A new set of variable-contrast visual acuity charts.

Using a computer plotting technique, we designed four variable-contrast visual acuity charts. The contrast of the first 3 is 90, 15, and 2.5%, respectively. The fourth is 90%, but the luminance of the optotypes and background are the reverse of the first chart. The main features of these charts are as follows. Both contrast sensitivity and spatial frequency are in geometric gradation, which observes the laws of Weber and Fechner. The mean average luminance, (Lmax + Lmin)/2, is constant for all four charts, which follows the concept of contrast sensitivity function (CSF). Charts 1 and 4, which have the same contrasts but different glare backgrounds, measure the glare that is related to the transparency of the refractive media of the eye. Because the charts are rotatable, patient memorization and guessing are minimized. Results compared with those of the conventional visual acuity test and are understandable by patients and eye care practitioners. The charts, which are simple, easy, and require little time, are inexpensive and portable.

A diagnostic ruler for strabismus and amblyopia.

We designed a diagnostic slide ruler for easier detection of strabismus and amblyopia, both of which begin in childhood. This new instrument makes the Parks three-step test easier to use and faster than other methods in diagnosing isolated cyclovertical muscle paralysis. Furthermore, the slide ruler tests visual acuity with both series letters and single letters. Incorporated into the instrument are Laurence's strabismometer, Haab's pupillometer, occluder, pinhole, and millimeter ruler. A laboratory model is now available, and this slide ruler can assist the ophthalmological practitioner in analyzing three-step test data more rapidly than graphs and computer programs can. This instrument can also diagnose pediatric patients in the early stages of microstrabismus and amblyopia to obtain the best therapeutic results.

Fundus reflectometry for photocoagulation dosimetry.

A dosimetry technique has been developed which utilizes three-wavelength fundus reflectometry, a quantitative model of fundus reflectance, and a model of thermal tissue damage to control photocoagulation lesion size. The fundus reflectance model uses Lambert-Beer's law exponential attenuators to describe the ocular media, retinal pigment epithelium (RPE), and choriocapillaris transmission characteristics while the choroid is described as a Kubelka-Munklike homogeneous scatterer/absorber. Three reflecting layers are included in the model at the retinal inner limiting membrane, Bruch's membrane, and the sclera. Measured lesion size variability contained components which resulted from variations in choroidal blood and melanin and RPE melanin concentration. Photocoagulation dosimetry was found to reduce the photocoagulation lesion size coefficient of variation for red light from 45% to 10% for the control and dosimetry cases, respectively. Similar improvement was noted for yellow photocoagulation light.

A new solid-state, frequency-doubled neodymium-YAG photocoagulation system.

We have developed a solid-state laser system that produces a continuous green monochromatic laser beam of 532 nm by doubling the frequency of a neodymium-YAG laser wavelength of 1064 nm with a potassium-titamyl-phosphate crystal. Photocoagulation burns of equal size and intensity were placed in two rabbit eyes with the solid-state laser system and the regular green argon laser system, respectively, using the same slit-lamp mode of delivery. Histologic findings of lesion sections revealed no important differences between the two systems. In theory, the longer wavelength of the solid-state laser offers the advantages of less scattering in ocular media, higher absorption by oxyhemoglobin, and less absorption by macular xanthophyll than the 514-nm wavelength of the regular green argon laser. The solid-state laser has impressive technical advantages: it contains no argon-ion gas tube that wears out and is expensive to replace; it is much more power efficient, and thus considerably smaller and compact; it is sturdier and easily movable; it does not require external cooling; it uses a 220-V monophasic alternating current; and it requires little maintenance.

Retinal illuminance using a wide-angle model of the eye.

A computer model of relative retinal illuminance, based on our optical wide-angle model of the eye, is proposed for the cases of Ganzfeld illumination and the Maxwellian view through a range of visual field angles from 0 degrees to 80 degrees. The proposed model is designed to be functionally correct and to represent closely the anatomical parameters of the eye. Unlike earlier proposed models, this model is based on our previously reported measurements of spherical aberration in 100 eyes in vivo and is designed to be correct in the peripheral field and with large pupils. Data are reported for pupil diameters of 2, 4, and 8 mm. The effect of crystalline lens extinction on retinal illumination is also estimated for average eyes of young (age 19 years) and old (age 63 years) individuals at two wavelengths (410 and 532 nm). In the Ganzfeld case, illumination of the retina decreases with increasing visual angle. In the Maxwellian view, retinal illuminance increases with increasing visual angle.

