The Lancer Ethnicity Scale.
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Dermatologic Surgical Procedures↗
Biomedical subjects
M L Wolbarsht
Publications and source records attributed to M L Wolbarsht.
Laser energy reaching the posterior pole during transscleral cyclophotocoagulation.
OBJECTIVE: To measure scattered laser energy reaching the posterior pole during transscleral cyclophotocoagulation. METHODS: Transscleral cyclophotocoagulation was performed on 4 cadaver eyes with Nd:YAG noncontact, Nd:YAG contact, and diode contact lasers. Energy was measured with a photodiode through a 7-mm trephined hole in the posterior pole. Average percentage power, average power, and average energy transmission were calculated. American Conference of Governmental Industrial Hygienists (ACGIH) guidelines were used to calculate allowable energy exposures for each laser. RESULTS: All 3 lasers transmitted 3% to 5% of the power to the posterior pole. The average energy transmission was 240 to 260 mJ for all lasers. The contact lasers had an average power transmission of 120 mW. The noncontact Nd:YAG laser, with shorter pulse duration, had an average power transmission of 13,000 mW, significantly greater than that of the other lasers. The ACGIH guidelines for allowable energy exposures were 93 mJ for the noncontact Nd:YAG laser, 1300 mJ for the contact Nd:YAG laser, and 440 mJ for the contact diode laser. CONCLUSIONS: Three percent to 5% of laser power delivered during cyclophotocoagulation reaches the posterior pole. Exposure energies may approach or exceed ACGIH guidelines. The clinical significance of these findings remains to be shown.
Aged↗
Diagnosis of the acute red eye.
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Eye Diseases↗
Reproducible estimation of retinal vessel width by computerized microdensitometry.
An objective method for reliably estimating the width of retinal vessels is presented. A computerized microdensitometer scans film negatives of fundus photographs and reconstructs black and white images of the fundus on a visual display terminal. After this initial scan, a desired region of a retinal vessel is selected with moveable cursors, and a cross-sectional density profile through the vessel is plotted. Vessel width is determined by the half-height width of the profile of the minimum (least transmitting) and average background film densities. Measurement sites can be accurately reproduced on different negatives by landmark mapping. A series of ten fundus photographs were taken of three healthy human eyes, and the width of the superior temporal vein was measured in two places on alle negatives. The coefficient of variation of the six sets ranged from 1.2 and 3.4% with an average of 2.2%.
Analysis of Variance↗
Transmission of a Gaussian scanning beam through circular, square, and slit apertures: Part I. Theory.
Energy and power values for Gaussian profile scanning laser beams through circular, square, and slit apertures may be required for hazard analysis in laser safety programs. Equations describing the transmitted power for a Gaussian beam concentric and eccentric with circular, square, and slit apertures are given. Simple expressions of transmitted power and energy with a scanning laser beam across the square and slit apertures are derived. For the circular aperture, the transmitted power and energy can be calculated conveniently by using the correction factors from the graphic values or from the computer programs.
Energy Transfer↗
Hyperoxia during reperfusion is a factor in reperfusion injury.
Imposition of ischemia should result in accumulation of lactic acid with an attendant drop in pH. Subsequent reperfusion would result in hyperoxia, in the affected tissue, due to the Bohr Effect. O2- should therefore be produced in greater than normal amounts, due to this transient hyperoxia, and may contribute to reperfusion injury. Tissue acidification, during extreme exercise or in diabetes mellitus, may similarly lead to hyperoxia and to tissue damage by O2-.
Free Radicals↗
Evaluation of ocular protection filters in field situations.
