Wendell Nakamura

LEARNING OBJECTIVES: Differentiate between “low vision” and “legal blindness”. Describe the role of occupational therapy in vision rehabilitation and identify other professionals with whom an individual with low vision or blindness may interact. Describe the components that make up vision and perception. Discuss the anatomy of the visual system, from the eyes to the visual cortex of the brain. Distinguish common health conditions that impact vision and occupational performance. Identify and administer various clinical tests of visual perception. Describe common occupational therapy interventions for people with visual impairments.

CASE STUDY: Jordan Rutherford is a 79-year old man who was recently diagnosed with bilateral, intermediate, age-related, wet macular degeneration. He lives alone in a single-level, two-bed, two bath home with a two-step entry with handrails. He is a retired information technology specialist who is independent with self-care needs (e.g., feeding, grooming, dressing, bathing, and toileting). Jordan is also independent with pet care and simple meal preparation in the microwave. He does not drive; instead, he take ride-sharing services to the grocery store, one time per week. Jordan hires contract services for weekly indoor (housekeeping) and outdoor (yard care) household maintenance. He expresses increasing difficulty with communication management (using his iPhone and computer), finance management (online), and medication management due to low vision. Read more about Jordan by following this link to his EHR.

Low vision is a visual impairment that cannot be corrected by medical or surgical intervention but is severe enough to interfere with ADL performance (Warren, 2020). While there is no universally accepted definition of low vision, the Centers for Medicare and Medicaid Services (CMS; 2002, §Coverage and limitations) defines “profound impairment in both eyes” as “best corrected visual acuity is less than 20/400 or visual field is 10 degrees or less”. Legal blindness is a severe loss of visual acuity, visual field, or both and is defined as “central visual acuity of 20/200 or less in the better eye with the use of a correcting lens” or “an eye has a visual field limitation such that the widest diameter of the visual field subtends an angle no greater than 20 degrees” (Social Security Administration, 2014, § How do we define statutory blindness?).

Vision loss ranks among the top 10 causes of disability in the U.S. (Centers for Disease Control and Prevention [CDC], 2024). The World Health Organization (WHO; 2023) estimates that approximately 2.2 billion people worldwide have some degree of near or distance vision impairment and that the leading causes of vision impairment and blindness are refractive errors and cataracts. Furthermore, the WHO (2023) estimates that only 36% of people with refractive errors and 17% of people with cataracts have received access to appropriate interventions.

Young children with early onset severe vision impairment are at risk for delays in motor, language, social, and cognitive development (WHO, 2023). Adults with vision impairment can experience lower rates of workforce participation, lower productivity, and higher rates of depression (WHO, n.d.). While vision impairment and vision loss can affect people of all ages, most people with vision impairment or blindness are over the age of 50 years (WHO, 2023). The most common complaints of older adults with low vision include difficulty reading, driving, functional mobility in and around the home, shopping, meal preparation, and managing prescription medication and financial statements (Kaldenberg & Smallfield, 2020). Older individuals with vision impairment are at higher risk for social isolation, have difficulty with household and community mobility, are more likely to experience falls and fractures, and are more likely to have early entry into long-term care facilities (WHO, 2023).

How social determinants of health affect vision health

Social Determinants of Health (SDoH) are non-medical factors that impact health outcomes and includes the conditions in which people are born, live, work, and age. Some examples of SDoH include income, employment, education, housing, environment, transportation, and access to health services. The CDC (2024) outlines the impact that four SDoH have on vision health:

• Income: People with lower incomes are less likely to access preventive vision care, such as annual eye exams, and are less likely to be able to afford corrective devices (e.g., eye glasses).
• Education: People with less than a high school education are more likely to forgo an eye care visit in the past year than people with at least a high school education.
• Environment: People who live in neighborhoods they consider to be less safe are less likely to participate in physical activity and more likely to experience stress. These factors have a direct impact on weight management and increase risk for diabetes mellitus, which can lead to diabetic retinopathy.
• Healthcare Access: People with a disability such as vision loss report greater challenges with accessing health care services. Challenges include cost, insurance coverage, access to transportation, and refusal of services. People with vision loss are less likely to be under-insured or uninsured.

According to the CDC (2024), people who reported vision impairments were more likely to:

• have lower educational attainment
• have health coverage through Medicaid
• have problems paying their medical bills
• have trouble establishing care with a physician or optometrist
• skip prescription medicines because of cost
• experience food insecurity

Occupational Therapy’s Role in Vision Rehabilitation

“Functional vision refers to the use of vision in everyday life and the impact of vision problems on activities of daily living, instrumental activities of daily living, work, and leisure as well as a person’s physical, cognitive, emotional, and social function” (Kaminsky & Powell, 2024c, p. 19). To help address the many challenges faced by individuals with low vision and blindness, an interdisciplinary team of vision specialists and non-vision specialists are available: ophthalmologists, optometrists, occupational therapists, vision rehabilitation therapists, orientation and mobility specialists, teachers of the visually impaired, and social workers (Whittaker et al., 2016).

