week 6: vision

Prevalence and conditions with high prevalence of visual impairment

Globally, 2.2 billion people have vision impairment or blindness (WHO, 2022)

• Globally, majority of people with vision impairment over age of 50 yrs (WHO, 2022)

The role of occupational therapy

• Evaluation for visual impairment

• Identify the limitation(s)

• Link the performance limitation to impairment

• Determine treatment

• Refer to specialists

• Optometrists, ophthalmologists, vision rehabilitation therapists, certified low vision

therapists

• Identify most appropriate Intervention

Functional vision screening

Visual screening falls within the domain of OT practice

• Safety

• occupational performance

• participation

How we see

• Light reflects off object hitting curve of the lens of the eye

• Light rays bend and converge at the focal point

• Image formed by the convex lens is upside down & is reversed left to right

• Light passes through lens and vitreous humor to the retina to excite

photoreceptors

• Electrical impulses transmitted to optic nerve

Visual processing

Processing in the primary visual cortex in the occipital lobe

• Processing in the visual association cortex

• Object recognition -- color, shape, size

• Visual spatial perception and movement

Mary Warren’s Visual Perceptual Hierarchy

Adaptation

through vision

Visuocognition

Visual memory

Pattern recognition

Scanning

Attention = alert and attending

Oculomotor control, visual fields, visual acuity

Pupillary response

Pupil’s ability to respond to changes in light may affect:

• The process of accommodation… affecting near acuity

• The ability to adjust/respond to changes in illumination

• Screen for pupil size, symmetry, and response to light stimulation using a pen

light

Near acuity:

• Clearly seeing, identifying and understanding objects within arm's length

• Distance acuity:

• Clearly seeing, identifying and understanding objects at a distance

Peripheral Field

• Recognition of “Where”

• Monitoring and interpreting what

is happening in the surrounding

field of vision

• Alerts the CNS to presence of

objects

• Precursor to recognition of “what”

• Central Field

• Recognition of “What”

• Requires more precise visual info

Contrast sensitivity acuity

• High contrast acuity

• Near

• Far

• Low contrast acuity (contrast sensitivity function)

Possible Clinical Observations

Blurriness

• Squinting

• Unable to read near and/or far

• Needs increased light

• Bumps into objects

• Difficulty recognizing faces or distinguishing colors

• Light sensitivity

Evaluation of acuity examples

• Snellen Chart

• biVABA

Oculomotor Function

• Ability to move the eyes together, coordinated

Eye movement

• Controlled by CN 3 (oculomotor), CN4 (trochlear), CN6 (abducens)

Extraocular muscles:

• Lateral, medial, superior, inferior rectus muscles, and the superior and inferior oblique muscles

Smooth Pursuits:

• The ability of the eye to move smoothly across a printed page or while following a moving object

• Convergence:

• Bringing the eyes together… a reflexive response elicited when attending to a target moving closer

• Saccades:

• Quick, simultaneous movement of both eyes between two or more phases of fixation in the same direction

Evaluation of oculomotor function

➢Observe behavior during functional activities

➢Use biVABA to assess

• Alignment

• Eye movements

Diplopia

• Double vision

Functional Implications:

• Judging distances

• Overreaching/under reaching

• Head turn/ tilt

• “Spaced out” appearance

• Avoidance of near tasks

• Blurred vision

• Balance and vestibular deficits

• Nausea

• Reading deficits

• Visual motor deficits

Diplopia – oculomotor assessments

• Scanning assessments – convergence and ocular range of motion/ mobility

• biVABA

Visual fields

• Ensures the presence of vision or that all of the environment is represented in the visual picture

• Binocular (both eyes combined) horizontal field = 180º

• Monocular (one eye) visual field -> see below…

Field Cut / Hemianopia prevalence and definition

• Visual field deficits common with acquired brain injury

• Most common visual disturbance associated with stroke

• TBI loss is often in superior fields

• Hemianopia – affects half of the visual field

• Homonymous hemianopia involves both eyes

Field Cut / Hemianopia

1. blindness of R eye d/t lesion of optic nerve;

2. bitemporal hemianopia d/t chiasmal lesions;

3. L homonymous hemianopia d/t lesion of right parietal or temporal

lobes w/ pressure on R optic nerve

4. L upper contralateral quadrantic anopsia;

5. 5 & 6 = partial lesions of the visual cortex, leading to partial lesions of

the opposite side.

Visual Field Cut (Only) 

• awareness of left field

• attempts to actively compensate

• confined to visual system (ex: should not see signs of personal neglect)

• Attentional demands should not change performance

hemi-inattention

• Decreased awareness of one side

• Not sure where left side is

• May be observed across sensorimotor functions (motor, auditory, tactile etc.)

• Symptoms predictably change with increased selective attentional demands and demands for sustained attention

Visual field deficits and occupations

• Can significantly impact ability to complete ADLs

• Can significantly impact safe interaction with the environment

• Impair ability to locate and search

• Limits scope and speed of scanning

• Decreases visual details

• Usually unaware of VFD at first

• With increased awareness, perceptual completion may occur

• Adopt adaptive protective strategies

• Inaccurate saccades

Saccades are less regular/ less accurate/ too small for organized scanning and reading

• Disorganized scanning

• Require longer visual search times

• Omit relevant objects in the environment

Hemianopia – additional impairments

• Focus on their intact hemi-field

• inaccurate saccades

• disorganized scanning

Potential functional changes with visual field loss

• Reading Difficulties

• Writing Difficulties

• Difficulty with ADLs

• Problems with functional Mobility

Emotional impact of visual field deficits

• Increased anxiety

• Decreased self confidence

• Increased passivity

• Social isolation

Evaluation of visual field deficits

• Observation: Look for functional changes

Standardized clinical testing:

• Automated perimetry test

• Scanning tests

• Confrontation testing

Certified Orientation Mobility Specialists

(O & M Specialist)

• Work with people who are blind or have low vision

• Train/instruct clients in the use of remaining senses to determine position in the environment

• Teach techniques for safe movement from one place to another

• Community based

• Goal Develop: independent travel skills

Certified Vision Rehabilitation Therapist

(CVRT)

• Provide instruction guidance in adaptive independent living skills

• Basic ADL’s, household management, Communication, education, leisure, &

orientation and movement in indoor environments

Optometrists - (FCOVD)

• Board Certification in Vision Development and Vision Therapy (FCOVD)

• Optometrists who successfully complete their certification process are board certified and are designated Fellows of COVD (College of Optometrists in Vision development)

• State-of-the-art clinical services in behavioral and developmental vision care,

optometric vision therapy and vision rehabilitation.

Ophthalmologist

• Complete a medical degree which is followed by a 1-year internship & a 3-

year residency in ophthalmology at an accredited program

• Specialize in the treatment of diseases & conditions of the eye & visual system

• Focus: diagnosing & medically managing conditions through surgery,

pharmaceuticals, or optic devices

Visual screening lab

✓ Pupillary Size

✓ Pupillary response to light

✓ Accommodation

✓ Responsiveness of pupils to accommodation

✓ Visual pursuit/tracking

✓ Saccades

✓ Convergence

✓ 1-Person confrontation

✓ 2-Person confrontation