Disability In Glaucoma
Open-angle glaucoma affects almost 2% of the American population greater than 40 years old, making the estimated number of Americans affected by the year 2020 to be almost 3.4 million. The World Health Organization estimated that the prevalence of blindness related to all types of glaucoma was approximately 8 million people, making glaucoma the second leading cause of blindness worldwide. Understanding disabilities caused by glaucoma and at which point in the disease process disabilities manifest is useful for treatment planning. This knowledge can also aid in the formulation of guidelines aimed to increase both the safety of the patient and the safety of the public.
Common Patient Complaints
Patients with glaucoma, particularly those with bilateral disease, experience difficulty with a variety of tasks. Difficulty performing tasks in both low and bright lighting conditions is the most frequent complaint of glaucoma patients. Contrast sensitivity has been shown to be a predictor of a patient’s ability to perform activities of daily living. Patients also report difficulty with reading, walking, and driving. Tasks involving central and near vision (such as reading), as well as mobility outside of the home are relatively more valued by patients with glaucoma, while tasks affected by glare, bumping into objects, and performing household chores are given relatively less importance.
Difficulty reading is the most frequent complaint of patients with any eye pathology. In the Salisbury Eye Evaluation (SEE), patients with advanced bilateral glaucoma were five times more likely to report difficulty with near vision tasks than those without glaucoma. It is worth noting that self-reported difficulty and demonstrated difficulty were strongly discordant. In fact, only patients with advanced glaucoma were objectively found to have diminished reading speed. A possible reason for this difference might be that if reading was tested for only a short period of time (~15 seconds), then any difficulties that occur with prolonged reading will not have had a chance to manifest. While it is not intuitive that patients with a disease process that primarily affects peripheral vision have problems with a central vision task such as reading, limited peripheral vision might result in difficulty following a line of print and/or finding the next line, and these tasks were reported as more difficult in patients with worse bilateral visual fields.
Compared to their aged matched controls, patients with glaucoma walk more slowly. Additionally, the walking speed of patients with glaucoma is strongly correlated with the mean deviation in the visual field of the worse eye. In the SEE, patients with bilateral (but not unilateral) glaucoma walked more slowly and bumped into things more often. The tendency to bump into things is likely due to visual field constriction, as can be demonstrated in normal individuals by artificially constricting their visual fields. Furthermore, patients with glaucoma tend to sway more than normal individuals, and greater sway is associated with more visual field loss in the better eye . That this difference in sway is not noted when the test is performed with the eyes closed supports the idea that the difference in visual function, rather than a vestibular one, is responsible for the difference in steadiness between groups. The disability caused by this assault on mobility is not trivial. Various studies have shown that elderly patients with difficulty walking are more likely to live in nursing homes or assisted living facilities, and that fear of falling leads to decreased quality of life, higher morbidity, and higher mortality.
Driving is the primary means of transportation for the elderly in the United States. Elderly persons who stop driving are more likely to move into a long term care facility, have higher rates of depression, and report lower quality of life.In the SEE, patients with bilateral, but not unilateral, glaucoma were more likely to stop driving than those without glaucoma. The odds of driving cessation doubled for every 5 dB of visual field loss in the worse eye. Interestingly, although driving limitations were NOT more common in glaucoma patients than in those without glaucoma, these patients were more likely to attribute any driving difficulties they might have to their visual abilities. While the SEE did not find more driving limitations in patients with glaucoma compared to those without, many studies have shown glaucoma to be associated with motor vehicle accidents (MVAs). McGwin et al. demonstrated that patients with advanced glaucoma had 3.5 times increased odds of being in a MVA. Haymes et al. similarly showed that glaucoma patients were more likely to be involved in an MVA than those without glaucoma, but they also showed that an impaired Useful Field of View (UFOV – a measure of visual field, discussed below) was the strongest risk factor for being involved in a MVA. Furthermore, in an on-road performance test, glaucoma patients with mild to moderate visual field impairments were able to complete a driving course, but were six times more likely to require instructor intervention. In 2010, Crabb et al. evaluated the eye movements of patients with glaucoma during simulated driving situations. The eye movements of nine patients with glaucoma were compared to those of ten age-matched controls. Over a series of 26 different simulated driving scenarios, patients with glaucoma made significantly more saccades per second, more fixations per second, and more smooth pursuits per second than those without glaucoma. The regions of interest in each scenario did not change in glaucoma patients despite the fact that hazards fell into areas of binocular visual field defects.
Facial Recognition/Social Interaction
In addition to having trouble with tasks that affect independent tasks such as those discussed above, patients with glaucoma also have difficulty recognizing faces. In a study by Glen et al., glaucoma patients with visual field and contrast sensitivity loss had more difficulty recognizing faces than their age-matched controls with normal vision. The ability to recognize faces is an important factor in social interactions with significant impact on quality of life.
