Diagnostic Testing Services

It is not uncommon for the physicians of the Spokane Eye Clinic to order diagnostic testing for a patient. Here is a list of the most frequently used testing equipment and the purpose of each particular machine.

Ascan (Optical Coherence Biometry Non- Contact Ascan and Ultrasound Contact or Immersion Ascan)

Available North, South, and Valley:  approximately 20-30 minutes in length

An Ascan is a test that is used to help the physician determine the power of intraocular lens that will be implanted during cataract surgery. This is achieved by using a mild infrared laser beam to measure the length of the eye and the curvature of the cornea. This is a non-contact measurement. In the event that your cataract is very dense and the laser beam cannot measure through it, a contact ultrasound or immersion ultrasound is used to measure the length of your eye. Your eye is anesthetized with a numbing drop and a shell is placed into the eye with saline solution.  A small probe which uses sound waves to measure, is placed in the shell or on your cornea to record the measurements. Multiple measurements will be taken. Those measurements are then calculated to determine the lens power. You do not need to be dilated for this test. This test takes approximately 20 to 30 minutes.

B-scan/ Diagnostic Ultrasound

Available North, South, and Valley: approximately 20-40 minutes in length

A small probe with gel is placed on the eye that is able to see through opaque media. Ultrasound uses sound waves that make a picture of the internal structure of the eye. The doctor can see the presence of retinal detachment, retinal holes, tears, foreign material, hemorrhages, and malignant melanomas. The B-scan helps determine the difference in tissue, i.e. malignant melanoma as opposed to metastatic tumors or a benign nevus. This procedure takes about 20 to 40 minutes.

Color Testing (D-15, Ishihara, HRR)

Available North, South, and Valley:  approximately 5 to 10 minutes in length

The D15 Color Test is a diagnostic test used to detect deficiencies in color vision. The patient is seated at a table and arranges color shaded discs in order. Other types of color vision tests include simply identifying shapes or numbers. Color vision tests generally take 5 to 10 minutes to complete.

Contrast Sensitivity

Available North, South, and Valley:  approximately 5 to 15 minutes in length

Contrast sensitivity testing measures how well you see fuzzy bars at different levels of contrast. Your ability to see these bars relates to how well you see everyday objects. This type of visual acuity can take 5-15 minutes.

Corneal Topography: Pentacam

Available North, South, and Valley:  approximately 5 to 15 minutes in length

The Pentacam scan is a device used to give a topographical map of the cornea. It measures the shape, thickness, and contour of the cornea as well as capturing images of the anterior segment of the eye. The Pentacam utilizes a rotating camera to generate 25,000 data points and creates a 3-dimentional image. No drops or any other aids are needed for this test. Some of the conditions in which this machine is helpful for include iLASIK, cataract, corneal, and glaucoma surgeries. This test takes an average of 5-15 minutes.

Electrophysiology

Available South only:  approximately 20-60 minutes depending on test being performed

Full Field electroretinogram (ffERG) and multifocal electroretinograms (mfERG) are electrical responses of the retina to photic stimulation.  A flash of light or bright appearance of a pattern elicits a biphasic negative/positive waveform. Chemical changes in the retina start in 18 nanoseconds. The a-wave is the initial electrochemical discharge of the rods (night receptors/scotopic) and cones (day/photopic and color receptors) and is fully formed in 10-15 milliseconds. The b-wave is generated by the mid-retina (bipolar and muller cells) where processing occurs before electrochemical signals are sent to the brain by the optic nerve.

The ERG reflects the electrical health of the retina and can be used to help differentiate vision loss from optic nerve dysfunction or retinal dysfunction.  It can also be used to differentiate between rod and cone photoreceptor dysfunction.  The mfERG is used to map the macular region detecting blind spots, dysfunction, and drug toxicitiy. 

