A variety of optical and electro-optical instruments are used for both diagnostic and therapeutic applications to the human eye. These generally expose ocular structures to either coherent or incoherent optical radiation (ultraviolet, visible, or infrared radiation) under unique conditions. We convert both laser and incoherent exposure guidelines derived for normal exposure conditions to the application of ophthalmic sources.

The light used when undertaking ophthalmic diagnosis or ophthalmic surgery can be hazardous and the need to address this from a clinical and practicable point of view is discussed. Not all patients are equally at risk. Age and health are risk factors that need to be taken into account, the aged eye being more at risk as is the eye with existing disease. The risk of photochemical damage to the retina is increased as a result of patients being examined with different ophthalmic instruments during a 24-h period. The ways in which the clinician needs to address these safety issues is discussed bearing in mind the guidelines that are being developed.

Objective To identify the source of unwanted glare images from a three-piece intraocular lens (IOL) implant following cataract surgery. Method The IOL and posterior capsule were examined under mydriatic and nonmydriatic conditions using direct focal illumination from a slit lamp biomicroscope. Direct focal illumination was undertaken with both a narrow beam (0.1 mm in width) and small spot (0.1 mm in diameter) to identify the points at which the glare images were stimulated. While observing the location of the beam with the slit lamp biomicroscope, the patient indicated when the glare images were stimulated. Results The nasal haptic insertion into the optic was identified as the source of temporal line images arising from lights such as headlamps from oncoming cars and street lamps. The adjacent edge of the IOL was also identified as the likely source of additional cob web-like light rays. Conclusions The haptic insertions in threepiece IOLs may, under certain conditions, interfere with light entering the pupil and produce extraneous images. Large mesopic pupils and decentred IOLs are conditions that increase the likelihood of unwanted glare images.

It is recognised that discrimination of fine detail is dependent on an intact macula with the peripheral retina being responsible for motion detection. There is evidence, however, to suggest that the peripheral retina does play a critical part in such discrimination. Studies of the performance of visually impaired school children have revealed levels of visual perception far exceeding anything that would be expected for individuals so severely handicapped. The art work of visually impaired youngsters was compared with the predicted results based on their visual acuity. The results showed detail that in theory could not have been resolved with such low acuity levels. All the youngsters had dense central scotomata. The peripheral retina, therefore, must have been involved in the discrimination of such detail. These results have implications not only for the visually impaired in terms of what they are capable of doing, but also for our understanding about the way the visual cortex processes information from the peripheral retina and the use that it makes of this relatively poor quality information.

A study was undertaken to determine whether involuntary user movement provides a basis for relaxing the measurement conditions for evaluating the potential optical radiation hazards to the eye from slit lamps and indirect ophthalmoscopes. This was accomplished by assessment of the extent to which light from these devices can be maintained in focus on a 1-mm-diameter fiber-optic cable for 45 s. The results suggest that, although involuntary user movements can be significant, they do not provide a basis for relaxing the measurement conditions for evaluating the potential optical radiation hazards to the cornea and lens from slit lamps and indirect ophthalmoscopes.