Ophthalmology – Low Vision

Basics

Description

Low vision is a permanent reduction in visual function caused by an ocular or neurologic disorder in which useful residual vision remains, but the impairment limits the patient’s ability to perform desired activities of daily living.

Unlike complete blindness, patients with low vision retain vision that can often be enhanced through optical devices, electronic aids, environmental modification, and rehabilitation.

Common causes include:

• Age-related macular degeneration
• Diabetic retinopathy
• Glaucoma
• Optic neuropathy
• Inherited retinal disease
• Disorders of the visual pathways
• Other irreversible ocular diseases

The primary goal of low-vision care is not necessarily to improve measured visual acuity, but to maximize functional use of the remaining vision.

Epidemiology

Low vision becomes increasingly common with age because many of its major causes are age-related.

Prevalence estimates vary considerably because definitions of:

• Low vision
• Visual impairment
• Legal blindness
• Functional visual disability

differ among studies and healthcare systems.

Children can also have significant low vision from congenital, hereditary, developmental, retinal, optic nerve, or neurologic disorders.

Geriatric Considerations

Older adults often require additional time for examination and rehabilitation.

Important considerations include:

• Reduced concentration
• Slower adaptation to new devices
• Presbyopia
• Reduced contrast sensitivity
• Mobility limitations
• Hearing impairment
• Cognitive impairment or dementia
• Multiple systemic illnesses

Near-vision activities are often particularly important because patients commonly identify reading as a major rehabilitation goal.

Pediatric Considerations

Children with low vision have different rehabilitation requirements.

Their accommodation can sometimes compensate for part of the optical demand produced by magnification.

Children may require:

• Distance magnification
• Telescopes
• Electronic magnification
• Large-print educational materials
• Classroom modifications
• Preferential seating
• Assistive technology

Very short working distances required for magnification can become increasingly difficult as accommodative ability changes with age.

Educational and developmental needs should always be incorporated into the rehabilitation plan.

Risk Factors

Risk factors depend largely on the underlying ocular disease.

Important general factors include:

• Increasing age
• Diabetes
• Hypertension
• Cardiovascular disease
• Smoking
• Genetic susceptibility
• Certain nutritional factors
• UV exposure
• Inherited retinal or optic nerve disease

Genetics

Many causes of low vision have an important genetic component.

Examples include:

• Retinitis pigmentosa
• Stargardt disease
• Hereditary optic atrophy
• Some forms of macular degeneration
• Congenital retinal dystrophies

Genetic counseling and testing may be appropriate when an inherited disorder is suspected.

Prevention

Low vision itself is managed through rehabilitation, but some causes of irreversible visual impairment can be prevented or slowed.

Important preventive measures include:

• Regular ophthalmic examinations
• Appropriate control of diabetes
• Blood pressure management
• Smoking cessation
• Cardiovascular risk reduction
• Appropriate eye protection
• Treatment of glaucoma
• Early treatment of retinal disease
• Appropriate UV protection
• Management of the underlying ocular disorder

Pathophysiology

The mechanism depends entirely on the underlying disease.

Low vision can result from abnormalities involving:

Ocular Media

Examples include irreversible corneal opacity or other media abnormalities.

Retina

Examples include:

• Macular degeneration
• Diabetic retinopathy
• Retinitis pigmentosa
• Inherited macular dystrophies

Optic Nerve

Examples include:

• Glaucoma
• Ischemic optic neuropathy
• Hereditary optic neuropathy

Visual Pathways

Neurologic disease can produce:

• Visual field defects
• Cortical visual impairment
• Impaired visual processing

Commonly Associated Conditions

Important associated disorders include:

• Diabetes mellitus
• Hypertension and vascular disease
• Age-related macular degeneration
• Glaucoma
• Optic neuropathy
• Inherited retinal disorders
• Neurologic disease

Diagnosis

Low-vision assessment is fundamentally a functional examination.

The clinician needs to determine not only what the patient can see, but also what the patient wants or needs to do with the remaining vision.

History

A detailed history should include:

Medical History

Identify systemic diseases contributing to visual impairment.

Ocular History

Determine:

• Cause of vision loss
• Stability or progression
• Previous treatments
• Surgical history
• Current ophthalmic treatment

Functional History

Ask what activities are difficult.

