Optic Nerve and Visual Field Interpretation

For optic nerve interpretation, measuring the vertical diameter of the disk is becoming increasingly important.  The size of the disk is critical as a small disk may demonstrate little cupping in a patient with early glaucoma, whereas in a patient with a large disk, considerable cupping may be manifest in the absence of glaucoma.   A small disk is less than 1.5 diameters and a large disk greater than 2.2 diameters.

At our early glaucoma diagnostic center, we use a Zeiss 450 fundus camera combined with Anka® Eye Route system to measure disk diameter and do baseline stereo-disk photography.  

 The “ISNT” is very useful in analyzing rim thickness abnormalities.  The inferior rim tissue is normally the thickest, followed by the superior, nasal and temporal rims.

With visual field testing, I use a standard Humphrey automated perimeter (SAP) on the Standard SITA mode. I pay more attention to the pattern standard deviation than to the gray scale. A normal Standard SITA does not rule out glaucoma. By the time a defect shows up on the SITA Standard, considerable nerve fiber layer loss has already occurred.

In patients with normal SITA fields, I use a blue/yellow (SWAP) or a double frequency technology (FDT) visual field tests.  These selective functional studies target nerve fiber layer receptors are more specific than SAP for early glaucomatous defects. We are one of the few centers to offer all modalities of visual field testing: this creates more specificity and sensitivity in our ability to detect and diagnose glaucoma.