• Ophthalmologists are physicians (MD [Doctor of Medicine] or DO [Doctor of Osteopathic Medicine]) who complete a residency in ophthalmology and specialize in the diagnosis and treatment of various eye diseases. Many also complete a fellowship specific to a specialized area of practice, including cataracts, glaucoma, retinal diseases (e.g., retinal detachment and diabetic retinopathy), corneal diseases, macular degeneration, pediatric ophthalmology, and neuro-ophthalmology. Treatments of eye diseases under the care of an ophthalmologist include medications or surgery.
• Optometrists are eye care professionals who complete a 4-year Doctor of Optometry (OD) graduate program and specialize in the diagnosis and treatment eye disorders, including refractive errors (e.g., myopia [nearsightedness], hyperopia [farsightedness], astigmatism, and presbyopia [inflexibility of the lens]), diplopia (double vision), color blindness, glaucoma, cataracts, retinopathies, and macular degeneration. Treatments include corrective appliances (e.g., glasses, contact lenses), medications, vision therapy, and low vision rehabilitation.
• Occupational therapists are healthcare professionals who are skilled at understanding how the body’s structures and functions impact occupational performance and participation. In the realm of low vision rehabilitation, occupational therapists assess a client’s occupational performance to identify ways the environment or occupation may be modified to accommodate the client’s visual impairments (Blaylock & Bewernitz, 2024). Interventions are targeted toward educating clients, caregivers, and families about the effects that low vision may have on occupations and potential progression of visual conditions as the client ages (Warren & Barstow, 2011). Additionally, occupational therapists provide training and education in the use of various optical devices (e.g., magnifiers).
• Certified Vision Rehabilitation Therapists (CVRTs) are non-occupational therapy vision professionals who earned either a bachelor’s or master’s degree or a certificate in vision rehabilitation therapy. They are certified by the Academy for Certification of Vision Rehabilitation and Education Professionals (ACVREP) but remain unlicensed in the United States. CVRTs provide instruction and training to individuals with low vision or blindness in home management, ADL, leisure, employment, and indoor orientation skills. At this time, CVRTs are not eligible to be Medicare providers.
• Certified Orientation and Mobility Specialists (COMSs) are vision professionals who have a master’s degree from a program that is accredited by the Association for Education and Rehabilitation of the Blind and Visually Impaired (AER). COMSs are certified by the Academy for Certification of Vision Rehabilitation and Education Professionals (ACVREP) and provide education and training to people with low vision and blindness to navigate outdoor spaces, use a sighted guide (e.g., guide dogs), and using a long cane. They teach route planning, analysis of street crossings, and the use of public transportation. Like CVRTs, COMS are not eligible to be Medicare providers.
• Teachers of the Visually Impaired (TVIs) are special education teachers who work specifically with infants, children, and youth of all ages who have low vision or blindness. They teach low vision and blindness strategies and how to use adaptive equipment, in addition to teaching Braille.
• Social workers provide individual and group counseling and facilitate access to community-based services.

The Components of Vision & Perception

The visual system comprises one of the five senses that we use to interpret and interact with our surroundings. It is so vital to occupational participation that four of the twelve cranial nerves are dedicated to vision. Visual sensation occurs as a result of a complex series of events starting with the eye and terminating at the visual cortex of the occipital lobe (Sánchez López de Nava et al., 2023). Visual perception is the process by which the brain analyzes and interprets the sensory information received by the visual cortex (Kaminsky & Powell, 2024b).

Vision is much more than just being able to see clearly. There are several components that comprise vision and visual perception on which we will elaborate. Together, these components allow us to take in and make sense of the sensory information.

• Near and distant acuity are probably the two most familiar components of vision. Visual acuity refers to the clarity or sharpness of an image. Near visual acuity is the clarity of an image approximately 16 inches from the client and is most frequently tested using the Colenbrander English Continuous Text Near Vision Card, a series of sentences with different sized fonts. Distance acuity is the clarity of an image approximately 20 feet from the client and is most frequently tested using a Snellen chart, a standardized display of different size stimuli (most often capital letters of the alphabet) read at a standardized distance from the client. Visual acuity is measured as a fraction; 20/20 where the numerator represents the distance (in feet) of the client to the chart and denominator represents the size of font that a person with normal vision can read at a given distance (Daiber & Gnugnoli, 2023). Visual acuity of 20/40 denotes someone who can see the letters at 20 feet what someone with normal acuity can read at 40 feet. Clients who cannot read the large “E” at the top of the Snellen chart have visual acuity less than 20/200, the threshold for legal blindness (Azzam & Ronquillo, 2023).



• Accommodation is the process by which the lens changes shape to focus light rays onto the retina (Motlagh & Geetha, 2022), allowing us to change from near vision to distance vision, and vice versa. With near vision accommodation, the lens takes on a rounder shape; with distance accommodation, the lens is much flatter. An example of visual accommodation is when shifting gaze between a blackboard in the classroom to a notepad on the desk.
• Vergence is the movement of the eyes in opposite directions in order to maintain a constant image on the retina as it moves closer or farther away from an individual. Convergence is when the eyes move toward each other (such as when viewing something moving closer) and divergence is when they move apart (such as when viewing something moving further away).



