Illumination through the ophthalmic microscope is important for visualization during cataract surgery. We use a combination of both coaxial and paraxial light sources to light up our surgical field. The coaxial lights are aligned co-axial to our oculars, hence their name. The paraxial light is just next to the path of our oculars, usually set a few degrees to the side. It is the balance of the coaxial to paraxial lighting that determines the best red reflex.
Keep in mind that with lens opacities that block light from entering the posterior segment, such as in a white or brunescent cataract, the red reflex will be diminished, even with the coaxial setting at its maximum. In these cases, if the paraxial illumination does not give enough of a view for the capsulorhexis, then the use of Trypan Blue dye is recommended to stain the anterior lens capsule.
When we are operating, the ratio of coaxial to paraxial lighting is typically between 25;75 and 50:50 to give the best balance. For filming videos for surgical teaching, we must skew this ratio for more coaxial lighting, with a ratio of about 75:25 because the camera sensors are not as sensitive as the surgeon’s eyes.
click below to learn the secret to optimizing the red reflex during cataract surgery: