Salvatore A. D'Anna

Comparison of Ivermectin and Diethylcarbamazine in the Treatment of Onchocerciasis

We compared ivermectin with diethylcarbamazine for the treatment of onchocerciasis in a double-blind, placebo-controlled trial. Thirty men with moderate to heavy infection and ocular involvement were randomly assigned to receive ivermectin in a single oral dose (200 micrograms per kilogram of body weight), diethylcarbamazine daily for eight days, or placebo. Diethylcarbamazine caused a significantly more severe systemic reaction than ivermectin (P less than 0.001), whereas the reaction to ivermectin did not differ from the reaction to placebo. Diethylcarbamazine markedly increased the number of punctate opacities in the eye (P less than 0.001), as well as the number of dead and living microfilariae in the cornea over the first week of therapy. Ivermectin had no such effect. Both ivermectin and diethylcarbamazine promptly reduced skin microfilaria counts, but only in the ivermectin group did counts remain significantly lower (P less than 0.005) than in the placebo group at the end of six months of observation. Analysis of adult worms isolated from nodules obtained two months after the start of therapy showed no effect of either drug on viability. Ivermectin appears to be a better tolerated, safer, and more effective microfilaricidal agent than diethylcarbamazine for the treatment of onchocerciasis.

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.

Noninvasive mapping of the normal retinal thickness at the posterior pole.

OBJECTIVE Objective and sensitive measurements of the retinal thickness at the posterior pole are useful to detect and delineate macular edema or retinal atrophy. The authors therefore developed an instrument, the Retinal Thickness Analyzer (RTA), to map the retinal thickness rapidly. The RTA was used to study the normal thickness at the posterior pole and to provide a pilot baseline. DESIGN Cross-sectional study. METHODS A green (540-nm) laser slit was focused on the retina via a scanning mirror placed at the conjugate plane of the pupil. The intersection between the laser slit and the retina was viewed at an angle and recorded by a video camera. Nine scans, each acquired in 200 to 400 msec, covered the central 20 degrees of the fundus. PARTICIPANTS The posterior pole was mapped in 29 normal subjects 19 to 76 years of age (mean, 48 years). RESULTS The thickness maps matched the posterior pole anatomy. Points with maximum thickness were located in the perifovea in a C-shaped manner extending from the disc to above and below the fovea. The local variation (standard deviation) in retinal thickness among the subjects was, on average, 15 microns. Age, gender, and race did not have a large effect (< 35 microns) on the values. CONCLUSIONS Rapid scanning thickness analysis with the RTA provides a detailed map of the retinal thickness. The relatively narrow range of thickness values in normal subjects indicates that the method may provide a sensitive detection of pathologic thickening or thinning of the retina.

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.

Measurement of oxygen saturation in the retina with a spectroscopic sensitive multi aperture camera

We introduce a new multi aperture system capable of capturing six identical images of the human fundus at six different spectral bands. The system is based on a lenslet array architecture and is well suited for spectroscopy application. The multi-aperture system was interfaced with a fundus camera to acquire spectroscopic sensitive images of the retina vessel and ultimately to calculate oxygen saturation in the retina in vivo. In vitro testing showed that the system is able to accurately reconstruct curves of partially oxygenated hemoglobin. In vivo testing on healthy volunteers was conducted and yielded results of oxygen saturation similar to the one reported in the literature, with arterial SO(2) approximately 0.95 and venous SO(2) approximately 0.5.

High-resolution photography of the retinal nerve fiber layer

Abnormalities in the appearance of the retinal nerve fiber layer can indicate the presence of optic nerve atrophy, but a major problem has been the difficulty of visualizing the nerve fiber layer in some individuals. By selectively illuminating the white nerve fiber layer in comparison with the red retinal pigment epithelium and choroidal background, red-free light increases the visibility of the nerve fiber layer. Compared with the standard red-free photographic technique, a 560-nm short-pass cut-off filter, used with extended-range, high-resolution, extremely fine-grain film (Kodak No. 2415 Technical Pan film), considerably enhanced the ability to resolve nerve fiber bundles.

