Aspects of vision – Visual field


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Raising a red flag

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Scotomas that manifest as visual field loss can be the result of a wide range of disease processes affecting either the optic nerve, the retina or the brain. Tests that identify scotomas – including their size, shape and location on the retina – can aid in the diagnosis of glaucoma and its associated optic nerve damage, diseases of the retina such as macular degeneration, retinal detachment, and retinitis pigmentosa, as well as systemic diseases that can cause retinal and/or optic nerve damage resulting in visual field loss such as diabetes, hyperthyroidism, hypertension and multiple sclerosis.

Visual field loss can also result from problems caused by tumors in the eye or optic nerve and damage caused by an eye injury. As well, visual field loss is not only caused by eye disorders but can be the result of problems is in the brain such as a pituitary tumor or tissue damage after a stroke.

Tracking the pattern of visual field loss provides important information about the progression of diseases associated with peripheral field loss such as glaucoma, retinitis pigmentosa and retinal detachment. Knowledge of scotomas is important for certain treatment decisions.

Glaucoma

Because glaucoma affects peripheral vision well before central vision, awareness of visual field loss is especially important in glaucoma treatment. Glaucoma often goes undiagnosed for long periods of time, as peripheral vision loss is often unnoticed by those with early glaucoma. Yet early detection of glaucoma is critically important, because once retinal cells are destroyed they do not regenerate. By the time one has noticed deterioration of visual function the loss is permanent.
Because optic nerve damage caused by glaucoma creates very specific visual field defects, visual field testing provides a picture of functional status of the visual system which can assists in diagnosing and following glaucoma

Macular degeneration

Macular degeneration is the result of degeneration of the nerve cells in the the macula, the center part of the retina responsible for detail vision (acuity). Someone with macular degeneration will lose central vision while retaining peripheral vision.

Visual field tests are often described as testing “peripheral vision” but your visual field includes both your central vision and side (peripheral) vision.

Those with early macular degeneration may still have relatively good acuity and little awareness of disruption to their central field while visual field tests indicate central scotomas. While these people may be having difficulty with central vision tasks such as reading, they may be unaware of the scotomas that are causing the difficulties.

As well, because untreated dry macular degeneration can progress to the more serious wet macular degeneration, visual field tests that catch the disease early on are invaluable.

Scotomas in the real world

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The visual field test allows those with diseases such as glaucoma and macular degeneration to see their blind spots (scotomas). This awareness is an essential step in learning to adapt to changes in visual abilities.

For those with glaucoma, visual field deficits often go unnoticed, because peripheral field information is largely processed unconsciously. When peripheral vision deficits are not noticed as real vision problems, the consequences of scotomas such as bumping into objects or tripping on curbs and steps are often interpreted as clumsiness. Seeing their scotomas may help those with significant visual field defects better assess whether it is safe for them to be driving a car.

Awareness of visual field defects is the first step in getting help from vision therapy resources who can help someone adopt strategies and tools for enhancing their vision and overcoming their visual deficits.
LINK to scotoma awareness module >>>

If the area of vision loss is small and not located in the center of the visual field, it may not affect your daily life significantly. If a scotoma is large, or there are many, or a scotoma obstructs central vision, activities of daily life such as moving freely, reading, cooking, and using a computer can be profoundly affected. While you might not even notice a large scotoma in a more peripheral part of the visual field, even a very small scotoma that affects central or macular vision can produce a significant visual handicap.

Scotomas can result in contrast sensitivity loss when a scotoma renders low contrast objects invisible while still allowing one to see higher contrast objects.

Visual field loss – particularly on the right side – can hinder reading ability. As you read, while you are fixating on the letters or word you are reading you are as well anticipating what’s to come as you scan to the right. When scotoma make scanning to the right more difficult, your eyes must scan more to the right and back again. If you can read short words easily but hesitate when reading longer words, there’s a good chance your functional area of vision has become constricted. Learning scanning techniques can help improve one’s reading ability.

As someone learns new skills for scanning their environment, a field test can then be used to document for them changes to their ability to see their surroundings.

Because peripheral vision remains when central vision is affected for those with macular degeneration, they can learn to use peripheral vision to see what they can not see if they look directly at something or somebody. While a scotoma may be blocking detailed central vision, an area just to the side of the scotoma may be unaffected. By looking slightly away from the subject to view it peripherally with another area of the visual field, less acute areas can act as a reasonable substitutes.

This technique, called eccentric viewing, takes training and practice; you are requiring the eyes and the brain to learn a new method of seeing, which means developing new habits and skills. This technique for maximizing existing vision begins with training isn identifying the blind areas (scotomas).