Visual Field Monitoring:

Standard automated perimetry (SAP)

The most common type of visual field testing flashes a white dot of different intensity and sizes on a white background.   The light tests 24 degrees of the peripheral vision as most early glaucoma defects show within this area (the total extent of the peripheral vision is 110 degrees.  (show picture).    By modulating the size and intensity of the light to the faintest light the patient is able to discern, the visual threshold is determined.  SAP testing is most useful when a visual field defect had been found and the doctor wishes to observe the defect for progression. Progression can occur be the defect either getting denser or larger. Because of normal fluctuations in test taking, at least three contiguous points must have worsened from previous testing, and this worsening must be verifiable on two subsequent tests to validate the progression.

Double Frequency Testing (DFT)

Another modality-double frequency testing flashes two images a microsecond apart in the same portion of the visual field. The patient perceives this as a single image. This double frequency image is uniquely processed by the M-ganglion. The M-ganglion, in contradistinction to other cell types of the nerve fiber layer, is only present in small numbers. The M-ganglion cell, being in such short supply, is much more sensitive to even a small loss of its cells. Hence, the double frequency stimuli have been found to be more sensitive in picking up early glaucoma field loss than white on white testing. Numerous clinical studies have confirmed the increase sensitivity of double frequency screening versus white on white testing in eralt glaucoma.

We find the Matrix to be a valuable early detection tool. Whereas the standard white on white was often normal in patients with ocular hypertensive and suspected early cupping, the double frequency matrix testing will often manifest a defect in these cases. And it can be quite reassuring if this test is normal in the presence of questionable nerve or visual field changes.

Next Page ->