Site of potential operating microscope light-induced phototoxicity on the human retina during temporal approach eye surgery

Objective: To determine the site of focal illumination on the retina of pha kic human cadaver eyes from an operating microscope positioned for temporal approach eye surgery. Design: Experimental study. Methods: A Zeiss OPMI-6SFR operating microscope (Zeiss Humphrey Systems, Du blin, CA) was positioned over two phakic human cadaver eyes to measure the site of the focal illumination on the retina by directly observing the illu mination on the posterior scleral surface of the globe. External localizati on of the foveola was made by direct observation using scleral indentation and indirect ophthalmoscopy. Various combinations of microscope angulation and field of view were analyzed. Main Outcome Measures: Distance of focal illumination from the operating ro om microscope relative to the foveola was measured. Results: The diameter of the "hot spot" of focal illumination on the retina was 4.0 mm, With the eye positioned straight ahead and the level operating room microscope positioned for temporal approach eye surgery, the center o f retinal illumination was 0.9 and 1.4 mm nasal relative to the foveola whe n the microscope field of view was centered over the cornea and temporal li mbus, respectively. With the microscope angled 5, 10, 15, and 20 degrees te mporally (oculars tilted toward surgeon), the center of the illumination wa s displaced nasal to the foveola by 1.1, 1.5, 3.8, and 5.1 mm, respectively , when the field of view was centered over the cornea and 1.5, 2.6, 4.7, an d 6.0 mm, respectively, nasal to the foveola when centered over the tempora l limbus, Conclusions: Retinal illumination from an operating microscope positioned f or temporal approach eye surgery has the potential for light-induced injury to the fovea, Angulation of the operating microscope by up to 10 degrees t emporally when the microscope field of view was centered over the cornea an d up to 5 degrees temporally when centered over the temporal limbus was not adequate to displace the focal illumination off the foveola when the eye w as in the straight-ahead position. Tilting the operating microscope 15 degr ees or more temporally when centered on the pupil and 10 degrees or more wh en centered over the temporal limbus should safely displace the retinal lig ht exposure away from the fovea during temporal approach surgery. Suggestio ns for reducing the risk of iatrogenic phototoxicity are reviewed. Ophthalm ology 2001;108:381-385 (C) 2001 by the American Academy of Ophthalmology.