• Saccades are rapid, ballistic eye movements that change the point of visual fixation. When you read a paragraph of text, for example, your eyes rapidly move from the end of one line to the beginning of the next line. When scanning an object, the eyes utilize saccades to focus details on the retina.



• Pursuits are a slower eye movement that are used to track objects and maintain the image on the retina. Normally, these eye movements are smooth, and the eyes move in the same direction at the same speed.
• Visual fixation is the ability to maintain gaze on a stationary object. The primary function of visual fixation is to allow the eyes time to converge and accommodate and keep the image on the retina.
• Stereopsis is the ability to perceive the three-dimensional aspects of an object and the environment. Put quite simply, it is depth perception. Because the eyes are spaced apart, each eye perceives a slightly different view of an object, resulting in binocular vision.



• Visual fields is the portion of space that is viewable during a steady fixation of gaze (Spector, 1990). Under normal circumstances, each eye can see approximately 50 degrees nasally, 50 degrees superiorly, 90 degrees temporally, and 60 degrees inferiorly (Spector, 1990).



• Contrast sensitivity is the ability to perceive minute differences in shading and patterns to distinguish sharp and clear outlines of small objects (Kaur & Gurnani, 2023). A measure of contrast sensitivity that is frequently used is the Pelli-Robson Contrast Sensitivity Chart. It features capital letters in grayscale with diminishing saturation. The client is asked to read the letters that they can identify. The client is assigned a score based on the contrast level of the last group of letters in which two or three letters were correctly identified. A score of 2.0 indicates normal contrast sensitivity at 100%. A score of 1.5 indicates visual impairment and a score of 1.0 or lower indicates visual disability (National Institute of Neurological Disorders and Stroke, 2022).



• Glare modulation is the ability to regulate ambient light that distracts from the task at hand. In times of high illumination, the glare source (e.g., oncoming traffic headlights, sunlight) may be significant enough to impair vision completely.

Anatomy of the Visual System

In order to better understand the health conditions that impact the visual system and what occupational therapists can do to assess and treat those conditions, we begin with an exploration of the structures and typical functions of the visual system. What follows is a basic overview of the visual system’s structures and functions.

Cranial-facial bones

The ocular globe (i.e., eyeball) is housed within the bony recess in the skull in what is called the orbit. The orbit is comprised of seven bones (Shumway et al., 2023). See Chapter 9 of this Course Manual to review the facial bones.

• frontal bone forms the roof and parts of the posterior, medial, and lateral walls of the orbit
• sphenoid bone forms part of the posterior and medial walls of the orbit
• zygomatic bone forms parts of the inferior and lateral walls of the orbit
• ethmoid bone forms part of medial wall of the orbit
• lacrimal bone forms the medial wall of the orbit
• palatine bone forms part of the floor of the orbit
• maxilla forms the floor and part of the medial wall of the orbit

Extraocular muscles

Also located within the orbit are six extraocular muscles that attach to each eye and move the eye in different directions when scanning the environment. They are formed from a specialized type of muscle fiber that is resistant to fatigue (Shumway et al., 2022). To view an interactive digital model of the extraocular structures, follow this link. To view a brief video of the extraocular movements, follow this link.

• The superior rectus is innervated by CN-III. Its primary action is elevation (a superior shift in gaze, looking upward). Its secondary action is adduction (a medial shift in gaze, looking nasally) when the eye is abducted. Its tertiary action is intorsion (a medial or internal rotation around the sagittal axis; right eye clockwise, left eye counter-clockwise).
• The inferior rectus is innervated by CN-III. Its primary action is depression (inferior shift in gaze, looking downward). Its secondary action is adduction (a medial shift in gaze, looking nasally) when the eye is abducted. Its tertiary action is extorsion (a lateral or external rotation around the sagittal axis; right eye counter-clockwise, left eye clockwise).
• The medial rectus is innervated by CN-III. Its primary action is adduction (medial shift in gaze, looking nasally). It does not have a secondary or tertiary action.
• The lateral rectus is innervated by CN-VI. Its primary action is abduction (lateral shift in gaze, looking temporally). It does not have a secondary or tertiary action.
• The superior oblique is innervated by CN-IV. The tendon of the superior oblique passes through a cartilaginous loop called the trochlea (trochlea = “pulley”). The trochlea changes the line of pull of the tendon of the superior oblique muscle. Its primary action is intorsion (medial or internal rotation around the sagittal axis; right eye clockwise, left eye counter-clockwise). This rotation occurs so that the image on the retina is stable as you rotate your head. To view a short video that demonstrates ocular rotation, follow this link. The superior oblique’s secondary action is depression (inferior shift in gaze, looking downward) when the eye is adducted (down and in). Its tertiary action is abduction (lateral shift in gaze, looking temporally).
• The inferior oblique is innervated by CN-III. Its primary action in extorsion (lateral or external rotation around the sagittal axis; right eye counter-clockwise, left eye clockwise). Its secondary action is elevation (superior shift in gaze, looking upward) when the eye is adducted (up and in). Its tertiary action is adduction (medial shift in gaze, looking nasally).

