Bernard F. Hochheimer

Retinal Damage from Light

Exposure of a monkey retina to the light from a slit lamp for 40 minutes produced a visible retinal change that disappeared after four weeks. Exposures of 20, ten, and five minutes produced no visible changes. Extensive retinal damage was produced in the macula of the other eye of the monkey by a one-hour exposure to the light from an operation microscope. This damage was almost unchanged one year later. Exposure of the monkey retina from the same operation microscope, for the same length of time, with the blue light filtered out, produced a much smaller lesion that, after one year, could not be seen visibly but was detected with fluorescein angiography.

Potential hazards from specific ophthalmic devices

Abstract The retinal light exposure a patient might receive from ophthalmoscopes, slit lamps, surgical microscopes, and overhead surgical lamps is documented. Monkey exposures to microscopes and slit lamps were performed to substantiate the findings. A “typical” indirect ophthalmoscope is seen to be “unsafe” after 23 sec of exposure in a patient with dilated pupils and clear media, if compared with laser safety standards. Slit lamp biomicroscopy of the macula produces 2–3 times greater retinal exposure than the indirect ophthalmoscope. Operating microscope internal light sources produce a surprising retinal exposure of up to 10 times greater than the indirect ophthalmoscope over an area of several disc diameters, causing severe choroioretinal lesions in monkeys after 1 hr of continuous exposure. The surgeons retina receives 44 mW/cm2 from the corneal specular reflection of the microscope source. Using the laser safety standards, this is “unsafe” after one minute. A prototype surgical illuminator is described which reduces retinal irradiance to 1/900th of that from conventional microscope light sources, while maintaining equivalent illumination of the anterior segment.

Quantification of indicator dye concentration in ocular blood vessels

The behavior of an indocyanine green (ICG) dye bolus as it passes through the ocular blood vessels provides a calibration standard which permits quantitative dye concentration measurements. Unlike fluorescein, ICG dye can be delivered to the eye in sufficiently high concentrations by intravenous injection that concentration fluorescence quenching takes place in the ocular blood vessels. The relative maximum fluorescence intensity occurring in every blood vessel in which quenching is observed always corresponds to a 0·03 mg/ml dye concentration. Knowing this point and dye concentration in blood as a function of intensity permits routine quantification of dye concentration in blood vessels of the living eye.

Simple device for objective measurements of haze following excimer laser ablation of cornea

We have developed a simple instrument for making objective measurements of haze that develops following excimer laser ablation of the cornea. It consists of an appropriately modified slit-lamp microscope, with a fiber optic pickup, a filter system for wavelength selection, and a photomultiplier detector. The scattered intensity at 120 degree(s) from the forward direction is determined. Preliminary tests were made by measuring the haze following a deep photorefractive ablation on a rabbit cornea under conditions which ensured that rather severe haze would develop. The VISX Model 20/20 laser system was set to produce a 6.0 mm diameter, -15 D correction, with a central depth of 236 micrometers . Measurements were made on the normal cornea prior to ablation and at various times up to 114 days post-ablation and are compared to slit-lamp photographs. Scattering peaked two weeks post-ablation at a value approximately 40X that of the normal (unablated) cornea and gradually decreased to approximately 11X the normal value at 114 days.