger than two degrees. The second method measures light scatter in an eye model including the focal point out to three degrees in the image plane. The measured amount of light scatter from an IOL is typically lower than that found in healthy donor crystalline lenses of various ages that are used as a basis for comparison.

Research paper thumbnail of Effects of glistenings in intraocular lenses

Biomedical Optics Express, 2013

Glistenings consist of multiple microvacuoles in intraocular lenses (IOLs) that cause retinal str... more Glistenings consist of multiple microvacuoles in intraocular lenses (IOLs) that cause retinal stray light and may affect quality of vision. For four IOL types, the microvacuole particle size distribution and particle volume density was measured using confocal light microscopy and dark field microscopy, and the corresponding extinction coefficient γ was determined. The light scatter contribution induced by microvacuoles was measured as function of both angle and extinction, and was verified by calculations using Mie theory. Two IOL types possessed significant glistenings having stray light levels higher than that of a healthy 20 year old crystalline lens corresponding to γ ≥ 0.08 mm −1 .

Research paper thumbnail of Impact of intraocular lens material and design on light scatter: In vitro study

Journal of cataract and refractive surgery, 2014

To determine the typical in vitro straylight levels for intraocular lenses (IOLs) of different ma... more To determine the typical in vitro straylight levels for intraocular lenses (IOLs) of different materials and designs. Abbott Medical Optics, Inc., Groningen, the Netherlands. Experimental study. Two optical bench setups were used to determine baseline straylight levels of IOLs placed in a saline-filled cuvette: one for forward scatter positions between 0.6 and 3.0 degrees and one for positions up to 22.0 degrees. Line-spread functions were measured using the small-angle setup, and scattered light intensity was measured using the wide-angle setup. From these measurements, the angular dependent straylight parameter was calculated. Ten IOLs of different materials (hydrophobic and hydrophilic) and designs (monofocal or diffractive multifocal and spheric or aspheric) were studied, and their measured straylight levels were compared with the levels in a 20-year-old and a 70-year-old healthy noncataractous human crystalline lens. Irrespective of the material or design, monofocal IOLs had st...

Research paper thumbnail of Rostock Glare Perimeter

Optometry and Vision Science, 2013

Disability glare induced by headlights of oncoming cars has been associated with reduced quality ... more Disability glare induced by headlights of oncoming cars has been associated with reduced quality of vision. This study aimed at developing the Rostock Glare Perimeter to quantify dysphotopsia effects under simulated realistic conditions. Sixty phakic subjects of different ages were dazzled by a bright light source centered at a projection screen 3.30 m away from the subject's eye. Using a projected marker moving outward from the screen center with angular steps of 0.25° in 12 directions, the area where the subject cannot distinguish the white spot from the glare effects of the light source was determined. A corresponding mean radius in a field angle relative to the subject's eye was defined as a measure for disability glare. Monocular and binocular measurements were performed, and a separate repeatability and reproducibility study was executed to determine the precision of the Rostock Glare Perimeter. A significant mean positive correlation of disability glare with age (r = 0.534, p < 0.001) was found. The disability glare ranged from 0.33° to 1.8°, and a strong (r = 0.93, p < 0.0002) binocular summation effect was found. The repeatability and reproducibility limit of the Rostock Glare Perimeter method is 0.14° for 95% confidence interval. The Rostock Glare Perimeter method is sensitive to detect age-related disability glare differences and to find binocular summation for disability glare in a healthy population for small field angles with high angular resolution. These findings suggest that the Rostock Glare Perimeter method is a helpful device to quantify symptoms of glare.

Research paper thumbnail of Single shot bulk damage threshold and conversion efficiency measurements on flux grown KTiOPO4 (KTP)

Optics Communications, 1993

ABSTRACT The single shot bulk laser damage threshold was measured on thirteen different flux grow... more ABSTRACT The single shot bulk laser damage threshold was measured on thirteen different flux grown KTP crystals. The measurements were made with the KTP oriented for type II phase matched second harmonic generation (SHG) at 1064 nm. The width of the O-switched Nd:YAG laser pulses was 8.5 ns. The crystals were grown under different experimental conditions. Some of the crystals were measured topographically in order to find possible differences in the damage thresholds between different growth sectors and to check the crystals for optical homogeneity. The measured average threshold for dielectric breakdown of KTP is 31.5±4GW/cm2. Topographic measurements showed, that the samples have a good optical homogeneity with the exception of trivalent cation doped KTP. The presence of Sc3+ and Cr3+ lowers the damage threshold of KTP and areas with preferential chromium incorporation in KTP show a lowered damage threshold in comparison with areas containing less chromium. The conversion efficiency for type II phase matching of the 1064 nm beam of a Nd:YAG laser has a maximum value of 55%. The measured deff was 3.1 pm/V.

Research paper thumbnail of Vergleich der optischen Qualität der Tecnis®-Linsen mit IOLs, die die sphärische Aberration der menschlichen Kornea teilweise kompensieren

Klinische Monatsblätter für Augenheilkunde, 2007

Research paper thumbnail of Diffraktive Multifokal Tecnis ZMB00 einteilige IOL: Optische Performance und Vergleich mit anderen asphärischen Multifokal-IOL

Klinische Monatsblätter für Augenheilkunde, 2010

Research paper thumbnail of Vergleich von Dysphotopsieeffekten bei phaken und pseudophaken Augen mit dem neuen Rostock Glare Perimeter

