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BITEMPORAL HEMIANOPIA

CONTENTS:

Definition Pathophysiology : >Visual Pathways >Visual Fields Etymology Causes Diagnosis:>Perimetry>Confrontation testing>Relation with underlying diseases Treatment

DEFINITION: Bitemporal heteronymus hemianopia is a

type of a partial blindness where vision is missing in the OUTER HALF or the temporal half of both the right and left visual fields.

Hemi-anopia means the absence of vision in half of the visual field of one eye.

PATHOPHYSIOLOGY VISUAL PATHWAYS:A normal visual pathway has the following components:o Retinao Optic nerveso Optic chiasm: where optic nerve fibres from

the nasal hemiretina of both sides decussate and pass to the opposite optic tract.

o Optic tractso LGNo Optic Radiation or geniculocalcarine tracto Primary Visual Cortex or Brodmann’s Area 17

In bitemporal hemianopia, the lesion or damage occurs in the region of OPTIC CHIASM.*(labelled B)*

VISUAL FIELDS:“The field of vision is the visual area seen by an eye at a given instant.”>The area seen to the nasal side is called the nasal field of division.>The area seen to the lateral side is called the temporal field of vision.>>In this disease, the nasal half of each retina is blinded which means the person is blind in the temporal field of vision for each eye because the image of the field of vision is inverted on the retina by the OPTICAL SYSTEM of the eye.

Paris as seen with normal eyes.

Paris as seen with bitemporal hemianopia.

ETYMOLOGY bi-: involves both left and right visual fields temporal: involves the temporal visual field hemi-: involves half of each visual field anopsia: blindness (formed by an, no + opsis,

vision) Why called heteronymus although both sided

temporal visual fields are involved?

The word heteronymus/homonymus hemianopia is used for the LEFT OR RIGHT sides of visual fields of both eyes.

Since, temporal side of right eye=right

temporal side of left eye= left ; so hetero.

CAUSES Tumors located at the mid-optic chiasm. Pituitary Gland tumors:They press upwards from the sella turcica (bony border) on the bottom of the optic chiasm. Tumors includeAdenomasCraniopharyngiomas

Aneurysm in the anterior communicating artery which passes superior to the chiasm.

Pituitary tumor causing lesion.

DIAGNOSIS PERIMETRY:>It is a procedure in which the visual field of the subject is found exactly and drawn on a chart.>Subjects look at a central spot.>A small dot of light or an object is moved in the field of vision.>Subject tells whether he can see the object or not and a graph is plotted in this way.>Digital perimeters are available now-a-days.

COMPUTERIZED AND ANTIQUE PERIMETERS

CONFRONTATION TESTING: It is the bedside method of determining the

visual fields. The doctor and patient are focussed on each

other and eye to eye. The doctor makes sure whether the finger in

his visual field is also in the patient’s field of vision or not.

Flicks his fingers or shows a number to count.

RELATION WITH PITUITARY TUMOR:

When there is pituitary tumor as the underlying cause, as it is most common, the levels of various hormones in the body are upset.

Eg, TSH, T3, T4, Prolactin, etc.Therefore, blood levels of these hormones are also determined.

CURE AND TREATMENT There is usually no cure for hemianopias, but

in some cases surgical procedure for removing pituitary tumor can be done.

Treatments include:>Research>Goggles> Audiovisual Stimulation Training >Explorative Saccade Training >Optical Visual Span Expanders >Visual Restoration TherapyMost doctors recommend the uses of a combination of these treatments.