Diagnostic Testing

It's not uncommon for the physicians of the Spokane Eye Clinic to order diagnostic testing for a patient. These tests help the doctor to treat and follow the progress of ongoing treatment if there are any eye health issues. Here is a list of the most frequently used testing equipment and the purpose of each particular machine. 

Technology at Our Clinics

Jump to:

• Ascan
• B-scan/Diagnostic Ultrasound
• Color Testing (D-15, Ishihara, HRR)
• Contrast Sensitivity
• Corneal Topography: Pentacam
• Electrophysiology
• Endothelial Cell Count
• External Photography (Pupil or Medical Documentation)
• Fluorescein Angiography (FA)
• Fundus Autofluorescence (FAF)
• Fundus Photography
• Goldmann Visual Fields (GVF)
• Humphrey Visual Field (HVF)
• Indocyanine Green (ICG)
• Optical Coherence Tomography (OCT)
• Pachymetry
• Slit Lamp Photography
• UBM Anterior Ultrasound
• Wavescan

Ascan

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

An Ascan is a test used to help the physician determine the power of the intraocular lens 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. If 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 using a saline solution. A small probe that 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.

B-scan/Diagnostic Ultrasound

A small probe with gel is placed on the eye, which can be seen through opaque media. Ultrasound uses sound waves to make a picture of the eye's internal structure. The doctor can see the presence of retinal detachment, 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.

Color Testing (D-15, Ishihara, HRR)

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. 

Contrast Sensitivity

Contrast sensitivity testing measures how well you see fuzzy bars at different contrast levels. Your ability to see these bars relates to your ability to see everyday objects.

Corneal Topography: Pentacam

 The Pentacam scan is a device that gives a topographical map of the cornea. It measures the cornea's shape, thickness, and contour and captures images of the anterior segment of the eye. The Pentacam utilizes a rotating camera to generate 25,000 data points and create a 3-dimensional image. No drops or other aids are needed for this test. Some of the conditions this machine is helpful for include PRK, cataract, corneal, and glaucoma surgeries.

Electrophysiology

Full Field electroretinogram (ffERG) and multifocal electroretinograms (mfERG) are electrical responses of the retina to photic stimulation. A flash of light or bright 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 help differentiate vision loss from optic nerve dysfunction or retinal dysfunction. It can also differentiate between rod and cone photoreceptor dysfunction. The mfERG is used to map the macular region, detecting blind spots, dysfunction, and drug toxicity. 

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 a computer. They are used to measure the functional integrity of the optic nerves and pathways to the brain's visual cortex. Ischemia, compression, infiltration, and inflammation can decrease the amplitudes. Demyelination prolongs the signal. Asymmetry of the signal can be used to diagnose albinism. 

• Visually Evoked Potentials/
• Electroretinograms and Electro-Oculograms in Clinics
• How Multifocal Electroretinogram is Performed

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 and then moves their 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 of less than 1.7 being considered abnormal. This can 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 earlobe 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 associated with different brainstem levels. This test can be 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. 

Electrophysiology testing can take between 20 and 60 minutes, depending on the test being performed. Dilation may be required. At this time, patients are referred to a different facility for the auditory brainstem response tests.

Endothelial Cell Count

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-like layer that is important for measuring certain corneal diseases. The camera makes the image, and then the program software counts the number of cells.

External Photography (Pupil or Medical Documentation)

External Photography is used to document conditions such as lid closures, eye muscle deviations, or Grave's disease. 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 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 eyelid, and photos are taken with a macro lens. Drops are then instilled, and after 30 minutes, more images are taken to document the change in the 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)

Fluorescein Angiography is a special type of diagnostic photography that documents 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 the treatment and diagnosis of the retina. This test is often 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 a driver with them for this procedure since they are dilated and can experience a rosy hue or colors of vision from the camera's flash after the photography session for a few minutes. This procedure usually takes approximately 20 to 40 minutes, including dilation time. 

Fundus Autofluorescence (FAF)

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.

Fundus Photography

This test requires the eyes to be dilated, so the total length of time involved can vary. Fundus photography documents the back of the 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 for a wide variety of eye conditions, including glaucoma, diabetes, and macular degeneration.

Goldmann Visual Fields (GVF)

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. It 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 the eligibility of upper lid surgery and map out the amount of vision blocked by droopy eyelids. Depending on the specified protocol or condition, this test can take 15-60 minutes. 

Humphrey Visual Field (HVF)

A visual field test measures an individual's entire scope of vision, that is, their central and peripheral (side) vision. Visual field testing 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 detecting central or peripheral retinal disease, optic nerve disease, and diseases affecting the visual pathways within the brain. Spokane Eye Clinic's advanced instruments to conduct this test take approximately 5-10 minutes per eye. No dilation is required for this test, and instruction and testing can take 30-45 minutes total.

Indocyanine Green (ICG)

This test requires dilation, and the total time may vary depending on how long the eyes 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 dye injected into the vein and imaged by the camera with a red filter. This procedure can last up to an hour when combined with an FA and often requires an IV to be placed while imaging.

Optical Coherence Tomography (OCT)

A cross-section view of the back of the eye, similar to an Ultrasound, only uses light waves instead of sound waves.  This allows the doctor to evaluate the various layers of the back of the eye. We use this equipment for a wide range of diagnoses, including 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 allows the doctor to treat and follow the progress of ongoing treatment.

Pachymetry

Pachymetry measures the thickness of the cornea. This is an important measurement for screening refractive eye surgery patients to ensure thick corneas and to calculate a more accurate eye pressure measurement for patients with glaucoma. The eye is numbed for comfort with numbing drops, and then a small ultrasound instrument is placed on the cornea for a few seconds. Multiple readings are taken for each eye to get an accurate average.

Slit Lamp Photography

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 by the patient is needed, including dilation or the need for a driver. 

UBM Anterior Ultrasound

A water-filled membrane touches the surface of the numbed cornea (the clear part of the 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. 

Wavescan

A WaveScan measurement is used to map your vision's unique characteristics. With this map, your doctor can accurately assess whether you're a good candidate for laser vision correction. Along with your doctor's other diagnostic tests, an individualized treatment plan can then be developed to address your unique vision needs.

To schedule an appointment, call (509) 456-0107