The Low Vision
The Low Vision Examination begins with an extensive history. Special emphasis is placed on the functional problems of the patient including such items as vision to read, functioning in the kitchen, glare problems, travel vision, the workplace, television viewing, school requirements, etc. It will also include a careful review of your ocular and medical history.
Preliminary test may include assessment of ocular functions such as depth perception, color vision, contrast sensitivity, curvature of the front of the eye. Careful measurements will be made of the visual acuity using low vision test charts followed by low vision refraction. Low vision test charts include a larger range of letters to more accurately determine a starting point for measurement of low vision. A low vision refraction determines the measurement of the patient's prescription by special techniques which may include changing the lighting levels, testing through filters and using larger changes which may be easier for you to view.
If the patient has decreased acuity, the doctor may test with various telescopic systems which magnify distance vision. These may be spectacle mounted or handheld. He may also assess your response to filters to control glare. Various reading aids including strong reading eyewear, magnifiers, electronic magnifiers and even electronic reading machines may be tested.
Visual fields are usually evaluated and if the patient has a reduced visual fields, field enhancing devices may be evaluated and simple therapies to improve the patient's use of their residual field may be prescribed.
Eye health testing may include a biomicroscopic examination of the external structures and a dilated internal examination. Glaucoma tests are performed
The doctor will counsel you on how your condition will effect your vision and what you may do to enhance and protect your vision. Independent living aids may be reviewed to fit specific patient problems.
Low vision testing usually requires two or three times the length of a standard eye examination.
More About Explanation of the Low Vision Examination
The low vision examination is quite different from the basic eye health and refractive examination routinely performed by primary care optometrists and ophthalmologists. The goals of the low vision exam include assessing the functional needs, capabilities and limitations of the patientís visual system, assessing ocular and systemic diseases and their impact on functional vision, evaluating and prescribing low vision systems and therapies. Also, educating and counseling the patient, family and other care providers, providing an understanding of the visual functioning to aid educators, vocational counselors, employers and care givers, directing further evaluations and treatments by other vision rehabilitation professionals and making appropriate referrals for medical and surgical intervention is all a necessary part of the low vision evaluation.
THE FUNCTIONAL HISTORY
The low vision examination begins with an extended case history including a chief complaint, any current problems, and treatments of their condition. Additionally, it includes a careful medical and social history. The emphasis of this history is to understand how the patient is functioning and what needs the patient has.
Low Vision Related Health Requirements: Does the patient have health problems or treatment requirements that will impact low vision recovery? If the patient is a diabetic, can the patient see to fill insulin syringes, read nutritional labels on food containers and see to monitor their foot care? Is the patient taking medications that may impact their vision and can the patient see to identify their medications?
Reading and Near Vision: What are the reading requirements and desires? Does the patient need or wish to read specific materials, a church newsletter, the newspaper or their mail? What happens when the patient attempts to read? What can the patient read (newspaper print, large print, or large headlines)? Is eyestrain or ocular fatigue present? Is the patient an avid reader? Has the patient used talking books? What low vision devices have been tried?
Intermediate Activities: Can the patient see to perform other near point and intermediate visual activities like writing, sewing, cooking, and viewing the computer? Can the patient see to write checks and balance their checkbook? Do they use large print (deluxe guide) checks? Can they see to use a calculator or a watch?
Activities of Daily Living: Are the patientís appliances marked to improve visibility? Has services of a rehabilitation teacher or occupational therapist to improve homemaking skills been consulted? Can the patient see to do other routine housekeeping duties like cleaning, paying bills, and laundry?
Computers: Are computers used? How large is the monitor? What type of work is being done? How close must the patient sit to the computer screen? Is computer enlargement or voice software used? Does the patient wear dedicated eyewear for the computer? Is the patient able to access the Internet?
Recreation: What is done for recreation? Does the patient have a hobby? Can the patient view the television? How close do they sit? How large is the television? How well do they see the colors on the screen?
Mobility: Are there any mobility issues? Can the patient travel independently? Does the patient use a long cane or guide dog? Does the patient run into objects or trip on curbs? Has the patient had mobility and orientation training? Does the patient take trips? How do they travel? Are their any difficulties? Does the patient have a handicapped-driving placard?
Driving: Does the patient still drive, and if so, when and with or without a valid license? Have there been accidents or traffic violations? When will the license expire? Does the family support continued driving? Has patient limited their driving? Is someone else available to drive? Is public transportation available?
Light & Glare: How does the patient function in bright sunlight, inside lighting and at night? Are sunglasses worn? What color and type? Does the patient use a hat or visor? Does light and glare affect the patientís mobility? Does the patient have difficulty changing from different light levels? Is there a residual decrease in vision after coming inside from bright light? How does the patient function at night?
Vocational: Is the patient employed or doing volunteer work? What type of work was done in the past and did the patient leave their job because of their vision problems? Is the patient now seeking employment? What are the visual requirements for their job? Has the lighting, visual environment of the job and position of equipment been adapted to fit the patient? Are their safety issues? Is appropriate eye protection worn?
Educational: Are there specific educational needs? Are educational programs adapted to the patientís visual abilities? What educational services are available? Does the student work with a visual impairment teacher? Does the student use large print textbooks? Can the student see the chalkboard? Are there computer requirements? Is the child attending a blind school or in a mainstream program? If a college student, what is the major area of study? Will the patient be able to handle the increased reading required in college? Will there be mobility or transportation issues in attending school? Is there access to computer technology adapted for visual impairment, closed circuit magnification, audio textbooks or a personal reader/note taker?
