Mathematical morphology in computerized analysis of angiograms in age-related macular degeneration.

This paper deals with image processing of numerical retinal angiograms in order to facilitate diagnosis and follow-up in age-related macular degeneration (AMD) which is currently the main cause of blindness in industrialized countries. A computerized scheme using principally mathematical morphology operators is proposed for detecting and counting drusen, which are precursor lesions of the ocular fundus. In order to check the feasibility of this approach, results relative to 58 retinal images are compared with those given by three retinal specialists independently. From manual counting measures it is found that interobserver correlation coefficients lie in the range 0.71-0.78. On the other hand, a correlation coefficient of 0.89 is obtained when the average of the three expert countings is compared with the drusen number given by the computerized method. This coefficient is improved from 0.89 to 0.93 by processing only frames captured immediately after the appearance of a dye consecutive to intravenous sodium fluorescein injection. Compared to the manual analysis which is, among other things, tedious and time consuming, the computerized analysis is both quicker and more objective. Validation by the practitioner is however necessary, given possible detection errors. The proposed computerized scheme for detecting and counting drusen may be easily automated and so should prove useful in clinical studies which involve high volume analysis of retinal angiograms.

[Correlation intervals between the power values of artificial lenses deduced from theoretical formulae and regression formulae]. / Espace de corrélation entre les valeurs de puissance de cristallins artificiels déduites de formules théoriques et de formules de régression.

We give a precise theoretical formula used to calculate the power of implants. A spatial representation is shown. It exhibits Dc (power of the cornea) and l (axial length) values which induce a good fit between the power of artificial lens deduced from theoretical and statistical (S.R.K.) formulae. These values are situated on a look like parabolic curve (C) centered on a 26.13 mm or 27.2 mm l value according to anterior or posterior implants. We show the existence of area of (Dc, l) points giving a fit between theory and statistic within a given uncertainty delta DI. This fit is depicted on a chart (Dc, l, delta DI) on which the different curves which correspond to various delta DI, are deduced from the curve of equal power (C) by single translations. We indicate that an uncertainty near 1 dioptre on the power of the cornea induces a deviation near 0.21 dioptre on the powers of the anterior implant when calculated using the two methods. Moreover, we establish that the power SRK is always higher than the theoretical power for axial lengths situated in the 24 to 28.5 mm range.

[Phototoxicity of ultraviolet rays on crystalline lens and retina. Study of the optic transmission of implants with or without anti-UV treatment]. / Phototoxicité des ultraviolets sur le cristallin et la rétine. Etude de la transmission optique d'implants traités et non traités anti-U.V.

The authors have checked absorbing U.V. IOLs. The use of these IOLs seems to be necessary because of the retinal damage due to direct exposure to near U.V., after lens extraction. Since about ten years a growing body of works has shown phototoxicity on lens and retina by U.V. radiation between 392 and 400 nm. This radiation transmitted by the cornea is not absorbed during the first decade. Progressively, cumulative effects of near U.V. on the lens involve fluorescent chromophore formations, pigmentation, and interferes with synthesis of lens proteins, catalyse insoluble proteins. Finally, cataract are produced as well as experimentally with U.V. lasers. In aphakic eyes the risk of retinal damage increases dramatically. Consequently IOLs absorbing U.V. radiation could protect the retina. A spectrographic check of U.V transmittance by standard IOLs and U.V. absorbing IOLs has shown that the U.V. absorbing IOLs block all radiations below 400 nm.

[A color after-effect: the McCollough effect]. / Etude d'un post-effet coloré: l'effet McCollough.

Coloured after-effect parameters have already been studied but the process involved in these events remains unknown. In the case of the McCollough effect, Shute has shown that the induced colour decreases rapidly at first and then more slowly. In a normal subject the effect can no longer be detected after approximately 2 hours. Results have been used to determine a relationship between the purity of the induced colour and time: I = I0 e-bt, where b is a typical parameter of the subject related to his physiological state. A figure of b approximately 0.03 min-1 was obtained in the normal subject. The rate of decay is influenced by certain drugs. In particular, a greater decrease in induced colour is obtained when caffeine is taken. In this case, the value of the decay constant b is about 0.06 min-1. Results obtained with anticholinergic agents are contrasted with those obtained with caffeine: slowed decay occurs. Hence the value of the decay constant is about 0.01 min-1. Data show that the McCollough effect could be an inhibitory mechanism in a visual pathway and which tends to suppress neural connections. It should be noted that the geometrical structures of patterns play an important part in the perception of the induced colour. For example, with square-wave gratings, the strength of the induced colour depends on spatial frequency and orientation. The McCollough effect mainly concerns the ways in which we perceive both pattern and colour. It may be located either within the retina or more centrally in the visual system.

[Direct heterochromatic comparison for color perception evaluation]. / Test de vision colorée par égalisation hétérochrome directe.

We analyzed the data obtained from the Malbrel chromatometer, a device that examines color vision. The principle of the chromatometer is based on the opponent chromatic receptive fields of the retina. It shows two adjacent luminous windows of small size that can be either red and green or yellow and blue. The patient's task is to adjust the brightness of the red window (or the yellow window) to a fixed green (or blue) window luminance. Several luminance levels were studied and data were recorded using specific software. The luminance and the chromatic coordinates of the windows have been determined. The aim of the statistical study was to compare the data with a simple distribution law and therefore to know if the chromatometre allows measurement of color vision. In this investigation, 95 eyes were studied. Each patient has to match 4 red/green brightness levels and 4 yellow/blue brightness levels. The main characteristics were evaluated: the means, medians and standard deviations. Then, from the qq-plots we verified that the data distribution was near normal distribution. The percentile curves allowed 3 types of color vision to be determined. Around the median normal color vision can be defined. Between the 10(th) and the 20(th) percentiles and between the 80(th) and the 90(th) percentiles, a small anomaly was present. Below the 10(th) percentile or above the 90(th) percentile, a substantial anomaly was present.

Variations énergétiques de l'absorption optique du lanthane et du praséodyme pris en couches minces.

Under static ultrahigh vacuum (10(-9) torr), we have studied the optical properties of lanthanum and praseodymium thin films. It is shown that these films behave similarly in the 2000-8000 A spectral range. Results are identical for other light rare-earth thin films. We suggest that indirect transitions are responsible for the presence of a maximum in the optical absorption near 5,8 eV.

Wavelet transform in human visual channels.

In this paper we report on an analysis of visual stimuli models by a wavelet function. The human visual process is compared with a wavelet transform. Wavelet functions have been built from the Haar function. Two stimuli were analyzed by a wavelet function: a sinusoidal luminance stimulus (spatial frequency ƒ) and a luminance-varying regular stimulus. The theoretical results obtained from the wavelet transform are compared with the physiological results of R. Blake [in Frontiers in Visual Science, S. J. Cool and E. L. Smith, eds. (Springer-Verlag, Berlin, 1978), pp. 209-219] and K. K. De Valois [in Frontiers in Science, S. J. Cool and E. L. Smith, eds. (Springer-Verlag, Berlin, 1978), pp. 277-285]. A theoretical curve conforms to the shape of the contrast sensitivity curves. Hence it can be concluded that the wavelet transform is a new approach to human visual mechanisms.

Les propriétés optiques de couches minces d'yttrium sous ultravide statique.

It is shown that yttrium presents a normal absorption band near 5.6 eV and another band whose characistics depend upon their film structure. The influence of temperature on the films shows the existence of an anomalous absorption phenomenon.