Multiple scales to assess the impact visual function has on quality of life (QOL) have been developed, with some targeting glaucoma-specific QOL.
National Eye Institute Visual Function Questionnaire (NEI-VFQ)
The National Eye Institute Visual Function Questionnaire (NEI-VFQ) is a survey that was validated in six university-based ophthalmology practices as well as the National Eye Institute clinical Center in 1998. It was validated amongst patients with five chronic eye conditions (age-related cataracts, age-related macular degeneration, diabetic retinopathy, primary open angle glaucoma, and cytomegalovirus) and/or low vision from any cause (Visual acuity of 20/70 or worse in the better eye, or visual field constricted to 20 degrees).
The scale consists of 51 items amongst 13 sub-scales, and attempts to assess both daily functioning as well as the emotional/psychological effects of vision loss:
- General Health (2)
- General Vision (2)
- Ocular Pain (2)
- Near Vision (7)
- Distance Vision (7)
- Vision-Specific Social Functioning (4)
- Vision-Specific Mental Health (4)
- Expectations for Visual Function (3)
- Vision-Specific Role Functioning (5)
- Dependency Due to Vision (5)
- Driving (4)
- Peripheral Vision (1)
- Color Vision (1)
In 2000, a shorter 25 question version of the NEI-VFQ, known as the NEI-VFQ 25 was shown to be reliable and valid compared to the original 51 question version when administered by an interviewer. The self-administered version has not been tested. It includes the same subsets included in the original version except "Expectations for Visual Function" and takes approximately ten minutes to complete. There are numerous other versions of the NEI-VFQ that have been developed, including a 39 question version and the NEI-VFQ 25 in languages other than English.
Glaucoma Symptom Scale (GSS)
The Glaucoma Symptom Scale was developed in 1998 by Lee at al. based off of a symptom checklist from the Ocular Hypertension Treatment Study. It was tested in four tertiary care centers and shown to be valid when compared to the distance NEI-VFQ subscale and another scale called VF-14 (discussed briefly below). The GSS was also shown to reliably distinguish between patients with glaucoma and those without. The test evaluates how bothersome (Very, Somewhat, A Little, or Not at all) patients find ten symptoms (6 non-visual and 4 visual):
- Burning, Smarting, Stinging
- Soreness, Tiredness
- Blurry/Dim Vision
- Feeling of Something in Your Eye
- Hard to See in Daylight
- Hard to See in Dark Places
- Halos Around Lights
The validity of the GSS as a measure of performance amongst different racial populations has been questioned  , possibly related to the fact that many of these symptoms are related to ocular surface disease.
The VF-14 is a questionnaire developed at Johns Hopkins in 1994 to assess visual function caused by cataract. It was validated and proven to be reliable over the practices of 70 ophthalmologists in three cities in America (Columbus, OH; St. Louis, MO; Houston, TX) and has since been validated in many languages other than English.
The questionnaire consists of asking patients to rate their difficulty (None, A Little, Moderate, Great Deal, Unable to Do) on 14 vision-dependent tasks of daily living such as reading, recognizing people, seeing steps, performing fine handiwork, writing, playing games, playing sports, preparing meals, watching television, and driving.
Glaucoma Quality of Life – 15 (GQL-15)/Glaucoma Activity Limitation (GAL-9)
The Glaucoma Quality of Life-15 questionnaire was developed in 2003. It was shown to correlate well with objective measures of visual function and discriminated between QOL in patients with glaucoma and those without.
The test evaluates the level of difficulty patients have with 15 different tasks (None, A Little Bit, Some, Quite a Lot, Severe):
- Reading Newspapers
- Walking after Dark
- Seeing at Night
- Walking on Uneven Ground
- Adjusting to Bright Lights
- Adjusting to Dim Lights
- Going from Light to Dark Room, Vice-Versa
- Tripping Over Objects
- Seeing Objects From the Side
- Crossing the Road
- Walking on Steps/Stairs
- Bumping into Objects
- Judging Distance of Foot to Step/Curb
- Finding Dropped Objects
- Recognizing Faces
Later analysis of the GQL-15 showed that removal of six items resulted in better precision – resulting in a new scale called the Glaucoma Activity Limitation (GAL-9) questionnaire.
Assessment of Disability Related to Vision (ADREV)
The Assessment of Disability Related to Vision (ADREV) was developed by the Glaucoma division at the Wills Eye Institute in 2009. It is a third-generation measure – based off the Assessment of Function Related to Vision (AFREV) developed in 2006. Unlike the other tests discussed above, the ADREV is a task test rather than a questionnaire, consisting of nine tasks that simulate activities of daily living:
- Reading in reduced illumination
- Recognizing facial expression
- Detecting Motion
- Recognizing Street Signs
- Locating Objects
- Ambulating on an Obstacle Course
- Placing Pegs into Different Sized Holes
- Matching socks.
