The department has a fully staffed diagnostic unit, with a full range of equipment, including fundus, slit lamp and external photography, electroretinography, electro-oculography, fluorescein angiography, specular microscopy, orbscan, optical coherence tomography, pachymeter, visual field studies, ultrasonography (both A- and B-mode) of the eye and orbit, IOL Master, Heidelberg Retinal Tomograph and visual evoked potentials.
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A B-scan is performed to image parts of the eye that are not visible to the ophthalmologist. A common phrase sometimes used by the ophthalmologist is, "it is like seeing with sound."
Conditions such as a vitreous hemorrhage, dense cataract, or scarred cornea make it impossible for the ophthalmologist to examine the back part of the eye, where the vitreous, the retina and the eye wall are located. In some cases of eye injury or trauma, where the eye is penetrated by an object, a B-scan would be performed to rule out the presence of a foreign body and also to see the extent of the damage in the eye.
A B-scan, along with a diagnostic A-scan, is used to document and differentiate eye lesions or tumours. Accurate measurements can be made to determine the size and height of an ocular tumour, as well as the shape and contour. It is also possible to make out the different types of tissue, which can help in the diagnosis of a benign or a cancerous tumour, and even if it is a cancerous tumour that has spread from its original site.
An ocular ultrasound usually takes about 10-15 minutes to perform. The patient is in a semi-reclining position in an examining chair, and most B-scans are performed by placing the probe directly on the eyelid. A small amount of coupling gel is used on the eyelid to ensure good contact between the ultrasound probe and the patient's eyelid. The patient is asked to move their eye in different directions throughout the scan so the entire eye area can be thoroughly examined.
There is virtually no discomfort experienced by the patient unless the eye has undergone recent eye surgery or has been injured.
The VEP consists of a large biphasic waveform, which occurs at 250 msec. after the onset of a visual stimulus. There are three electrodes attached to the patient's head -one on the forehead, one at the back of the head and one on the centre of the scalp. Several readings are taken and computer averaged.
Visual Evoked Potentials assesses the central retina, optic nerve and visual pathways, and may reveal the presence of gross retinal dysfunction, demyelinating disease, e.g. multiple sclerosis (M.S.) or compressive lesions (tumors) affecting the optic nerve.
To carry out this test the pupil of the eye must be dilated by using special eye drops. Skin-type electrodes are placed on the patient's forehead and earlobe, and then the patient sits in a completely dark room for 30 minutes wearing special eye patches. This is called "dark-adapting" and is necessary to ensure maximum response of the rod function. At the end of the 30-min dark adaptation, topical anesthetic drops are placed in the eye and a special fibre electrode is placed inside the patient's lower eyelid. The test entails the patient watching several different colours of light being flashed, which stimulates the rods and cones in the retina.
This test takes approximately 1.5 hours in total.
Axial eye length A-scan or biometry is the most common type of ocular ultrasound performed today. An axial eye length reading (measurement taken along the visual axis between the cornea and retina) and keratometry readings (measurement of the corneal curvature) are necessary for intraocular lens calculations. These calculations help determine the correct power or strength of lens necessary for the eye to restore vision to near normal after cataract surgery. Some patient's also require additional glasses, mostly reading glasses.
An intraocular lens is an artificial lens implanted in the eye during cataract surgery in the same location as previously occupied by the natural lens.
These measurements take approximately 15 - 20 minutes and are usually preformed during the "pre-op" visit or assessment prior to the cataract surgery.
The technician will instill a drop of topical anesthetic in the eye(s) to numb the corneal surface and then position the patient's head comfortably. Some readings are performed where a patient is positioned in a slit lamp type of apparatus and some measurements are done with the technician holding the A-scan probe in his or her hand. *The probe is then brought close to the patient's eye and it gently touches the cornea where a reading or axial eye length measurement is obtained. Several readings are necessary as these measurements need to be extremely accurate.
*The patient is asked to fixate on a red target light found at the end of the A-scan probe.
There are new state of the art technologies that measure and analyze the optic nerve in a more precise way, and allow for detection of subtle changes over time. These technologies are called the Heidelberg Retinal Tomograph (HRT) and Ocular Coherence Tomography (OCT). These tests take digital images of the back of your eye and computers evaluate the images to provide information about your glaucoma.
Data from these tests may help to determine when treatment is necessary, and if you are already on treatment, whether it is adequate. These tests will most likely need to be repeated on a regular basis.
These tests are completely safe, cause you no discomfort, and take only minutes to complete.
At present OHIP, does not cover HRT testing, but does cover OCT. The cost is charged to the patient, and includes both a hospital fee and a physician fee to cover the costs of administering and interpreting the test results. A receipt will be issued for health insurance or income tax purposes.
It is your choice to have these tests. They are being recommended, but should you decide to decline these tests, the standard of care will continue to be delivered to you and every effort will be made to manage your glaucoma in the best manner possible.