Laser pointers: toys, nuisances, or significant eye hazards?

BACKGROUND: Laser pointers have been used inappropriately to harass and "dazzle" victims. Reports of retinal damage caused by pointers have also been circulated in the popular press. METHODS: Information on pointer abuse was collected from the literature and through discussions with specialists. RESULTS: Few, if any, documented cases of permanent retinal damage caused by laser pointers could be found. For actual damage to occur, viewing, times need to exceed approximately 10 seconds. Exposures of this duration would require the person being lased to cooperate by holding fixation on the laser beam. CONCLUSIONS: Although the risk of permanent retinal damage from a laser-pointer beam is minimal, other risks include dazzle, annoyance, and concern that a weapon-aiming device rather than a pointer is generating the laser beam.

The Drug Evaluation Classification Program: using ocular and other signs to detect drug intoxication.

BACKGROUND: A systematic approach to determining drug intoxication has been developed for use by police officers. By considering specific physiological signs, trained officers can detect the effects of seven major drug types. METHODS: Officers follow a 12-step testing sequence and evaluate signs such as pupil sizes and responses, eye movements, heart rate, body temperature, mental timing, and balance. A matrix is then used to compare that subject's signs to those that would be produced by the seven types of drugs. If a pattern match is found, the officer concludes that the subject is under the influence of a drug and specifies the drug type. RESULTS: Several field and laboratory validation studies have been conducted using these procedures. In general, officers were 70% to 90% accurate in determining intoxication status and drug classification, but poly-drug use and drug rebound effects can sometimes cause problems in interpretation. CONCLUSION: Ocular and other physiological signs can be used to detect drug intoxication and classify the type of drug taken. Knowledge of the procedures used in the Drug Recognition Program can enable optometrists to serve as consultants to the police and as expert witnesses in cases involving the use of ocular signs that indicate illicit drug use.

Vertical and horizontal eye displacement during static pitch and roll postures.

The positions of both eyes were measured objectively in the dark following "look straight ahead" instructions for 16 subjects at 27 combinations of static pitch and roll postures over 360 degrees of space, using an infrared video technique. Shifts in vertical version, or the doll reflex, varied sinusoidally with pitch and roll angle. At 0 degree roll, the average response has a peak-to-trough amplitude of 9.28 degrees and is symmetric about a downward eye position of 4.63 degrees. The proposed Dual Otolith Model (DOM), based on a combination of utricular and saccular inputs, provided excellent fits to the present data (R2 = 0.876) and to the data of previous studies (R2 = 0.916 to 0.994). Deviations in horizontal version varied sinusoidally with roll angle, with no significant effect of pitch angle. In general, clockwise (right-ear-down) rolls produced rightward eye movements, and counterclockwise (left-ear-down) rolls produced leftward eye movements. The average versions were symmetric about a leftward eye position of 1.14 degrees, with a peak-to-trough amplitude of 3.76 degrees. The data were well represented by the proposed Horizontal Version Model (HVM; R2 = 0.796), which depended only on utricular input.

Absence of adaptive plasticity after voluntary vergence and accommodation.

Subjects maintained their eyes crossed (verged) for a period of 8 min in darkness with monitoring provided by an infrared video system. Changes in resting vergence (RV) and resting focus (RF) were examined. Results showed: (i) visual stimulation was not necessary for adaptation of either RV or RF, but (ii) these purely motor effects were significantly smaller and more dissipative than those attributable to visually driven adaptation, and (iii) voluntary vergence amplitude was negatively correlated with pupil size. Assuming that voluntary vergence is driven by accommodation, then the voluntary signal must enter the oculomotor control system prior to the cross links between channels, but beyond the site of the visually driven adaptive elements.

A Badal optical stimulator for the Canon AutoRef R-1 optometer.

