XIX. DIAGNOSTIC TESTS AND SERVICES

Fundus Photographs are color slides taken of your retina by a specially trained technician. These photographs document your eye condition and help to follow its progress.

Fluorescein Angiography is another type of photographic test. As you sit at a camera, a nurse will inject an orange colored dye (fluorescein) into a blood vessel of your arm. The dye circulates through your body, including your eyes. Within 10-25 seconds the dye becomes visible in your retina, and rapid sequence photographs (not x-ray) are taken. These black and white photographs detect abnormalities in the retina that are not visible by other tests. Immediate printing of the photographs taken permits their evaluation without delay.

Indocyanine Green Angiography (ICG) is a technique used to visualize abnormal blood vessels in the choroid, beneath the retinal tissue of the macula. The ICG dye is quite different from fluorescein dye, as are the results of the investigation. The two studies are complementary. ICG pictures are recorded on video and are analyzed immediately to determine possible treatment.

Visual Field Testing measures the extent of both your central vision and side vision. Central visual fields are used to evaluate the macula, the area of the retina responsible for seeing fine detail. During a central field, you are seated in a dim room, and the examiner brings a small spot of light into view on a flat surface. The areas where you don't see the light are plotted on a chart. During testing of your side vision, a similar small light is projected within a hemispherical dome.

Other Psychophysical Tests are subjective measures of visual function. They involve the presentation of different test objects and the recording of the patient's responses. Measurements of contrast sensitivity, color vision, dark adaptation and potential acuity assessment (PAM) are some of the psychophysical tests that your doctor may request.

The SRA Foundation is one of the few clinics, in this country, where Infant Vision Testing is performed.  It utilizes special testing to evaluate the visual function of infants and young children who cannot describe what they see. Included among these painless and risk-free tests is optokinetic nystagmus (OKN) where a striped drum is rotated and reflex eye movement is noted.   Preferential looking (PL),is  a test in which the infant's choice of looking at a plain or patterned surface is recorded. 

Ultrasonography, uses harmless sound waves to form a picture of the tissues within the eye. The test is especially useful when it is impossible to see inside the eye because the cornea, lens or vitreous are cloudy and block the doctor's view. Ultrasonography helps to evaluate conditions such as retinal detachment, ocular bleeding, trauma and tumors. The size and shape of the contents of the globe are best determined by combining the A and B scan ultrasonic technology.

Vision Enhancement: Most patients who have lost a substantial amount of their sight have the potential for improved vision. Following a specialized examination with the scanning laser ophthalmoscope (SLO), appropriate low vision aids may be prescribed. These enable patients to make maximal use of their remaining vision, enhancing occupational, educational and daily living capabilities.

Vision Rehabilitation Training: Whether or not you receive a specialized visual aid, instruction and demonstration of methods for coping with impaired sight are available by appointment with a vision rehabilitation professional.

Scanning Laser Ophthalmoscope (SLO) The SLO, developed by our clinical researchers, is an important but frequently unused diagnostic instrument in the evaluation of macular function. By using a TV-like image of the macula, two important measurements can be taken of the patient’s macula: outline of any blind spots, and status of the central point of fixation.  Then the level of eccentric visual acuity can be documented with an accuracy that no other method can approach.

In laser treatment of the "wet macula", the SLO, in conjunction with the angiogram, informs the MD using the laser which leaking areas can be treated aggressively (the areas away from fixation) and which must be approached with particular caution (those areas near fixation).

In evaluating the "dry macular degeneration" the information the SLO supplies permits close follow-up of the changes between periodic visits, i.e. blind spot progression, fixation area, and acuity of the functioning retina surrounding the central scar. Biannual or annual follow-up exams often help the patient plan for his/her visual future.

Visual acuity of the retina adjacent to a central macular scar can be accurately measured by projecting an isolated letter "E" of variable size onto functioning retina adjacent to the scar. Often a visual acuity can be documented that is significantly higher than that noted on the eye chart. If so, this may allay fears of severe visual loss by the patient.  This technique can also be useful to evaluate vision in cases of potential malingering

Observation. An 18-year-old female had a macular scar in her right eye. Vision was count fingers at 3 feet by routine chart acuity. Vision in the left eye was 20/20.  If the left eye were to be injured, the right eye vision of count fingers at 3 feet would leave the patient functionally blind. The patient and her family were very concerned over this. The macular scar size suggested a better vision was possible. The E-step test revealed a vision in the left eye of 20/100, which is considerably better than finger counting at 3 feet. As a result, a great anxiety was lifted from the patient and her family.

Mapping of the macular blind spots is called microperimetry.  It permits one to correlate anatomic changes with functional deficit with an accuracy totally unavailable by any other method. Some anatomic changes may result in visual loss and others may not, but the SLO can tell.

Regarding maculas: If you have more concerns than your HMO does, think about having an SLO examination.

