Glaucoma
Glaucoma is an optic nerve degeneration caused mainly, but not exclusively, by an increase in the pressure of the intraocular fluid called aqueous humor.
It's a slow, progressive disease that irreversibly damages nerve fibers in the optic nerve, Therefore, early detection is of utmost importance. Once detected, the disease treatment should be individualized to achieve the fundamental goal of halting the disease’s progression. To do this we have different antihypertensive drugs treatments, laser therapy, and various surgical techniques that can lower the intraocular pressure.
ICOftalmología’s Glaucoma Unit has been working with the most advanced diagnostic techniques and treatments for the past 15 years and has received great clinical and scientific recognition, both in Spain and among the important international teams.
Early Detection of Glaucoma
Chronic open-angle glaucoma is the most common type of glaucoma in the general population, comprising up to 70% of all cases. Some 250,000 Spaniards have glaucoma, although nearly 50% remain undiagnosed because the disease has no symptoms.
For this reason, there have been multiple screening campaigns carried out in this country in recent years. They all measured intraocular pressure and assessed the state of the optic nerve in different ways.
The presence of elevated intraocular pressure usually related to optic nerve damage is commonly known as glaucoma. However, there are exceptions: not all patients with elevated eye pressure develop glaucoma in the future (this is called ocular hypertension) and not all patients with glaucoma have high ocular tension (normal tension glaucoma). That is why early glaucoma detection cannot be limited to just measuring intraocular pressure, but must be accompanied by a thorough study of the anatomical and functional state of the optic nerve.
With the hope of achieving an earlier diagnosis, exploratory techniques have recently been developed that enable a much earlier identification of the disease to avoid an irreversible loss of vision. The following form part of the routine diagnostic protocol at our center:
A Perimetry test (or visual field test) allows for the detection of visual defects in the visual field and has thus far been the mainstay of glaucoma diagnosis. Since initial visual loss in glaucoma is detected in the mid-periphery, it often goes unnoticed by the patient. By conducting a perimetry test, such defects can be highlighted. We currently use the Humphrey perimeter in most cases, which has short-term programs that can detect minimum visual defects of incipient glaucoma in less than 5 minutes.
To increase the sensitivity of the visual field and detect the disease at an earlier stage, we have established other tests in our practice such as the visual field of short wavelength (SWAP, also called blue-yellow perimetry) and frequency doubled perimetry (FDT).
Optical coherence tomography (OCT), widely used in studies of the retina, is a new non-invasive method for early glaucoma diagnosis. It uses a beam of near-infrared light that measures the thickness of the layer of optic nerve fibers. After scanning for a few minutes, layers within the retina can be differentiated and the thickness of retinal nerve fibers can be measured which allows us to detect patients with a very early stage of glaucoma. The new generation OCT allows close comparison between tests, thus detecting progression.
Confocal scanning tomography (Heidelberg Retinal Tomography-HRT II) quantifies the image of the optic nerve and mathematically detects subtle changes in the shape and thickness. With this technique we are able to obtain a topographical map of the intraocular portion of the optic nerve, known as papillae. This high-resolution spatial map is analyzed by our technicians and recorded for further comparisons. In this way we can detect changes over time, or what remains the same in the dreaded progression of glaucoma.
The retinal microphotographs of the optic nerve, which keep record of their appearance to help us not only in diagnosing the disease but also in the follow-up by comparing different images of the disease progression over time. These pictures can even be stereoscopic (in relief) to give a better visualization of the volumes of the papilla. Since they are made with special filters, they can capture the nerve fiber layer of the retina and its defects.
Risk of Glaucoma:
The risk of glaucoma is not the same for everyone. Recently published studies show that age (after age 40, 4-7% of the population has high eye pressure), race (blacks have a higher risk of developing glaucoma), corneal thickness (having a thin cornea increases the probability of glaucoma), high myopia, and family history are all risk factors. Together with ocular hypertension, these factors can lead to the development of glaucomatous degeneration in the optic nerve.
The Genetic Study of Glaucoma
Genetic studies of glaucoma are essential to establish the role of genes in the causal mechanism of disease in different populations. By identifying the gene responsible for glaucoma in a given individual, a correlation with clinical features can be established to offer a short and long-term visual prognosis for the patient and family members that are affected. By doing this we can anticipate the future of the disease by modifying our early approach to treatment.
The mutational screening (genetic studies) not only help to determine an individual's predisposition to develop glaucoma but also for predicting the progress of the disease. This helps the ophthalmologist decide on the optimal treatment for each individual patient. Early glaucoma detection in these individuals who carry the mutation (or genetic load) but who are still asymptomatic (without signs or symptoms of glaucomatous disease) allows early treatment to be initiated and thus prevents or delays the onset of glaucomatous optic neuropathy.
On the other hand, genetic analysis can establish the probability of transmitting the disease to subsequent generations, which allows us to offer genetic counseling to all family members.
ICOftalmología is currently developing the first genetic study of glaucoma in Spain, with a collection of blood samples and genetic analyses from glaucomatous families in our centers as well as any new cases who wish to benefit from this innovative research. Many ophthalmologists from around the country are sending their patients’ information to be included in the novel protocols of this study.
