Glaucoma: Diagnostic Modalities - Dr. Barun Kumar Nayak, Dr. Sarika Ramugade Glaucoma is a leading cause of blindness in the world, especially in older people. Early detection and treatment by ophthalmologist are the keys to preventing optic nerve damage and vision loss from glaucoma. What is glaucoma? Glaucoma is a group of diseases that can damage the eye's optic nerve and result in vision loss and blindness. Glaucoma occurs when the normal fluid pressure inside the eyes slowly rises. However, with early treatment, a person can often protect his eyes against serious vision loss. What is the optic nerve? The optic nerve is a bundle of more than 1 million nerve fibers. It connects the retina to the brain. The retina is the light-sensitive tissue at the back of the eye. A healthy optic nerve is necessary for good vision. When a significant number of nerve fibers are damaged, blind spots develop in the field of vision. Once nerve damage and visual field loss occurs, it is permanent. Most people don't notice these blind areas until much of the optic nerve damage has already occurred.if the entire nerve is destroyed, blindness results. Glaucoma is a group of diseases that can damage the eye's optic nerve and result in vision loss and blindness What are the most common types of glaucoma?
Primary Open-Angle Glaucoma Signs and Symptoms: Frequent change of reading glasses Difficulty in dark adaptation Constant watering Gradual loss of peripheral vision, usually in both eyes Tunnel vision in advanced stages Angle-Closure Glaucoma Signs and Symptoms: Halos around lights Reddening of the eye Sudden onset of visual disturbance, often in low light Blurred vision Severe eye pain Nausea and vomiting (accompanying the severe eye pain) Both open-angle and angle-closure glaucoma can be primary or secondary conditions - primary is when the cause is unknown and secondary is when the condition can be traced to a known cause, such as eye injury, inflammation, tumor, or advanced cataract or diabetes. In secondary glaucoma, the signs and symptoms can include those of the primary condition as well as typical glaucoma symptoms. Glaucoma is a leading cause of blindness in the world, especially in older people Diagnosis The commonly accepted parameters that are used for the glaucoma diagnosis are: Raised intraocular pressure (IOP)
Visual field defects and Visual acuity Optic disc changes It is well established fact that 50% of the patients have an IOP within normal range at the time of presentation. Field defects are picked up by standard automated perimetry when an irreversible loss of almost 50% retinal nerve fiber layer has already occurred. Thus in most of the cases when a confirmative diagnosis is established,the eye has already had some irreversible changes, owing to the disease. Decision of whether to change therapy or to operate often requires confirmation of the disease progression with certainty. The upcoming technologies and newer diagnostic modalities may enable us to make a preperimetric diagnosis and pre-empting the progress of the disease which means diagnosing the condition in very early stages. Glaucoma evaluation Ophthalmologists combine a clinical examination with anciliary tests and various imaging techniques, to identify a suspected case of glaucoma and to establish progress. Clinical evaluation Visual acuity test: measures central vision at various distances. Tonometry: measures the pressure inside the eye. Tonometers used include: Goldmann Applanation Tonometer: measures the intra ocular pressure. Doctor places an anaesthetic eye drop in patient's eye. With the patient seated at a slitlamp, the plastic prism of the tonometer is moved forward to barely touch the cornea. The test is quick, easy and painless. This is the most sensitive tonometer and is considered to be the gold standard in tonometry, and should be done for all patients. Schiotz tonometry: is quite popular, but is far from ideal due to the inaccuracy of the values. Air puff or noncontact tonometer: eye pressure is measured by the eye's resistance to a puff of air. It is mainly used as a screening tool.
The electronic indentation method: measures pressure by directly contacting anesthetized eyes with a digital pen-like instrument. PASCAL Dynamic Contour Tonometer: is a revolutionary new digital tonometer that provides a direct trans-corneal measurement of intra-ocular pressure. Gonioscopy: allows the doctor to view the angle of anterior chamber of eye with help of special lens which touches the eye, to determine if the iris is closer than normal to the back of the cornea. This test can help differentiate closed-angle glaucoma from open angle glaucoma. Angle of anterior chamber is responsible for the drainage of aqueous fluid out of the eye. Dilated eye examination: Drops are placed in eyes to dilate, the pupils. An ophthalmoscope, is used to examine retina and optic nerve for signs of damage and other eye problems. Its color and appearance can indicate whether or not damage from glaucoma is present and how extensive it is. After the examination, patients near vision may remain blurred for several hours, due to dilation. Anciliary tests These tests are done for assessment of functional and structural damage. The Visual Field Test: Perimetry is a subjective test that depends upon patient responses. This tests the peripheral vision and functional damage. The nerve fiber analyzers adopt a different objective strategy that is not dependent on patient responses. By measuring changes in nerve fiber layer thickness over time these tests can detect glaucoma progression and structural damage. The validity of these tests have been established in many peer reviewed reports. Perhaps these tests will become the 'gold standards' in the future as more experience is gained with these tests. In glaucoma the field of vision is the first to be affected. By the time the central vision is affected, glaucoma is already far advanced with almost all peripheral vision permanently lost. That is why glaucoma is called the 'sneak thief of vision'. When we test vision on an eye chart only the central vision gets tested, but no comments can be made about the peripheral field of vision.
