They called him “the silent thief of sight”. Because, in most cases, it progresses slowly, showing no signs of itself until the advanced stage. It is glaucoma, damage to the optic nerve often caused by an increase in eye pressure. Glaucoma affects around 800,000 Italians and it is estimated that 1 in 3 patients is unaware that they suffer from the disease.
It is caused by “an increase in pressure inside the eye which depends on the degeneration of a sort of intraocular ‘strainer’ which regulates the amount of liquid that the eye is able to drain”, explains Stefano Gandolfi, director of the Clinic Ophthalmology University of Parma and member of the Siso board of directors.
To understand what’s behind this rather complex disease, let’s try to simplify the concepts. Chronic open-angle glaucoma, the most common form, is a disease driven by a set of genes, in which there are two sides to the damage. A degeneration of the optic nerve and an increase in eye pressure. Let’s start with this.
Glaucoma: Increased pressure in the eye
“The eye must be maintained at the correct pressure by a colorless and transparent fluid (aqueous humour), in balance between continuous production, which takes place behind the iris, and drainage in the anterior corner between the cornea and the iris», explains Antonio Scialdone, head of the ophthalmology unit of the IRCCS Policlinico San Donato (Milan). When everything works properly, the amount of outgoing fluid balances the incoming one and the eye pressure is kept within the correct values. Which, although they vary on an individual level, are usually between 12 and 19 millimeters of mercury.
However, if the drainage is reduced, the fluid is not eliminated sufficiently. As a result, the intraocular pressure rises above the tolerated values and gradually damages the optic nerve. Which is the bundle of fibers for transmitting images from the retina to the brain, allowing the image to be perceived. To be clear, the system works like a small hydraulic tank with an always open faucet and drain. If the latter is altered, the container fills up to excess and trouble begins. In chronic glaucoma, in fact, it is the trabecular meshwork, the outflow structure, which is altered and loses its filtering capacity and causes the pressure increase.
Glaucoma: degeneration of the optic nerve
The other side that contributes to vision loss is the degeneration of the optic nerve. Even when blood pressure is controlled with drugs, the disease often slows down a lot, but is not completely stopped, and a slow loss of vitality of the optic nerve continues.
cause of glaucoma
At the basis of both factors is genetic predisposition. This means, concretely, that if one of the two parents presents the pathology or transmits the altered genes to their children, the children are more likely to manifest it. Other possible risk factors are refractive disorders of vision, especially high myopia. And the presence of certain pathologies (diabetes, migraine, arterial hypertension, cardiovascular alterations).
The symptoms of glaucoma
In the progressive stages of the disease, which last for years, with pressures usually above 21-22 millimeters of mercury when left untreated, symptoms are practically absent. Without an ophthalmological examination, the patient does not notice anything.
Inaccurate, clouded vision, even colored halos (like a rainbow around the lights) appear when the intraocular pressure exceeds 25-30 millimeters of mercury. Meanwhile, the progressive damage to the optic nerve fibers causes areas of vision loss, of which there is no awareness for a long time, and a gradual narrowing of the visual field, starting from the peripheral areas, to then affect the central ones.
Many glaucoma patients are surprised by tests that show damage, in the face of a personal perception of “normal vision”. If the pathology is not diagnosed or is neglected, it leads in the most serious cases, even to blindness. In any case, the damage cannot reverse.
Prevention: eye examination after the age of 45
To avoid all of this, planning in advance is essential. “After the age of 45-50, it is good for everyone to carry out an eye examination aimed at establishing whether there is a risk of developing glaucoma”, recommends the expert. In the office, the ophthalmologist first measures the pressure in the eye with special instruments, such as the Goldman tonometer or the murmur tonometer. Then, with the biomicroscope (slit lamp), he analyzes the fundus of the eye, studying the back of the eyeball.