Visual evoked potentials (VEP, VER) are recorded from the scalp overlying the visual cortex at the back of the head.  This is similar to electroencephalograms (EEG), and the data is obtained by signal averaging performed by computer. They are used to measure the functional integrity of the optic nerves and pathways to the visual cortex of the brain. Ischemia, compression, infiltration, and inflammation can decrease the amplitudes.  Demyelination prolongs the signal.  Asymmetry of the signal can be used to diagnose albinism. 

webvision.med.utah.edu/book/electrophysiology/visually-evoked-potentials/

webvision.med.utah.edu/book/electrophysiology/the-electroretinogram-clinical-applications/

http://www.youtube.com/watch?v=dvWvywkV2G8

Electro-oculograms (EOG) measure the potential between the cornea and the back of the eye. This difference produces a dipole field with the cornea electrically positive and the retinal pigment epithelium being electrically negative.  Movement of the eye produces a shift of this electrical potential. For the procedure the patient keeps their head then moves the eyes back and forth between two red lights.  The movement of the eyes produces a voltage swing of approximately 5 millivolts which is smallest in the dark and largest in the light. The two responses are compared and should be near 2:1, with a ratio less then 1.7 being considered abnormal.  This can be used to help diagnose retinal disease, most commonly Best's dystrophy. 

Auditory brainstem responses (BAEP, BAER, ABR) are recorded by placing an electrode at the top of the head and a reference electrode on the ear lobe or mastoid process. Click stimuli of varying intensities are presented to one ear through earphones. A computer then averages the brain potentials evoked by the clicks and produces small amplitude potential with five peaks that are associated with different levels of the brainstem.  This test can by useful for detecting demyelination in patients with multiple sclerosis and has been shown to be abnormal in patients with Duane's retraction syndrome and Marcus-Gunn ptosis. 

Eletrophysiology testing can take between 20 and 60 minutes depending upon which test is being performed.  Dilation may be required.  Patients are referred to a different facility for the auditory brainstem response tests at this time.

Endothelial Cell Count

Available South only:  approximately 10-20 minutes in length

An endothelial cell count is a special camera that images the very last layer (of the six layers) of the cornea, the endothelial layer.  This layer is a honeycomb looking layer that is important to measure for certain corneal diseases.  The camera makes the image then the program software counts the amount of cells.

External Photography (Pupil or Medical Documentation)

Available South Only: approximately 20 - 60 minutes or longer in length

External Photography is used when documenting certain conditions such as lid closures, eye muscle deviations, or Grave's disease.  A series of photos are taken using different angles and positions with a macro lens that are digitally saved into an electronic chart.  Another variation of this photo series requires the use of drops that can constrict or dilate the pupils.  Use of the drops may vary depending on the condition and protocol that the doctor is trying to determine.  Small rulers are placed under the eye lid and a series of photos are taken with a macro lens.  Drops are then instilled and after 30 minutes more photos are taken to document the change in appearance of the pupils.  More drops may be administered and another 30 minutes would be needed to see if any other changes occur.  The constricting drops can cause a headache for some patients.  Having a driver is helpful if dilated.

Fluorescein Angiography (FA)

Available South only:  Approximately 20-40 minutes in length

Fluorescein Angiography is a special type of diagnostic photography to document the circulation of the retina. The test requires the eyes to be dilated so the total length of time involved can vary.  This helps the retinal specialist with treatment and diagnosis of the retina. Most often this test is ordered for macular degeneration, diabetes, or occlusion of the retina. Your physician will review this test to help determine if there is leakage, swelling, or blockage in the retina. Fluorescein Sodium dye is injected into a vein of the arm, forearm or hand. At the same time a rapid sequence of photographs with a special filter is taken, to document the appearance of the dye in the retina. Most people will need to have a driver with them for this procedure since they are dilated, and can experience a rosy hue or colors of vision from the flash of the camera, after the photography session for a few minutes. This procedure usually takes approximately 20 to 40 minutes, including dilation time.

Fundus Autofluorescence (FAF)

Available South only: approximately 15 to 30 minutes in length

Autofluorescence is a type of fundus photography that uses a filter to highlight the natural bioluminescence of the retinal tissue.  The test requires the eyes to be dilated so the total length of time involved can vary.  Unlike regular color fundus photography, the image is monochromatic, and will show areas of deposits from cell dysfunction.  This test usually takes around 15-30 minutes.

Fundus Photography

Available North, South, and Valley: approximately 20-40 minutes in length

This test requires the eyes to be dilated so the total length of time involved can vary.  Fundus photography documents the back of eye (retina), and can be performed with colored filters or specialized dyes. They are visual records that document the current ophthalmoscopic appearance of a person's retina. Fundus photos are routinely ordered in a wide variety of eye conditions, including glaucoma, diabetes, and macular degeneration.

