Low Vision

Useful Terms

Low vision = a loss of sight significant enough to make the performance of everyday tasks, such as reading or driving, more problematic

Central vision = used when one looks directly at someone or something; can be impaired due to macular degeneration, diabetic retinopathy, and other diseases

Peripheral vision = used when one looks to his/her sides or around the edges; can be negatively affected by diabetic retinopathy, glaucoma, or strokes

Contrast sensitivity = a feature of sight that gives one the ability to differentiate the similar but different color tones of a person or object; any and all eye maladies may impact it

Depth perception = a feature of sight that gives one the ability to relatively assess people or objects at different distances; recent loss of vision in one of the two eyes may decrease it

Visual processing = a procedure in which what one sees is interpreted as information by the brain; the lens focuses light onto the retina -> the retina changes the light into electrical signals and transmits them to the optic nerve -> the optic nerve sends these signals to the brain -> the brain translates these signals into the images that one sees; interruptions during this process or problems with one or more of the steps may result in different effects regarding vision loss

Common Symptoms

  • Loss or significant impairment of central vision
  • Loss or significant impairment of peripheral vision
  • Blurred or hazy vision
  • Blindness during the nighttime
  • Major difficulty in performing everyday tasks that require healthy vision
  • Dimmed lights
  • Impaired contrast sensitivity
  • Phantom Visions

    • These are associated with Charles Bonnet syndrome
    • They affect about 20 to 30% of those adults who experience loss of vision
    • These visions appear to be vivid and intricate hallucinations that are recurring in nature
    • The people who have these visions are aware of their lack of reality
    • It may be helpful to perceive them as substitutions generated by the brain in place of the lack of images that are formed by the afflicted eye

Risk Factors

  • History of eye injury
  • Having eye diseases such as macular degeneration or glaucoma currently

Causes

  • Eye Cancer
  • Albinism
  • Brain Injury
  • Age-Related Macular Degeneration

    • Dry Form

      • The formation and growth and increase in number of yellow deposits called drusen under the retina directly lead to the dimming and blurring of the central vision
      • As the disease progresses, the drusen will eventually damage the macula to a state of atrophy, which leads to blind spots in the central vision before it is totally lost
    • Wet Form

      • In choroidal neovascularization, there is a growth of abnormal blood vessels in the choroid, which lies beneath the retina
      • They will start to leak blood and fluids that cause the blurring and distortion of central vision that in time may spread to both of the eyes and cause an eternal loss of the central vision
  • Cataracts

    • Advanced Age

      • The lens is mostly composed of water and protein
      • As the body ages, additional layers will form on the surface of the lens and solidify, losing transparency and flexibility, but also thickening in the process
      • The tissues within the lens begin to break down and lead the protein to clump together, resulting in cloudiness in some areas.

        • The lens focuses the light onto the retina for visual processing
        • The cloudiness scatters this and thus downgrades the quality of the images that as they are sent to the retina
        • Therefore, vision will become clouded, dimmed, and/or blurred
    • Nuclear Cataracts

      • These cataracts affect the center of the lens
      • Initially, the vision problems may appear in the form of more nearsightedness (myopia), or conversely, a temporary improvement in reading vision
      • As time passes, the lens will gradually become more yellow, which will result in further cloudiness in the lens
      • Later on, the cataracts will turn the lens from yellow to brown. The denser yellow or brown colors of the lens will greatly hamper contrast sensitivity
    • Cortical Cataracts

      • These cataracts affect the edges of the lens and initially appear as whitish, wedge-shaped streaks on the outer cortex of the lens
      • As they develop, the streaks will spread to the center of the lens, which prevents it from focusing light onto its center
      • These cataracts cause increased sensitivity to glare
    • Posterior Subcapsular Cataracts

      • These cataracts impact the back or rear of the lens
      • At its onset, these start as a small and cloudy area at the back of the lens, which is right in the path that light travels to get to the retina
      • These cataracts cause impaired vision in bright light, reading vision, and glare
  • Diabetic Retinopathy

    • Nonproliferative Diabetic Retinopathy (NDR)

      • Macular Edema

        • There is a leakage of fluids into the macula that causes its inflammation and thus restricts its ability to function properly
        • This is by far the most common cause of vision loss for those who have diabetes
      • Macular Ischemia

