Vision, Low Vision and Visual Foundation Skills

Any condition in which a person's vision is not adequate for his or her needs. Based on acuity, covers from 20/80 to 20/1000 to total blindness from 20/1250 to 20/2500. Treatment
- train the pt. to use remaining vision as efficiently and effectively as possible to complete daily activities and use of optical devises.
- environmental adaptation
- compensatory techniques
- assistive devises
- pt. and family education

Cataracts
- acuity can be good , but decreased contrast sensitivity with clouding of the lenses occurs; surgical treatment is typically successful.

Glaucoma
- results in decreased peripheral vision; generally controlled medically.

Diabetic neuropathy
- bleeding from small blood vessels in retina leads to serious vision loss.

Macular degeneration
- results in loss of central vision; no effective medical or surgical treatment.

Lens tends to yellow
- changes color perception; glare maybe a problem.

Lighting
care must be taken not to increase glare; move closer to task; increase lighting.

Contrast
change the background to increase contrast; use different colors ( blue plates on a white place mat ).

Pattern
keep the environment uncluttered and simple.

Task demands
break it down, start with something simple and gradually increase the demands.

Print size
enlarge print, increase contrast, increase print quality.

Working distance
important for both near and far activities, especially with both bifocal and trifocal lenses, which are distance specific;
normal working distance is about 16 inches.

- A basic eye history, including premormid visual conditions
( congenital strabismus, ocular trauma )
- Interviews with the pt and/or family as to complains or symptoms ( difficulty concentrating, double vision, eyestrain, bumping into objects on one side )
- Observation of the pt during functional activities.
- Screening of the foundation skills ( visual acuity, visual fields, oculomotor control/function and scanning ); these skills must be evaluated to differentiate perceptual dysfunction and visual system deficits.

The clarity of vision both near and far. Distance acuity ( far ) is the ability to see objects at a distance. Near acuity is the ability to see objects clearly as they come close to the eye. The ability to see small visual detail. The ability of the eyes to make what is seen sharp and clear ( 20/20 vision ). Acuity contributes to the capability of the CNS to recognize objects. The greater the quality of the visual input, the more precise the image created by CNS processing. The more precise the image, the faster and more accurate the ability of the CNS to recognize the object and discriminate it from other features in the environment. Good acuity therefore enables speed and accuracy of information processing and facilitates decision making. Deficits in visual acuity may be the result of refractive errors, poor eye health with inability to process the image ( cataract, macular degeneration, diabetic retinopathy ) or poor transmission of the image by the optic nerve.

Reduce visual acuity
Myopia ( nearsightedness )
Hyperopia ( farsightedness )
Astigmatism
Functional Description of Deficits
Complaints: blurred near or far vision; print too small, too faint; headaches, squinting, eye strain. Effects on function: inattention; holds objects too close to face; loss of facial recognition; fear of new environments; lack of interest in environment; difficulty finding objects; loss of interest in reading; vision fluctuating throughout the day; bumps into low - contrast objects.
Evaluation/Screening
- conventional letter charts ( Snellen Chart: 20/20, 20/50 )
Acuity should be examined in each eye for both near ( 16 inches or less ) and far ( 20 feet or more ) vision.
- contrast sensitivity
It indicates the person's ability to see objects in various levels of contrast and how he or she will perform functionally. The tester presents a series of sine wave gratings that vary in orientation, contrast and frequency. the pt. must indicate the orientation of the grating.

Intervention
- modify the environment and activities and enable the pt. to use his or her remaining visual acuity by increasing the visibility of the environment and tasks through manipulation of physical context
- increase background contrast; changing background color to contrast with an object can help pt. see objects more clearly ( mark steps with bright marker or tape )
- increase illumination; increasing the intensity and amount of available light enables objects and environmental features to be seen more readily and reduces the need for high contrast between objects ( use brighter light bulb in the room )
- reduce background pattern ( use solid colors for background, organize and simplify closets )
- enlarge objects or features that need to be seen
( use/provide large print, increase contrast: black on white ) organize ( establishing routines, simplify steps of the tasks, organize closets, keep important or frequently used items on lower shelves or in one place )
- access community services or support group

The available vision to the right, left, superior and inferior. Area that one sees when looking out into the environment. Central visual field: central 30 degrees where vision is clear and focused. Peripheral visual fields: area seen other than central where vision is not as clear, but used for motion detection and orientation.
Deficit
homonymous ( deficit is the same in both eyes ) hemianopsia ( loss of vision in one half of the visual field in the eye; homonymous hemianopsia ( the left temporal field and right nasal field are affected )
Functional Description of Deficit
Complains: bumps into objects; difficulty reading. Effect on function: difficulty moving in crowded or busy environments; anxiety; startle response; difficulty with self-care and IADLs, mobility, writing; unsafe, reduced ability to scan in the environment; difficulty navigating and finding objects within the environment, can't find things; loss of self - confidence.