One other muscle that some sources consider to be a seventh extraocular muscle is the levator palpebrae superioris. Its innervation is the Oculomotor Nerve (CN-III). It elevates and retracts the upper eyelid. When the levator palpebrae superioris is not functioning properly, a condition called ptosis (drooping eyelid) results, which may be unilateral or bilateral. To view a brief video of the causes of ptosis, follow this link. Depending on the severity of ptosis, the visual field may be partially or completely obstructed (Shahzad & Siccardi, 2023).

FOCUS ON CLINICAL APPLICATION: Clinicians can easily assess the function of the extraocular muscles (EOM) and their respective cranial nerves by conducting a simple test, called the oculomotor screen. You may recall that we conducted a cranial nerve screen in Section 8.1; the cranial nerve screen assesses oculomotor function (CN-III, CN-IV, & CN-VI). Students will note that there are many sources on the internet that offer different explanations of which muscles perform which actions during a clinical exam. Keep in mind that our responsibility as occupational therapists is to complete a vision screen with clients and if any irregularities are noted in oculomotor functioning, to refer to an ophthalmologists or optometrist. We do not diagnose oculomotor problems; it is beyond the scope of our practice. To view a brief video of an EOM test being administered, follow this link. Another brief video that demonstrates EOM during an exam may be found by following this link, beginning at 14:12. A more standardized method to assess EOM is outlined by the Northeastern State University College of Optometry (NSUCO). The NSUCO Oculomotor Test is a direct observation of the client’s quality, speed, and accuracy of ocular movement (Kaminsky & Powell, 2024a). The NSUCO Oculomotor Test uses two visual targets (5mm reflective balls mounted on dowels. and assesses a client’s ability to visually track the target (smooth pursuits) and ability to shift gaze quickly between two targets (saccades). Testing procedures are available by following this link. The scoring is available by following this link.

FOCUS ON CLINICAL APPLICATION: When a problem with oculomotor control presents, clients will generally present with a dysconjugate gaze. Conjugate eye movements means that the eyes move together and in the same direction. Examples of dysconjugate gaze were shown in this video, beginning at 1:40. When there is a misalignment of the eyes due to weakness of extraocular muscles, a condition called strabismus occurs. To view an interactive digital model of esotropic strabismus, follow this link. There are four different kinds of strabismus, depending on the direction of gaze: Esotropia occurs when deviation is in a nasal (medial) direction. Exotropia occurs when deviation is in a temporal (lateral) direction. Hypertropia occurs when the deviation is in a superior direction. Hypotropia occurs when the deviation occurs in an inferior direction. People who have strabismus may report diplopia, or double vision. The diplopia may be vertical, horizontal, or diagonal, depending on the direction of strabismus. To learn about the different causes of diplopia, follow this link. Sometimes, the diplopia is not severe enough to impact functional vision and the brain compensates for the differing images through a process called supression, when the brain “ignores” the incoming image from the weaker eye and just processes the image from the stronger eye. If suppression is severe enough and impacts eye development or the health of the eye (as during childhood), a condition called amblyopia emerges.

FOCUS ON CLINICAL APPLICATION: Screening for deficits in a client’s visual fields is important because problems may be indicative of early scotomas (blind spots), glaucoma, or CNS dysfunction. Visual field deficits can have functional implications, as people with field deficits may have increasing difficulty with occupational performance areas such as safety during mobility (both moving around personal space [e.g., home, school, or work]) and in the community [e.g., neighborhood, driving]), ADL/IADL performance, employment, education, play/leisure, and health management. There are two widely used methods for screening visual fields: the finger counting method and the Confrontation Test. To view a brief video demonstrating these two methods, follow this link. The finger counting method is a very simple and easy screening to administer in a clinic or community setting. Each eye is tested separately. The procedure to administer the finger counting method is as follows (Anderson et al., 2009): The examiner is seated across from the client with their faces approximately 2 feet apart. The client is instructed to cover one of their eyes and focuses their uncovered eye at the examiner’s opposite eye. To test the client’s left eye, the examiner should close their left eye and instruct the client to fixate their gaze on the examiner’s right eye (so that the examiner’s visual field approximates the client’s visual field. If the client does not fixate their gaze, remind the client to keep looking at the examiner’s opposite eye. The examiner tells the client, “I’m going to hold up a number of fingers in front of you. I want you to tell me how many fingers you see in total.” Starting with the superior fields, hold up both hands about 20 to 60 degrees above the point of fixation. The examiner’s right hand will be positioned in the client’s left visual field and the examiner’s left hand will be positioned in the client’s right visual field. The examiner will hold up one or two fingers on each hand (may be different for each hand) and flash for approximately 1 second before returning to a closed fist. Repeat the procedure for the inferior fields and with the other eye. If the client does not report the correct total number of fingers accurately, screen each quadrant separately to determine the specific area the client is not perceiving. The Confrontation Test is also a very simple and easy screening to administer in a clinic or community setting. Each eye is tested separately. The procedure to administer the Confrontation Test is as follows (Ruddy et al., 2024): The examiner is seated across from the client with their faces approximately 2 feet apart. The client is instructed to cover one of their eyes and focuses their uncovered eye at the examiner’s opposite eye. To test the client’s left eye, the examiner should close their left eye and instruct the client to fixate their gaze on the examiner’s right eye (so that the examiner’s visual field approximates the client’s visual field. If the client does not fixate their gaze, remind the client to keep looking at the examiner’s opposite eye. The examiner tells the client, “I’m going to bring my fingers from the edge of your vision and slowly move it to the center. As soon as you see my fingers, say ‘yes.'” The examiner should start by placing their fingers from behind the client’s head, gradually moving it toward the center. Test all four quadrants (upper right, upper left, lower right, and lower left). Repeat the procedure with the client’s other eye.