Klinische Monatsblätter für Augenheilkunde, 2013

Pseudophakic dysphotopsia as unwanted side effect after cataract surgery are becoming increasingl... more Pseudophakic dysphotopsia as unwanted side effect after cataract surgery are becoming increasingly important. The so-called glare perimetry allows a realistic quantification of these phenomena. The article presents the method on the example of healthy subjects and pseudophakic patients. Using glare perimetry phakic and pseudophakic subjects were examined for differences in disability glare. For this, data from 60 phakic persons of different ages (45 ± 17.1 years) were used. As pseudophakic subjects 31 carriers of monofocal lenses (70 ± 6.7 years) and 25 carriers of multifocal lenses (71 ± 8.5 years) were tested. Disability glare was significantly smaller in the phakic group (1.00 ± 0.336°) than in the pseudophakic group (1.56 ± 0.622°). Among the pseudophakic eyes those with a multifocal lens (1.69 ± 0.367°) were significantly more sensitive to glare than those with a monofocal lens (1.43 ± 0.492°). Glare perimetry allows an objective quantification of effects of dysphotopsia under realistic conditions. Pseudophakic eyes show a higher sensitivity to glare than eyes with the natural clear lens. Here, eyes with multifocal lenses prove to be particularly sensitive to glare.

Research paper thumbnail of Intraocular lens designed for the newborn infant eye

Journal of Cataract & Refractive Surgery, 2001

To evaluate the effects of an intraocular lens (IOL) designed for small eyes after clear lens ext... more To evaluate the effects of an intraocular lens (IOL) designed for small eyes after clear lens extraction in an animal model. St. Erik's Eye Hospital, Karolinska Institute, Stockholm, Sweden. Clear lens extraction was performed in both eyes in 19 3-week-old rabbits. In 1 randomly selected eye of each rabbit, a small IOL with long haptics was implanted. Axial length, corneal thickness, corneal diameter, and intraocular pressure were measured preoperatively and every month for 6 months postoperatively. Six months after surgery, the wet mass of the after-cataract was determined. The IOL remained well centered in all eyes. Four animals developed severe glaucoma in 5 eyes (3 aphakic and 2 pseudophakic) soon after surgery and were excluded. In the 15 animals completing the study, signs of glaucoma evolved in 7 animals (5 aphakic and 4 pseudophakic eyes). In aphakic eyes, significant amounts of after-cataract (median 250 mg) developed in all 15 surviving animals. In pseudophakic eyes, small amounts of after-cataract (median 30 mg) were present. During the first 2 months after surgery, ocular growth was less in pseudophakic eyes than in aphakic eyes. Results indicate that implantation of a down-sized IOL with long haptics in small eyes is safe. Considerable less after-cataract was found in eyes with the IOL than in aphakic control eyes.

Research paper thumbnail of Determination of type I phase matching angles and conversion efficiency in KTP

Applied Optics, 1995

Measurements of the conversion efficiency of second-harmonic generation in KTP 1KTiOPO 4 2 by the... more Measurements of the conversion efficiency of second-harmonic generation in KTP 1KTiOPO 4 2 by the use of type I phase matching for different fundamental wavelengths of a mode-locked picosecond Ti:sapphire laser are presented. The observed phase matching angles are in agreement with the calculated phase matching curves. At a fundamental wavelength of 834 nm and an intensity of 100 MW@cm 2 the conversion efficiency is 4% at maximum, and the corresponding effective nonlinear coefficient d eff is equal to 0.32 pm@V. The experimental values of d eff are related to d 11 15 0.46 pm@V2 of quartz and are in line with the predictions.

Research paper thumbnail of Model eyes for evaluation of intraocular lenses

Applied Optics, 2007

In accordance with the present international standard for intraocular lenses (IOLs), their imagin... more In accordance with the present international standard for intraocular lenses (IOLs), their imaging performance should be measured in a model eye having an aberration-free cornea. This was an acceptable setup when IOLs had all surfaces spherical and hence the measured result reflected the spherical aberration of the IOL. With newer IOLs designed to compensate for the spherical aberration of the cornea there is a need for a model eye with a physiological level of spherical aberration in the cornea. A literature review of recent studies indicated a fairly high amount of spherical aberration in human corneas. Two model eyes are proposed. One is a modification of the present ISO standard, replacing the current achromat doublet with an aspheric singlet cut in poly(methyl methacrylate) (PMMA). The other also has an aspheric singlet cut in PMMA, but the dimensions of it and the entire model eye are close to the physiological dimensions of the eye. They give equivalent results when the object is at infinity, but for finite object distances only the latter is correct. The two models are analyzed by calculation assuming IOLs with different degrees of asphericity to elucidate their sensitivity to variation and propose tolerances. Measured results in a variant of the modified ISO model eye are presented.

Research paper thumbnail of Explanted multifocal intraocular lenses

Journal of cataract and refractive surgery, 2015

We report 2 cases in which single-piece multifocal acrylic intraocular lenses (IOLs) were explant... more We report 2 cases in which single-piece multifocal acrylic intraocular lenses (IOLs) were explanted because of complications related to the presence of glistenings in the bulk of the IOL optic. In both cases, the patients complained about blurry or hazy vision. In vivo slitlamp examinations prior to IOL explantation confirmed the presence of severe glistenings in the IOL optic in 1 case and moderate glistenings in the second case. In the first case, the symptoms resolved and both corrected and uncorrected distance visual acuities improved by 4 lines following IOL exchange with a monofocal IOL. In the second case, the visual symptoms persisted with a hard contact lens. Symptoms resolved following an exchange with a monofocal IOL that was free of glistenings. These findings indicate that straylight caused by IOLs with glistenings may be clinically significant in cases in which multifocal IOLs are implanted and patients require optimized retinal sensitivity. Mr. van der Mooren, Ms. Lan...