BIO Lenses

Binocular Indirect Ophthalmoscopy (BIO) is a diagnostic procedure by which a practitioner uses a condensing lens and a head mounted ocular system to look at the retinal structures. This technique has a greater scope for dynamic examination due to the mobility offered by the oculars not being fixed to a table top. The patient can be in a supine position or sat with the head tilted at a comfortable angle. The condensing lenses used for BIO examination have a higher magnification and lower field of view profile when compared to slit lamp biomicroscopy lenses. As the names suggests, the image formed is indirect in nature meaning it is inverted and reversed. The distance at which the lens needs to be held in front of the patient’s eye varies depending on the power of the lens. As a general rule of thumb, as the dioptric power of the lens increases, the field of view increases, magnification decreases and the working distance decreases. It is general practice to dilate patients for a BIO exam, in cases where dilation is not possible, or patients inherently have small pupils (neonates or geriatrics) higher power lenses are appropriate.