The Visual System

We now turn our attention to the visual system, which allows us to see and interact with our environment. We begin at the eye and travel inward toward the visual cortex in the occipital lobe. Along the way, we will discuss various pathologies of the visual system that are sometimes seen in occupational therapy practice.

• Light enters the visual system first through the cornea, the clear, outermost portion of the eye. The cornea protects the eye from particulates in the environment and from ultraviolet radiation and refracts light onto the lens.
• Surrounding the cornea is the sclera, a dense packing of connective tissue that composes the white parts of the eye.
• The iris is the colored part of the eye that regulates the amount of light entering the eye. The iris is innervated by CN-III and is responsible for photopupillary response to light (recall Step 2 of the Cranial Nerve Screen in Section 8.1).
• The pupil is the opening at the center of the iris through which light passes. It constricts to allow less light to pass through the iris (such as with exposure to bright light) and dilates to allow more light to pass (such as with low illumination conditions). The photopupillary response of the cranial nerve screen assesses brainstem function (Belliveau et al., 2023). An abnormal photopupillary response may be indicative of injury to the optic nerve (CN-II), injury to the oculomotor nerve (CN-III), the presence of brainstem lesions (such as tumors), or the presence of barbiturates (Belliveau et al., 2023).
• The lens is a biconvex structure located just posterior to the iris in the anterior cavity. It is fed nutrients and oxygen and eliminates waste through the aqueous humor, a water-like substance (Sunderland & Sapra, 2023). The shape of the lens can be altered through the contraction of the ciliary muscles that surround it to focus the light on the retina at the back of the eye through accommodation.

FOCUS ON CLINICAL APPLICATION: Under normal circumstances, the amount of aqueous humor in the anterior cavity is regulated at a near constant pressure, through a process of secretion and absorption (Sunderland & Sapra, 2023). When drainage of aqueous humor slows, intraocular pressure (IOP) increases, resulting in a condition called glaucoma. IOP can be measured clinically by an ophthalmologist or optometrist by blowing a puff of air against the cornea. The amount of air pressure required to deform the cornea is an indicator of IOP. Glaucoma is a progressive, irreversible disease of the eye in which the IOP is pathologically high and can ultimately lead to visual field loss and blindness (Dietz et al., 2024; Sunderland & Sapra, 2023). The most common type of glaucoma is primary open-angle glaucoma (POAG) and if left untreated, results in slow, painless damage to the optic nerve and resulting blindness (Sunderland & Sapra, 2023). In its earlier stages, POAG results in a decrease of peripheral visual fields, or tunnel vision, in one or both eyes. Glaucoma is not curable, but symptoms are treated with medications and sometimes, surgery. Follow this link to view a brief video of glaucoma. To view an interactive digital model of glaucoma, follow this link.

