Acta ophthalmologica. Supplement最新文献

The purpose of the present study was to establish a method for objective measurements of visual readaptation after flash exposures and to define a model for measurements. Influences of target direction, luminance and velocity on optokinetic nystagmus (OKN) were investigated under scotopic conditions. Visual readaptation was measured using OKN as an indicator of visual perception after exposure to a flash. The interval between the triggering of the flash and the reoccurrence of OKN was defined as the visual readaptation time (RAT). A Goldmann perimeter hemisphere was used for flash stimulation. A horizontally moving vertical grating projected inside the hemisphere was used as the OKN stimulus. Eye movements were recorded by DC electrooculography (EOG). The dependence of RAT on the dose of the flash, the wavelength of the flash and the luminance of the OKN target were investigated. The precision of the measurement method was studied. This includes the analysis of the variance due to the experimental occasions, the repeated exposures, the sexes of the subjects, the methods for recognition of OKN and the ways of visual adaptation before measurements. The contributions of retinal receptor and the neural activity to RAT were investigated by electroretinography (ERG). The influences of target direction and luminance on binocular motion perception and OKN as well as monocular OKN were examined at various target velocities. The dependence of the frequency and amplitude of eye jerks during monocular OKN on target luminance and velocity were also examined. It was found that RAT increases with increasing doses of the flash or decreasing luminance of the grating. RAT is most extended after flashes near 520 nm. RAT does not differ between experimental occasions, between a manual and a semi-automatic method for recognition of OKN, between the sexes and between goggle adaptation and ordinary dark adaptation. There is a reduction of RAT due to repeated flash exposures. The data collected indicate that a well-defined model is crucial for measurements of RAT. The measurement of ERG showed that RAT is mediated by both retinal receptor and the neural activities. The receptor component depends on the wavelength of the flash while the neural component is wavelength-independent. Moreover, it was found that motion perception and OKN gain does not differ between right and left target directions. For a given target velocity, motion perception and OKN gain under both binocular and monocular viewing conditions increase with increasing luminance of the target with an exponential decay. The maximum OKN gain decreases as target velocity increases.(ABSTRACT TRUNCATED AT 400 WORDS)

The measurement of fluorescence in the human eye can be made using relatively simple instruments. Fluorescence is evoked when illumination is absorbed by intrinsic fluorophores in the eye or by artificially introduced extrinsic fluorophores. Intrinsic fluorescence is evidence of important molecular characteristics of the ocular tissues, whereas the extrinsic fluorophores are used primarily in the study of the barriers between the anatomical and physiological compartments of the eye. Blood-retina barrier leakage of fluorescein can be examined after the intravenous injection of fluorescein by quantitative determination of fluorescence in plasma and in the vitreous. From these measurements of the distribution of fluorescein, the permeability of a hypothetical spherical interface between the blood and the retina can be estimated using a mathematical model of the barrier. The use of fluorescein as a tracer is problematic because of its rapid metabolic conversion to fluorescein glucuronide. This metabolite disturbs ocular fluorescence measurements because it fluoresces over the same part of the spectrum as the parent compound. Additionally, the glucuronide occurs in markedly different concentrations depending upon the patient's renal function. With the previously used fluorometry techniques it has been impossible to determine the contribution of fluorescein glucuronide to the vitreous fluorescence. The primary objective of the studies described in this thesis was to develop a method for the determination of fluorescein and fluorescein glucuronide in the human eye and in plasma, and to calculate the blood-retina barrier permeabilities of the two substances. The necessary methodological improvements included a detailed description of the geometrical optics of the eye and the optical filter properties of the lens. A new method was developed for the determination of the spatial locations of ocular fluorescence measurements and the intrinsic lens fluorescence was used to estimate lens transmittance. The new techniques were applied to clinical studies in patients with diabetic retinopathy. It was shown that in insulin-dependent diabetes mellitus, the apparent rate whereby fluorophores are accumulated in the lens is increased in inverse proportion to the quality of metabolic control, i.e. patients who have had consistently poor control have higher fluorescence than patients who have been in good control. An increase in lens fluorescence was also found in the presence of diabetic nephropathy. The results support the assumption that lens fluorometry can provide a rough estimate of cumulative glycaemia and that glucose is involved in certain age-related changes in the lens.(ABSTRACT TRUNCATED AT 400 WORDS)

Retinopathy of prematurity (ROP) is a leading cause of severe visual impairment and blindness in infancy. Transscleral cryotherapy has been shown to be effective in arresting the progression of ROP into the sight-threatening fibrovascular stages of the disease. It is currently recommended that all eyes reaching 'threshold' ROP should be treated. If both eyes of an infant reach 'threshold', both eyes should be treated. For centers that handle a limited number of infants with ROP it is suggested that the cryotherapy should be done under general anesthesia.

