C. E. T. Krakau

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 ΔD1 from the “normal” refractive power of the cornea, using the formula kD · (1 + Δ B/D), where ΔB = Δ + 0. 84 ΔD1. 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 + 0.017Δ B).

Regression analysis of the central visual field in chronic glaucoma cases. A follow-up study using automatic perimetry.

90 glaucoma cases (160 eyes) with field defects in at least one eye have been subjected to automatic perimetry on at least 5 occasions. The condition of the fields is summarized in single numbers. Regression analysis has been applied to series of such performance numbers. The trend of the development of the field defect is represented by the regression coefficient. The frequency distribution of the coefficients in groups based on references to age, sex, intraocular pressure, exfoliations, haemorrhages and therapy illustrates the possible importance or insignificance of these factors to the decay. The need for several consecutive examinations to establish with some significance a progression of field defects is demonstrated.

Disc haemorrhage and glaucoma.

The present material comprises 51 patients with at least one disc haemorrhage in at least one eye. A total of 127 hh were observed. The probability of finding a disc h increases with the number of examinations. The hypothesis that hh occur in all cases of glaucomatous destruction of the papillary tissue cannot be rejected, though not proven. H. seems to be connected with progression of field defects, though its effects are not immediately recognized. H. is detectable very early in the glaucomatous process; the denotation ‘forerunner’ is most likely justified. Hh. are highly specific for a glaucomatous process, but it has not been possible to connect h. with some clearly delimited group of glaucoma.

SOME ESSENTIAL OPTICAL FEATURES OF THE ZEISS FUNDUS CAMERA

The imaging system of the Zeiss fundus camera comprises a front lens and a mirror with a central opening in the anterior focus of a camera objective. Focusing is achieved by changing the distance between the film and the camera objective. The principal point of the examined eye is imaged in the central opening of the mirror when the camera is correctly positioned. By applying reasoning current in elementary geometrical optics it was found

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. Gesunde Probanden zeigen bei der Perimetrie bis zu einer Untersuchungszeit von 30 min nur unbedeutliche Änderung der Schwellenwerte der Netzhautempfindlichkeit bei einer Darbietungszeit der Stimuli von 0.5 s Testpunkte im gesunden Gesichtsfeldbereich von Glaukompatienten verhalten sich ähnlich, während Testpunkte im Bereich relativer Gesichtsfeldausfälle nicht nur geringere sondern auch eine abnehmende Empfindlichkeit und/oder eine größere Variabilität der Schwellenwerte aufweisen. Eine Veränderung der Darbietungszeit zeigte einen erheblichen Effekt auf den Schwellenwerten bei relativen Skotomen; eine Zunahme der Darbietungszeit auf 1 s zeigte eine Stabilisierung auf erhöhter Empfindlichkeit, eine Abnahme der Darbietungszeit auf 0.25 s ergab eine starke Verschlechterung. Die Ergebnisse werden diskutiert unter dem Aspekt der Informationsübertragung unter Beimengung von Rauschen. Nach diesem Modell könnte eine vergrößerte Amplitude des Rauschens bei herabgesetzter Netzhautfunktion eine Verschlechterung des Schwellenwertes und die größere Variabilität bedingen. Anderseits kann die verlängerte Expositionszeit mit einer Stabilisierung des verbesserten Schwellenwertes als eine Reduzierung der Rauschen-Amplitude gewertet werden.

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.

Visual field decay in normal subjects and in cases of chronic glaucoma

Visual field information obtained with the automatic Computer-Perimeter (‘Competer’) can be condensed into a single numerical value. This performance measure was applied to a normal population to determine the physiologic decay of retinal sensitivity with aging. Further, the development of this performance measure was followed in 54 glaucoma eyes which were divided into three groups: Untreated, treated with satisfactory intraocular pressure (IOP) regulation, and treated with unsatisfactory IOP regulation. All eyes were examined perimetrically on at least three separate occasions. Decaying performance measures were found in the preponderance of glaucoma eyes. Therapy aimed at lowering the IOP did not offer a protective effect. Papillary hemorrhage and a significant decay in performance are usually found in the same eye. Die Leistung einer Untersuchung mit dem automatischen Computer-Perimeter (‚Competer’) kann in einer einzigen Zahl zusammengefaßt werden. Dieses Leistungsmaß wurde an einer Normalpopulation angewandt, um die physiologische Verschlechterung der retinalen Empfindlichkeit mit dem Altern festzustellen. Weiter wurde die Entwicklung des Leistungsmaßes in 54 Glaucomaugen verfolgt. Diese waren in drei Gruppen verteilt: unbehandelte, behandelte mit guter Druckeinstellung, und behandelte mit unbefriedigender Druckeinstellung. Alle Augen wurden mindestens zu drei verschiedenen Zeitpunkten perimetriert. Man fand ein signifikantes Übergewicht in Augen mit fallenden Leistungswerten. Eine Schutzwirkung durch drucksendende Behandlung konnte nicht gesichert werden. Papillenblutung und signifikanter Abfall der Leistung sind in der Regel in den gleichen Augen zu finden.

Treatment versus no treatment in chronic open angle glaucoma

Abstract. In a controlled randomized study 15 patients (20 eyes) with chronic open angle glaucoma and visual field defects were followed for > 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.

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.

Short term effects of timolol in chronic glaucoma. A double blind study using computerized perimetry.

15 patients with glaucomatous field defects in at least one eye were subjected to computerized perimetry and IOP, systemic blood pressure and pulse rate measurements before and after timolol or placebo instillation in both eyes. A significant decrease of IOP and pulse rate was found 2 h after timolol. The visual fields were not improved, the correlation between IOP and visual field performance being (though not significantly) positive. The lack of improvement could not be attributed to the decrease in pulse rate.