Examples include:

• Reading
• Recognizing faces
• Watching television
• Shopping
• Cooking
• Using a telephone or computer
• Managing medications
• Seeing prices
• Signing documents
• Mobility
• Educational activities
• Employment
• Driving

Specific functional goals should be established before selecting low-vision devices.

Visual Acuity

Measure both:

• Distance visual acuity
• Near visual acuity

Standard high-contrast charts may not completely represent the patient’s real-world visual function.

Near acuity should be measured carefully because reading is frequently one of the patient’s primary goals.

Refraction

A meticulous refraction is important even in patients with severe visual impairment.

Small improvements can produce meaningful functional gains.

Useful strategies include:

• Trial-frame refraction
• Larger lens-power changes when appropriate
• Handheld cross-cylinder testing
• Careful bracketing of the endpoint

Patients with central vision loss may benefit from being encouraged to use eccentric viewing during testing.

Eccentric Viewing

Patients with central scotomas may see better when they look slightly away from the object of interest.

They may develop a preferred retinal locus (PRL) outside the damaged fovea.

Rehabilitation can teach patients to use this area more effectively for:

• Reading
• Face recognition
• Detail discrimination

Slit-Lamp and Fundus Examination

A complete ocular examination remains essential.

Evaluate:

• Cornea
• Anterior chamber
• Lens
• Vitreous
• Retina
• Macula
• Optic nerve

The clinician should identify any treatable component of the visual loss before attributing disability entirely to permanent low vision.

Corneal Evaluation

Depending on the underlying disease, assessment may include:

• Keratometry
• Corneal topography

This can be useful when irregular astigmatism contributes to reduced vision.

Functional Vision Assessment

Visual acuity alone is insufficient.

Additional assessment can include:

• Reading speed
• Critical print size
• Contrast sensitivity
• Visual fields
• Glare testing
• Color vision when relevant
• Mobility performance

Reading charts such as MNREAD can help quantify functional reading ability.

Magnification

Magnification is one of the central principles of low-vision rehabilitation.

Several approaches are available:

• Relative-size magnification
• Relative-distance magnification
• Angular magnification
• Optical magnification
• Electronic magnification

The device selected should be based on the specific task, rather than simply the measured visual acuity.

Near Magnification

Near magnification can be provided with:

• High-add spectacles
• Hand magnifiers
• Stand magnifiers
• Electronic magnifiers
• Tablets or smartphones
• Closed-circuit television/video magnification systems

High-plus lenses require progressively shorter working distances.

Patients must therefore be trained to hold reading material at the correct focal distance.

Distance Magnification

Distance tasks may require telescopic systems.

Telescopes can help with activities such as:

• Reading signs
• Seeing a classroom board
• Watching television
• Recognizing distant objects

The lowest magnification that accomplishes the desired task is generally preferred because increasing telescope power reduces the field of view and can make stabilization more difficult.

Electronic Magnification

Electronic systems are particularly useful because they can provide:

• Adjustable magnification
• Contrast enhancement
• Reverse contrast
• Brightness adjustment
• Large fields of view
• Variable working distance

Devices include:

• Desktop video magnifiers
• Portable electronic magnifiers
• Smartphones
• Tablets
• Computer accessibility systems
• Head-mounted electronic devices

Treatment

Low-Vision Rehabilitation

The cornerstone of management is vision rehabilitation.

Treatment should be individualized according to:

• Visual impairment
• Visual field
• Contrast sensitivity
• Cognitive ability
• Manual dexterity
• Living environment
• Educational or occupational requirements
• Patient goals

First-Line Rehabilitation

Initial rehabilitation often focuses on improving visual strategies.

These can include:

• Eccentric viewing
• Scanning techniques
• Reading eye-movement training
• Large print
• Improved lighting
• Increased contrast
• Reduced glare

Optical Devices

Near Devices

Options include:

• High-add reading spectacles
• Handheld magnifiers
• Stand magnifiers
• Spectacle-mounted microscopes

Distance Devices

Options include:

• Handheld telescopes
• Spectacle-mounted telescopes
• Bioptic telescopes where appropriate and legally permitted

Nonoptical Aids

Simple environmental modifications can produce major improvements.

