Iris clipping of a diode laser beam when performing retinal photocoagulation

The Microlase infrared diode laser has recently become available for retinal photocoagulation. It uses a laser beam with a large convergence angle (23 degrees). This gives rise to a laser beam with a relatively large cross section at the subject's pupil. In this study the pupillary area required to view the fundus at the slit-lamp with a 90-dioptre lens is determined. It is found that the pupillary area required to view the fundus is smaller than the cross section of the Microlase laser beam at the pupil. Thus iris clipping of the laser beam can occur even though the surgeon has a clear and bright view of the fundus. Care should be taken to use the Microlase only in the presence of a widely dilated pupil.