A little-known disease affecting 80 million people …
Glaucoma is a disease in which damage to the optic nerve leads to progressive and permanent loss of vision which can ultimately lead to blindness.
Glaucoma affects tens of millions of people around the world and its frequency increases exponentially after age 60, yet many people are unaware that they have it! This is explained by a slow progression which, in its early stages, is mostly asymptomatic. It is only late that glaucoma results in vision loss, most often peripheral first, then central. However, early treatment would slow down or stop the progression of the disease!
This can be explained by the fact that the disease is slow and essentially asymptomatic in the early stages. Glaucoma does not lead to vision loss until late; peripheral vision is often affected first, then central vision. However, early treatment can slow or stop the course of the disease.
THE OPTICAL NERVE IS AGING ALSO…
The inside of the eye is lined with a set of light-sensitive cells forming the retina. Nerve fibers carry signals light received by the retina to the brain. The latter travel first from the eye to the brain in the form of a bundle of fibers, the optic nerve, then within the brain itself to the occipital lobe where the images. For this reason, when the fibers nerves making up the optic nerve are damaged, part of the light signals picked up by the retina is lost. We are born with a million nerve fibers, and naturally lose about 2,500 per year until the age of 50, then 7,500 per year then. Nerve fibers not regenerating, damage caused by glaucoma are irreversible, underscoring the importance of prevention.
The exact process leading to the loss of nerve fibers in glaucoma is not still known, however, it is now clear that intraocular pressure plays an important role. The latter is governed by the balance between the formation and excretion of the fluid that fills the front structures of the eye: the aqueous humor. This fluid is secreted by a collection of cells called the ciliary body, located behind the iris. It then circulates around the lens, through the pupil, before leaving the eye through the trabecular meshwork – a tangle of cells forming a circular filter around the edge of the iris, in the corner iridocorneal. It drains the aqueous humor to the venous system. A small proportion of fluid is also evacuated by an alternative route called uveoscleral, through the ciliary muscle.
There are two main mechanisms responsible for two classes of glaucoma: open-angle glaucomas and angle-closure glaucomas. Both can occur spontaneously (primary) or be the consequence of other anatomical or physiological abnormalities, they are then called secondary.
A DISEASE, MORE FREQUENT THAN YOU THINK …
Glaucoma is the number one cause of irreversible blindness worldwide. We think that by 2020, nearly 80 million people around the world will have glaucoma, and more than 11 million of them will be blind. The main factors of risk include age, family history, myopia, African origins, and fineness of the cornea.
The main classes of glaucoma
Intraocular pressure is measured, like blood pressure, in millimeters of mercury (mmHg). However, its normal values range from 9 to 21 mmHg. It fluctuates widely during the day, depending on the position and the activities practiced. An increase in intraocular pressure in the absence of optic nerve abnormalities is not not glaucoma, but is a risk factor for it. The risk of developing glaucoma for a patient with untreated intraocular hypertension is 9.5% out of five years. The addition of anti-glaucomatous eye drops halves this risk.
Open angle glaucomas represent 90% of glaucomas. They are characterized through an open iridocorneal angle, allowing aqueous humor to flow freely up to the trabecular meshwork. However, a progressive obstruction of this network leads to a chronic rise in intraocular pressure. The latter, over time, leads to loss of nerve fibers, which in turn causes loss of vision.
The increase in intraocular pressure is most often moderate and asymptomatic, and the initial visual impairment is usually peripheral, going unnoticed in its early stages. The evolution, gradual over several months or years, results in later stages of total and irreversible loss of vision. Current treatments slow or stop the progression of the disease, but do not to date not to regenerate the lost nerve fibers. This is why the identified risk factors and regular check-ups are essential to detect cases early before permanent visual impairment appears. Indeed, a treatment early reduces the risk of progression by 50%.
The first treatment aims to reduce intraocular pressure, by eye drops anti-hypertensives or using laser treatments targeting the trabecular network. Extensive choice of surgical procedures allow a reduction in intraocular pressure in cases refractory to medical treatment, improving mood filtration aqueous or, more rarely, by reducing the production of this liquid.
Glaucoma at normal pressures
Open-angle glaucoma may develop and progress in the presence of normal intraocular pressures. This is called normal pressure glaucoma. He is diagnosed in the presence of optic nerve or visual field damage suggesting glaucoma, and in the absence of other causes. Although intraocular pressures are normal, it has been shown that pressure still plays a role in this type of glaucoma, and its reduction allows, as in open-angle glaucoma, to slow down the progression.
Angle-closure glaucoma is much less common than angle-closure glaucoma. open-angle, and unlike the latter, hyperopia and Asian origins are risk factors. It occurs when the iris comes in contact with the cornea, obstructing thus the iridocorneal angle through which the aqueous humor drains. The most common causing the angle to close is the pupil block, in which the lens affects the iris and blocks the passage of fluid through the pupillary area. The obstruction can be sudden and complete, this is called an acute glaucoma attack. Intermittent closure is chronic angle-closure glaucoma.