Examples include:

• Increased illumination
• High-contrast markings
• Large-print material
• Large-button telephones
• Talking clocks
• Audio books
• Tactile markers
• Organization of medications
• Contrasting kitchen equipment
• Glare-control filters

Occupational Therapy

Occupational therapists specializing in low vision can help patients adapt their homes and routines.

Training can address:

• Cooking
• Medication management
• Personal grooming
• Financial tasks
• Reading
• Computer use
• Mobility
• Fall prevention

A home evaluation can identify environmental barriers that are not apparent during an office examination.

Orientation and Mobility

Patients with severe field loss or markedly reduced vision may benefit from orientation and mobility training.

This may include:

• Safe navigation
• Street-crossing strategies
• Cane training
• Environmental scanning
• Public transportation training

Mental Health

Permanent visual loss can contribute to:

• Depression
• Anxiety
• Social isolation
• Loss of independence

Patients showing significant psychological distress should be referred for appropriate mental-health evaluation and support.

Management of the Underlying Disease

Low-vision rehabilitation does not replace treatment of the underlying ocular disease.

Patients should continue appropriate specialty care for conditions such as:

• Macular degeneration
• Diabetic retinopathy
• Glaucoma
• Retinal dystrophy
• Optic neuropathy

Systemic diseases such as diabetes and vascular disease also require appropriate medical management.

Surgery

Before labeling visual impairment as permanently rehabilitative, clinicians should determine whether a surgically correctable problem remains.

Examples can include:

• Cataract
• Corneal opacity
• Retinal pathology
• Other treatable structural abnormalities

Surgery should be considered when the expected functional benefit outweighs the risks.

Follow-Up

Early follow-up during rehabilitation is important because successful low-vision care usually requires training and repeated adjustment, not simply prescribing a magnifier.

Follow-up may initially occur within several weeks and subsequently at longer intervals depending on progress.

Reassessment is needed when:

• Vision changes
• The underlying disease progresses
• A device is no longer effective
• Functional goals change
• New technology becomes appropriate

At minimum, ongoing ophthalmologic assessment is generally required.

Patient Education

Patients should understand:

• The cause of their visual impairment
• Whether the underlying disease is stable or progressive
• Which visual functions are permanently impaired
• How rehabilitation can maximize remaining vision
• How to use prescribed devices correctly
• Appropriate lifestyle and safety modifications

Useful resources can include:

• Large-print materials
• Audiobooks
• Screen readers
• Smartphone accessibility features
• Support groups
• Transportation assistance
• Vocational rehabilitation
• Educational accommodations

Driving

Driving ability should be discussed when visual impairment affects:

• Visual acuity
• Visual field
• Contrast sensitivity
• Reaction to glare

Requirements vary by jurisdiction.

Patients who no longer meet legal or functional driving requirements may require counseling regarding:

• Public transportation
• Paratransit
• Family transportation
• Community mobility services

Diet

Dietary recommendations depend on the underlying disease rather than low vision itself.

For example, selected patients with age-related macular degeneration may qualify for AREDS2 supplementation according to their stage of disease.

Prognosis

The prognosis depends primarily on:

• Underlying ocular diagnosis
• Stability or progression of disease
• Residual visual function
• Cognitive and physical abilities
• Rehabilitation participation
• Availability of appropriate assistive technology

Although lost vision often cannot be restored, functional ability can frequently be improved substantially through appropriate rehabilitation.

Complications

Consequences of inadequately addressed low vision include:

• Loss of independence
• Reading disability
• Difficulty managing medications
• Falls and injuries
• Reduced mobility
• Social isolation
• Depression and anxiety
• Educational or occupational impairment
• Driving limitations

Key Clinical Pearls

• Low vision means useful vision remains, but permanent visual impairment interferes with everyday function.
• Management is primarily rehabilitative rather than curative.
• Always establish the patient’s specific functional goals before prescribing a low-vision device.
• Refraction should not be neglected simply because visual acuity is poor.
• Central vision loss may benefit from eccentric viewing and preferred retinal locus training.
• Near tasks can be improved with high adds, magnifiers, and electronic magnification.
• Distance tasks may benefit from telescopic devices.
• Environmental changes involving lighting, contrast, glare control, and accessibility can be as important as optical magnification.
• Low-vision care is most effective when ophthalmology is integrated with occupational therapy, orientation and mobility training, assistive technology, and psychosocial support.