Low Vision and Vision Rehabilitation in Glaucoma
Glaucoma is an optic neuropathy characterized by elevated intraocular pressure leading to visual field loss. It is the leading cause of irreversible blindness globally . Visual impairment experienced by glaucoma patients can result in challenges with activities of daily living (ADLs), increased morbidity, and consequent negative impacts on mental health. While disease progression is targeted with medicine and surgery, irreversible vision related disabilities can be addressed through low-vision services (LVS). This article presents information on how to recognize and respond to glaucoma patients with low-vision needs.
Definition of Low Vision
According to the American Academy of Ophthalmology’s Preferred Practice Patterns (PPP) for Vision Rehabilitation, low vision is defined as a visual impairment caused by eye disease in which visual acuity is 20/50 or worse in the better-seeing eye and cannot be corrected or improved with regular eyeglasses, contact lenses, medicine, or surgery. It is further qualified as uncorrectable vision loss that may be better than 20/50 acuity, but which involves loss of visual field, reduced contrast sensitivity, increased glare, or difficulty with daily activities.
The International Classification of Diseases, Ninth Revision (ICD-9) and the International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10 CM) define low vision as patients who fall within Category of Visual Impairment 1 or 2, which includes patients with visual acuity 20/70 or worse in the better-seeing eye, or with any loss in visual field that impacts ADLs.
Glaucoma and Low Vision Epidemiology
An understanding of the epidemiology of glaucoma patients with low vision is limited to prevalence figures estimated through combined meta-analyses and census data ranging from 2010 to 2015. It is also limited by the way in which terms are defined, with glaucoma definitions varying by visual field testing or intraocular pressure measurements, and low vision being defined through the limited scope of visual acuity, which is often not the primary complaint in glaucoma.
In 2013, the number of people (40-80 years of age) worldwide with glaucoma was estimated at 64.3 million, projected to include 76.0 million by 2020 and 111.8 million by 2040. The most up-to-date estimates for the United States indicate that there are 2.7 million Americans with glaucoma3, (1.9% of the population). Low vision (when defined as visual acuity 20/50 or worse in the better-seeing eye) was last estimated in 2010 to affect 2.9 million people in the United States (2.04% of the population).
From a few studies defining symptomatic complaints in glaucoma, there is some understanding of the overlap of low vision in glaucoma patients. For example, a small survey study found that 57% of glaucoma patients reported needing more light, 55% reported blurry vision, 46% reported glare, 36% reported noticeable visual field losses, and 30% reported contrast sensitivity losses. Glare, visual field losses, and contrast sensitivity losses would directly qualify patients as having low vision as defined by the Academy’s PPP, and as such are visual disabilities targetable by LVS. There are a significant number of people affected by glaucoma, and, of those patients, many are symptomatic in ways that meet the criteria for low vision. A cross-sectional study describing demographic and clinical characteristics of a glaucoma patient population attending vision rehabilitation found that patients reported the greatest difficulty with reading (88%), writing (72%), adn mobility (67%). Most glaucoma patients attending low vision rehabilitation were functionally monocular, but not legally blind.
Vision Impairment and Disability
The loss of peripheral vision as detected by visual field testing is the most commonly followed measurement of glaucoma progression. The severity, magnitude, and rates of change in binocular visual field sensitivity are significantly correlated with quality-of-life measures in glaucoma patients, especially in later disease. However, patients can experience a decline in quality of life and increase in disability even in early stages of glaucoma, and these changes may not always correlate with clinical measures.
The Collaborative Initial Glaucoma Treatment Study (CIGTS), found that more than 25% of newly diagnosed glaucoma patients report blurred vision, difficulty adapting between light and dark, trouble seeing in the dark, and problems with bright lights, and that visual field testing was only modestly correlated with patient complaints. These findings underscore the importance of screening glaucoma patients for visual disability outside of clinical testing. Vision related quality of life may be a more useful patient-centered outcome measurement, as well as something that can be targeted through LVS.
The most common glaucoma patient complaints are difficulties with mobility, reading, and driving. When glaucoma patients were surveyed about their mobility, a review found 49% of patients have difficulty with steps, 42% with shopping, and 36% with crossing the road. This difficulty was correlated with a significant increase in falls, entry into assisted living, restricted physical activity, and a decreased quality of life, leading to an overall increase in morbidity and mortality. For glaucoma patients surveyed about reading 40% of patients endorse general difficulty. Research examining the extent and cause of the reading deficit found reading difficulty in glaucoma patients even with retained acuity, difficulty following a line or moving to the next line, difficulty with small print or low contrast, and decreased reading speeds to the point of reading impairment (less than 80 words per minute) in sustained silent reading. Finally, glaucoma patients surveyed about driving reported increased perceived difficulty with driving, particularly at night, with mixed data on increased risk of collisions and resulting morbidity and mortality. However, glaucoma patients are three times more likely to stop driving due to their perceived deficits, which is associated with higher rates of entry into assisted living, lower quality of life, and depression. The resulting loss of function in all three categories of mobility, reading, and driving is correlated with increased rates of depression and anxiety.