Tests to diagnose glaucoma
In case you suspect the presence of the pathology, he performs an examination of the thickness of the nerve fibers and an examination of the visual field. A survey aimed at measuring the breadth of the viewing space. Specifically, for the latter, the patient must press a button every time he perceives a small light spot, of different sizes and brightness, projected by a computer onto a dome. The computerized reconstruction of the answers brings out the areas of minor or absent visual perception.
The other examination, now routine, to quantify the extent of glaucomatous damage is the measurement of the thickness of the fibers of the optic nerve, performed by optical coherent tomograph-retinal nerve fiber layer , OCT-RNFL). “By putting together the results of all these tests, the ophthalmologist has a complete picture of the visual conditions of each patient,” continues Scialdone. «These investigations are periodically repeated according to the indications of the specialist. In particular, people at high risk of developing the disease will have to repeat them at least every year or more frequently if it is not stabilized. And every two-three years, individuals who only have a familiarity or a suspicion».
Once the diagnosis of glaucoma has been formulated, the specialist implements the most appropriate strategy to counter it. “It is a treatable disease, but not curable,” the ophthalmologist immediately clarifies. “However, today the therapeutic possibilities are varied, all with the aim of decreasing ocular pressure to preserve the health of the optic nerve”.
Treatment of glaucoma: drugs
“Generally, at the beginning of therapy, the doctor prescribes eye drops, which on average are able to reduce eye pressure by 25-30%,” explains Scialdone. «If the result is not satisfactory, a second eye drop is added, which reduces the pressure by a further 10-15%, or the laser is suggested. If the outcome is still not adequate, a third eye drop can be added, which decreases the pressure by another 5%. If the desired results are not obtained with three eye drops, ie the so-called target pressure is not reached, which is mostly below 15 millimeters of mercury, and the damage continues, surgery should be used to cure glaucoma».
Glaucoma treatment: laser
Laser treatment of the trabecular meshwork, the outflow pathway, has been shown to be as effective at reducing eye pressure as eye drops. It can therefore be proposed in the first instance. Or if the first eye drops weren’t enough. In some cases it loses effect in a few years.
Treatment of glaucoma: trabeculectomy
It is the most traditional and still the most widespread intervention to treat glaucoma. Developed in the 70s, it consists in creating an alternative way out for the aqueous humour. Under the upper eyelid, an opening of about one mm is created in the sclera (the fibrous white wall that covers most of the eyeball) protected by a sort of flap.
The procedure, which is performed under local anesthesia and lasts about 30-40 minutes, is not, however, free from uncertainties, even for the most expert surgeons, in always obtaining the most adequate level of filtration, of the value of microlitres. In fact, it may happen that the latter proves to be too scarce. Or, on the contrary, it is excessively abundant, requiring adjustments. Furthermore, after stabilization, this type of surgery leaves a “point of weakness” in the eye, at the flap.
It is no coincidence that about 1-2% of operated patients undergo an intraocular infection over the years. A rather serious event. Furthermore, five to six years after the operation, up to about 50% of the flaps close again. Just as if it were a healed wound, thus losing its functionality. To overcome these problems, numerous variants of the intervention have been devised over time, but without a significant change in the results obtained.
Treatment of glaucoma: minimally invasive surgery
A few years ago, thanks to continuous advances in technology, microvalves were designed for glaucoma surgery. Devices of various shapes to be implanted in the eye with the aim of restoring the correct outflow of the liquid.
There are currently three main types available. IStent, a titanium device measuring 360 microns (one micron equals one millionth of a metre). And Xen, a tube about six millimeters long and the thickness of a hair, both implanted from the inside with an incision of a couple of millimeters. The Preserflo is, on the other hand, a micro-valve implanted from the outside.
«As recent studies also confirm, thanks to these innovations it is now possible to perform a safer operation. Less invasive and with lower long-term risks than trabeculectomy», declares the expert. “Furthermore, following the implant, many patients are able to reduce and sometimes stop taking the drugs”. The operation takes about 15-20 minutes, takes place under local anesthesia and in day surgery. If necessary, it can be associated with cataract removal surgery.