Optical Coherence Tomograph

This instrument was invented by professor Fujimoto, of the Massachusetts Institute of Technology, Boston.  After dilation of the pupil, it produces, non-invasively, an extraordinary image of the retina, namely a cross-section of the retina (Fig.37).  It also measures the variations in the thickness and composition of the retina.  It can measure the thickness of the nerve fibers at their entrance in the optic nerve, which is indicative of the presence of glaucoma.  Other diseases studied with the OCT are macular hole, macular edema, macular pucker, pigment epithelial detachment, serious retinal detachment, retinoschisis and many more. It is particularly useful to detect abnormal changes in the macula.

Measurement of Blood Speed in the Retina.

The blood speed in the retina is obtained with the Laser Doppler Flowmeter (LDF) invented by one of our senior research scientists, Gilbert Feke, Ph.D.  It records fifty times a second and noninvasively the speed of blood in one of the retinal vessels.  This speed is closely related both to the health of the circulatory system itself and to the nerve tissue it supplies.  Our measurement is obtained by shining a low-power laser beam in the eye.  It interacts with the moving blood cells.  The light returning from the eye has information encoded which is analyzed to provide the blood speed.  The instrument also provides additional information that measures blood flow, which is key to the health of the tissue irrigated by the vessels.

Another instrument, also invented by Dr. Gilbert Feke, measures blood circulation in the optic nerve (Fig.38).  Since individual optic nerve vessels are too small to measure, the movement of blood corpuscles in the capillaries is measured, thereby informing us about the activity of the circulation in the optic nerve.

These two instruments tell us about the location and degree of disturbances of blood flow within the retina and optic nerve, as well as the viscosity (stickiness) of the blood itself.  They also give us information about circulation in the body.

Patients tested include those with diabetes, glaucoma, various forms of vascular occlusive disease within the eye, those with symptoms following surgery for correction of retinal detachment, those with vascular obstruction external to the eye, those with cerebrovascular disease, and those with systemic diseases associated with abnormal blood components or hypercoagulation.

These instruments are now in use at the SRA Foundation.  They have been under development for 20 years. No other retinal blood flow instrument exhibits an accuracy and ability that allows us to compare circulating abnormalities among patients.

ERG The electroretinogram (ERG) measures the electrical activity of the cells within the retina in response to light stimulation. It provides objective information about widespread retinal function and also about function of the inner retinal layers sersus function of the outer retinal layers.  It indicates how well the retina, pigment epithelium and optic nerve are functioning.  Electrical messages are picked up by small electrodes attached to the skin.  These tests are the visual counterpart of the electrocardiogram (EKG) which determines how well one’s heart is working.  The ERG is considered the primary diagnostic test for retinitis pigmentosa and other night blinding disorders, as well as inflammatory, vascular and toxic disorders.

Multifocal ERG Multifocal electroretinogram is an advanced technology based on the standard ERG. The multi focal ERG records from more than a hundred closely spaced locations in the retina to generate a three dimensional map of retinal activity. It provides objective information about focal impairment and early retinal disease affected in small area on the retina. It is useful to identify central or localized retinal disturbances, such as macular degeneration and dysfunction, including premacular membrane and macular hole, and is helpful in cases of decreased vision and narrowed visual field of unknown etiology.

VER Visual-evoked response (VER) measures the electrical signal generated by the visual cortex in the brain in response to visual stimulation. VER is helpful in assessing visual pathway function from the retina to the visual cortex in the brain. It is very sensitive to detect abnormal function of the macula and optic nerve. The pattern - VER is particularly useful in diagnosing macular or optic nerve dysfunction.

EOG The electrooculogram (EOG) measures the resting potential that exists continuously between the cornea and the posterior pole of the eye. It can evaluate retinal pigment epithelial dysfunction, and is particularly useful in the diagnosis of macular dystrophy such as Best disease.

Glare Sensitivity Testing Glare can be very debilitating. It causes decrease in vision, pain and discomfort in the eyes. The sources of glare are usually

(1) overhead artificial lights especially fluorescent lights
(2) oncoming automobile headlights
(3) lights from computer displays
(4) direct sunlight and indirect reflection off smooth surfaces

You may have a glare sensitivity problem which is often associated with the following:

(1) corneal opacities including peri-limbal lipid rings, arcus senilis, corneal edema and degeneration
(2) pre-cataracts often found in patients with a history of UV (ultraviolet) over-exposure and primary and secondary cataracts
(3) light-colored eyes with large pupils
(4) ocular inflammation, or
(5) age-related macular degeneration, diabetic retinopathy, glaucoma, retinitis pigmentosa, and cone-rod dystrophy

Certain measures are effective in reducing the intensity of the lights, for example, sunglasses, visors, computer screens, and lens anti-reflection coating. However, measures taken are often based on relief of subjective symptoms or complaints rather than quantitative testing. We now have a glare testing service and invite your participation. In conjunction with contrast acuity testing, tinted shields and filters will be tried and if proved effective, a prescription with appropriate tints will be recommended.