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Biomedical subjects

A C Kooijman

Publications and source records attributed to A C Kooijman.

At least 19 recordsLinked to original sources
PubMed1992

Towards a classification of visual impairment.

For the rehabilitation of people with impaired vision, it is essential to have adequate (preferably quantitative) information about their residual visual functions. Special attention is given to the extra information provided by the results of measurement of the contrast sensitivity, especially in combination with the results of other measurements, such as the visual field, the amount of intraocular straylight and the visual acuity. The value of the contrast sensitivity function as a predictor of the extent of dysfunctioning in the visual activities of everyday life, such as outdoor vision, reading and recognition of faces, will be discussed. As far as this is concerned, a comparison is made between the value of visual acuity and contrast sensitivity as measures of the extent of vision and visual dysfunctioning.

Contrast Sensitivity↗
PubMed1991

Illumination research as part of a visual assessment of visually impaired individuals.

In this paper we describe a method for the preliminary assessment of the illumination needs of partially sighted individuals. The method is based on determining the smallest readable lettersize under different levels of illumination. Half of the partially sighted in our population had a performance that was dependent upon the level of illumination. At the same time, most of those for whom no improvement in performance was found, did express a preference for a certain level of illumination. Therefore, there remain discrepancies between the objectively determined optimal level and the preference for a certain level. We conclude that the current method is a useful but insufficient method of determining the illumination needs of partially sighted individuals.

Adolescent↗
PubMed1991

Lens reflectometry with a CCD video camera and computer image analysis.

Lens reflectometry is a useful method of determining the back scatter of light from the cataractous lens. Making use of normal programmes, the personal computer can be used for the quantitative determination of the lens reflex, as seen in the slit-lamp image. If three different images of the same eye are compared, it appears that the mean variation in the back-scatter readings made by our method is 8.3%.

Aged↗
PubMed1991

Prolonged electro-retinal response suppression (PERRS) in patients with stationary subnormal visual acuity and photophobia.

Neural adaptation to light stimulation in the dark-adapted retina can be demonstrated by double-flash electroretinography. The first flash is a conditioning flash, the second flash is the test flash. Interstimulus intervals are in the range of 0.2 to 30 seconds. Suppression of the response to the test flash is assumed not to be related to photopigment regeneration, as in normal human subjects the recovery after strong conditioning flashes is completed in about 2 seconds. In this paper we demonstrate the results of double-flash electroretinography on four patients, two of whom are brother and sister. Each of them showed a five- to ten-fold prolonged suppression time compared to normal measurements. Clinical aspects of all the patients were a stationary, though fluctuating, subnormal visual acuity of about 0.5, some photophobia, and difficulties in adaptation to changes in luminance levels. We assume that the PERRS indicates changes in the restorative reactions to phototransduction in the photoreceptors, or in the neural transmission mechanism, either in the rod-driven lateral inhibitory neural processes or in the cone-driven rod inhibitory processes, caused by a cone dysfunction.

Adult↗
PubMed1991

Clinical evaluation of two non-contact tonometers.

The precision and speed of two non-contact tonometers were examined and compared. The Goldmann applanation tonometer was used as the standard for precision. On the average the results obtained with the non-contact tonometers were not significantly different from those obtained with the Goldmann tonometer. The variation in the values obtained with the non-contact tonometers was greater. The speed of measurement differed between the two non-contact tonometers.

Evaluation Studies as Topic↗
PubMed1990

Clinical and physical measurements of the cataractous lens.

In connection with the clinical trial of an anti-cataract drug (Bendazac lysine) a number of examination methods were used to assess the progress of the cataract: slitlamp examination, visual acuity determination, and the measurement of the contrast sensitivity, light scatter in the eye and the autofluorescence and transmission of the lens. In this article the measurements of 43 patients (43 eyes) are presented, taken at the time that medication was started. In this way we can get an impression of the value of these measurements for the study of cataractous lenses. The contrast sensitivity of the cataractous eye is lowered for all spatial frequencies as compared with the normal population. Light scatter is greatly increased. The autofluorescent profile of the lens with nuclear cataract differs markedly from that of the lens with cortical cataract.

Aged↗
PubMed1989

Intra-ocular light scatter in pseudophakia.

In 22 patients (23 eyes), who had undergone an uncomplicated cataract extraction with implantation of a posterior chamber lens in otherwise normal eyes 11 to 44 weeks previously, the intra-ocular light scatter was measured with an IOI stray light meter. All the eyes examined had little or no after-cataract. A regression curve for stray light values in normal eyes as function of age was used as reference. The measurements show that the intra-ocular light scatter in pseudophakic eyes with little or no after-cataract increases by a factor 2. This increase must be caused by the combination implant lens-posterior capsule.

