Biomedical subjects

C E Krakau

Publications and source records attributed to C E Krakau.

At least 19 recordsLinked to original sources

PubMed1992

Correction of optic disc measurements on fundus photographs.

If defined as diameter of image/diameter of object, the magnification M of the eye-camera system is kB, where k is a camera constant and B represents the vergence of the internal axis of the eye. The magnification may be assessed (1) from the length l of the eye, using the formula 1.336 k/(l-0.0016); (2) from the glass refraction G, using the formula kD/(1-G/D), in which D is the "normal" refractive power of the eye; or (3) from the principal point refraction A and the deviation delta D1 from the "normal" refractive power of the cornea, using the formula kD.(1 + delta B/D), where delta B = A + 0.84 delta D1. If k is 0.042 m, as in the Zeiss camera, and D is about 60 dpt, the formulas may be written as (1) M = 0.056/(l-0.0016); (2) M = 2.5/(1-0.017 G); and (3) M = 2.5.(1 + 0.017 delta B).

Fundus Oculi↗

PubMed1992

Measurement of progressive disc change in glaucoma.

We describe a videographic procedure for detecting minute changes in disc topography of glaucomatous eyes that involves measuring the displacement of selected circumlinear vessels. The problem of recognizing the difference between parallactic errors and true changes in topography is emphasized.

Female↗

PubMed1992

Calculation of the pulsatile ocular blood flow.

Based on reasonable assumptions, it is theoretically possible to determine the pulsatile ocular blood flow. The pertinent parameter is not the pulse amplitude but the steepest decay value of record (ie, the minimum of dV(t)/dt). Some advantages of developing the record in Fourier series are discussed. The importance of careful analysis of the recording system is stressed.

Blood Flow Velocity↗

PubMed1991

High frequency of asymptomatic visual field defects in subjects with transient ischaemic attacks or minor strokes.

The hypothesis that asymptomatic visual field defects can be found in patients with carotid transient ischaemic attacks (TIA) or minor strokes was tested. Twenty-two consecutive male patients with TIA and 18 patients with minor strokes from the carotid artery territory were examined by perimetry, cerebral computerised tomography and regional cerebral blood flow. Asymptomatic visual field defects were found in many TIA and minor stroke patients, 29% (5/17) and 57% (8/14), respectively (NS). Eighty-five per cent (11/13) of the scotomas were solely or predominantly located in the upper part of the visual field (P = 0.008 for absolute defects and P = 0.03 for relative defects). We conclude that both carotid territory TIA and minor stroke patients have a high frequency of asymptomatic visual field defects, predominantly located in the upper part of the visual field.

Adult↗

PubMed1991

Computerized patient record system for the glaucoma ward.

A system for computerized glaucoma patient record, developed from a data base called 'Advanced Revelation', is described. The record is made up from free text as well as from choices among listed alternatives. All data are stored on magnetic media and also printed out on paper in a well disposed and easily surveyable form. Apart from saving personnel and time in the clinical routine, the main advantages of the system is a powerful tool for clinical research. Data retrieval occurs on 'list', 'count', or 'sort' orders, facilitating retrospective studies. The system has been used for over a year at a glaucoma ward (Lund) to increasing satisfaction.

Glaucoma↗

PubMed1991

Correlations in series of perimetric performance values.

The correlation function for consecutive performance (P) values in a material of simple glaucoma is studied. The outcome of perimetry sessions recorded with about 2 min intervals are significantly correlated, whereas those obtained 2 h apart or more are not so. Partial correlations of the right and left P values as well as IOP and P value are estimated and discussed in connection with a statistical model for the sensitivity fluctuations. A slow trend, a random error component and an irregular undulation of sensitivity are discerned. The cause of the fluctuations as well as procedures for reducing the dispersion of performance values are discussed.

Glaucoma, Open-Angle↗

PubMed1991

Occurrence of disc haemorrhages in open-angle glaucoma treated with pilocarpine or timolol.

1573 examinations were performed on 397 eyes. hh was found in 55 eyes--thromboses included--at 91 examinations. Part of this material qualified for use in a comparative study with pilocarpine in 81 eyes and timolol in 82 eyes. The relative frequency of hh in the treated groups and in the pretreatment group was not significantly different from that of the whole material. No indication of pressure reduction with effect on the occurrence of hh could be detected. The average probability of hh at an examination chosen at random was 6 per cent in this material of ordinary simple and capsular glaucoma cases. The occurrence of haemorrhages in relation to age, sex, general hypertension and diabetes are discussed.

Aged↗

PubMed1989

Visual field testing with reduced sets of test points. A computerized analysis.

A computerized analysis of visual fields is described. In a second step these results are condensed into a 'reduced' set of test points so constructed that if testing is limited to 6-8 points nearly all defective visual fields would have been spotted with at least one defective point. The 'reduced' set involves the testing of few points several times in a session rather than spending very few trials on a great number of points. This is a new approach which merits further investigation.

Algorithms↗

PubMed1989

Observations concerning the course of glaucoma.

Four cases with glaucomatous damage to the optic nerve head preceding a rise in intraocular pressure from normal or borderline to high values, are reported. The question of whether such cases are exceptional or typical and, therefore, best explained by a coincidence of diseases or by one disease going through successive stages is discussed on the basis of 10 further cases from a population study. Many clinicians claim that there are two groups of patients: a large one with 'ordinary' glaucomas supposedly caused by high intraocular pressures and a small one with low tension glaucomas presumed to have low perfusion pressures for other reasons. This classification circumvents the discussion on etiology and gives theoretical support to conventional treatment. Accumulated clinical observations indicate, however, that it should not be accepted without discussion. We describe here a few selected cases with glaucomatous damage to the optic nerve head preceding a rise in the intraocular pressure from normal or borderline to high values.