        • The blood capillaries within the retina close off and prevent proper blood flow into the macula, which leads to the blurring of vision
    • Proliferative Diabetic Retinopathy (PDR)

      • This particular condition is deadly in that it can significantly impair both the central and peripheral vision
      • Vitreous Hemorrhage

        • The new weak and delicate blood vessels bleed into the vitreous gel, which prevents light from being properly focused onto the retina
        • Those vitreous hemorrhages that are small may result in a few floaters
        • Those vitreous hemorrhages that are large could block out all vision, reducing vision to an extent that the patient can only perceive light and dark
        • This alone is not enough to cause a permanent loss of vision
        • Once the blood clears, the vision may return to its prior level unless the macula has been injured
      • Tractional Retinal Detachment

        • The scar tissue that comes with the growth of new blood vessels will lead to the wrinkling and detachment of the retina from its regular position
        • This can also lead to the wrinkling of the macula and consequent distortion of vision
        • As long as the macula and significant portions of the retina are detached, there may be a severe vision loss
  • Glaucoma

    • Elevated Eye Pressure (Intraocular Pressure: IOP)

      • A clear fluid known as the aqueous humor flows in and out of the anterior chamber (between the lens and cornea) through a small drain called the trabecular meshwork to stabilize the eye pressure and nourish any tissues that are nearby

        • This drain is comprised of a complex network of cells and tissues in the area called the drainage angle
      • Open-Angle Glaucoma

        • The aqueous humor flows out of the trabecular meshwork too slowly, resulting in a backup of aqueous humor
        • Consequently, there will be a slow but steady rise in the IOP
        • It is called open-angle glaucoma because the angle between the various structures within the eye (s) appears to be open
        • This is the most common form of glaucoma
        • Later symptoms of this disease include:

          • 1) Blind spots in the peripheral vision
          • 2) Impaired night vision
      • Narrow-Angle Glaucoma

        • The aqueous humor is prevented from flowing due to a complete blockage of the drainage angle, which rapidly increases the IOP
        • This is followed by a narrow-angle glaucoma attack with severe eye and brow pains, nausea, and vomiting
        • Early symptoms include:

          • 1) Blurred or indistinct vision
          • 2) Mild eye pains
        • Later symptoms may also be symptoms in the initial stages of the condition and can also include:

          • 1) Blurred vision
          • 2) Sharp eye pains
        • This attack should be considered a medical emergency and must be treated immediately
      • Normal (Low) Tension Glaucoma

        • IOP levels measure regularly below 21 mm Hg
        • Even so, those people will still have impaired optic nerves and blurred vision or loss of vision
      • Congenital Glaucoma

        • This is a rare form of glaucoma that is contracted by infants and young children
        • This is caused by an incorrect or improper development of the drainage system within the eye (s) before birth
        • It may be hereditary in nature
      • Secondary Glaucoma

        • This type of glaucoma is caused by another co-occurring or pre-existing eye injury, such as:

          • 1) Injury to or in the eye (s)
          • 2) Inflammation
          • 3) Blockage of the blood vessels in the retina
          • 4) Formation of abnormal blood vessels due to diabetes
          • 5) The use of medications that contain steroids, including pills, eyedrops, sprays, and others
          • 6) Tumors
          • 7) Long-term steroid therapy
          • 8) Pigment dispersion

            • Small particles from within the iris called granules may circulate within the aqueous humor
            • This can cause the blockage of the trabecular meshwork
  • Retinitis Pigmentosa

    • This disease is usually hereditary and appears in childhood or adolescence
    • It is caused by anomalies in the photoreceptors or retinal pigment epithelium
    • Blindness during the nighttime is the most common symptom to initially appear
    • As it develops, the condition will slowly but surely severely damage night vision and peripheral vision to the point of complete and utter destruction

Diagnosis

  • The diagnosis for low vision differs from the routine eye examination
  • There will be a review of both ocular and medical history in the patient
  • It is important to find any difficulties that one may have with daily functioning
  • Low Vision Test Charts

    • These have a larger range of letters than the standard eye charts in order to better determine the standard at which to measure low vision and test for visual acuity and clarity
  • Low Vision Refraction

