What instrument is primarily used by eye doctors to examine the interior of the eye?

The instrument primarily used by eye doctors to examine the interior of the eye is the ophthalmoscope. This device allows the practitioner to view the retina, optic disc, and other structures inside the eye by utilizing a system of lenses and a light source. By directing light into the eye, the ophthalmoscope creates a magnified image of the internal eye structures, enabling the detection of various eye conditions such as diabetic retinopathy, glaucoma, and macular degeneration.

While stethoscopes are utilized in a variety of medical examinations to listen to internal sounds of the body, primarily in the heart and lungs, they are not suited for eye examinations. Retinoscopes are helpful in determining the refractive error of the eyes but do not provide a view into the interior structures of the eye itself. Tonometry is a method used to measure intraocular pressure and can indicate the risk of glaucoma, but it does not facilitate a direct view of the interior anatomy. Thus, the ophthalmoscope remains the key tool for interior eye evaluation.