Apparatus for the measurement of retinal visual acuity by moiré fringes.

Moiré fringes generated by two equal gratings in contact, looked at in Maxwellian view, are well suited for the assessment of retinal visual acuity. High-contrast fringes practically free from spatial harmonics (higher Fourier components) are obtained if, instead of the zero diffraction order, one first-order diffraction spectrum from each of the gratings is isolated by a stop. Thus a pair of coherent light sources is produced, the distance of which can be varied by relative rotation of the gratings. The resulting fringe pattern of variable pitch is characterized by achromatic intensity minima seen against a background of variable color depending on the direction of viewing. These colors can, however, be compensated for by an additional dispersing element near the gratings, e.g., a spectral prism. The device then is an achromatic interferometer, enabling the use of white light. Results do not systematically deviate from those obtained with a monochromatic interferometer using a laser. If desired, fringe contrast can be measurably varied by superimposition of a white light beam, with the intensities of both fields being controlled by polarizers.

'Contact glass for use with high power lasers--geometrical and optical aspects', by P. Roussel and F. Fankhauser (1).

Roussel and Fankhauser have proposed contact glasses with a collecting front surface centred on the bundle focus for use with high power lasers. We demonstrate here that the main contribution to the gain in energy density within the focus spot must be attributed to the front surface of the glass. This is at variance with the explanation given by Roussel and Fankhauser, namely that the energy gain is due to the difference in refractive index between the glass and the aqueous humour.

Dependence of magnification upon the camera-to-eye distance in the Zeiss fundus camera.

The magnification of the Zeiss type of fundus camera depends, except for the case of emmetropy, on the camera-to-eye distance. Its relative variation is equal to the product of the patient's ametropia and the difference in the camera-to-eye distance. Moreover, magnification is also affected by changing the diopter range scales on the camera.

[A fixation lamp for panoramic fundus pictures (author's transl]. / Fixationsleuchte für Panorama-Fundusaufnahmen.

A fixation lamp is described that enables a rational generation of panoramic fundus pictures with the Zeiss, Oberkochen, or other fundus camera of similar field, provided the patients collaborate. An illuminated marker at infinity is perceived centrally on the one hand, and on the other hand the marker is guided along a circle of 22 degrees eccentricity by a rotatable mirror system with click stops at every clock position 1 to 12 hours. If the camera is provided with angle scales, and use is made of its horizontal and vertical excursions, another circle of pictures at 38 degrees eccentricity can be obtained. With a total of 19 pictures a field of 96 degrees diameter is thus completely covered in a regular manner (see Fig. 6). Resolution wide-angle composite pictures of this kind is as good as resolution obtained by other means.

Optics in Switzerland.

Present work in optics in Switzerland is surveyed, covering universities, research institutes, and industry; the review is introduced by a brief historical section. The survey was sponsored by the Swiss Society for Optics.

Fundus drawings versus photography.

Under adverse optical conditions (turbidity of the media) a well-trained observer/artist, using slit-lamp stereomicroscopy, is able to display in a drawing considerably more correct information about a fundus than what a fundus camera records. To a lesser degree this holds under favorable conditions too. General advocation of photography for being more objective is questioned; even if true, meme objectivity, i.e. no false information, would not make up for loss of important details. This paper intends to prove these points experimentally on an object (a nummulite shell) unfamiliar to the artist charged to do the drawing. The latter and photographs taken under varying conditions were compared inter se and with a high resolution scanning electron micrograph.

A theoretical model for the eye of new-born infants.

A Gullstrand model for the eye of new-born infants is proposed, based on intra-ocular distances obtained by ultrasonography and lens radii measured on sections of deep-frozen preparations (v. Pflugk, 1909). Refractive indices of the media are assumed to be equal or nearly so to those of the adult eye, since no experimental data are available. The focal length of the model is 15.74 mm, the power 84.8 dptr, that of the lens alone 43.4 dptr, and the refractive error +2.8 dptr. A simplified model where the inner surface of the cornea is omitted, has a focal length of 15.63 mm, a power of 85.3 dptr and a refractive error of +2.4 dptr. When the data of v. Pflugk are analyzed statistically it is found that the spread of the lens power is considerably smaller than that which would be expected from the spread of the radii.

Quantitative studies in stereochronoscopy (Sc): application to the disc in glaucoma. I. Phenomenology.

