A wide-angle, high-power negative contact lens was designed for observation and coagulation of the retina and choroid. The new contact lens has a lateral magnification of 0.44 and a field of view of 64 degrees. Due to the prismatic of its biconcave structure, the field of view may be shifted by tilting the lens, induced eye movements beyond the equator of the retina, or both. Because only a negative refractive surface is required, optical aberrations are significantly reduced. Safety during laser irradiation tasks is increased compared with the use of positive wide-angle contact lenses because the irradiance of the crystalline lens is significantly reduced.

In adults with familial hypercholesterolaemia (FH), cholesterol lowering with statins has been shown to improve the endothelial function, a hallmark of early atherogenesis. Currently, therapeutic options for treating high cholesterol levels in FH children are limited. Plant sterols safely and effectively reduce serum cholesterol concentrations by inhibiting cholesterol absorption. Therefore, we evaluated the effect of plant sterols on cholesterol and vascular function in prepubertal children with FH. We included 41 children (5–12 years old) with FH in a double-blind crossover trial using spreads containing 2.3 g of plant sterols (mainly sitosterol and campesterol) per 15 g spread and a placebo spread for a 4-week period, separated by a 6-week washout period. Lipid levels and endothelial function were assessed after both 4-week treatment periods. Endothelial function was assessed as flow-mediated dilation (FMD) of the brachial artery using a wall tracking system. Data were compared to those of 20 healthy controls. Intake of 2.3 g plant sterols per day decreased total cholesterol (-11%) and low-density cholesterol (-14%) as compared to placebo spread in FH children. FH children treated with placebo spread were characterized by an impaired FMD compared to healthy control children (7.2 %± 3.4% versus 10.1%±4.2%, p < 0.005). However, the reduction of LDL in FH children did not improve FMD (placebo: 7.2% ± 3.4% versus plant sterols: 7.7% ± 4.1%). In conclusion, the present study shows a clear reduction of LDL cholesterol by plant sterol treatment. However, short-term plant sterol treatment does not improve the endothelial function in FH children.

BACKGROUND AND OBJECTIVE:To show that sclerostomy, a glaucoma filtering surgery, can be performed using an Er:YAG laser. Scarring at the filtering site, a recurrent problem, may be reduced through proper positioning of the sclerostomy by using an intraocular endoscope. MATERIALS AND METHODS:Ab interno full-thickness sclerostomies were performed on eye bank eyes with an Er:YAG laser through a custom made optical delivery system. The intraocular laser probe consisted of a low OH silica fiber inserted in a metallic tapered sheathing. A rigid intraocular endoscope based on gradient-index lenses allowed visualization of the filtration site. RESULTS:A clear view of the anterior chamber angle was obtained through the endoscope, allowing for precise location of the sclerostomy. Full-thickness sclerostomies could then be performed at the desired location. Histologic sections showed thermal necrosis less than 50 microm thick in tissue adjacent to the sclerostomy. CONCLUSIONS:A sclerostomy performed with a combined procedure using an Er:YAG laser and intraocular endoscopy increases the speed of the procedure. The use of a high-resolution intraocular endoscope may increase the success rate of ab interno laser glaucoma surgeries.

PURPOSE Acute white-light damage to rods depends on the amount of rhodopsin available for bleaching during light exposure. Bleached rhodopsin is metabolically regenerated through the visual cycle involving the pigment epithelium, or photochemically by deep blue light through photoreversal of bleaching. Because photoreversal is faster than metabolic regeneration of rhodopsin by several orders of magnitude, the photon catch capacity of the retina is significantly augmented during blue-light illumination, which may explain the greater susceptibility of the retina to blue light than to green light. However, blue light can also affect function of several blue-light-absorbing enzymes that may lead to the induction of retinal damage. Therefore, this study was conducted to test whether rhodopsin and its bleaching intermediates play a role in blue-light-induced retinal degeneration. METHODS Eyes of anesthetized rats and mice that did or did not contain rhodopsin were exposed to green (550 +/- 10 nm) or deep blue (403 +/- 10 nm) light for up to 2 hours. Rats with nearly rhodopsinless retinas were obtained by bleaching rhodopsin in animals with inhibited metabolic rhodopsin regeneration-that is, under halothane anesthesia. In addition, Rpe65(-/-) mice that are completely without rhodopsin were used to test the susceptibility to blue-light damage of a rodent retina completely devoid of the visual pigment. Effects of illumination on photoreceptor morphology were assessed 24 hours or 10 days thereafter by morphologic and biochemical methods. RESULTS Exposure to blue light resulted in severe retinal damage and activation of the transcription factor AP-1 in rats. In contrast, green light had no effect. When rhodopsin was almost completely bleached by short-term green-light exposure while metabolic regeneration (but not photoreversal) was prevented by halothane anesthesia, blue-light exposure induced distinct lesions in rat retinas. When both metabolic rhodopsin regeneration and photoreversal of bleaching were almost completely inhibited, blue-light exposure caused only very moderate lesions. When mice without rhodopsin were exposed to blue light, no damage occurred, in contrast to wild-type control mice. CONCLUSIONS Short time exposure to blue light has deleterious effects on retinal morphology. Because damage was observed only in the presence of the visual pigment, blue-light-induced retinal degeneration is rhodopsin mediated. Absorption of blue light by other proteins is not sufficient to induce light damage. Photoreversal of bleaching, which occurs only in blue but not in green light, increases the photon-catch capacity of the retina and may thus account for the difference in the damage potential between blue and green light.