Unlabelled: INTRODUCTION AND HYPOTHESES: Exposure to short-wave optical radiation is a potential hazard for vision. In the present study, blue-light damage is studied in rat retina. It was hypothesized that the absorption of blue light by cytochrome oxidase in rat retina inhibits this enzyme, and may reduce the retinal oxidative metabolism. Irreversible inhibition of the oxidative metabolism may decrease the activity of the Na/K-ATPase, hence redistribute ions, increase intracellular osmotic pressure and cause cellular edema. Severe retinal edema may be the cause of retinal degeneration.

Methods: A quantitative histochemical method, a combination of histochemical staining and densitometrical measurement, was established to measure the activity of cytochrome oxidase. The distribution of chlorine and potassium in rat retina was estimated with a nuclear microprobe. Microradiography was adopted for measuring the protein and lipid density, which is an indirect estimation of retinal edema and retinal refractive index. The damage to the photoreceptor cells was estimated from the thickness of the outer nuclear layer.

Results and conclusions: Blue light inhibited cytochrome oxidase at a retinal dose of about 110 kJ/m2. This inhibition was reversible, and is probably related to the light regulation of retinal metabolism. At a retinal dose of about 380 kJ/m2, the inhibition of cytochrome oxidase was followed consecutively by a probable redistribution of chlorine and potassium in the inner and outer segments, damage to the mitochondria in the inner segments, edema in the inner and outer segments, and progressive degeneration of photoreceptor cells. Dark adaptation did not increase the blue-light retinal injury. These findings support the hypothesis that inhibition of cytochrome oxidase is one of the causes of blue-light retinal damage. The alteration of enzyme kinetics after in vitro exposure to short-wave optical radiation was estimated using lactate dehydrogenase as a model. The ultraviolet-radiation exposure inhibited lactate dehydrogenase with a significant decrease in maximal velocity, while Michaelis constant remained unchanged.

Registration of visual impairment is compulsory in Denmark for the age group 0-17 years. With birth years 1974-91 141 subjects were in the register with retinopathy of prematurity as basic disease, giving a frequency of 13.1 per 100 000 liveborn. Compared with other countries this is a high figure, and the trend over the period is a slight annual increase. Further analysing the data for trends in time the material was subdivided chronologically into thirds, each group comprising 47 subjects. Birth weight and gestational age showed a decline: median values in the three groups were 1250, 1100, and 960 g, and 30, 28, and 27 weeks, respectively. Associated CNS handicaps were recorded in 17, 38, and 34%. Visual impairment was serious in all groups, the median corrected acuity of the better eye being below 1/60. Geographically there was a striking shift towards a Copenhagen area preponderance of heavy ROP cases, with one of the two NICUs to account for the main part of registered cases in the most recent period.

In a group of infants and children of very preterm delivery (gestational age 30 weeks or less, n = 411, Rigshospitalet Copenhagen 1983-89) 13 got blind due to retinopathy of prematurity (3.2%) while another 13 with sequelae retained useful vision of at least one eye. One child later acquired bilateral retinoblastoma, with a free interval of one year from a protracted course of ROP stage 2-3 eventually to regress. The 411 surviving subjects being recruited from a total of 515 of a similarly low gestational age, the survival rate in the 7-year period under study was just below 80%. No doubt, the high survival rate in this very pre-term group is of importance for the risk of developing retinopathy of prematurity, but the role of the ophthalmologist in controlling the infants is also emphasized. Generally, stricter observation schemes are recommended. Probably, the ROP frequency in the sample of 23.6% is an underestimate.

Data concerning observation of 40 pre-term infants referred to the Copenhagen University eye clinic 1986-91 for evaluation of ROP, predominantly of advanced stages, have been analysed. Twenty-one eyes in 13 subjects underwent cryotherapy at stage 3 (-4), on day 50-172 after delivery (median 72 days). Out of 19 eyes available for follow-up 10 obtained good of fair function; nine eyes ended with no L. Four subjects with ROP stage 4-5 at referral underwent vitrectomy and one trabeculectomy, all in eyes where surgery on beforehand was considered palliative or 'mainly experimental'. No indication for therapy was recorded in 22 infants; they mainly appeared for evaluation rather late in the course of ROP, to have the feasibility of reconstructive anatomy considered. The mean age of the infant at first discovery of ROP was 55 days when only stage 1-2 was found, 63 days when stage 3, and 69 days when at least stage 4 was described. Altogether, the range was 30-100 days. The inhomogeneity of the data is stressed. Though the possible benefit of earlier recognition cannot be proven, the investigation clearly indicates the need of uniform observation schedules nationwide and clearer indications for referral to the vitreo-retinal department.