A variety of tests can be carried out to confirm a problem or to determine the extent or severity of the disorder. Each eye is tested separately.
Fluorescein angiography allows a doctor to clearly see the blood vessels at the back of the eye. A fluorescent dye, which is visible in blue light, is injected into a vein in the person's arm. The dye circulates through the person's bloodstream, including the blood vessels in the retina. Shortly after the dye is injected, a rapid sequence of photographs is taken of the retina. The dye inside the blood vessels fluoresces, making the vessels stand out. Fluorescein angiography is particularly useful in the diagnosis of macular degeneration, blocked retinal blood vessels, and diabetic retinopathy.
Electroretinography allows a doctor to examine the function of the light-sensing cells (photoreceptors) in the retina by measuring the response of the retina to flashes of light. Eye drops numb the eye and dilate the pupil. A recording electrode in the form of a contact lens is then placed on the cornea, and another electrode is placed on the skin of the face nearby. The eyes are then propped open. The room is darkened, and the person stares at a flashing light. The electrical activity generated by the retina in response to the flashes of light is recorded by the electrodes. Electroretinography is particularly useful for evaluating diseases, such as retinitis pigmentosa, in which the photoreceptors are affected.
The eye can be examined by ultrasonography (see see Common Imaging Tests: Ultrasonography). A probe is placed gently against the closed eyelid and painlessly bounces sound waves off the eyeball. The reflected sound waves produce a two-dimensional image of the inside of the eye. Ultrasonography is useful when an ophthalmoscope or slit lamp cannot view the retina because the inside of the eye is cloudy or something is blocking the line of sight. Ultrasonography can be used to determine the nature of abnormal structures, such as a tumor, inside the eye. Ultrasonography can also be used to examine blood vessels supplying the eye (Doppler ultrasonography) and to determine the thickness of the cornea (pachymetry).
Pachymetry (measuring the thickness of the cornea) is very important in refractive eye surgery, such as laser in situ keratomileusis (LASIK).
Pachymetry is usually done by using ultrasonography. For ultrasound pachymetry, the eye is numbed with drops, and an ultrasound probe is placed gently onto the surface of the cornea. Optical pachymetry methods do not require numbing eye drops because the instruments do not touch the eye.
Computed Tomography and Magnetic Resonance Imaging
These imaging techniques (see also see Common Imaging Tests: Computed Tomography and see Common Imaging Tests: Magnetic Resonance Imaging) can be used to provide detailed information about the structures inside the eye and the bony structure that surrounds the eye (the orbit). Computed tomography is particularly useful for locating foreign bodies inside the eye.
Last full review/revision December 2006 by Kathryn Colby, MD, PhD