A computer program has been developed to simulate eye movement during pursuit tracking to test the effectiveness of filters protecting the eyesight of individuals exposed to laser radiation. Two types of retinal damage are considered: macular lesions and retinal injury causing vitreous or subretinal hemorrhage. The retinal damage caused by optical radiation in the visible and near infrared of the spectrum differs from almost all other types of hazards in their proabilistic nature. That is, a small movement of the laser beam or change of eye position decreases or increases the probability of injury by several orders of magnitude. A laser beam combines the problem of a small source with extreme directionality with the probabilistic nature of this hazard location in space, and we now add the probabilistic nature of the action of the protective filter, i.e., a dependence upon angle of incidence. From this combination, an even more probabilistic picture of injury or disablement emerges. When it is necessary to plan the probabilities during military operations of mission fulfillment or injury with regard to various types of lasers in the battlefield ++environment, the problem must be analyzed very carefully. Our solution of the problem indicates the type of injuries to be expected and their dependence upon the various parameters of the angle of incidence of the lasers on the protective filters in the viewing system.
Computer Simulation↗
Future applications of lasers in surgery and medicine: a review.
The experimental use of lasers in surgery and medicine began only shortly after the development of the first working laser system. However, the development of practical, effective, and safe surgical lasers has been lengthy with many obstacles and delays. Today the laser is used for a wide variety of surgical operations. The fundamental limits and potential for future applications of lasers in surgery and medicine are discussed.
Forecasting↗
Evaluation of retinal exposures from repetitively pulsed and scanning lasers.
Threshold damage in the macaque retina is shown to be equivalent for the argon-krypton (Ar-Kr) 647 nm and the helium-neon (He-Ne) 632.8-nm lines for exposures to continuous wave (CW) radiation from 1 to 1,000 s. This equivalence allows interpolation from experiments with 647-nm, exposures at power levels that are unavailable with the He-Ne laser. To simulate He-Ne laser scanner exposures, 40-microseconds pulses of 647-nm light transmitted through a revolving disk with holes in the periphery were used to expose the retinas of monkeys under deep anesthesia at pulse repetition frequencies (PRFs) of 100, 200, 400, and 1,600 Hz for exposure durations of 1, 10, 100, and 1,000 s. The thresholds between laser exposure at 488 nm (Ar-Kr) and between laser exposure at 647 nm (Kr) are compared to assess thermal versus photochemical effects on the retina. The threshold for 488-nm pulses was consistently lower than that for 647-nm pulses at all PRFs and exposure times. The difference in thresholds increased with exposure time and PRF. The sharp decreases in 488-nm thresholds at 100-s exposure times for each PRF can be interpreted as a basically photochemical effect. The radiant exposure required for damage at 647 nm was several orders of magnitude above the radiant exposure from typical He-Ne scanner applications. From the similarity of the macaque retina to the human retina, it is concluded that no realistic ocular hazard exists from exposure to scanning laser systems of 1 mW or less, operating at higher than 100 Hz.
Animals↗
Phenylephrine-induced anterior chamber hypoxia.
The effect of topical phenylephrine 10% solution on anterior chamber oxygen tension (PO2) was studied in cats using an oxygen-sensitive electrode inserted into the midanterior chamber. A decrease in anterior chamber PO2 was usually observed within eight to 25 minutes and declined steadily thereafter. Within two hours, the drug caused a dramatic 60% reduction in anterior chamber oxygen tension (P less than or equal to .0005). We suggest that the mechanism for this phenylephrine-induced anterior chamber hypoxia is reduced blood flow, mediated by the direct vasoconstrictive effect of the drug and compression of the iris vasculature (induced by dilatation). The resulting decrease in the caliber of the iris arteries produced a parallel decrease in blood volume and flow which resulted in diminished PO2. Phenylephrine 10% may contribute to hypoxia and exacerbate the underlying pathology in those disorders where hypoxia plays an important causal role.
Animals↗
Nonionizing radiation protection. Optical radiation, with particular reference to lasers.
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Eye↗
Reply to comments on editorial about radiofrequency standards.
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Humans↗
The effect of timolol on anterior-chamber oxygenation.