These tasks were selected based on the results of a previous study that aimed to develop a ‘Task Performance Test’ and showed that patients with glaucoma had difficulty performing similar tasks compared to a reference group. All of the above nine tasks were made difficult to the point where only 90% of normal people could complete them. By asking patients to perform tasks rather than give their opinions of their visual function, the ADREV attempts to eliminate the error that is incorporated by the subjective translation of disability into a grading system. Possibly as a result, the ADREV correlates more highly to clinical tests than the NEI-VFQ 25. However, the practicality of administering a performance-based measure is low, limiting its ability to be used by clinicians in assessing their patients.
Useful Field of View (UFOV)
The Useful Field of View (UFOV) test is a computer based test created by the Visual Awareness Group (www.visualawareness.com). The test measures the speed at which one can process information in a thirty-degree field, in a single glance, under various conditions. It also assesses the ability of the test taker to divide attention and to ignore irrelevant information. It has been associated with driving performance and motor vehicle accidents and only takes about 15 minutes to complete.
Glaucoma Outcomes Survey (GOS)
A vision-targeted QOL questionnaire was constructed to assess functional limitations, vision-related symptoms, aesthetics, psychosocial issues, and surgical satisfaction for glaucoma patients who are candidates for minimally invasive glaucoma surgeries (MIGS). Questions were based on the NIH Toolbox Vision-Related QOL instrument and refined based upon input from physician and patient focus groups. Cognitive interviews were used to ensure that questions were understandable to respondents. The questionnaire aims to improve understanding of how surgical interventions such as MIGS impact vision-targeted health-related QOL in glaucoma patients.
Self-Reported versus Direct Measures
Measures of disability are either self-reported (NEI-VFQ, GSS, VF-14, GQL-15/GAL-9, GOS) or direct (ADREV, UFOV). Self-reported measures include the patients’ perception of their disease and are easy to administer. These questionnaires ask patients to assess their own task performance in real-world situations. The down side to self-reporting is that not all reported symptoms are directly attributable to ocular pathology. The clinical significance of self-reported scores is also unclear. Furthermore, when patients’ visual disability causes them to stop performing a task, impairment during performance of this task will go unreported. While self-reported measures may not be an accurate reflection of true functionality, they can be a realistic assessment of patients' own sense of well-being, which direct measures are not able to do. Directly measured outcomes have the benefit of testing abilities under standard conditions, but may not accurately recapitulate real-world settings. While direct measures are less subject to reporting bias, they can be more difficult to administer and require more of the subject.
Resources for Patients
Low vision centers and local agencies for persons with disabilities can provide services and equipment to help those with visual disability function efficiently and independently. Some organizations that aid with low vision teaching and services include LightHouse, Lions Club, and for veterans, Low Vision clinics at the Veterans Affairs hospitals.
More and more devices to aid low vision patients with reading are increasingly available. Not only do digital readers and tablets have the option of enlarging the print and improving contrast, but also available are numerous magnifiers – hand held or desk-top, with and without lights, or even on necklaces. There are even guides to help patients to see where they need to sign their name on documents, how to fill in checks, or jumbo print items like playing cards, keyboards, telephones, or watches. Closed-circuit televisions (CCTVs) are also very helpful but can be expensive. Cell phones can be made more user friendly by the addition of vaulted stickers on certain number keys so that patients can use their sense of touch rather than their sense of sight to determine if they are pressing the correct number. Talking devices with text-to-speech softwares, such as watches, digital readers, and GPS can also significantly improve quality of life for low vision patients. Finally, learning braille is an option for certain motivated patients, and the organizations mentioned above (LightHouse, Lions Club, VA hospitals) as well as local organizations can help with braille education.
Walking & Balance
Stabilizing devices such as walking canes or walkers can aid patients who have difficulty maneuvering. Non-slip bath mats and portable bathtub and bedside handles can also aid in making activities of daily living safer for patients.
Perhaps the most difficult aspect of visual dysfunction is assessing mobility outside of the home. There are various options that those with limited vision can consider:
- Travel Training – Public transport agencies as well as local aging organizations provide free instruction to persons with disabilities so that they might learn to navigate public transportation systems safely and independently.
- Taxi Services
- Public Transit/Fixed Route Service
- Volunteer Driver Programs – Usually local faith-based and/or nonprofit organizations provide flexible transportation for various activities through volunteers.
- Paratransit Services – these can be either door-to-door or curb-to-curb services through public transit, aging organizations, or private agencies.
- Door-through-Door (Escort) Services – these are generally private companies that provide hands-on assistance in getting to and from their final destinations.
- Transportation Vouchers – Local disability resource agencies sometimes provide vouchers and/or fare-assistance for those with disabilities to employ providers for transportation needs.
Requirements for Disability in America
According to the American Foundation for the Blind, legal blindness, defined as " best corrected visual acuity of 20/200 or less in the better eye, and/or a visual field of 20 degrees or less," is the level of vision loss that determines eligibility for benefits.
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