Automated (computerized) field analyzers, such as the Humphrey or the Octopus perimeters are used to perform the field of vision test. Procedure of Visual Field Testing : In computerized visual field testing, patient will be asked to place his chin on a stand which appears before a concave computerized screen. Whenever he sees a flash of light he has to press a buzzer. At the end of this test, doctor will receive a printout of his field of vision, the responses are analyzed statistically and compared with a database of normal responses. This test takes 30 minutes to 45 minutes approximately. Patient should perform this test when they are not tired. New software has been developed to help ophthalmologist analyze these tests as well as monitor progression of visual field loss over successive tests. Strategies for monitoring the visual field: WOW Strategy: The most commonly used is the WOW (white on white) strategy, that is the white stimulus on white background. Serial tests allow the treating ophthalmologist to monitor whether the disease is stable. This test has to be repeated depending on the severity of disease for e.g. 3 monthly, 6 monthly or yearly. Short wave Automated Perimetry(SWAP): is also known as blue on yellow perimetry. This test picks up glaucomatous field defect much earlier than standard white on white perimetry,but takes longer time. SITA (Swedish Interactive Thresholding Algorithm): A different software is used which reduces duration of testing. Frequency doubling perimetry (FDP): This is one of the newer perimetric methods,which measures the function of M cells.these are damaged earliest in
glaucoma.these cells respond to high temporal and low spatial frequency,which is the basis of FDP. It is less time consuming (approximately 5 to 7 minutes),portable, good for screening with a high sensitivity and specificity. This test may have to be combined with field of vision test. Imaging techniques Optic nerve imaging helps document optic nerve changes over time and thus aid in the diagnosis of glaucoma and help in the detection of glaucoma progression. All four techniques are painless and non invasive. Stereo Optic nerve photographs Confocal scanning laser ophthalmoscopy (Heidelberg Retinal Tomograph or HRT-II): It helps in acquisition and quantitative analysis of three-dimensional images of the posterior segment. HRT-II has high sensitivity and specificity thus allowing it to have a very high precision in early diagnosis, allowing us to pick up pre-perimetric glaucoma and detect early progression. Optical coherence tomography (OCT): Is a new diagnostic tool that provides information about posterior segment with higher resolution than conventional system. It shows cross-sectional view of the retina and optic nerve with a resolution of 5 microns approximately. It can measure the changes that occur on the optic nerve head and the retinal nerve fibre layer. Scanning laser polarimetry (GDxVCC): It is believed that almost 50% of the RNFL (Retinal nerve fibre layer) are lost before a visual field defect is picked up with reliability on standard perimetry. GDx measures the thickness of peripapillary RFNL. This test helps in diagnosis of pre-perimetric glaucoma and early detection of progression. Pachymetry: Uses an ultrasonic wave instrument to help determine the central corneal thickness (CCT) and better evaluate eye pressure. Eye pressure gets measured differently (higher or lower) depending upon the corneal thickness. Thicker corneas cause falsely higher eye pressure reading and thinner corneas cause falsely lower eye pressure readings.
Ultrasound biomicroscopy (UBM): It uses high resolution ultrasound to evaluate the structural details of the anterior segment structure at almost microscopic resolution. In patients with glaucoma, it is helpful especially in cases where corneal edema and corneal opacity hinders with gonioscopic assessment. Conclusion If you have one or more of following risk factors for glaucoma, talk to your doctor about scheduling more frequent eye examinations. Family history of glaucoma Advancing age Near-sightedness [myopia] Any injury to eyes Secondary to other ocular conditions [thin cornea, cataract, inflammation, tumours] Long-term medication [cortisone] Diabetes, hypertension Glaucoma in other eye. Be aware that a severe headache or pain in your eye or eyebrow, nausea, blurred vision, or rainbow halos around lights may be symptoms of an narrow angle glaucoma. If you experience two or more of these symptoms together, seek immediate care at an emergency room or an eye doctor's (ophthalmologist's) office. The routine screening eye examinations (once in year) are mandatory since glaucoma usually causes no symptoms (asymptomatic) in its early stages. Once damage to the optic nerve has occurred, it cannot be reversed. Thus, in order to preserve vision, glaucoma must be diagnosed early and followed regularly.
Patients with glaucoma need to be aware that it is a lifelong disease,and ophthalmologist decides the schedule for follow up visits depending on the individuals progress of disease and associated risk factors. Compliance with scheduled visits to the eye doctor and with prescribed medication regimens offers the best chance for maintaining vision. We Offer At Hinduja Hospital: Visual acuity testing Intraocular pressure measurement by: Goldmann applanation tonometer Air puff or noncontact tonometer The PASCAL Dynamic Contour Gonioscopy Dilated eye examination Visual field test by Humphrey perimeter [Short wave Automated Perimetry (SWAP), SITA (Swedish Interactive Thresholding Algorithm)] Frequency doubling perimetry (FDP) Pachymetry Heidelberg Retinal Tomograph or HRT-II Optical coherence tomography (OCT)