Determination of absolute size of fundus objects.

BACKGROUND: Creating multiple beam interference fringes on the retina using the "retina fringe projector" (RFP) provides us with a scale which can be used to determine the absolute size of objects at the fundus. METHODS: The procedure is tested on an model eye, the optical parameters of which are varied in order to simulate different refraction conditions. The RFP was used to determine the size of a known object at the model fundus; the result was then checked against the real value of the object. In a second series of measurements, the RFP fringes were included in fundus photos of 52 patients with varying levels of ametropia, taken at the University Eye Clinic in Jena using the FF450 fundus camera (manufacturer: Carl Zeiss Meditec AG) for diagnostic purposes. The distance between the fringes was determined using both the RFP and the Littmann method. RESULTS: The differences to the real value of the fundus size of a known object deviated on average by 1 to 2%, and always remained under 3% in the model eye. A very good correlation between RFP and Littmann methods results could be found in the clinical part of the study. The resulting deviations are below 2.5%. CONCLUSION: Integration of a RFP in a fundus camera permits measurement of absolute values of the retina, regardless of the type of observation or documentation. Knowing the real size of fundus objects holds a potential in many clinical classification scales of fundus objects such as drusen or vessels, or in optimizing photodynamic therapy spot size measurement.

Laryngeal morphometry with a new laser 'clip on' device.

BACKGROUND AND OBJECTIVES: Qualitative laryngoscopic investigations belong to diagnostic routine in laryngology. Nevertheless, quantitative morphometric measurements of intralaryngeal structures have been difficult by now. STUDY DESIGN/MATERIAL AND METHODS: The development of a two-point-light projection method for endolaryngeal measurements that works with a double reflecting mirror and green laser light is shown. RESULTS: The laser beams that have a distance of exactly 2 mm are very well visible at the surface of laryngeal structures. The technique can be used during a routine videoendoscopic examination. CONCLUSION: In our opinion this method enables accurate quantitative morphological measurement within the larynx that could be used even in clinical routine. The two-point light projection technique helps to reduce former limitations of endoscopic investigations.

Study of the effect of involuntary user movement on the potential light hazards from some ophthalmic instruments.

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.