Emotional: How motivated is the patient? What support is available to the patient? Does the patient have family or friends to provide support, help with housework or transportation? How is the patient adapting emotionally? Have there been signs of clinical depression? Has the patient reported visual hallucinations? Visual hallucinations in the visually impaired have been reported for over two hundred years since first described by Charles Bonnet, a Swiss naturalist, who observed these hallucinations in his grandfather.[i]
UNIQUE ASPECTS OF THE LOW VISION EXAM
Following the detailed history, vision functions are assessed. The tests and techniques are adapted to fit the patientís visual impairment. And are adapted to help assess the patientís vision.
A more accurate measure of the patientís refractive status and visual acuity can be obtained with low vision refractive techniques. These tests employ larger testing charts, control of illumination, the use of trial frame refraction, and techniques that allow for eccentric viewing. In 1992 as outlined by Windsor, many of these special testing techniques were outlined.[ii] Best visual acuity in an examination room, however, may not be duplicated in the patientís home where lighting and contrast may be poor. [iii] In infants and non-verbal patients, special testing techniques can be employed. The use of Teller acuity cards may be a good test for moderately impaired infants and children. Additionally, a functional battery, which involves observing the patient in a variety of activities, may provide strong evidence of the childís visual function.[iv]
Additional understanding of the patientís functional vision can be obtained through the use of the Amsler grid, contrast sensitivity, the laser-scanning ophthalmoscope, visual evoked potential and electroretinogram. Contrast sensitivity tests the eyeís ability to discriminate subtle changes in vision rather than the absolute black-on-white contrast of a visual acuity chart. Contrast sensitivity is a better predictor of real world functioning.[v] The use of a laser-scanning ophthalmoscope allows one to plot the precise area used by the patient with central retinal damage.[vi] The visual evoked potential or VEP, a form of electroencephalogram, shows an increasing role in the assessment of patients with a brain injury.[vii] Electroretinograms are helpful in the differential diagnosis of many retinal diseases. [viii]
Ocular motility testing should be carefully evaluated. Rundstrom demonstrated the importance of binocular vision testing in low vision patients. [ix] Also, Schlageter found 30 out of 51 patients had impaired eye movements and reduced ocular convergences after suffering a traumatic brain injury.[x] Additionally, patients with severe tunnel vision may experience a breakdown in binocular vision. Pituitary tumor patients with bitemporal hemianopsias may experience hemifield slide, a unique form of double vision where rather than seeing two objects, the patients sees two halves of the object.
While visual field testing is used to diagnose ocular and neurological diseases, it can also predict how the low vision patient may function in day-to-day activities and how well the patient may respond to various rehabilitative approaches.[xi] Visual fields may be tested by confrontations, manual perimeters or by computerized perimetry.
The Behavioral Inattention Test is a helpful screening test for unilateral neglect.[xii] In the right brain injury patient, unilateral neglect or hemifield neglect may mimic hemianoptic field loss. Visual neglect, however, is a spatial inattention. It can occur independently or as an accompaniment with homonymous hemianopsia.
Another very important part of the low vision exam is the dilated internal examination, intraocular pressures and external eye health evaluation. These ensure that there are no ocular diseases or complications that may require treatment or referral to another specialist.
[i] Teunisse RJ, Crusysberg JR, Hoefnagles WH, Verbeek AL, Zitman FG. Visual Hallucinations in psychologically normal people: Charles Bonnetís syndrome. Lancet 1996 Mar 23;347(9004):794-7.
[ii] Windsor RL. Management of Low Vision Who Are Homebound or in LongĖterm Care Facilities. Prob Opt 1992 Mar;4(1):133-54.
[iii]Silver JH, Gould ES, Irvine D, et al. Visual Acuity at home and in eye clinics. Trans Ophthalmol Soc UK 1978; 98(2)252-257.
[iv] Droste PJ, Archer SM, Helveston Em. Measurement of low vision in children and infants. Ophthalmology 1991 Oct;98(10):1513-8.
[v] Owsley C, Sloane E Contrast sensitivity, acuity and the perception of real world targets. Br J Ophthalmol 1987; 71(Oct):791-796.
[vi] Fletcher DC, Schuchard RA. Scanning laser ophthalmoscope macular perimetry and applications for low vision rehabilitation clinicians. Ophthalmol Clin North Am 7(2):257-265, 194.
[vii] Padula WV, Argyris S, Ray J. Visual evoked potentials (VEP) evaluating treatment for post-trauma vision syndrome (PVTS) in patients with traumatic brain injuries. Brain Inj 1994 Feb-Mar;8(2):125-33.
[viii] Freed S, Hellerstein LF. Visual electrodiagnostic findings in mild traumatic brain injury. Brain Inj 1997 Jan;11(1):25-36.
[ix] Rundstrom MM, Eperjesi F. Is there a need for binocular vision evaluation in low vision? Ophthalmic Physiol Opt 1995 Sep;15(5):525-8.
[x] Schlageter K, Gray B, Hall K, Shaw R, Sammet R. Incidence and treatment of visual dysfunction in traumatic brain injury. Brain Inj 1993 Sept-Oct;7(5):439-48.
[xi] Jose R, Ferraro J. A functional interpretation of visual fields of low vision patients. J Am Optom Assoc 1983 Oct;54(10):885-93.
[xii] Hartman-Maeir A, Katz N. Validity of the Behavioral Inattention Test (BIT): relationships with functional tasks. Am J Occup Ther 1995 Jun;49(6):506-16.