Week 7 Review

Perimetry- the science of measuring the peripheral vision in order to determine the visual field. (The art of determining boundaries of the visual field.)

Visual field- the portion of visual space which is visible to an individual at any given moment.

Isopter-Boundaries of VF areas of equal or greater sensitivity. Isopters are used in Goldmann perimetry. Each isopter is labeled with the size and intensity of the stimulus.

Threshold-A stimulus intensity which has a 50% probability of being seen. This test compares what has the probability of being seen with the possible inaccuracy of the test. Computerized perimetry only.

Asb- intensity value of a stimulus. Used in static perimetry. Smaller asb= greater retinal sensitivity.

dB- intensity value of a stimulus. Larger dB= greater retinal sensitivity.

scotoma

Scotoma Visual loss, either

blindness (absolute) or decreased sensitivity (relative).

Island of visionAn analogy for visual field testing.

Physiological blind spotNormal visual field boundaries

95-100 degrees=temporal 75 degrees= inferior 60 degree= nasal 60 degrees=superior

Computerized VF tests

30-2 and 24-2 threshold- white lights, varying in intensity. Tests 30 or 24 degrees off the macula in all meridians on dilated patient.

Macula- white lights, varying in intensity. Tests 5 degrees off the macula in all meridians on dilated patient.

Plaquinil- red lights, varying in intensity. Tests 5 degrees of the macula in all meridians on dilated patient. Used for the drug “Plaquinil” which can damage cone photoreceptors.(RA)

Bleph- White lights, fixed intensity testing the superior region of the visual field on an undilated patient. There is a lower fixation light.

False positive-no light shown, patient responded. (“trigger happy”.)

False negative-no response to a previously seen target.

30-2 threshold VF Central 10/macular VF

Computerized VF tests

Screening tests Minimal information done on a computerized VF. Takes much less time to perform. C= central region P= peripheral region FF= full field The number after the letter indicates how many

targets will be shown to the patient. The targets are fixed intensity. It does not print out in grey scale- screening

tests will show a circle for seen targets and a black square for unseen targets.

Confrontation visual field Amsler grid

Goldmann manual VF

Technician moves target, changes target intensity and size, watches fixation, plots chart, investigates a depression or scotoma.

Goldmann VF testing can be done with static or kinetic targets.

Isopters are used and are color coded or labeled to indicate intensity of target.

Types of scotomas

Hemianopia- Binocular- Monocular- Homonymous- Congruent- Incongruent- Bi nasal- Bi temporal- Altitudinal- Central cecal- Nasal step-( bjerrum) Temporal wedge-

Types of scotomas

4 visual pathway zones

Monocular retinal zone Nerve fiber/ optic nerve zone Binocular chiasmal zone Post chiasmal zone

4 majors visual pathway zones

Monocular retinal zone This zone includes the retinal layer, sub retinal layer,

rod and cone dystrophy or damage, retinitis pigmentosa, and macular pathology.

Characteristics All defects will be monocular. Most pathology will be visible with a scope. Lesions temporal to fovea present nasal of VF.

(inverted field image) Lesions can cross meridians. Central scotomas will cause abnormal VA and color

vision will be compromised.

4 major visual pathway zones

Nerve fiber/optic nerve zone This zones includes glaucoma, papilledema, and

nerve fiber bundle defects. Characteristics All defects will be monocular. Both eyes can have the same disease causing

congruent or incongruent scotomas. Most defects will be visible with a scope. Defects will points to the disc since nerve fibers are

traveling towards this point. Glaucomatous scotomas will respect the horizontal

meridian.

4 major visual pathway zones

Binocular chiasmal zone This zone includes pathology or damage to the

pituitary gland. Charateristics Defects will be bilateral, most commonly bi temporal

but bi nasal defects can also occur. NOT visible with a scope, a CT-scan or MRI will be

ordered. Defects here are not an eye problem, this problem is

in the brain and effects both eyes because the nasal axons or nerve fibers have crossed to the opposite side at the chiasm.

Defects will respects the vertical meridian and be hemianopic.

4 major visual pathway zones

Post chiasm zone This zone includes the optic tract, lateral geniculate

body, optic radiations and the occipital cortex. Characteristics Most defects will respect the vertical meridian. Defects will be homonymous and hemianopic. This is NOT an eye problem, this is a brain problem

and a CT-scan or MRI will be ordered. Nerve fibers from the nasal VF of one eye and

temporal fibers of the other eye will be effected on one side of the brain giving the defect a classification of left or right even though is effects both eyes. The left or right relates to the side of the brain effected.

4 major visual pathway zones

Good luck on the test and have a great summer! See you in September.