The early detection of glaucoma is key to controlling its progression and preventing further damage. Comprehensive eye examinations, including tests aimed at measuring the pressure in your eyes (tonometry), evaluating the appearance of your optic nerve (ophthalmoscopy), observing the drainage angles (gonioscopy), and checking for the presence of any loss in peripheral vision (visual field testing), are critical to properly diagnosing glaucoma.
Measuring Intraocular Pressure (Applanation Tonometry)
The tonometry test measures the intraocular pressure of the eye. Drops are used to numb the eye. Then your doctor or technician will use a special device called a tonometer to measure your eyeâs pressure.During this procedure, you are asked to position your head and rest your chin in the slit lamp (microscope) and look straight ahead while sitting very still. The test itself takes just a few seconds and requires minimal interaction from you. The intraocular pressure is measured in millimeters of mercury (mmHg). The end result of this test is a number relative to your intraocular pressure determined by the resistance of your eye to the applanation (pressure) of the tonometer.
Examination of the Optic Nerve (Ophthalmoscopy)
Ophthalmoscopy is used to examine the inside of the eye, especially the optic nerve head. In a darkened room, your doctor will look into your eye by using an ophthalmoscope (a special magnifying instrument with a small light on the end). There are two types of ophthalmoscopes, direct and indirect. Both work by shining a bright light into your eye that allows your doctor to examine a magnified image of your optic nerve. Your doctor will pay special attention to the shape and color of the optic nerve and check for signs of cupping. This test can be done within minutes and, other than the discomfort caused by the bright light, this test is painless. It is a very important test in determining the appearance of your optic nerves.
Gonioscopy is an essential test in determining the type of glaucoma you may have. It is performed by placing a mirrored lens on an eye, numbed by eye drops, and observing the trabecular meshwork, the drainage component of the eye. This test is crucial in determining if the drainage angle is open or closed. With this lens your doctor can evaluate the entire 360 degrees of the drainage angle around the iris.
This is another test that requires your minimal interaction and is usually performed by an ophthalmic assistant or technician. To acquire fundus photographs (pictures of the inside back of your eyes), you will be asked to sit before a camera and look at a blinking fixation light. The camera is then used to photograph areas of the retina, optic nerve and macula. The photographs are repeated annually and analyzed and compared to previous photographs by your doctor to aid in the prompt diagnosis of worsening conditions.
Optical Coherence Tomographer (OCT)
The OCT uses state-of-the-art technology to generate cross-sectional imaging of your retinal tissue and optic nerves. This cross-sectional imaging actually allows your doctor to see what lies beneath the outermost layer of your retinas and optic nerves. This test is repeated annually to monitor any change of the glaucoma condition.
Visual Field Testing
Visual field testing is crucial in determining unnoticed peripheral vision loss, the first part of your vision that is lost to glaucoma. The visual field testing instrument uses random flashing lights to detect retinal sensitivity. Lights are flashed in different areas of a large white screen at varying levels of brightness and speeds. You are asked to respond every time you observe a flashing light by pressing a handheld button. The trick is you cannot look around for the lights. You must look straight ahead at a fixation light in the center of the large white screen. The test usually takes about 10 minutes to complete, but may take longer depending on your level of vision. Unlike the other tests, visual field testing requires your undivided attention and participation.
Corneal Thickness Measurement (Pachymetry)
Recent studies have proven that the accuracy of the measurement of intraocular pressure can be affected by your corneal thickness. People with very thick corneas might have “high pressures,” but actually not be at significant risk for glaucoma. Likewise, someone with unusually thin corneas might have “normal pressures,” but in reality have high pressures and require treatment. Normal corneal thickness ranges from about 500 to 575 microns. The pachymetry test measures the thickness of your corneas and gives your doctor very pertinent information regarding the accuracy of your intraocular pressure measurement. The patient places their chin on the chinrest and is instructed to look at the fixation light. The machine will take a measurement of the central cornea area by optical means. This is a noncontact method.
The Diopsys NOVA-VEP (visually evoked potential) is new technology being used to diagnose and monitor glaucoma. VEP technology objectively assesses the function of the entire vision system by measuring the electrical energy created in the retina which travels to the visual cortex. This technology helps assess damage from glaucoma in the early stages. The set up for this test takes about five minutes. Sensors are placed in the patient’s forehead and back of the head.
Patient’s distance correction prescription is placed on the patient with a trial lens frame. The room is darkened and the patient is instructed to look at the screen in front of them. The screen viewed by the patient uses a checkerboard stimulus (low contrast dark gray and light gray boxes with high contrast black and white boxes. In the center of the screen is a red circle. The patient fixates on the red circle while music is played during the test. This test takes approximately 38-53 second per eye.
GDx Nerve Fiber Analyzer
This computer-operated instrument detects retinal nerve fiber layer damage up to six years before visual field damage is evident. It uses a scanning laser to detect and measure optic nerve thickness. The GDx usually takes about three minutes per eye to complete and generates a serial analysis printout that clearly shows specific areas of disease progression.