Evaluation/Screening
- confrontation testing ( static and kinetic )
Can be done at bedside. Screen one eye at a time and pt's visual fields are compared to the normal visual fields. Normal limits of visual field are 60 degrees superior, 75 degrees inferior, 60 degrees nasal and 100 degrees temporal. Must correlate their findings with clinical observations.
- clinical observations during dynamic functional activities ( ex: walking through crowded area with moving objects ) or daily activities. Important tool.
- automated perimetry
A more accurate description and print out of the pt's visual field deficit. Completed by ophthalmologist or optometrist.
- the tangent screen
Completed by ophthalmologist or optometrist.
- the Damato Campimeter
A portable test card that provides a precise measurement of central 30 degrees of the visual field.
- the Visual Skills for Reading Test (VSRT)
Provides an effective way to measure the interference of the visual fields deficit on reading performance. Designed to assess the influence of a scotoma ( or field loss ) in the macula on the visual components of reading, including visual word recognition and eye movement control.

Intervention
- addressing limitation in mobility
A combination of remediation and compensation strategies used. Remediation strategies focus on increasing speed, width, and organization of the search pattern. First, pt must learn to quickly turn the head and completely search the blind visual field. Then, practice these skills during ambulation. Then, practice in dynamic and in unfamiliar environments. Practice these skills during functional activities.
- addressing limitations in reading
Pre-reading exercises and commercially available word and number searches ( to improve reading speed and accuracy ). As skill improves, large print book of familiar stories used. Compensation starategies used to enhance visibility of tasks and environments such as adding color and contrast to the key features in the environment needed for oriatation ( door frames and furniture ) help to locate these structures; using black felt-tip pens to heighten the contrast in writing materials; adding bright light to reduce errors and increase speed; reducing clutter to reduce pattern in the enviroment and using solid - colored objects enhances pt's ability to locate items.
- patient education

Control of eye movements. The purpose of ocolomotor function is to achieve and maintain foveation of an object. Ocolomotor function ensures that the object the person wishes to view is focused on the fovea of both retinas ( to ensure clear image ) and that focus is maintained as long as needed to accomplish the desired goal. The role of the occupational therapist is to describe its functional effect and formulate the critical questions for the ophthalmologist or optometrist. Foveation is achieved and maintained by eye movements that keep the target stabilized on the retina during fixation, gaze shift and head movement. Another function of ocolomotor control is to provide binocular vision.

It allows us to resolve two images , one from each eye, into one. Motor component: muscles and nerves align the eyes with the object. Sensory component: activity within the cortex allowing perception of one image. It depends on good eye alignment and the ability of the eyes to converge and adjust focus at a range of distances.
Functional Description of Deficit
Complaints: double vision; difficulty sustaining visual work effort; eye fatigue with sustained work; eyes look crossed; blurred vision; headaches. Effect on function: poor eye contact, inability to concentrate, avoidance of activities at near distance, loss of vision, difficulty with activities requiring death perception, difficulty with ball sports, reading is shaky ( eyes jump and down move smoothly from side to side).

Deficits
- paralytic strabismus
The muscles controlled by cranial nerve are weakened or paralyzed. The eye is unable to move in the direction of the paretic muscles and may even be unable to maintained a central position in the eye socket ( it drifts in or out ).
- paralysis of cranial nerve II, IV and VI
- diplopia ( double vision )
Functional Description of Deficit
Complaints and behaviors with limited eye - movement control: loss of place when reading, re-reading, poor reading comprehension, inconsistent sport performance, difficulty copying from one place to another ( blackboard ), anxiety and frustration; difficulty with ADLS and IADLS which depend on the presence of diplopia and were it occurs within the focal range.

Assessment/Screening
- To determine whether the client is experiencing limitations in daily occupations due to dysfunction within the oculomotor system.
- " listen and look " approach
Listen pt's complains and observe for deviations in ocolomotor control that may contribute to these complaints.
1) To obtain a visual history from the client ( asking questions )
2) Observing the client's eyes and eye movements for deficiencies ( ex: test convergence )
3) Diplopia testing
- screen binocular vision including eye alignment, convergence, accommodation, smooth pursuits and saccades.

Intervention
- occlusion
- prisms
- eye exercises
- surgery