Adolescent↗
PubMed1989

Double-flash electroretinography in human eyes.

A tri-color Ganzfeld stimulator with light-emitting diodes as light sources is used to study the suppression of the second electroretinographic response in human eyes to double-flash stimulation. The mechanism suppressing the a- and b-waves of the response to the second (test) flash has a scotopic spectral sensitivity to the first (conditioning) flash. Responses to mild test stimuli are more sensitive to suppression by a conditioning flash than responses to strong test stimuli.

Color Perception↗
PubMed1986

A tricolor light source for stimulation and adaptation in electroretinography.

A Ganzfeld light source, fitted on an electroretinogram contact lens, is described. The light source can provide blue, green, or red flashes with intensities over a range of 3.6 log units. It can also be used to provide a continuous light-adapting background in each of the above-mentioned colors, simultaneously presenting the possibility of emitting flashes. The control unit and the light source can be powered by a small battery pack.

Adaptation, Physiological↗
PubMed1986

Minimum procedures for visual electrodiagnostic testing.

A set of procedures for the electroretinogram, electrooculogram, and pattern and luminance visual evoked cortical potentials was defined by representatives from all Dutch University Eye Clinics in order to promote standardization of procedures for routine diagnostic testing. The procedures have been selected to obtain an answer to most electrodiagnostic questions of frequent occurrence with a minimum of equipment and examination time. An individual examiner may add other procedures to the proposed program to extend and diagnostic possibilities.

Electrodiagnosis↗
PubMed1986

Ganzfield light distribution on the retina of human and rabbit eyes: calculations and in vitro measurements.

Retinal illumination was measured in 3 excised human eyes and 14 excised rabbit eyes. The eyes were exposed to Ganzfeld illumination. Illumination was measured at three or four peripheral points at eccentricities up to 60 deg (human) or 90 deg (rabbit). Theoretical light-distribution curves were calculated from eye model data. Theoretical and experimental results for rabbit eyes agree within experimental errors. The experimental curve for human eyes shows a slightly steeper descent toward the periphery than the theoretical curve. Retinal illumination decreases only gradually toward the periphery in both human and rabbit eyes.

Animals↗
PubMed1986

The homogeneity of the retinal illumination is restricted by some ERG lenses.

Are all types of available electroretinographic contact lenses suited for Ganzfeld stimulation? To answer this question, calculations have been made of the retinal light distribution with several types of ERG lenses placed on a theoretical eye. The results make possible a division of the ERG lenses into three categories. Category 1: Lenses with which the homogeneity of the retinal illumination is nearly perfect and independent of pupil size. These lenses are especially well designed for Ganzfeld electroretinography. Category 2: Lenses which illuminate a large retinal area but with which the light distribution depends on the size of the pupil. The suitability of these lenses is questionable, because Ganzfeld electroretinography is used in order to obtain a homogeneous retinal light distribution under most conditions. Category 3: Lenses with which the size of the illuminated retinal area changes strongly with the size of the pupil. These lenses are unsuitable for Ganzfeld electroretinography.

Animals↗
PubMed1983

Fluoro-photometry in myotonic dystrophy.

We found pigment alterations in the anterior segments of the eyes of patients with myotonic dystrophy. We therefore performed fluoro-photometry in a group of ten myotonic patients and the results were compared with those of a group of normal persons. The fluorescence levels in the aqueous and vitreous of the myotonic eyes appeared to be two or three times higher than in the normal eyes. This brings us to the conclusion that myotonic eyes have a defect in the blood-ocular barriers.

Aqueous Humor↗
PubMed1983

Light distribution on the retina of a wide-angle theoretical eye.

In a theoretical eye with spherical and aspheric surfaces, the retinal illumination is calculated if a Ganzfeld luminance field is used. The resulting retinal light distribution is nearly homogeneous over the whole retina. The homogeneity is not much influenced by the size of the optical surfaces. The corresponding retinal area and the luminous flux entering the eye are calculated as functions of the size of the visual field. The values of the length of the light path through the crystalline lens and of the angle of incidence on the retina are described as functions of the angle in the visual field.

Humans↗
PubMed1978

Pathological-optic approach of cataract and lens.

By weighing cataractous lenses and by scanning lenses of patients with acute diabetes with an ultrasonic A scan, it is made probable that hypermetropization in those cases is to be atributed to alterations of the refractive index of the lens.

Acute Disease↗
PubMed1978

[Fixing the time and date of photograph (author's transl)].

A system is described to obtain on photographs and slides an automatic printout of patient number, eye and time. The time is recorded in minutes, seconds and tenth of seconds or in minutes and seconds. The time-recording can be switched off if only patient and eye identification is needed.

Documentation↗