Background: The physical laws are considered that need to be taken into account for optimal photothermal treatment of solid and vascular tumors, as well as other vascular anomalies of various etiology of the retina and choroid. Optimal irradiation therapy should take into account the distribution of both radiant and thermal energy in tumors, such as retinoblastomas, malignant melanomas and vascular malformations. Strict confinement of the extent of photothermal damage is critical since such pathological entities are frequently located close to the macula or optic nerve head. Methods: A formal treatment of the optical quantities related to these requirements is presented. In this analysis we emphasize the following topics: Arrhenius’ law, the kinetics of protein denaturation, the electromagnetic radiation field, wavelength, laser pulse duration (exposure time), optical properties of tissue, photocoagulation and thermotherapy.

There are reasons to classify a number of apparently disparate diseases as "condensation" (or molecular aggregation) diseases. Examples of such condensation diseases include the late phase of diabetes mellitus, Alzheimer's disease and others. With an expanding knowledge, the list of these diseases is likely to increase. We shall describe the underlying common mechanisms, the aim being to find anticataractogenic drugs based on this insight. The common, most important denominator of various clinically differing condensation diseases derives from the interaction of the macromolecules which is in part attractive and in part repulsive. Aggregation resp. clumping of the macromolecules of the crystalline lens, the reasons for light scattering, may be prevented by introducing a number of molecules of various designs into the original macromolecular complex which reduce the tendency of aggregation. Cataract inhibitors of this category may be regarded as effective if they are able to increase the time constant of the normal aging process (i.e. the increment of scatter) by about 20%.

There are reasons to classify a number of apparently disparate diseases as "condensation" (or molecular aggregation) diseases. Examples of such condensation diseases include the late phase of diabetes mellitus, Alzheimer's disease and others. With an expanding knowledge, the list of these diseases is likely to increase. We shall describe the underlying common mechanisms, the aim being to find anticataractogenic drugs based on this insight. The common, most important denominator of various clinically differing condensation diseases derives from the interaction of the macromolecules which is in part attractive and in part repulsive. Aggregation resp. clumping of the macromolecules of the cristalline lens, the reasons for light scattering, may be prevented by introducing a number of molecules of various designs into the original macromolecular complex which reduce the tendency of aggregation. Cataract inhibitors of this category may be regarded as effective if they are able to increase the time constant of the normal aging process (i.e. the increment of scatter) by about 20%.

In endoscopic ophthalmic procedures care has to be exercised that the retina is protected from overexposure. Accordingly, it is advantageous if the endoscope is equipped with a stable and reliable automatic illumination control. To this end, an illumination control system has been devised, which consists of a mechanical iris and a digital control algorithm. The iris is designed such that it influences neither the spectral composition of the lightsource nor its aperture. It is furthermore linear with respect to the light intensity such that a fast control algorithm based on the data of a digital video camera used for observation purposes can be implemented. In order that no false signals are induced from specular reflections caused, e.g., by operating tools held in front of the camera, the control algorithm is designed such that reflections and true overexposure are distinguished from each other. For this purpose, the field of view is subdivided into small sectors and a statistical evaluation is made. The application under realistic conditions shows that the unit provides the user with a well illuminated image while the retina is reliably protected from overexposure.

The surgical techniques proposed to restore accommodation past the onset of presbyopia can be categorized in two classes, those based of scleral expansion and those based on intraocular lens implantation and lens capsule refilling. This paper describes and discusses the different techniques and summarizes the results of clinical and experimental animal trials. Restoration of accommodation has been demonstrated by at least two different teams in non-human senile primates using modifications of the lens capsule refilling technique originally described by Julius Kessler in the late fifties. The advent of recent advances in microsurgery, devices, and injectable polymers are very promising and human clinical trials may soon be envisaged.