[A universal laser for intraocular treatment]. / Laser universel pour traitement intraoculaire.

The creation of a single apparatus incorporating the different lasers applicable to intraocular pathology derives from the idea of possessing the means, with one device, of objectively comparing the effects and parameters of various lasers in order to pursue a more precise line of treatment. This has led to our fabrication of the universal intraocular laser. The word universal means the ability of the machine to act on each kind of intraocular tissues with all of the various infrared or other-colored radiations, as well as with different modalities. The unit is transportable. It only requires a source of electric power (110 or 220 V) and includes an independent cooling system. The Nd: YAG laser has selectable operating parameters: pulsed or continuous excitation, Q-switched or mode-locked mode, mirror or fiber optic transmission. It is used also as the basic system of the coloured module. The colour module can provide the three clinically useful radiations: green, red, yellow. The green (532 nm) is obtained by transmission of the I.R. beam brought a birefringent crystal (KTP). Red (650 nm) and yellow (575 nm) come from two incorporated dye lasers excited by the green radiation.

A step-zoom probe for laser endophotocoagulation: I. Design.

A step-zoom probe for laser endophotocoagulation of the eye has been developed, using fiber optics and a gradient index (GRIN) rod lens. It provides the operator with five or more focused spots ranging in size from 50 to 500 microns, and the spot size on the target is independent of the media filling the vitreous cavity, i.e., fluid or air. Each spot is located at the waist of the beam and therefore can be easily placed on the target, reducing the potential for overtreatment. A prototype model is currently undergoing animal testing.

[Modernization of ophthalmoscopic techniques]. / Modernisation des techniques d'ophtalmoscopie.

The great principles of ophthalmoscopy have been known for many decades. This paper intends show the new possibilities allowed by modern technology, especially in two fields. First of all, it is possible, even in keeping basic principles, to improve previous machines with, for example, better magnification, new ophthalmoscopic lens, or to create new materials as telescopes for clinical practice or intra-ocular surgery, wide angle or high magnification fundus cameras for posterior pole examination. Secondary, by revolutionary principles, it is possible to introduce laser in the ophthalmoscopic field and to imagine new ophthalmoscopes: SLO i.e. Scanning Laser Ophthalmoscope or SLM i.e. Scanning Laser Microscope, which opens a window on the future.

[Stabilization of the laser on the target. Scanning photocoagulator: the SLC (scanning laser coagulator)]. / Stabilisation du laser sur la cible. Photocoagulateur à balayage: S.L.C.

When lasers are used to cause burns on the retina they necessitate systems of great precision especially in the posterior pole. Different possibilities are now offered. The best one is based on the intensification of the same laser beam used for the observation in the Scanning Laser Ophthalmoscope: S.L.O. when it is at a point selected from the angiogram, converting this machine into a Scanning Laser Coagulator: S.L.C.

Calculation of an IOL from the wide-angle optical model of the eye.

Currently used paraxial formulas for calculating the power of an intraocular lens (IOL) ignore the pupillary aperture of the eye (3.5 mm) and assume that the locations of the principal planes of the crystalline lens and cornea are known. For calculating IOL performance, only the axial point in the field is considered. The eccentricity of the ocular optical system and the probable error in the IOL centering are also ignored. The use of a wide-angle optical model of the aphakic eye for computation of the IOL would result in values that approach more closely those in the real eye. The performance of the implanted IOL could then be calculated in conditions that are much closer to reality. To obtain information on the precision required in preoperative measurement of the asphericity of the cornea, we have studied the effect of corneal asphericity on IOL performance.

Automation in krypton laser photocoagulation.

