A visual field test is a method of measuring an individual's entire scope of vision, that is their central and peripheral (side) vision. Visual field testing actually maps the visual fields of each eye individually. The visual field test is a subjective examination, requiring the patient to understand the testing instructions, fully cooperate, and complete the entire test in order to provide useful information.

Visual field testing is most frequently used to detect any signs of glaucoma damage to the optic nerve. In addition, visual field tests are useful for detection of central or peripheral retinal disease, eyelid conditions such as ptosis or drooping, optic nerve disease, and diseases affecting the visual pathways within the brain. The visual pathways carry information from the eye to the visual or occipital cortex in the brain, where this information is processed into vision.
There are a variety of methods utilized to measure the visual fields. Virtually all visual field testing is performed one eye at a time, with the opposite (contralateral) eye completely covered to avoid errors. In all testing, the patient must look straight ahead at all times in order to avoid testing the central vision rather than the periphery. Most modern visual field testing devices also continuously monitor fixation, or the ability of the patient to maintain a consistent straight ahead gaze.

WHAT IS AN A-SCAN?

A scan is an amplitude modulation scan. An A-scan ultrasound biometry, commonly referred to as an A-scan, is a routine type of diagnostic test used in ophthalmology. The A-scan provides data on the length of the eye, which is a major determinant in common sight disorders. The most common use of the A-scan is to determine eye length for calculation of intraocular lens power.

WHAT IS AN ENDOTHELIAL CELL COUNT
(ECC)?

A corneal cell count will tell you how many endothelial cells are present in the inner layer of your cornea. Ophthalmologists do not routinely perform this procedure, but it may be used to evaluate the cornea before cataract surgery. A normal cell count for people ages 40-70 is 2,000 to 3,000 cells per mm2 (cells per square mm). When your cell count drops below 500 per mm2, your cornea might begin to swell and your vision may be blurry.

For intraocular surgery, such as cataract surgery, a cell count of greater than 1,500 cells per mm2 is recommended. The recommended number of cells for intraocular surgery can vary depending on the clinical situation.

OPTIC DISC PHOTOGRAPHY

Photographic images of the optic disc; essential for monitoring glaucoma. Stereoscopic disc photos of the optic nerve are helpful in providing a baseline of information about the optic nerve’s condition for future comparison. These photographs are taken in the ophthalmologist’s office using a special camera that can create a stereo image.