Visual System Anatomy & Treatment

Objectives

• Understand visual system anatomy and related impairments.
• Learn basic visual screening techniques.
• Learn to create basic treatment plans for visual impairments.
• Describe the occupational therapist's role in visual assessment and treatment.

Visual Skills Pyramid

• Adaptation through vision sits atop this skills pyramid.
• The levels of the pyramid from top to bottom are:
  • Visuocognition
  • Visual memory
  • Pattern recognition
  • Scanning
  • Attention or alert and attending
  • Oculomotor control
  • Visual fields
  • Visual acuity

Visual Anatomy: Eye Structures

• Cornea: Protects from dust and UV radiation, and reflects light onto the lens.
• Lens: Changes shape to focus on near or far objects.
• Ciliary Body: Contains muscles that contract or relax to adjust lens shape.
• Sclera: Tissue wrapping around the eyeball for protection and support.
• Choroid: Vascular layer providing oxygen and nutrients, and regulating intraocular pressure.
• Retina: Contains rods, cones, and nerve cells that convert light into nerve signals.
• Macula: Central retina area for central vision, details, and color vision.
• Fovea: The macula's center, containing a high concentration of cones.
• Optic Disc: "Blind spot" that doesn't process visual information.
• Optic Nerve: Composed of ganglion cell axons carrying visual information from each eye.

Image Perception

• Light is focused in the fovea.
• There are two types of photoreceptors
  • Rods
  • Cones
• Rods: Found outside the fovea, function in low light (scotopic vision), offer low visual acuity, number around 100 million, and are insensitive to color.
• Cones: Densely packed in the fovea (three types), function in bright light (photopic vision), provide high visual acuity, number around 5 million, and enable color vision.
• Mesopic Vision: A combination of rods and cones, used in low to moderate lighting, like "twilight" vision.
• Photons stimulate photoreceptors, creating an action potential along the optic nerve.

Visual Pathways

• Optic Nerve: Transmits visual data from either the right or left eye.
• Optic Chiasm: Splits visual data from each eye into right and left visual fields.
• Optic Tract: Pathways linked to either right or left visual fields.
• Lateral Geniculate Nucleus (LGN): This contains the primary visual pathway's only synapse. It acts as a relay between the retina and visual cortex.
• Optic Radiations: Nerve bundles carrying information from the LGN to V1.
• Visual Cortex: Located in the occipital lobe, it is the primary area for visual processing.

Ocular Alterations

• Myopia (nearsightedness), hyperopia (farsightedness), and astigmatism are common ocular alterations.
• Visual impairment is secondary to ocular alterations.

Congenital Visual Impairments

• Color Blindness: Loss or abnormality in genes for cone pigments.
• Stationary Night Blindness: Poor night or dim-light vision due to impaired rod function.
• Retinitis Pigmentosa: Progressive retinal degeneration leading to blindness, affecting rods first.

Retinopathy of Prematurity (ROP)

• Can occur in infants born before 31 weeks of gestation, if weighing less than 1250g.
• Symptoms include jerky eye movements, decreased response to light, difficulty tracking objects, and eye rubbing.
• Severe cases involve detached retinas.
• Possible long-term outcomes consist of vision loss or blindness.

Visual Impairment and Alterations to the Visual Pathway

• Deficits include:
  • Monocular vision loss
  • Bitemporal hemianopia
  • Homonymous hemianopia
  • Homonymous superior quadrantopia
  • Homonymous superior quadrantopia with macular sparing
  • Inferior homonymous quadrantopia with macular sparing
  • Homonymous hemianopia with macular sparing

Disorders of Binocular Vision

• Impairments can be associated with disorders of binocular vision:
  • Nystagmus: Repetitive, uncontrolled eye movements which are monocular or binocular.
  • Strabismus: Ocular misalignment which can cause amblyopia.
  • Amblyopia: Poor visual acuity in one eye.
• These can result in poor depth perception, headaches, eye strain, fatigue, and clumsiness.
• The causes may include incomplete visual system development linked to :
  • Early life brain injury: Perinatal stroke
  • Hypoxic ischemic encephalopathy (HIE)
  • Prematurity
  • White-matter damage of immaturity (WMDI)
  • Stroke
  • Brain injury, including concussion
  • Cranial nerve injury that involves CN III and CN IV

Oculomotor Impairment

• Convergence/divergence
• Saccades
• Smooth pursuits.
• These can affect eye movements.
• Diplopia (double vision) can result from ocular misalignment and convergence insufficiency or binocular vision which may lead to horizontal/vertical/diagonal challenges

Visual Field Defects (VFDs) & Functional Deficits

• When there are VFDs it can result in an impaired insight into VFD.
• IADL is more affected than BADL.
• How it can affect function:
  • Frequently losing items in blind field
  • Tripping over items/children/pets in the area of field loss
  • Walking into objects/people
  • Difficulty functioning in busy environments
  • Reading.
• There may be a temporary or permanent driving cessation.

Visual Hx

• Is there any history of ocular disease?
• Hx:
  • Glasses
  • Number of pairs
  • Lens purpose
  • Age of prescription
• What activities are affected?
• Do loved ones of caregivers notice anything?

Observation

• Where does the client spend most of their time looking?
• Is there head tilt?
• Is there squinting?
• Is there eye closing?
• Can the body face the target?

Screenings & assessements

• Brain Injury Visual Assessment Battery for Adults (biVABA).
• VISA
• VISA-F
• NSUCO
• Damato 30-point Multifixation Campimeter (Brain Injury Visual Assessment Battery for Adults – biVABA)
• Humphrey's visual field analyser
• Goldman perimetry

Assessments of ADLS

• Mobility
• Potential falls
• Medication Management
• Driving skills
• Performance in tasks of importance to the client: reading, cooking outdoor walking
• Implement compensatory strategies/adaptive aids

Low Vision Treatment

• Environmental modifications
  • Lighting
  • Contrast
  • Tactile stimulation
  • Clutter reduction
  • Magnification
  • Large print.
• Speech-to-text
• Audiobooks
• Organizational strategies
• Environmental choices
• Mobility aids
• Aid with high & low-tech options.

Oculomotor Impairment Treatments

• Strategies for pacing and managing symptoms.
• Providing specific task practice.
• Brock string use.

Intervention for Visual Field Defects

• Compensation is implemented in area of field loss.
• Insight is required for intervention.
• Area of vision loss does not typically return.
• Compensatory strategies
  • Scanning (turning eyes and/or head)
  • Environmental modifications
  • Improve safetey in mobility and ADLs.

Non-OT Rx Treatments

• Eye drops for glaucoma
• Monitor intraocular pressure of the eyes
• Focus on nutrition for AMD to keep macular cells healthy
• Orthoptics using prisms.
• Optometry, Vision therapy, & CAO position statement
• Compensatory techniques.