Histologic study of lesions produced by krypton red (647.1 nm) and krypton yellow (568.2 nm) laser lights reported here suggests advantages in alternating these two wavelengths in photocoagulation. Selection of the best wavelength to be used in a given location on the retina should result from pre-determined absorbance conditions in that location. The feasibility of the relative measurement of absorbance in different fundus locations by measurement of the relative reflectance is discussed. Instrumentation for these measurements and for switching from one wavelength to the other is described. Instrumentation for the possible expansion of krypton laser applications to clinical problems in the anterior segment also is suggested.

Wide-angle optical model of the eye.

There are two approaches to the design of a wide-angle optical model of the eye. One approach is based upon data on biological and physical characteristics of the eye (cornea, crystalline lens) collected from the literature or from in vivo or in vitro measurements. From these data a model is built whose configuration is as close as possible to that of a living eye. Then the visual function of the model is calculated and checked for its conformity with the living eye. The second design approach starts with measurements of the optical performance of a living eye. Then the unknown parameters (asphericity of the cornea, distribution of the thicknesses of the individual layers of the crystalline lens, their curvatures and refractive indices, and sphericity of the layers) can be calculated by fitting the curve of the corresponding optical performance calculated from the model to the curve measured in vivo. Using this approach, we measured the axial spherical aberrations in 50 emmetropic volunteers (100 eyes), calculated the best fit to all the measurements, and used it as the average curve of axial spherical aberrations of an emmetropic eye. In this paper we present the results and calculations and discuss the validity of this approach.

An optimized zoom ophthalmoscope.

An indirect ophthalmoscope that could provide higher magnification (up to 15X) would offer definite advantages in fundus diagnosis. If it could also supply an erect fundus image, it could advantageously replace the surgical microscope in vitrectomy operations. The surgical microscope requires the use of a contact lens, which restricts the surgical techniques and may damage the corneal epithelium, and it reduces image brightness when the magnification is increased. In contrast, an indirect ophthalmoscope does not require a contact lens and keeps the image brightness constant regardless of magnification. Increased magnification can be obtained in an indirect ophthalmoscope by incorporating telescopes in the ophthalmoscope oculars. The possible use of two telescopic systems, Keplerian and Galilean, and the problems of stereopsis and image inversion are discussed. A new, optimized ophthalmoscope is described, with Keplerian telescopes, that provides a range of magnifications from 2X to 15X as well as options for an erect or inverted fundus image.

Telescopic eyepieces in indirect ophthalmoscopy.

A new attachment that can be used with optimized ophthalmoscopes is described. Readily removable and interchangeable eyepieces containing small, lightweight Galilean telescopes approximately double the magnification. The influence of this device on some of the optical properties of binocular indirect ophthalmoscopy including magnification, field of view, brightness of the fundus image, and stereopsis, are reviewed briefly.

A method to predetermine the correct photocoagulation dosage.

Relative absorbance in different locations on the retina has been studied by measuring the relative reflectance. Using this measurement it is possible to predetermine the correct dosage of light power in any new location on the retina by comparing the new reflectance with the reflectance in the test location. It is important to measure the reflectance with the aiming beam in its actual setting for application because the absorbance is affected by the angular orientation of the beam. A method is proposed for measuring, when needed, the relative concentration of blood and melanin at different points of the retina.

Time and location analysis of lesion formation in photocoagulation.

Fourteen eyes from seven owl monkeys were used for study of the time and location within the retinal layers of the formation of the white reactions produced by photocoagulation with green (530.9 nm), yellow (568.2 nm), or red (647.1 nm) krypton wavelengths. Locations on the retina with equivalent conditions of absorbance were chosen. The white reaction formed in the first 100 ms of application. The depth at which the most damage occurred depended on the wavelength used. The final shape of the lesion depended on the location (in depth) of the white reaction first formed and on the power of the laser beam. The cauterizing power of the krypton yellow was evident.

In vivo coronary angioscopy.

The feasibility of in vivo coronary angioscopy was tested utilizing a 1.8 mm angioscope in vessels where blood had been replaced by optically clear liquids, including a new perfluorocarbon emulsion. After trials in postmortem canine and human coronary arteries, in vivo intraluminal visualization was accomplished in the dog with a catheterization technique and in patients during open heart surgery. The results demonstrate the feasibility and potential clinical usefulness of direct visualization of intravascular anatomy and disease, analogous to endoscopy of other organ systems.