FOCUS ON CLINICAL APPLICATION: Axial length is the distance from the cornea to the retina (Bhardwaj & Rajeshbhai, 2013). In adults, the average axial length is approximately 22-25mm (Bhardwaj & Rajeshbhai, 2013). Under normal circumstances, the cornea and lens refract light in such a way that the image is focused directly on the retina. Refractive errors, where the shape of the eye prevents light from focusing directly on the retina, results in blurred vision. Four of the most common refractive errors that we will cover are myopia (near sightedness), hyperopia (far sightedness) presbyopia (age-related far sightedness), and astigmatism. Myopia is the most common refractive error in children and young adults (Subudhi & Agarwal, 2023). The American Academy of Ophthalmology (n.d.) estimates that approximately 41.6% of the population in the U.S. has myopia, a doubling over the past 50 years. While not the cause of myopia, prolonged screentime with digital media has increased its progression among this population (Subudhi & Agarwal, 2023). With myopia, the axial length of the eye is longer than the focal point of light, so the image appears out of focus. People with myopia can see fairly clearly when objects are up close, but have difficulty when viewing things in the distance. Myopia can easily be corrected with glasses, contact lenses, or refractive surgery (Subudhi & Agarwal, 2023). To view an interactive digital model of myopia, follow this link. The American Academy of Ophthalmologists (n.d.) estimates that approximately 10% of people over the age of 40 in the U.S. have hyperopia. With hyperopia, the axial length of the eye is shorter than the focal point of light (Majumdar & Tripathy, 2023). As a result, people with hyperopia have difficulty seeing objects up close, but can easily see things in the distance. Hyperopia can easily be corrected with glasses, contact lenses, or refractive surgery. To view an interactive digital model of hyperopia, follow this link. Presbyopia is the leading cause of low vision in older adults (Singh & Tripathy, 2023). It is the progressive decrease in the lens’ ability to accommodate (bend) for near vision. resulting in the behavior of holding objects or printed materials at a farther distance. Onset usually begins around age 40. Uncorrected presbyopia results in complaints of difficulty reading, eye fatigue, and drowsiness (Singh & Tripathy, 2023). Presbyopia differs from hyperopia in that presbyopia is a result of stiffening of the lens, whereas hyperopia results from axial length. Presbyopia may be corrected with corrective lenses (eye glasses or contact lenses) or with surgery. To view an interactive digital model of presbyopia, follow this link. Astigmatism is a common refractive error, accounting for approximately 13% of cases (Gurnani & Kaur, 2023). It is a condition where either the cornea or lens is of an irregular shape such that parallel rays of light do not converge at a single focal point on the retina, but instead have multiple focal points. People with astigmatism usually have complaints headaches, eye fatigue, difficulty focusing, transient blurring, and drowsiness (Gurnani & Kaur, 2023). Astigmatism is treatable with corrective lenses (eye glasses or hard contact lenses) or surgery. To view an interactive digital model of astigmatism, follow this link.

FOCUS ON CLINICAL APPLICATION: Cataracts is an eye disease where the normally clear lens gradually becomes opaque to the point that light no longer focuses on the retina (Nizami et al., 2024). Cataracts can affect people of all ages throughout the lifespan, but predominantly affects older adults in the fifth or sixth decades of life (Nizami et al., 2024). People with cataracts most often complain of decreased or blurred vision, diplopia (double vision), halos around light sources, and sensitivity to glare. In the early stages of cataracts, ADL and IADL performance may not be impacted. In the later stages, however, people with cataracts may begin to self-limit their driving (especially at night) or shift their occupational habits to those that require less visual acuity (such as fine needlework or fine tool use). In most instances, cataracts affect the central field of view, making it challenging to see what’s directly in front. The only reliable treatment for cataracts is surgery.

• The posterior cavity (also known as the vitreous chamber) lies between the lens and the poster surface of the eye ball. The posterior cavity contains vitreous fluid, a thick, gel-like substance that helps the eye ball retain its shape to maximize its refractive ability (Rehman et al., 2023).
• The retina lines the posterior portion of the eye and is comprised of layers of specialized cells that convert light energy into electrical impulses that the brain can interpret. Especially important are two photoreceptors: rods and cones. Rods are tube-like structures that comprise about 95% of the photoreceptors in the eye (Mahabadi & Al Khalili, 2023). Rods predominantly function to allow vision in low illumination. Cones detect color and are comprised of photoreceptors that detect red, blue, and green wavelengths (Mahabadi & Al Khalili, 2023).
• The macula is a small section of the retina (approximately 5mm in diameter) at the posterior wall of the eye that is responsible for central vision, the central 30 degrees of the visual field. The macula has a higher concentration of cones than the rest of the retina and detects fine detail and most of the color that we see.
• The fovea centralis is at the very center of the macula (about 1.5mm wide) and is a small depression in the center. It is densely packed with only cone cells (Mahabadi & Al Khalili, 2023) and is responsible for sharp, central vision.

FOCUS ON CLINICAL APPLICATION: Age-related macular degeneration (ARMD) is the most common cause of blindness, especially in people over age 60 and is more prevalent in people of European ancestry (Ruia & Kaufman, 2023). Other risk factors include smoking, cardiovascular disease, hypertension, hypercholesterolemia, and obesity (Feldman et al., 2024). The degeneration of the macula and fovea is due to the deposition of drusen, yellow deposits of lipids and proteins. Additionally, there may be thinning of the macula (Dry ARMD) or bleeding into macular tissue (Wet ARMD). Because the macula and fovea are affected, people with ARMD report loss of central vision. Other symptoms include faded colors, difficulty recognizing faces, and straight lines appearing wavy (Ruia & Kaufman, 2023). For an interactive digital model of dry macular degeneration, follow this link. For an interactive digital model of wet macular degeneration, follow this link. One method for assessing for ARMD is the use of an Amsler grid, which is made up of horizontal and vertical lines evenly spaced on a sheet of white paper and a central dot for visual fixation. People with ARMD may see distortion, have blind spots, or blurriness. A downloadable Amsler grid with instructions may be found by following this link.

