Dr. Leon O. Vaughan (left), consultant ophthalmologist, uses the hi-tech HRTII to evaluate patient, Marlene Williams, for signs of the eye disease, glaucoma.
-Ricardo Makyn photo
THE EYE disease, glaucoma, is a very stealthy one. It creeps up, mainly on blacks, Indians, Asians, without sign or symptom, until one day, some vision is loss and if the progress is left unchecked, eventually complete vision loss blindness occurs.
Older persons, those over 65 years, are also more at risk for glaucoma (the result of defects in the eye's optic nerve) with a prevalence rate of one in nine and with more than one-half of them being unaware of the condition. It is because glaucoma is largely a silent condition, results in irreversible blindness and is so prevalent here, that consultant ophthalmologist, Dr. Leon O. Vaughan, says that the management focus should be
on prevention.
"Unless you go for your routine screening and evaluations, glaucoma might not be picked up. People should screen routinely for glaucoma in the same way that one would for hypertension, diabetes, breast, prostate and cervical cancers," he said.
Hi-tech and precision screening for glaucoma is facilitated by the diagnostic tool, the HRTII scanner, now available at the newly-opened Glaucoma Diagnostic Unit in Kingston.
"The HRT scanner is an objective test that detects structural deficits. Now the structural deficits may be present up to six years in advance of the functional deficits, so we can now detect changes far in advance and be able to institute treatment much earlier in glaucoma... that is the importance of this test and screening instrument," said Dr. Vaughan.
The effectiveness of the HRTII examination a painless test that takes only a few seconds in the doctor's office is connected to its high-resolution laser scanning camera. This camera, in a few seconds, takes a series of three-dimensional scans of the optic nerve, measuring up to 28 million individual points per examination. The equipment is attached to a computer that compiles and analyses the scanned information, producing an image which Dr. Vaughan uses to diagnose the small, early structural changes which are linked to
glaucoma.
"This test is especially important for persons in the high-risk group for glaucoma... as it allows one to detect progression of the disease much earlier. If you are diagnosed with glaucoma and you want to detect whether your treatment is working or not, or progressing or not, this test will now pick up progression much, much more earlier than the visual field would," he said.
Before the HRTII, the visual field examination was the standard test for glaucoma. It is still used, though it has its limitations, being a functional deficit test that picks up problems after the patient has lost up to 40 per cent of optic nerve function. Dr. Vaughan said that this earlier test detects defects in the visual field, the peripheral vision in particular, because peripheral vision is lost initially in glaucoma.
"After peripheral vision gets more advanced, then you start seeing defects that more affect the patient, in that the patient starts to notice that he is not seeing so well. By that time, however, the condition is far advanced," he said.
Glaucoma first affects the patient's peripheral vision and as it progresses, the condition encroaches upon the
central vision, causing narrowing of the patient's vision and causing what
ophthalmologists call tunnel vision. Peripheral and central visions are therefore evaluated during the diagnostic testing.
The visual field analyser can also be used to detect defects anywhere along the visual pathways, and these defects may be caused by strokes, intracranial tumours (such as pituitary tumours). Dr. Vaughan explained that enlarged pituitary tumours squeeze the area where the optic nerves join and present themselves as field defects.
"Specific types of field defects are indicative of specific types of legions and we can look at the visual field defect and determine to a large extent where the legion is in the brain, so we work in tandem with neurologists and neurosurgeons," he said.
Meauring the thickness of the cornea (the transparent circular part at the front of the eyeball), is also important in glaucoma diagnosis. This is done through ultrasound with the corneal Pacchymetry. Dr. Vaughan said that research is being done locally on the impact of corneal thickness on the
diagnosis of glaucoma because it is believed that black people have thinner than average cornea, and the thinner the cornea, the less resistant it is when
measuring intraocular pressure. Therefore, the specialists could get false values in these cases.
"You may think (in these cases) that the pressure is low so the patients don't really have glaucoma when, in fact, if you take into consideration the thickness of the cornea and factor that into your interpretation, then you can actually arrive at a better pressure (for example, a pressure of 17 may actually
be 25)," he said.
