The Oculus system fits most operating microscopes. It allows the surgeon to operate in the eye without using a contact lens or having an assistant holding a lens in front of the eye for the duration of the operation.
The BIOM (Binocular Indirect Ophthalmo Microscope) holds a lens away from the eye allowing fine focus and a panoramic view, even through small pupils. When necessary, the BIOM can either be swung away from the operating field if another procedure is required or the lens can be changed to allow different procedures such as macula hole surgery.
Wide-field lenses invert the image, which is not acceptable, hence the use of the SDI (Stereo Diagonal Inverter) which rectifies the image for the surgeon.