FOCUS ON CLINICAL APPLICATION: Diabetic retinopathy is the most common and severe visual complication of diabetes mellitus (Shukla & Tripathy, 2023) Poor glycemic control may lead to vision-threatening damage to the retina and eventually, blindness. (Shukla & Tripathy, 2023). Other risk factors include hypertension, obesity, and hyperlipidemia (Shukla & Tripathy, 2023). Sustained hyperglycemia (high blood glucose) may lead to microaneurysms (ballooning arterial walls), abnormal growth of new blood vessels in the retina (called neovascularization), retinal edema, and in severe cases retinal hemorrhages, where blood seeps into the vitreous humor. An interactive digital model of diabetic retinopathy may be found by following this link.

The Cortical Pathway

Thus far, we have explored the pathway of light energy from the eyes to the retinas. You will recall that the cornea and lens invert the images in the visual fields onto the retinal surfaces. In the illustration below, images in the right visual field (blue) land on the left sides of the retina for both eyes. Likewise, images in the left visual field (green) land on the right sides of the retina for both eyes.

Now we turn our attention to the pathways of electrical energy from the optic nerves to the visual cortices. Nerve cells in the retinas synapse at the optic disc, where nerves leave the ocular globe to form the optic nerve (CN-II). It is at this point that there is a blind spot in the visual field. The axons of nerves that originate from the nasal half (medial visual field) of the retina decussate (or cross sides) at the optic chiasm (Dragoi, 2020). The overall result is that the visual pathway for images in the right visual field (blue) is processed by the left side of the brain and the visual pathway for images in the left visual field (green) are processed by the right side of the brain.

After the optic nerves decussate at the optic chiasm, each side forms the optic tract. Each optic tract continues posterolaterally to synapse with four areas (Dragoi, 2020):

• lateral geniculate nucleus of the thalamus for visual processing. It is sometimes referred to as the relay station of visual information from the retina to the primary visual cortex (V1) in the occipital lobe.
• superior colliculus of the tectum in the mesencephalon integrates visual information, head orientation, and oculomotor function. It is responsible for our ability to track faces and react to emotional stimuli (Zubricky & Das, 2024). It is hypothesized that children with some forms of autism spectrum disorder have damaged superior colliculi, and that is the reason that they do not attend to faces (Zubricky & Das, 2024).
• pretectum of the mesencephalon is responsible for the photopupillary response, constricting or dilating the pupils.
• hypothalamus regulates circadian rhythms for the sleep-wake cycle. The sleep-wake cycle can be significantly impacted, based on the amount of light to which the eyes are exposed.

From the lateral geniculate nuclei, axons follow a tract called optic radiations. These radiations terminate at the primary visual cortex (V1) in the occipital lobe. To view an interactive digital model of the visual pathway, follow this link. Visual information from the primary visual cortex is the routed to the secondary visual cortex (V2), depending on the type of information that needs processing. There are two pathways for visual information to be processed: the dorsal stream and the ventral stream (Dragoi, 2020).

• The dorsal stream leads from the primary visual cortex of the occipital lobe to the parietal lobe. It is responsible for processing spatial orientation, depth perception, and the location and movement of objects in space. The dorsal stream processes information about the “where” of the visual stimulus. Lesions to the dorsal stream result in impaired spatial orientation, impaired motion detection, impaired visual tracking, and hemi-inattention (e.g., lack of awareness of the contralateral field of view). Hemi-inattention is different from a visual field cut. A person with visual field cut simply does not perceive or see objects in the contralateral visual field. A person with hemi-inattention, however, can perceive or see objects in the contralateral visual field, but simply does not attend to it.
• The ventral stream leads from the secondary visual cortex in the occipital lobe to the fusiform gyrus in the medial temporal lobe and the limbic system. It is responsible for the recognition of objects, reading text, and learning and remembering visual objects (e.g., words and their meanings). The ventral stream processes information about the “what” of the visual stimulus. Lesions of the ventral stream result in impaired visual attention, prosopagnosia (inability to recognize familiar faces), and interpret facial expressions.

FOCUS ON CLINICAL APPLICATION: Depending on their location, lesions along the cortical pathway produce various impairments of the visual field (Patel et al., 2021). Damage to the optic nerve results in ipsilateral monocular vision loss. Note: The location of the lesion and resultant visual impairment that is depicted in number 2 below is inaccurate and should be omitted. Damage to the optic chiasm results in bitemporal hemianopsia (labelled as bipolar hemianopia below). Damage to the optic tract results in contralateral homonymous hemianopsia. Damage to the pariental (medial) fibers of the optic radiationresults in contralateral homonymous inferior quadrantanopsia. Damage to the temporal (lateral) fibers of the optic radiation results in contralateral homonymous superior quadrantanopsia. Damage to the entire optic radiation results in contralateral homonymous hemianopsia