An acute glaucoma attack is recognizable by the sudden onset of severe pain in the eye accompanied by a red eye, nausea, and decreased vision. Diagnosis and management must be done urgently, as very high intraocular pressures can damage the optic nerve in just a few hours. The goal of treatment is to lower intraocular pressure by making an opening into the iris using a laser. This opening called an iridotomy, allows the flow of direct aqueous humor through the iris, balancing the pressures between the compartments of the eye, and resolving the seizure. A prophylactic iridotomy should also be performed in the healthy eye to prevent a future seizure.
Intermittent or chronic narrow-angle glaucomas are characterized by occasional or progressive occlusion of the angle resulting in pressure peaks intraocular, most often when the patient is in the dark and in position lying down. Unlike acute glaucoma, they are often asymptomatic and diagnosed late. The treatment begins with an iridotomy.
A DISEASE, NOT A FATALITY…
Treatments and surgeries
The first-line treatment for open-angle glaucoma in adults involves most often anti-hypertensive eye drops. These are grouped into four major pharmaceutical classes: prostaglandin analogues, beta-blockers, carbonic anhydrase inhibitors, and alpha-agonists. The choice of medication depends on the type of glaucoma, and combinations are possible if eye drops alone are not sufficient to control intraocular pressures. If the pressures remain high despite three classes of drugs, or the use of drops is problematic, surgical treatment is being considered.
The surgical options are numerous. The most frequently used techniques aim to create an artificial filtration channel through the trabecular meshwork, towards an artificially created space under the conjunctiva: the filtration bubble. Other techniques use filtration tubes under the conjunctiva or more deeply, under the sclera, to increase the drainage of aqueous humor. There are still methods aimed specifically at the trabecular meshwork, in order to reduce its resistance to the flow of liquid, with incisions or with tiny stents. Finally, cyclodestruction helps, by destroying the ciliary body, lower intraocular pressure by reducing the production of aqueous humor.
Lasers can be used for several reasons. In some open-angle glaucomas, laser treatment located at the iridocorneal angle allows to increase the filtration of aqueous humor through the trabecular meshwork, and so decrease intraocular pressure. This treatment is called trabeculoplasty or SLT (Selective Laser Trabeculoplasty). This technique can be an alternative to drug treatments, but its effectiveness is usually limited in time. In narrow or closed-angle glaucomas, YAG laser iridotomies allow preventing complete occlusion of the iridocorneal angle by making an opening at the top of the iris, creating a bypass blockage for the aqueous humor. Still, other techniques, such as iridoplasties, allow the inclination of the iris to be changed so that it is away from the cornea and further opens the iridocorneal angle.
THE IMPORTANCE OF SCREENING: WHAT TO EXPECT…
Examinations and screenings
Screening for glaucoma involves evaluating different risk factors. This do, it systematically includes a list of any symptoms and history, measurement of intraocular pressure and corneal thickness, examination of the optic nerve, and assessment of the opening of the iridocorneal angle. These are produced by ophthalmologists using an applanation tonometer, a pachymeter, and ophthalmic microscope, and a gonioscope. Glaucoma screening is recommended annually for patients at risk or over the age of sixty. In all cases, a regular ophthalmological check-up by a specialist doctor is essential to guarantee the health of the eye, and initiate or adjust any treatment according to the progression of the disease. Glaucoma therapy should never be stopped without appropriate control and monitoring by the ophthalmologist.
If glaucoma is suspected, additional examinations are performed. According to the indication they can include: a visual field which assesses the functional impairment of the peripheral vision; OCT optic nerve imaging (OCT-RNFL) to visualize the thickness of the layers of nerve fibers; a daytime voltage curve (CTO) for measure the variations in intraocular pressure during the day; or an electroretinogram pattern (P-ERG) which observes the functioning of the optic nerve.
THE TECHNIQUES OF TOMORROW…
Research and scientific advances
Medical research is constantly evolving, and this is particularly true in the area of glaucoma. Among the many research projects, we note the development of glaucoma diagnostic and monitoring techniques, including angiographic examination of altered retinal vasculature in eyes with glaucoma, or the advent of screening techniques assisted by artificial intelligence. In matter treatment, new therapies are being tested, such as rhokinase inhibitors which, instilled by eye drops, could not only help reduce pressure intraocular but also improve the vascularity of the retina. Surgically, new filtration techniques and methods are emerging every year, such as recently the Eyewatch system, a valve allowing to adjust the filtration rate of aqueous humor postoperatively. But the most ambitious projects of tomorrow remain surely those aimed at the regeneration of nerve cells damaged by disease, maybe one day to finally be able to say that we have cured glaucoma.
- It is estimated that by 2020, nearly 11 million people will have lost their sight cause of glaucoma.
- Intraocular pressure plays an important role in the glaucoma process. Open-angle glaucoma is a chronic disease with slow progression and insidious, requiring regular screening to prevent vision loss.
- Closed-angle glaucoma can be acute or chronic. Its acute form is strongly symptomatic and requires urgent ophthalmic treatment.
- Treatments for glaucoma in adults most often involve first intention antihypertensive eye drops or laser treatment.
- Regular monitoring of glaucoma is essential to detect possible progressions of disease and optimize treatment.
- A multitude of surgical techniques can be used to treat glaucoma refractory, pediatric, or in which the use of eye drops is problematic.