The visual field refers to the entire area a person can see when looking straight ahead, including central and peripheral vision. This field is measured in degrees.
  • A person with normal vision can typically see about 160-180 degrees horizontally (side to side) and about 120 degrees vertically (up and down).
  • The central one-third of the visual field is where the two eyes overlap.
  • Visual field loss can affect any area, central, peripheral, or both.
  • A person is considered to have low vision if the visual field in their better-seeing eye is 40 degrees or less; severe impairment is defined as 20 degrees or less.​​

Central Vision: The "What System"

​Central vision, also called macular vision, is the part of our visual system responsible for recognizing fine detail, identifying objects, and perceiving color. It is often described as the brain’s “what system” because it helps us determine what we are looking at, such as letters, faces, symbols, and small objects.
Central vision plays a critical role in:
  • Sharp, detailed vision
    This includes tasks such as reading print, recognizing faces, seeing details on the board, and identifying small objects.
  • Color perception
    The macula contains cone cells that are responsible for distinguishing color and fine patterns.
  • Reading and other close or distant detail tasks
    Whether a student is reading a book, copying notes, viewing a diagram, or seeing details at a distance, they rely heavily on central vision.
Corrective lenses such as glasses or contacts typically help refocus light for clearer central vision. However, if the macula itself is damaged, missing, or underdeveloped, clarity cannot be restored through glasses alone. This is why some individuals continue to experience blur, distortion, or blind spots even with the proper prescription.

Peripheral Vision: The "Where System"

Peripheral vision refers to the ability to see out to the sides and detect what is happening outside of central (straight-ahead) focus. It is often described as the brain’s “where system” because it helps us understand the location, movement, and overall layout of our surroundings. While central vision helps us see detail, peripheral vision helps us stay oriented and safe in the environment.
Peripheral vision is essential for:
  • Detecting movement. It allows a person to notice objects approaching from the side, sudden motion, or potential hazards that are not in direct view.
  • Navigating in dim lighting or low contrast. Peripheral vision is more sensitive than central vision in low-light conditions, which supports night travel and movement in shadowed or unfamiliar spaces.
  • Mobility and spatial awareness. It provides the broad visual field needed to understand where objects, people, and obstacles are located in relation to oneself. This helps with walking through hallways, crossing streets, climbing stairs, or participating in sports.
Loss of peripheral vision can significantly impact safe mobility, independent travel, and confidence in unfamiliar environments.
Common Conditions Affecting Peripheral Vision
Several eye conditions may reduce or gradually narrow peripheral vision. These include:
  • Glaucoma. A group of eye diseases that damage the optic nerve, often due to increased intraocular pressure. Glaucoma typically causes gradual peripheral vision loss, leading to “tunnel vision” if untreated. 
  • Retinitis Pigmentosa (RP). A genetic eye disorder that causes degeneration of the retina. RP commonly begins with night blindness, followed by progressive peripheral vision loss. Over time, the field of vision can become increasingly restricted, affecting orientation and mobility.
  • Retinal Detachment. Occurs when the retina lifts or pulls away from its normal position. Depending on the location and severity, a detachment may result in sudden loss of peripheral vision, flashing lights, or shadowed areas. It is a medical emergency requiring immediate treatment.
  • Chorioretinitis. An inflammation of the choroid and retina, often caused by infections or autoimmune conditions. Depending on the area affected, chorioretinitis may lead to patchy peripheral vision loss, blind spots, or distortions in the visual field.

​Combined Central and Peripheral Vision Loss

Common Conditions Affecting Central Vision
  • Macular Degeneration. A progressive disease affecting the macula, leading to loss of sharp central vision. It can cause distortions in straight lines, blurred detail, and central blind spots (scotomas). While more common in older adults, some children may have juvenile forms (Stargardt disease).
  • Cone Dystrophies. A group of inherited disorders that affect cone cells in the retina. These conditions cause loss of central vision, decreased color perception, and sensitivity to bright light. Symptoms may worsen gradually over time.
  • Central Scotomas. A scotoma is a blind spot in the visual field. A central scotoma blocks the area required for reading, facial recognition, and fine-detail tasks. Students may try to use eccentric viewing, looking slightly away from an object, to compensate.

Types of Visual Field Loss

There are different types of visual field loss. 
  • Scotoma: A blind spot anywhere in the visual field
  • Hemianopsia: Loss of half the visual field in one or both eyes
  • Tunnel Vision: Loss of peripheral vision with retention of central vision
Note: Losing vision in one eye does not reduce vision by 50%. While the affected side loses visual input and depth perception is diminished, the unaffected eye still provides substantial central and peripheral vision.
It is possible to:
  • Have good central vision with limited peripheral vision
  • Have good peripheral vision with limited central vision​​

Eccentric Gaze

Students with scotomas (blind spots) may adopt an eccentric gaze. This means:
  • They may look slightly above, below, or to the side of an object to see it clearly.
  • This can appear as if they’re not looking directly at what they are trying to see, even though they are using their best remaining vision.
*Ward, Marjorie E., Foundations of Low Vision: Clinical and Functional Perspectives. AFB Press 2004. p. 73 

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