FOCUS ON CLINICAL APPLICATION: CONDUCTING A VISION SCREEN The purpose of screening the visual system is to get a general sense of whether the client has a vision problem that impacts occupational performance. If the screening indicates the presence of a problem, a more thorough assessment should be completed by a vision specialist, such as an ophthalmologist or optometrist. Vision history and client goals. Finding out if the client already has an established vision diagnosis will alert the occupational therapist to potential difficulties with occupational performance. Keep in mind that the presence of a diagnosis does not necessarily indicate impairments in function. Ask the client when the last time they saw a vision specialist or received vision care. Has their vision undergone any recent changes? The Canadian Occupational Performance Measure (COPM) may be a useful tool in uncovering any occupational performance problems. A semi-structured interview will also reveal the client’s goals related to vision. Eye dominance. The dominant eye is the eye a person unconsciously uses to guide fixation on an object in the environment. Most people are right eye dominant and dominance generally follows handedness. It is important to establish eye dominance because most people will automatically use that eye to fixate on an object even if it is the weaker eye. For example, they may hold a magnifier up to their right eye to read, even if it has poorer acuity and may need to be trained to use their non-dominant, better-seeing eye for reading tasks. To determine eye dominance, provide the client with a cardboard with a hole punched in it or a cardboard tube (e.g., toilet paper roll) and ask the client to view an object. Do not tell them what you are observing. They will usually hold the cardboard up to their dominant eye. Visual acuity. As discussed above, visual acuity may be measured using a Snellen chart. The occupational therapist should assess near acuity (13 to 16 inches; e.g., reading, writing, dialing a cell phone), intermediate acuity (20 to 40 inches; e.g., looking at a computer screen or seeing the dashboard of a car), and distance acuity (>40 inches; e.g., reading street signs, watching television, recognizing faces). The LEA Numbers Intermediate Acuity Test Chart (part of the Brain Injury Vision Assessment Battery for Adults [biVABA] may be used to assess intermediate acuity. Contrast sensitivity. Also described above, contrast sensitivity is closely associated with reading, mobility, driving, and other common daily activities. It generally decreases with age and with eye diseases such as macular degeneration and glaucoma. A person can have good near acuity to read a test chart, but experience difficulty reading newsprint because it has lower contrast. Assessing contrast sensitivity may be completed by using the Pelli-Robson Contrast Sensitivity Chart or the LEA Numbers Contrast Sensitivity Chart. Peripheral Visual Field. The visual field may be divided into quadrants (upper left, upper right, lower left, lower right) and also includes the central visual field and peripheral visual field. To assess peripheral visual fields, the Confrontation Test or the finger counting method may be used. To assess central visual fields, the Amsler grid may be used. Stereopsis is depth perception. As mentioned above the Titmus Stereopsis Test is one method to assess a client’s ability to perceive depth using binocular vision. Smooth pursuits (Tracking). Tell the client, “Watch the dot as it goes around. Don’t take your eyes off the dot.” Using one target (e.g., a tongue depressor with a colored dot on one end) held approximately 16 inches from the client’s face, slowly (approximately four seconds per rotation) circumscribe a circle in the air. Perform two rounds in a clockwise direction, followed by two rounds in a counter-clockwise direction. Note how many rotations the client is able to complete in each direction without breaking fixation. Saccades. Tell the client, “When I say ‘red’, look at the red dot. When I say ‘green’, look at the green dot. Don’t look at the dot until I tell you.” Using two stimuli (e.g., tongue depressors with colored dots on one end) held approximately 16 inches from the client’s face and approximately 16 inches apart, direct the client to fix their gaze in alternating colors, at irregular intervals, for a total of five round trips (starting with red and ending with red). Note how many round trips the client is able to successfully complete. Visual perception. A commonly used test for visual perception is the Motor-Free Visual perception Test (MVPT). It comes in both a horizontal and a vertical format. It is a normative test that assesses five areas: spatial relationships, figure-ground discrimination, visual discrimination, visual closure, and visual memory. Scanning. Visual scanning is the ability to use vision to search in a systematic manner, such as top to bottom and left to right. A person will use scanning to avoid obstacles in the environment and locating items. Common scanning screens include Letter Cancellation Test, Bells Test, and Star Cancellation Test. A client’s strategy for scanning the visual field may be indicate hemi-inattention or cognitive disorganization. See Section 20.8 of this Course Manual to download a copy of the Letter Cancellation Test. Spatial relations are the relationships between objects in space. A commonly used instrument used to assess for hemi-inattention or visual field cut is the Schenkenberg Line Bisection Test. Clients are presented with a series of lines on a paper and are instructed to draw a cross hatch mark dividing each line in half. Reading performance is the ease with which a person can read printed material. Visual acuity alone does not necessarily predict how well a cleint will be able to read. Assessing their speed can provide valuable information to the occupational therapist. Maximum reading speed is the speed when reading is not limited by print size. Reading speed may be influenced by amount of illumination, text characteristics (serif or sans serif fonts), and letter spacing. Handwriting performance should be assessed by having the client write a short paragraph from dictation. The occupational therapist can evaluate the client’s body posture, head position, prehension pattern, writing legibility and quality of the writing. Did the client’s writing stay on a line or drift either up or down? Are the letters spaced appropriately? Is the writing legible?

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