Corneal endothelial changes after argon-laser iridotomy and panretinal photocoagulation

We performed argon-laser peripheral iridotomies on the right eyes of eight cynomolgus monkeys and administered panretinal scatter photocoagulation to the left eyes of the same monkeys. Both eyes of each monkey were photographed and studied with a slit lamp, pachymetry, and direct and indirect specular microscopy. After follow-up periods of 0 to 31 days, the monkeys were killed and the enucleated eyes studied by light and scanning electron microscopy. Scanning microscopy were deposits showed that the changes observed by specular microscopy were deposits on the endothelium. Only minimal damage occurred and there were no significant changes in endothelial cell density after either treatment.

Heat Effects on the Retina

BACKGROUND AND OBJECTIVE To study the heat and power dissipation effect of anintraocular electronic heater on the retina. The determination of thermal parameters that are nonharmful to the retina will aid in the development of an implantable intraocular electronic retinal prosthesis. MATERIALS AND METHODS In dogs, five different retinal areas were touched with a custom intraocular heater probe (1.4 x 1.4 x 1.0 mm) for 1 second while the heater dissipated 0 (control), 10, 20, 50, or 100 mW. In a second protocol, the heater was mechanically held in the vitreous cavity while dissipating 500 mW for 2 hours while monitoring intraocular temperature. The animals were observed for 4 weeks with serial fundus photography and electroretinography. The procedure was then repeated in the fellow eye. The dogs were killed and both eyes were enucleated and submitted for histology. RESULTS In experiments using protocol 1, heater settings of 50 mW or higher caused an immediate visible whitening of the retinal tissue. Histologically, this damage was evident only if the eyeswere immediately enucleated. Permanent damage was caused by heater settings of 100 mW or higher. Under protocol 2, no ophthalmologic, electroretinography, or histologic differences were noted between the groups. Temperature increases of 5 degrees C in the vitreous and 2 degrees C near the retina were noted. CONCLUSIONS The liquid environment of the eye acts as a heat sink that is capable of dissipating a significant amount of power. An electronic chip positioned away from the retina can run at considerably higher powers than a chip positioned on the retinal surface.

Absence of ocular effects after either single or repeated exposure to 10 mW/cm2 from a 60 GHz CW source

This study was designed to examine ocular effects associated with exposure to millimeter waves (60 GHz). Rabbits served as the primary experimental subjects. To confirm the results of the rabbit experiments in a higher species, the second phase of the study used nonhuman primates (Macaca mulatta). First, this study used time-resolved infrared radiometry to assess the field distribution patterns produced by different antennas operating at 60 GHz. These results allowed us to select an antenna that produced a uniform energy distribution and the best distance at which to expose our experimental subjects. The study then examined ocular changes after exposure at an incident power density of 10 mW/cm(2). Acute exposure of both rabbits and nonhuman primates consisted of a single 8 h exposure, and the repeated exposure protocol consisted of five separate 4 h exposures on consecutive days. One eye in each animal was exposed and the contralateral eye served as the sham-exposed control. After postexposure diagnostic examinations, animals were euthanized and the eyes were removed. Ocular tissue was examined by both light and transmission electron microscopy. Neither microscopic examinations nor the diagnostic procedures performed on the eyes of acute and repeatedly exposed rabbits found any ocular changes that could be attributed to millimeter-wave exposure at 10 mW/cm(2). Examination of the primates after comparable exposures also failed to detect any ocular changes due to exposure. On the basis of our results, we conclude that single or repeated exposure to 60 GHz CW radiation at 10 mW/cm(2) does not result in any detectable ocular damage.

A Primate Model of Anterior Segment ischemia after Strabismus Surgery: The Role of the Conjunctival Circulation

Fornix conjunctival incisions in strabismus surgery may provide partial protection against anterior segment ischemia by preserving the perilimbal conjunctival-Tenons circulation, which is disrupted with limbal conjunctival incisions. Six adult cynomolgus monkeys underwent tenotomies of three or four rectus muscles by making limbal conjunctival incisions in one eye and fornix incisions in the other. Iris fluorescein angiography and slit-lamp biomicroscopy were used to monitor changes. The eyes that had limbal incisions exhibited more severe anterior segment ischemic changes than the eyes that had fornix incisions in every instance of four rectus muscle surgery.