In some details our standard procedure of stereochronoscopic disc picture-taking has been improved. For clinical use (demonstration of a change in the disc surface) a semi-quantitative evaluation with a stereoscope is generally sufficient. For a more accurate and quantitative analysis a flicker comparator is used. A graphical or numerical display of the results allows the follow-up of changes at a given location on the disc over any time interval, e.g. several years in glaucoma simplex, if pictures are taken every 2-4 months. Characteristic curve courses result, of which we describe (1) to and fro movement of the position of a given object on the disc, "papillary unrest" (2) progression of parallax, and (3) "events". The difficulty of judging the efficacy of a therapy is made evident. Here stereochronoscopy should prove to be useful when employed in the form of control charts.

Rapid detection of changes in the optic disc: stereochronoscopy. III. Retinal venous pulse as an interfering factor.

In the evaluation of stereochronoscopic pairs of fundus pictures (Sc) venous pulse is an interfering factor. Visual observation and photography show that when a magnification of 15x is used, as in our case, venous pulse is seen only at the emerging part of the big veins and in their immediate neighborhood, whereas veins of 100 microns diameter or less show no pulsation. Over relatively short time intervals (some minutes) the temporal course of venous pulse in terms of vessel width is a more or less periodic phenomenon; for longer periods (months) a study is underway. In the majority of cases the filling state of pulsating veins seems to reach a minimum shortly after the R peak of the ECG. An investigation as to whether the interference of venous pulse can be reduced by coupling the camera flash to the R peak has been begun. However, for the time being, it appears that the best method is to pass over the pulsating vessel parts, and to observe Sc effects only in the small vessels, when Sc evaluation is applied. Statistics show that venous pulse is significantly more frequent in suspected and early glaucoma subjects (T greater than 21 mm appl.) than in healthy subjects. We feel that with the methods proposed all conditions pertaining to an extensive follow-up of ocular hypertension and early glaucoma cases are now established.

[Stereochronoscopy]. / Uber Stereochronoskopie.

If fundus photographs are taken at different times under strictly observed conditions of centering, temporal changes of the disk surface can rapidly be detected by stereoscopic methods. In glaucoma (early or late stages) such changes are found earlier than by routine perimetry. Hence, the onset of glaucoma can more easily be distinguished from real ocular hypertension, and success of therapy can be judged more accurately than by visual field determinations.

Optical attachment to the O'Malley photocoagulator.

An optical attachment (originally developed for the Zeiss-Oberkochen photocoagulator), which provides slitlamp observation and energy delivery through a fundus contact glass, can also be coupled to the Clinitex Log-2 photocoagulator described by O'Malley. Excellent image quality out to the far periphery is obtained. The system has been successfully used for the prophylactic treatment of retinal detachment in the presence of retinal hole formation, the treatment of various conditions of diabetic retinopathy, localized fluid accumulations occurring after retinal surgery, and irradiation of the iris.

Rapid detection of changes in the optic disc: stereochronoscopy. II. Evaluation technique, influence of some physiologic factors, and follow-up of a case of choked disc.

A simple device for viewing stereochronoscopic (Sc) picture pairs under any azimuth is described. The influence of pulse, irradiation, time, and ocular pressure on disc configuration of some healthy and affected subjects is investigated. To test the sensitivity of Sc as compared to that of conventional steroscopy (St), a case of choked disc in which pictures of both kinds had been taken was followed up. This material also served to test 10 observers as to their ability to detect St and Sc effects in fundus pictures. Despite good stereo vision in all observers as tested by the Titmus charts, considerable differences were found in the analysis of fundus pictures. Detailed instruction resulted in improved results. Two cases of glaucoma simplex incipiens are presented in which a change of disc configuration could be detected by SC while ocular pressure and visual field remained normal in one case and did not change in the other.

[Contact glass for the study of the corneal endothelium and epithelium in the slit-lamp radius]. / Kontaktglas für die Untersuchung des Hornhautendothels und-epithels im Spiegelbezirk.

Specular endothelioscopy can be improved by an appropriate contact glass in three ways: The blurring front reflex of the cornea disappears, a two-fold magnification permits the use of routine slit-lamps for observation at higher magnification, and the field of specular illumination is increased considerably. The posterior surface of the contact glass is made plane, which offers the following advantages: a fluid chamber in front of the cornea is created which avoids any deformation of the cornea through the contact glass; the reflex of the posterior surface can be deflected by tilting the contact glass slightly so that the weak specular reflex of the epithelium becomes visible.