Visual Field Analysis
Field of vision describes the side vision when one is looking straight ahead. The testing of the extent of the side vision is important in the diagnosis and follow up of several disease including glaucoma, and diseases relating the eye with the brain (neuroopththalmology). The test is usually done on computerized machines ( Humphrey field analyzer). The machine is programmed to test several points , sometimes repeatedly with varying illumination. The test may take time depending upon the defect in a given patient. The computer has an inbuilt software that enables comparison of the field charting on repeat testing of the same patient.
HESS AND DIPLOPIA CHARTING
These two tests enable the measurement of misalignment between the two eyes. This type of problem leads to a condition of double vision in a patient. The extent of the double vision and the direction in which it is maximal can be charted by using these two tests. The tests are done using red and green goggles where in one colored glass is placed in front of one eye and the other in front of the other.
CONTRAST SENSITIVITY TESTING
Certain disease of the retina and optic nerve leave behind subtle defects of sensitivity. A patient is very symptomatic of these deficiencies but the commonly performed tests like the vision testing do not reveal the true extent of the defect. Measurement of contrast sensitivity enables one to understand these subtle defects in the visual function. This test involves identification of patterns of grey on grey background.
COLOR VISION TESTING
Color vision is an important component of human vision. Defects in this can be by birth or due to any acquired diseases. The testing is done using one of the two methods.
In this, many charts are presented and the patient is asked to identify the letters or numbers in the chart.
FARNSWORTH-MUNSELL 100 HUE TEST
In this the patient is asked to arrange several caps of different hues in their order. The test is done in good illumination.
VISUALLY EVOKED POTENTIAL (VEP)
In this test bright light or patterns of dark and light bands are projected on to the eye. The electrical potentials that are generated in the brain as a result of the light or pattern are recorded. This gives valuable information regarding the functional intactness of the optic nerves and the optic pathways that normally conduct these impulses to the brain.
CT scanning is a computerized system where in x- rays are used to construct images of thin slices of tissues allowing detailed evaluation of the tissues under consideration. By manipulating the soft ware, the image quality and detail can be enhanced. Additional information can be got by injecting some drugs called contrast agents. CT scanning is very useful in the evaluation of diseases of the orbit (bony cage in which the eye is located) as well as some diseases of the eye itself. Injury related problems – especially presence of foreign bodies is easily picked up and located on CT scanning.
MRI scanning is a different technology and looks at the tissues in a different perspective. Sometimes both CT and MRI scanning may be needed to understand some diseases. MRI is especially useful in diseases of brain that may affect the eye. By using some specialized soft ware, one can even image the blood vessels of the brain without injecting any drug ( MR Angiography).