Aged↗

PubMed1989

Temporal summation and perimetry.

The threshold sensitivity at perimetry was determined experimentally as a function of the exposure time of the test objects. The summation capability of the retina is expressed as a 'memory' function with approximately exponential decay. The efficient stimulus is found from the convolution integral of the functions for memory and light stimulus. The effacing of relative defects by a prolonged exposure time is explained by means of a hypothetical model, based on the rarefaction of optic-nerve fibres.

Diagnosis, Computer-Assisted↗

PubMed1988

Treatment versus no treatment in chronic open angle glaucoma.

In a controlled randomized study 15 patients (20 eyes) with chronic open angle glaucoma and visual field defects were followed by greater than 1 year, 12 of them were followed for 3 years. Half of the group were untreated controls, the other half treated with pressure reducing medical therapy. At least 5 consecutive computerized visual fields were recorded (COMPETER) on each eye, and the linear regression coefficient was calculated. With the reservation for uncontrolled compliance no significant difference in the line of favourable effect of pressure reduction could be spotted, in spite of an average pressure reduction in the treated group of 4 mmHg. More important than this result, which is open to criticism for the smallness of the material, uncontrolled compliance etc, is the lesson that a randomized experiment with treated and non-treated glaucoma cases carried out in accordance with the Helsingfors convention is hardly feasible.

Aged↗

PubMed1988

Disc haemorrhages and glaucoma in a general ophthalmic practice.

The composition of the clientele from an ophthalmological practitioner's office is described with special reference to the occurrence of glaucoma and disc haemorrhages (h in singular; hh in plural). This study could not be planned as an epidemiological survey and gives no clue to sensitivity or specificity of hh in glaucoma. During a period of about 10 years ending with 1986 there were 731 patients with h and/or glaucoma. When detected, 185 patients had h but no glaucoma, 33 had both h and glaucoma and 513 had glaucoma but no h. During the follow-up period hh were detected in 83 cases of glaucoma, and glaucoma developed in 27 cases with hh. The detection rate of hh among glaucoma was low but steady, indicating that hh may occur at any stage of the glaucoma process. This study shows no predilection for hh in cases with general hypertension or diabetes, nor is the frequency of hh among pseudoexfoliation cases significantly lower than among cases without this stigma.

Adolescent↗

PubMed1986

Hazards in evaluation of visual field decay.

To evaluate the trend in a series of observations, blurred by random fluctuations, is a problem encountered in follow-up studies of visual fields from glaucoma patients. The imminent risk of falsely estimating, say, the effects of therapy by incautious sampling and insufficient number of observations is described in the present communication.

Argon↗

PubMed1986

A system for a computer-assisted glaucoma care unit.

A computerized system for a glaucoma care unit is described. The aim is to examine and record every patient classified as a case of glaucoma in a way which permits subsequent use of the data in studies of the natural history of glaucoma. A main topic concerns the choice of those examinations, treatments etcetera which have to be included in the records to satisfy clinical and scientific requirements. The system is distensible by allowing the introduction of new parameters to be introduced. Graphic presentation of IOP and visual field development over long periods improve the surveyability to a large measure. So far about 200 patients from the glaucoma care unit have been included in the system.

Computers↗

PubMed1985

A statistical trap in the evaluation of visual field decay.

Computerized perimetry has made it possible to evaluate quantitatively the visual field decay in glaucoma and other cases. The performance fluctuates with considerable amplitude and therefore the heart of the matter concerns the detection of a signal in presence of noise. How insufficient number of observations and uncautious sampling may result in false conclusions as to the effect of therapy etc is described in the present paper.

Glaucoma↗

PubMed1979

Variability of glaucomatous visual field defects in computerized perimetry.

Normal subjects are able to maintain a stable level of performance throughout a test session of 30 min, using 0.5 s exposure time. Test points placed in normal areas of glaucoma cases behave similarly, whereas test points in relative scotomatous parts of the field show not only a lower sensitivity level but also a tendency to a decline of the performance level and/or a higher threshold variation. Change of exposure time showed remarkable effects on the performance level at defect points, an increase to 1 s causing a stabilization on an improved level and a decrease to 0.25 s giving a deterioration. The results are discussed in terms of noise admixture to the signal. According to this model an increased noise amplitude by impaired retinal function reduces the performance level and augments the variation. On the other hand, an increased exposure time of the test object, which causes a stabilization of the process on an improved performance level, may be interpreted as a reduction of the noise amplitude.

Adult↗

PubMed1979

Flicker comparison of fundus photographs. A technical note.

A method for comparison of two fundus transparencies by means of alternating flickering light is described. Spurious differences between the pictures are reduced by making the exposures in a fixed position of the pulse cycle. Small haemorrhages are readily detected. Pulse variations of the vessels and changes in size of cup and disc can be measured.

Flicker Fusion↗

PubMed1979

Automatic perimetry in a population survey.

Automatic perimetry was performed in 2998 eyes of 1511 subjects comprising 78% of all persons born 1907--1921 and resident in a certain small area. Unreliable or abnormal tests were repeated. The average number of tests per person was 2.25. About 90% of all tests in normal eyes were performed in less than 3 min. The screening was considered negative in 2887 eyes, incomplete in 20 eyes and positive in 91 eyes (3%). Eighteen of the positives were previously unknown glaucomatous defects. There was only one unexplained "false positive". We concluded that the method is quick, sensitive, specific and dependable. The apparatus is simple to manage and cheap to run.

Aged↗