    • This helps to measure the vision and prescription needed for any glasses
    • This is done through a variety of techniques:

      • 1) Changing the levels of lighting
      • 2) Testing through the use of filters
      • 3) Providing more detailed and eccentric viewing
  • Amsler Grid

    • This consists of a pattern of lines that resemble a checkerboard
    • A patient who sees wavy or missing lines would be found to have poor vision
    • This is an excellent way of testing for functional vision, specifically the central vision
  • Contrast Sensitivity

    • There are two different ways to test for this: the Pelli-Robson test and MARS contrast test
    • This is a crucial part of functional vision and is very important to accurately measure because low levels of contrast sensitivity may inhibit orientation and mobility outdoors
  • Perimetry (Visual Field Test)

    • A patch will be temporarily applied to one of the eyes to allow for each eye to be individually tested
    • The patient will be seated and asked to look straight ahead at some specified target
    • The computer being used will make a noise and random points of light will flash around the bowl-shaped instrument called the perimeter
    • The patient is to press a button whenever he/she sees a light

      • Not every noise that the computer makes will be followed by a light
    • This method checks for blank spots within the peripheral field of vision, especially those that the patient may not notice
    • This testing is done every 6 to 12 months to check for any changes
  • Ophthalmoscope

    • This can be used to check for precise areas of the eye that may have damage to the central retina
  • Visual Evoked Potential (VEP)

    • This is a variant of an electroencephalogram and involves sitting in front of a screen which features an alternating checkerboard pattern
    • This is helpful with a differential diagnosis of a plethora of retinal maladies in that it is used to check for any signs of compromised transmission along the pathways of the optic nerve

Treatment

  • Once you have low vision, it’s permanent and can never be recovered, which prompts patients to adapt to their current situations and make the most of the vision that they do have
  • Preferred Retinal Locus (PRL)

    • When there are blind spots in the central vision, then it is advised to find the next best spot, which is the PRL
    • This can be found by imagining that the object that the patient wants to see is at the center of a large clock face
    • Then, the eyes should be moved along the numbers until the patient sees the center object with the most acuity and clarity
    • That same viewing direction should be used to see other objects and people, if necessary
  • Low Vision Aids

    • Improve lighting with the use of a gooseneck lamp or penlight
    • Reduce glare with the usage of yellow clip-on or fitover glasses indoors, dark yellow or amber glasses outdoors, or visors both indoors and outdoors
    • Increase the contrast with a black ink gel pen or felt pen and abstain from using ballpoint pens
    • Move closer to the TV and up front at performances or events and enlarge and magnify images whenever possible
    • E-readers, smartphones, and tablets are able to adjust font size and contrast settings of the display to best suit the needs of the patient

      • Reversed-polarity backgrounds are especially helpful in that there are white letters on black backgrounds, for example, that reduce glare and increase the contrast

        • They may not be available for some E-readers
      • There are apps specifically designed for those with low vision or even have options to magnify and illuminate the text, such as iRead, iLoupe, Magnify, and others
      • SightBook uses near vision tests to measure functional vision and wirelessly communicates any changes in vision to the ophthalmologist
    • Audio Interface

      • Substitute the damaged sight with healthy hearing and use electronic books, audio books, e-book readers, and just about any other voice interface to make the performance of daily tasks easier
      • EyeNote is a free app for Apple licensed products that can scan and identify the various denominations of paper money and read them aloud or emit a certain number of beeps or vibrations for each denomination
      • MapQuest is available for both Apple and Android licensed products and has an app that offers voice-guided directions and automatic re-routing when a wrong turn is made
      • Voice interfaces such as Siri (for Apple products) can check the weather, e-mail, calendar, and other vital tasks without having to rely on a visual medium to do so

        • Android products feature their own voice interfaces that can check e-mails and texts and dictate them without needing to type anything
  • Low Vision Rehabilitation

    • This teaches patients how to make the most of their remaining vision
    • They can be prescribed certain devices, as previously described, that suit their particular needs
    • They can also get training on how to perform everyday tasks, such as reading, shopping, cooking, and others by adapting to the poor vision and finding ways around it
    • Additionally, they may inquire about other resources and support groups
    • Furthermore, they may also find out how insurance plays a role in covering their rehabilitation expenses