The effect of timolol maleate, a nonspecific beta-blocking agent, on anterior-segment oxygenation was studied using oxygen-sensitive microelectrodes inserted into the mid-anterior chamber of 13 cat eyes. The anterior-chamber oxygen tension was monitored continuously for two hours following the topical application of three drops of timolol 0.5%. Although a small, but significant, decline in oxygen tension of 19% was observed over the initial 90 minutes (P less than or equal to .05), the overall 10% decrease at the end of two hours was not considered either clinically or statistically significant when compared with a group of controls. Timolol, since it does not contribute significantly to hypoxia, may therefore be a more prudent choice for lowering intraocular pressure in disorders where hypoxia is believed to play an important role, such as in neovascular glaucoma and sickle-cell hyphema.
Animals↗
Retinal oxygenation from the choroid in hyperoxia.
The extraordinarily high rate of blood flow in the cat choroid allows the choroidal oxygen tension to rise to levels close to the arterial PO2, even with oxygen enriched breathing mixtures. The high PO2 in the choroid can elevate the oxygen tension of the inner retina above the saturation PO2 of hemoglobin when oxygen enriched breathing mixtures at one atmosphere or less are used as shown by polarographic oxygen tension measurements in the preretinal vitreous in cats.
Animals↗
Incidence and characteristics of McCollough aftereffects following video display terminal use.
After using video display terminals (VDT), some persons notice that achromatic patterns appear faintly colored hours after terminal use. We investigated the incidence of this effect, the McCollough effect (ME), among 125 VDT users. Subjects completed a questionnaire regarding work habits and certain life-style aspects. They were shown photographs of varying spatial frequencies to identify the adapting stimulus responsible for the ME. The incidence of ME after routine use of VDTs was 19.1%. The adapting stimulus was the repeating character lines of the VDT. No aspect of life-style investigated appeared to predispose an individual to develop the ME. Those subjects who developed the ME did not differ from those who did not in age, sleep, caffeine consumption, use of medication, refractive errors, or computer usage, nor did they have a higher incidence of ocular defects or eye strain.
Computer Systems↗
Ocular oxygenation: the effect of phenylephrine on anterior chamber oxygen tension.
Phenylephrine preparations are widely used in medicine for their vasoconstrictive and mydriatic effects. The effect of phenylephrine, a powerful alpha-receptor stimulant, on anterior chamber oxygen tension (Po2) was studied using a polarographic electrode inserted into the mid anterior chamber of cats. A commercial 10% solution was applied topically. A decrease in anterior chamber Po2 was usually observed in 8-24 minutes and declined steadily thereafter. Prior to treatment, the mean anterior chamber Po2 was 26 +/- 3 torr; 1/2 hour after treatment it decreased to 20 +/- 7 torr. After 1 hour it dropped to 13 +/- 8 torr and was further reduced to 11 +/- 6 torr by 2 hours. By 90 minutes, the drug had caused a 58% reduction in anterior chamber oxygen tension. This drop is similar to that reported for epinephrine. It is suggested that the mechanism for most of this decrease is reduced blood flow, mediated by the direct vasoconstrictive effect of the drug in addition to compression of the iris vasculature induced by dilation. The resulting change (reduction) in caliber of the iris arteries produces a parallel change (reduction) in blood volume and flow resulting in a diminished Po2. The clinical implications of this conclusion in disorders where hypoxia is felt to play a causal role such as neovascular glaucoma, diabetes, pregnancy and hyphema in sickle cell disease are explored.
Administration, Topical↗
The relationship between retinal vessel tortuosity, diameter, and transmural pressure.
Increases in retinal vein tortuosity are thought to be caused by increases in vascular transmural pressure. We have attempted to determine the relationship between retinal vessel tortuosity, diameter, and transmural pressure by examining the effects of changes in transmural pressure on latex tubes with fixed ends. As the transmural pressure is raised, tube diameter increases, but tortuosity does not begin increasing until a critical pressure is reached. Above the critical pressure, tortuosity increases more rapidly than diameter. Our results support the above hypothesis and also suggest that at high transmural pressures, retinal vessel tortuosity is a more sensitive indicator than is the diameter of changes in retinal venous transmural pressure, but diameter is more sensitive than tortuosity at lower pressures.
Humans↗