PURPOSE:To determine whether blue light induces photoreversal of rhodopsin bleaching in vivo. METHODS:Eyes of anesthetized albino rats were exposed to either green (550 nm) or deep blue (403 nm) light, and the time course of rhodopsin bleaching was determined. Rhodopsin was isolated from whole retinas by detergent extraction and measured photometrically. To inhibit photoreversal of bleaching, rats were perfused with 70 mM hydroxylamine (NH(2)OH), a known inhibitor of photoreversal. To determine whether blue-absorbing, photoreversible photoproducts were formed, rhodopsin was bleached to near completion with green light and then exposed to blue light. Finally, experimental results were simulated on a computer by means of a simple, three-component model involving a long-lived photoreversible photoproduct. RESULTS:Photoreversal of bleaching in blue light occurs in vivo as evidenced by the following: In the absence of NH(2)OH, bleaching of rhodopsin by blue light was slow and complex. In the presence of NH(2)OH, however, blue light bleached rhodopsin very fast with a simple, pseudo-first-order kinetic. A long-lived bleaching intermediate produced by green light exposure was photoreversed to rhodopsin by exposure to blue light. The three-component computer model, invoking a blue-absorbing, photoreversible, long-lived intermediate accurately described the data. CONCLUSIONS:Because of the instantaneous, nonmetabolic regeneration of rhodopsin by the process of photoreversal of bleaching, blue light exposure permits the absorption of large numbers of photons by rhodopsin and by a photoreversible intermediate of bleaching in vivo. These data may have an important impact on resolving mechanisms of blue light-mediated damage to the retina.

Currently over 50 kinds of intraocular lenses (IOLs) are approved for patient use in the treatment of cataracts and ametropia. These lenses are manufactured from at least 2 kinds of silicones as well as several kinds of acrylic polymers including polyHEMA, Poly HOXEMA, a range of polymethacrylate and polyacrylate formulations. We sought to measure spectral transmission curves of a range of IOLS in the UV-visible and near IR spectral regions in order to better characterize their optical properties and to provide a baseline from which to assess their alteration following implantation over time. Consideration of how this may best be achieved are discussed. The variable ability of both explained IOLs and some samples from a range of manufacturers to block UV wavelengths is commented upon.

Purpose The electroretinogram (ERG) is an appropriate method to evaluate the retinal function in a variety of animal models. In this study we present suitable conditions of stimulation and recording in the dark-adapted mouse.Methods Mice (n = 15) were dark-adapted during 14 hours and anesthetized with a single intraperitoneal injection of xylazine/ketamine. Pupils were dilated and a d.c.-silk-silver electrode or a AgCl-contact-lense electrode was placed on the cornea. The electroretinogram (ERG) was obtained by Ganzfeld stimulation over a range of 6 log units of intensity (8 x 10(-2) - 8 x 104 cd/m(2)). Intensity, duration and the intervall of the light stimuli were varied separately.Results Reproducible values of the intensity-response functions are obtained for the a-, b- and c-waves of the ERG under well controlled adaptation- and stimulus-conditions. C-wave amplitudes are best evaluated using d.c.-recording and a stimulus duration of 4 seconds. The position of the d.c.-silk-silver electrode on the cornea can affect the ERG-amplitudes. Using a contact-lense electrode, the recorded b-wave amplitudes are on average 20% below these recorded with a centrally positioned d.c.-silk-silver electrode. Stimulus-intervalls of at least 60 seconds are recommended at high intensities.Conclusions An unequivocal assessment of retinal function requires reproducible ERG-values over a wide range of intensities. To obtain these, well controlled and standardized experimental conditions are required.

glasses have been proposed 17-1 11. In all such designs, it can be seen that rays are passing throughthe cornea at large angles of incidence. Therefore, not only should spherical aberration be consideredbut also astigmatism of oblique incidence. In close similitude with astigmatism of toric surfaces, aStUrm's conold is produced in this case, with two focal lines perpendicular to each other and a circle

BACKGROUND AND OBJECTIVE The purpose of this experiment was to compare biconcave contact lenses with other contact lenses already used for observation and irradiation of the retina and choroid. MATERIALS AND METHODS The optical performance of different biconcave lenses is described in terms of magnification, resolution, and field of view. The optical properties of the eye were taken into account using the Gullstrand's model of the human eye. RESULTS The performance of biconcave contact lenses represents a compromise between that of Goldmann's and wide angle indirect contact lenses. An upright image, with good peripheral image quality and an intermediate field of view is characteristic of such design. In addition, laser irradiation with large spot sizes is less hazardous when using such negative contact lenses compared to positive lenses of the same absolute refractive power. CONCLUSIONS Biconcave contact lenses qualify as a complement to planoconcave lenses for chorioretinal observation and irradiation tasks. For the same magnification factor, the field of view is smaller than that obtained with indirect contact lenses but the image degradation in the periphery of the retina is reduced.