Glaucoma Diagnostics GDX

Available North only:  approximately 5 to 15 minutes in length

The GDx/VCC is used for diagnosing and following diseases and disorders that occur in the back of the eye (posterior pole). It measures the retinal nerve fiber layer which is the tissue first damaged by glaucoma. This test takes 5-15 minutes.

 Goldmann Visual Fields (GVF)

Available South only:  upperlids approximately 15-20 minutes / Glaucoma GVF 60 minutes

Goldmann visual field testing helps determine the amount of peripheral and central vision an individual will have per eye. Unlike the HVF this test goes further out to the peripheral vision and will help the ordering Physician determine if there have been changes or progression of diseases such as glaucoma, more peripherally. This test is also used to help determine eligibility of upper lid surgery, and mapped out the amount of vision being blocked by droopy eye lids. This test can take 15-60 minutes depending on the specified protocol or condition being tested.

Humphrey Visual Field (HVF)

Available North, South and Valley:  approximately 30-45 minutes in length

A visual field test is a method of measuring an individual's entire scope of vision, that is their central and peripheral (side) vision. Visual field testing actually maps the visual fields of each eye individually. The visual field test is a subjective examination, and is most frequently used to detect any signs of glaucoma damage to the optic nerve. In addition, visual field tests are useful for detection of central or peripheral retinal disease, optic nerve disease, and diseases affecting the visual pathways within the brain. Spokane Eye Clinic's advanced instruments used to conduct this test take approximately 5-10 minutes per eye to complete. No dilation is required for this test, and can take 30-45 minutes total for instruction and testing.

Indocyanine Green (ICG)

Available South only:  approximately 20-60 minutes in length

This test requries dilation and the total amount of time may vary depending upon how long it takes for eyes to dilate.  Indocyanine green is a type of photography that images the very outer level of the retina called the choroid. It uses a special green type of dye that is injected into the vein, and is imaged by the camera with a red filter. This procedure can last up to an hour when combined with an FA, and often will require an IV to be placed while imaging. The entire process can take between 20 and 60 minutes.

Optical Coherence Tomography (OCT)

Available North, South, and Valley:  approximately 10-15 minutes in length

A mild beam of laser scans through the layers of the retina, making a picture. This helps your doctor see what is going on in the back of your eye from macular swelling, macular holes, macular degeneration, macular puckers and optic nerve swelling. These are just some of the conditions that the OCT can help diagnose, which helps the doctor to treat and follow the progress of ongoing treatment. The procedure takes about 10 to 15 minutes to complete.

Pachymetry

Available North, South, and Valley:  approximately 5 to 10 minutes in length

Pachymetry measures the thickness of the cornea. This is an important measurement for screening iLASIK patients to ensure thick corneas, and also for calculating a more accurate eye pressure measurement for patients with glaucoma. The eye is numbed for comfort with numbing drops, and then a small instrument that uses ultrasound is placed on the cornea for a few seconds. Multiple readings are taken for each eye to get an accurate average. This test usually takes 5-10 minutes.

Slit Lamp Photography

Available South only:  approximately 10 to 20 minutes in length

Slit lamp biomicroscopy photography, is documenting the structures of the eye. This type of testing is usually anteriorly, taken with a camera mounted to a microscope. Corneal disease, pterygiums, corneal scars, cataracts, pigmented areas, or perhaps trauma are all reasons to take slit lamp photos. No special preparation to the patient is needed, including dilation or the need for a driver.

UBM Anterior Ultrasound

Available South only: approximately 20 to 40 minutes in length

A water filled membrane touches the surface of the numbed cornea (clear part of eye), while an ultrasound moves under the membrane. The sound waves give an image of the cornea, iris, lens, and behind the iris. This ultrasound can determine if there is a narrow angle which can happen in glaucoma, foreign bodies from injuries, lesions or cysts. This test does not require dilation, but a numbing drop is instilled for the patient's comfort.  The test takes 20- 40 minutes.

Wavescan

Available South only:  approximately 10 to 20 minutes in length

A WaveScan measurement is used to map the unique characteristics of your vision. With this map, your doctor will be able to accurately assess whether you're a good candidate for laser vision correction. Along with the other diagnostic tests that your doctor performs, an individualized treatment plan can then be developed to address your unique vision needs. The Scan takes 10 to 20 minutes depending on the patient's eyes.

 

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