Visual Field ExaminationsWeek 5

Glaucoma is a disease of the optic nerve. Progressive loss of axon or nerve fibers

cause irreversible visual field loss. The area of visual field loss is determined

by where the damage has occurred either on the rim of the optic nerve or the nerve fiber layer.

Pressure readings higher than the normal, 10-21mm hg will be observed. The higher than normal pressure readings will cause a loss of axons throughout the nerve with concentric enlarging of the cup and thinning of the rim.This type of damage causes a generalized decrease in sensitivity.This type of VF loss is seen in the early stages of glaucoma.

When viewing a VF automated printout, readings for the average “normal” VF should be in the lowers 30’s centrally and upper 20’s-lowers 30’s in the peripheral VF.A patient with high tension glaucoma will have lower than “normal” readings across the whole VF.Progressively, the high tension patient will have a “ring around the collar” effect.

This "collar” will get progressively worse over the years and close in to tunnel vision and end stage glaucoma.

This is an example of high tension glaucoma shown over a period of years.

A computer printout from the Humphrey VF allows the technician to printout a comparison of all VF’s done a one patient.

This allows the doctor to see all of the VF’s done on a patient so he doesn’t have to flip through the chart to get the comparison.

Patient’s with low tension glaucoma will have pressure readings within the “normal” limits of mm hg.( between 10-21mm Hg)

The damage from low tension glaucoma may occur in a more focal manner, with enlargement of the cup toward the superior and/or inferior poles of the disc.

This will result in nerve fiber bundle defects in the VF.

IMPORTANT NOTERED=MACULAPINK=DEFECT

Nerve fiber bundle defects will always show opposite of the damaged area on the visual field.

If the defect is on the inferior retina, it will show superior on the VF.

ARCUATE ARCUATE

This nerve fiber layer has damage inferiorly but shows superiorly on the VF.

This “reversal” will always happen with any defect before the chiasm.

Any defect in the retina, macula, and nerve will show opposite of the damage on the VF.

NASAL STEP NASAL STEP

TEMPORAL WEDGE TEMPORAL WEDGE

After years of glaucoma, the individual defects get worse.New nerve fiber bundle defects can occur and worsen.

In advanced glaucoma or end stage glaucoma all of the individual nerve fiber bundle defects start to combine into one large defect, resulting in tunnel vision.