Evaluation of Low Vision in Glaucoma
Screen for patient functional complaints, patient quality of life, and ability to perform ADLs.
- Activities of Daily Vision Scale (ADVS)
- National Eye Institute Visual Functioning Questionnaire (NEI-VFQ)
- Visual Function Index (VF-14)
- Visual Activities Questionnaire (VAQ)
- Glaucoma Quality of Life (GQL-15)
Test with high contrast charts and bright lighting. Encourage the patient to shift their gaze or move their head to find the optimum fixation point for best vision.
- Projection charts: Not appropriate due to low contrast and presentation in a dark room
- Sloan chart: Use brightly lit at 10 ft
- Early Treatment Diabetic Retinopathy Study (ETDRS) chart: For visual acuity <20/100
- Designs for Vision Distance Test Chart for the Partially Sighted: For severe acuity loss
Carefully evaluate due to common patient complaints regarding reading.
- Bailey-Lovie Near Reading Card: Tests whole word reading acuity, more useful in evaluating patients for reading aids than single letter acuities
Evaluate what remaining field is available for rehabilitation.
- Goldmann perimeter: Large stimuli for easier assessment
- Humphrey automated 10-2 field: For remaining central field in advanced glaucoma
Important for resolving objects in daily visual tasks, such as recognizing a face, distinguishing between pills, or resolving where steps begin and end
- Pelli-Robson Contrast Sensitivity Chart: One size letters with decreasing contrast, patients must be able to see 40M-sized letters
- VISTECH contrast test: Sine-wave/bar patterns for vision less than 20/40
Observation of Patient
Observe the patient performing visual tasks, e.g., reading, writing, walking, navigating steps.
- Quality of continuous reading, reading speeds, print size, errors in certain field locations
- Speed of walking, head swing and room scanning, missed objects/bumping into items
Management of Glaucoma Patients with Low Vision
The goal of LVS is to increase the patient’s ability to maximize function with their remaining vision.
- Handheld/stand/electronic magnifiers: Electronic magnifiers are the gold standard in LVS due to variable magnification, high contrast, and black/white reversible polarity
- Computer Screen magnification programs, screen readers
- Scanning: Head swings, eye sweeps, slower approach speed. Helps patients to increase their awareness of the areas that need to be processed and develop a systematic plan for search patterns
- Field Expanders: Minifiers, reverse telescopes, or prisms to reduce the entire field into the central field or transfer the peripheral field onto the central field. Helps patients in static scenarios (spotting objects, viewing from a stable position), not for dynamic use (walking)
- Discomfort glare: Causes discomfort and reduces visual task efficiency but not resolution
- Manage by turning down lights, adjusting angle of incoming light, absorptive lenses
- Disability glare: Reduces the resolution/ ability to identify visual stimulus
- Manage with polarizing lenses, anti-reflective coatings, incandescent lighting
- Referred retinal locus and eccentric fixation training for preserved, non-central vision
- Room lighting: Even, without shadow, adequate for mobility and ADLs but without glare or reflections
- For missing visual field: Typoscope, signature guide, place markers
- Tactile aids: Dots, plasticized marking pens, bold line markers
- Talking devices: Watches, clocks, calculators, phones
- Orientation and mobility training
Mental Health Impairments
- Networking, social support system, team concept: Important for combating increased rates of depression and anxiety
LVS treatment outcomes have been evaluated using clinical questionnaires in multiple studies prior to and after completion of 3 to 9 months of therapy. A wide range of measures have been used, and many categories were found to be improved by a statistically significant amount from baseline following treatment including overall visual ability, reading, visual information processing, mobility, near tasks, social functioning, and emotional well-being. The improvements in overall visual ability in particular showed clinically meaningful improvements in nearly half of the patients attending LVS. The magnitude of the improvement in all categories and across studies was characterized as moderate.
However, these data are for all patients utilizing LVS and the majority of LVS referrals are patients with central vision loss, such as in age-related macular degeneration (AMD). In one study evaluating the effect of LVS on glaucoma patients, those with best-corrected visual acuity (BCVA) between 20/70 and 20/400 in the better-seeing eye and a diagnosis of glaucoma were randomized to either low-vision examination and treatment or only low-vision examination. A significant improvement was found in reading ability and overall visual ability following LVS when compared to the control group.
The data for low vision in glaucoma patients is still developing. It is clear that there is a large population of glaucoma patients, many of which have visual functional deficits that meet criteria for low vision. In the setting of these irreversible deficits, patient disability can be targeted through low vision examination and services. It is important to identify these patients, discuss strategies for improved functionality, and refer them to the appropriate LVS in a timely fashion.
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