The Canon AutoRef R-1 optometer is currently in use by several investigators in studies of accommodative response and open loop accommodation. It has the capability for frequent (1.4 s cycle time in "single shot" mode) objective measures of the refractive state of the eye and, because it uses near infrared radiation, it provides no stimulus to accommodation. In this paper we describe a compact device which can be mounted on the R-1 optometer, coaxial with the measurement optics of the optometer, to provide controlled optical vergence, i.e., accommodative stimulus, from +10.0 to -20.0 D while maintaining a constant visual angle.

Modulation transfer functions and contrast sensitivity through low vision telescopes.

Telescopes are coherently coupled to the eye. Because their wavefront aberrations may be altered by the optics of the eye, especially by accommodation, some researchers question the ability of their modulation transfer functions (MTF) to predict changes in contrast sensitivity functions (CSF) through them. We measured the CSFs of visually normal and aphakic subjects through telescopes. We found that MTF appears to be useful for ranking the telescopes, and accommodation appears to improve focus and partly balance wavefront errors. Our results suggest that cascading (multiplying the contrast of the instrumental MTF with the unaided CSF at each spatial frequency) is useful for predicting visually aided CSFs to within 4 dB.

An instrument for measuring the modulation transfer functions of low power telescopes and telemicroscopes.

An instrument using an electro-optical Fourier method for measuring the modulation transfer function (MTF) of low power telescopes and telemicroscopes is described. Because these devices are afocal, or nearly so, relay optics are needed to form real images at the detection section of the apparatus. The system is capable of measuring the MTF in monochromatic and white light, at any target azimuth, across the field of view, and through focus. The target system contains 14 square-wave gratings with spatial frequencies that range from 2.5 to 156 cpd. Images of these gratings are scanned across a slit. The output data are fed to a first-order recursive digital Butterworth bandpass filter for MTF analysis. The apparatus is diffraction limited at f/31.4. Therefore, it negligibly affects the measurement of the MTF of telescopes and telemicroscopes tested with exit pupils of up to 6.4 mm.

Modulation transfer functions of low power telescopes.

The modulation transfer functions (MTF's) of 131 low power Galilean and Pechan roof prism Keplerian telescopes comprising 20 models from 7 vendors were measured. MTF results are compared according to model, by type (Galilean or Keplerian), and magnification. Measurements were made on-axis and at the +/- 0.7 field angles. In addition to measuring tangential and radial MTF's some devices were tested with target grating azimuths of 45 degrees and 135 degrees. We also measured the effect of 3 and 6.4 mm exit pupil diameters on the MTF, and compared a color-corrected with a non-color-corrected design in monochromatic and white light. Galilean telescopes exhibited superior MTF's compared to Keplerian designs. The MTF's of Galilean telescopes tested on-axis with vertical and horizontal gratings were equivalent, as expected of rotationally symmetrical devices. However, similarly tested Keplerian telescopes exhibited significantly higher MTF's with vertical gratings. Tests at +/- 0.7 field angles showed that the tangential MTF's of Galilean telescopes were consistently poorer than radial MTF's, but the opposite was true for Keplerian telescopes. The comparatively poorer results obtained with the Keplerian telescopes are due to image doubling and deviation errors of the roof prisms that are dependent on the azimuthal orientation of the prism roof edge. Failure to adopt and maintain the same orientation of hand-held prism monoculars may result in experiencing a variable sharpness of image each time that they are used. Prism deviations of binocular devices must be controlled to avoid vertical disparities.

Optical properties of low vision telescopes.

Angular magnification, resolving power, astigmatism, field of view, eye relief, and light transmittance of 157 low power telescopes comprising 25 models from seven manufacturers were measured. Roof-prism Keplerian telescopes provided about one-half the resolution, 30% lower transmittance, and more objectionable image flare than Galilean designs. The roof-prism was responsible for producing overlapping doubled images that appeared astigmatic-like. The prism further compromised rotational symmetry by deviating the image in a direction along the roof edge. The Keplerian telescopes, however, had about twice the field of view of the Galilean telescopes. Notably, several Keplerian telescope models from different suppliers were found to be optically identical, although they varied 50-100% in price.