Perimetry

Methods for visual field examination

Assessment of the visual fields is a crucial step in neuro-ophthalmological examination. In clinical practice, two main approaches are used to evaluate the boundaries of visual perception.

Clinical (rough) examination This method allows the physician to quickly assess the state of the visual fields without using complex equipment.

• The patient covers one eye and fixes their gaze steadily on the bridge of the examiner's nose.
• The physician slowly moves an object (e.g., a neurological hammer or simply their fingers) along an arc.
• The movement starts from the far periphery, which is knowingly located outside the normal borders, moving toward the center.
• The examination is carried out in all main directions: right, left, top, and bottom.
• The patient's task is to report the exact moment the object first appears in their visual field.

Instrumental examination For more detailed and accurate diagnosis, instrumental perimetry is used. This examination is performed by a specialist (neuro-ophthalmologist). During perimetry, the precise boundaries of visual perception and identified defects are plotted on special charts (perimetrograms). Normally, the visual field borders for the right and left eyes exhibit characteristic smooth physiological contours with no areas of visual loss (defects).

Normal visual field borders

When tested with a white stimulus, the physiological borders of a healthy person's visual fields have strictly defined angular values. They are not perfectly symmetrical due to the anatomical structure of the face (influence of the nose and brow ridges).

Normal values (for white color):

• Outer border: 90°
• Lower border: 70°
• Inner border: 60°
• Upper border: 60°

Types of defects and topical diagnosis

The nature of visual field changes directly depends on the level at which the visual pathway is damaged. Several main types of defects are distinguished.

Scotomas A scotoma is an isolated blind spot (defect) within the visual field that does not merge with its peripheral borders.

• Central scotoma represents the loss of the central part of the visual field. This symptom, much like complete blindness of the affected eye, is characteristic of pathology in the macular region of the retina, the optic disc, or partial damage to the optic nerve trunk.
• Loss of the inner parts of the visual fields also falls under scotomas.

Lesion of the optic chiasm (chiasma opticum) The pattern of impairments when the chiasm is damaged is extremely variable. It depends on the severity and exact localization of the pathological process (whether the upper or lower surface, anterior or posterior part of the chiasm is affected). The most illustrative and characteristic form is bitemporal hemianopsia—the symmetrical loss of the outer (temporal) halves of the visual fields in both eyes.

Lesions of retrochiasmal structures Retrochiasmal structures include:

1. Optic tract (tractus opticus).
2. Lateral geniculate body (corpus geniculatum laterale).
3. Visual cortex (cortex visualis).

Unilateral damage to any of the listed structures leads to homonymous hemianopsia on the opposite side (contralaterally). In this case, symmetrical parts of both visual fields are lost (completely or partially, e.g., quadrantic/sectoral).

Unlike homonymous hemianopsias, non-homonymous (heteronymous) hemianopsias represent asymmetrical losses of visual field halves (as in the case of bitemporal hemianopsia).

Disturbances of visual perception

In addition to visual field constriction and decreased visual acuity, patients may encounter qualitative disturbances of visual perception.

• Distortion of size and shape: patients may see objects unnaturally small (micropsia) or too large (macropsia). Distortion of object shape is called metamorphopsia.
• Elementary sensations: the emergence of visual images unrelated to actual light stimulation. A prime example is phosphenes, which can occur due to mechanical pressure on the eyeball or trauma.
• Complex phenomena: the formation of visual illusions and full-fledged visual hallucinations.

Class and exam questions

What else to study on this topic

• Dependence of defect shape on localization within the chiasm (upper/lower, anterior/posterior parts)
• Symptomatology of optic radiation damage (radiatio optica)
• Types and mechanisms of formation of visual illusions and hallucinations
• Differences between complete blindness of the affected eye and a massive central scotoma
• Features of quadrantic and sectoral homonymous hemianopsias

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.