PURPOSE:The electroretinogram (ERG) is an appropriate method to evaluate the retinal function in a variety of animal models. In this study we present suitable conditions of stimulation and recording in the dark-adapted mouse.METHODS:Mice (n = 15) were dark-adapted during 14 hours and anesthetized with a single intraperitoneal injection of xylazine/ketamine. Pupils were dilated and a d.c.-silk-silver electrode or a AgCl-contact-lens electrode was placed on the cornea. The electroretinogram (ERG) was obtained by Ganzfeld stimulation over a range of 6 log units of intensity (8 x 10(-2) - 8 x 104 cd/m2). Intensity, duration and the interval of the light stimuli were varied separately.RESULTS:Reproducible values of the intensity-response functions are obtained for the a-, b- and c-waves of the ERG under well controlled adaptation- and stimulus-conditions. C-wave amplitudes are best evaluated using d.c.-recording and a stimulus duration of 4 seconds. The position of the d.c.-silk-silver electrode on the cornea can affect the ERG-amplitudes. Using a contact-lens electrode, the recorded b-wave amplitudes are on average 20% below those recorded with a centrally positioned d.c.-silk-silver electrode. Stimulus-intervals of at least 60 seconds are recommended at high intensities.CONCLUSIONS:An unequivocal assessment of retinal function requires reproducible ERG-values over a wide range of intensities. To obtain these, well controlled and standardized experimental conditions are required.

Endoscopes are key elements in the application of minimally invasive medical procedures. Thereby, image quality, ease of application and safety are of decisive importance for the user. This communication is primarily concerned with aspects relating to image quality. Standard television technology is presently used in endoscopes for image presentation purposes. It is however shown, that the inherent optical quality of most endoscopes exceeds the performance of standard TV. Accordingly, a special purpose advanced digital television system exhibiting true colour performance has been developed. Since endoscopic images usually are circular, its aspect ratio is quadratic with a spatial resolution of 1000 x 1000 pixels. It has furthermore a temporal resolution of 1 to 30 Hz noninterlaced and a contrast resolution of 56.6 dB. The design and performance of the system is documented.

Purpose: In scanning photorefractive keratectomy, the corneal surface is reshaped by laser ablation with a scanning beam for the correction of myopia or astigmatism. A precise knowledge of the volume of corneal tissue removed by each laser pulse is necessary to be able to develop accurate ablation algorithms for scanning photorefractive keratectomy. The purpose of this study was to measure the ablation per pulse created on PMMA surfaces with a Q-switched frequency-quintupled Nd:YAG laser emitting at 213 nm. Methods: A frequency-quintupled Nd:YAG laser emitting at: 213 nm with a pulse duration of 5 ns and a pulse energy of 1.2 to 1.5 mi was used. The laser beam was focused on the surface of PMMA blocks and ablation craters were produced with 10, SO and 100 pulses. The shape of the ablation craters was measured with an optical profilometer and compared with the beam profile measured with a laser beam diagnostic system. Results: The beam intensity distribution in the near-field consisted of two quasi-Gaussian peaks. The ablation craters contained two peaks. Assuming a Gaussian intensity distribution, the ablation per pulse in PMMA at 213 nm can be modeled by a parabolic function Conclusions: Optical profilometry can be used to accurately measure, the ablation per pulse and evaluate the homogeneity of the beam.

Purpose. The goal of the study is to measure the group refractive index of the human cornea in vitro to improve the accuracy of corneal thickness measurements Methods Corneal buttons were trephined from 23 human cadaver eyes and the group refractive index of the cornea was measured at lambda = 840 nm using a low-coherence Michelson interferometer and the technique proposed by Sorin and Gray (Phot. Tech. Left. 4:105-107, 1992). The effect of dehydration on the measurement was studied by measuring the corneal optical thickness as a function of time. Results. Preliminary measurements of the group refractive index at 840 mn gave n(g) = 1.450 +/- 0.024 for the human cornea, which is much higher than a calculated group refractive index of n(g) = 1.387. Because of dehydration, the optical thickness of the cornea decreased at a rate of 5.5 mu m/min which led to an artificially high value for the group refractive index. Conclusion The calculated group refractive index of n(g) = 1.387 appears to be an accurate value for the purpose of corneal thickness measurements using low-coherence interferometry, and corneal group refractive index measurements can be performed in vitro if the measurements are performed rapidly to avoid the effect of dehydration.

Over the past years ophthalmic endoscopes with intraocular diameters as small as 0.89 mm have been developed for the observation of certain internal structures of the eye which cannot be easily visualized through conventional slit lamp/microscope arrangements. Unlike other observation systems, endoscopes feature a magnification factor that increases as their distal part nears the object to be observed. Consequently, an endoscope can also be of help as a high magnification microscope. Such an instrument has been enhanced for this purpose and is described.