Program monitoring and detecting the progression of glaucoma
Once a patient is diagnosed with glaucoma, treatment becomes mandatory and is aimed at preventing the progression to blindness. The purpose of the treatment is to reach an eye pressure that the physician considers to be “safe” for that particular case. This pressure, which may change over time depending on the progress of each patient, is what we call “target pressure.” According to the guidelines of the European Glaucoma Society, the target pressure is heavily dependent on the age of the patient, the pressure at the time the glaucoma was detected and the stage of disease. Today, we know that in advanced glaucoma the pressure can decrease to a greater extent if we slow the disease progression. However, during the early stages the treatment may be less aggressive.
Current Glaucoma Treatment
Treatment:
Currently, the first glaucoma treatment, with rare exceptions, is based on the use of drugs in the form of drops (eye drops) to lower intraocular pressure. They all have different characteristics (which give them a certain potency) and adverse effects that should be individually taken into account for each patient. For this reason, ophthalmologists should have a thorough knowledge of their patients’ medical history and any other diseases and drugs being taken at the moment. Often, patients with glaucoma do not realize that some adverse effects may be due to the eye drops administered by the ophthalmologist, so they do not report the problems. Doctor-patient communication is very important as well as maintaining patient records to ensure that medications do not have adverse effects.
The most common eye drops used for treating glaucoma are:
The Prostaglandin Analogue: Latanoprost, Travoprost, Tafluprost and Bimatoprost
The beta-blocking drugs with Timolol maleate, levobunolol, carteolol and betaxolol.
Agonist drugs with adrenergic receptors, such as brimonidine, apraclonidine and clonidine
The carbonic anhydrase inhibitors, sulfonamide derivatives such as dorzolamide and brinzolamide.
Cholinergic drugs, such as pilocarpine, that were first used as a treatment for chronic glaucoma are of little use today because of the visual changes that lead to its direct effect on accommodation and pupillary dynamics.
In order to facilitate compliance with medical treatment, eye drops have recently come on the market that contain fixed combinations of two drugs, such as the combination of timolol maleate and dorzolamide (derivatives of prostaglandins with timolol maleate), and finally brimonidine with timolol maleate. The use of fixed combinations can reduce the number of drops needed throughout the day and improve tolerance to eye drops so fewer preservatives are needed in the composition. Recently, the introduction of preservative- free eye drops, has improved the topical armamentarium in glaucma treatment.
Laser Treatment:
The argon laser trabeculoplasty (TPL) is used for certain types of glaucoma in order to improve the drainage of aqueous humor from the eyeball through small burns in the trabecular meshwork (structure located in the angle between the cornea and iris). Not all types of glaucoma respond to treatment with TPL nor is it possible to utilize in all cases because of the unique anatomy of each patient.
Surgical Treatment:
In some cases, eye drops and laser treatments are not enough to safely achieve a reduction in intraocular pressure. For these cases various surgical techniques that reduce this pressure by facilitating the drainage and outflow of aqueous humor are used. Our institution’s Glaucoma Unit has demonstrated expertise in these techniques, having been responsible for introducing one of them in Spain.
Filtering surgery :
Filtering surgery uses various methods to find an alternative outlet for the aqueous humor: the classic trabecular fistula or Trabeculectomy, as well as the innovative deep sclerectomy. We recently introduced the use of small drainage devices to allow output to jump and overcome the major resistance tissue, the yuxtacanalicular tissue within th etrabecular meshwork, wich causes the accumulation of aqueous humor and thus the increase in intraocular pressure. In some cases it is necessary to implant a Drainage Device (Molteno, Baerveldt or Acritech implants, Ahmed Valves, etc.) which consists of a silicone tube that drains the aqueous humor into some extraocular reservoirs to allow diffusion of the aqueous and consequently lower intraocular pressure.
Ciliary body ablation surgery.
In cases of refractory glaucoma that is glaucoma unresponsive to any treatment, the choice could be limited to one: the partial destruction of the ciliary body (the organ that secretes the aqueous humor). This applies to the endocyclophotocoagulation and to the diode ab exerno cycloablation, which are performed under local anesthesia in the operating room using a Diode Laser.
Acute angle-closure glaucoma
Much less frequent but no less important, is the acute angle-closure glaucoma. This is a very different entity when compared to chronic open angle glaucoma and has different visual consequences.
Acute glaucoma, as the name defines, is caused by an abrupt increase in intraocular pressure. The term “closed-angle” informs us that the elevation of intraocular pressure is caused by the closure of the anterior chamber angle. The chamber angle is formed by the intersection of the cornea with the iris. This is where the trabecular meshwork and Schlemm’s canal structures are located which allow the drainage of aqueous humor.
The aqueous humor can access this tubular structure if the “angle is open.” If, for any functional or anatomical reason the angle is closed, angular structures are buried and the aqueous humor is immediately blocked. This phenomenon is much more common in people who are farsighted because their anterior chambers are shallow and their angles are narrow. There are other causes of blockade, cases that occur less often where the special shape of the iris easily covers the angle to temporarily close, or some type of cataracts in an advanced stage, that can induce a blockade in small eyes as they grow.
The angle closure and the sudden cessation of aqueous circulation, causes a rapid rise in intraocular pressure at levels which can interrupt the blood supply to the front of the eyeball. Eye pain is intense, sometimes unbearable, and can cause nausea and vomiting. Failure to achieve a quick reduction in pressure can cause severe consequences.
The high pressures of acute glaucoma cause cell death in many ocular tissues: nerve cells of the optic nerve, muscle and iris stroma, and the crystalline and corneal endothelial cells. It is important to deal with these cases in an experienced Emergency Department where the appropriate antihypertensive therapy (medical, laser or surgical), can be administered to reduce the pressure as soon as possible.
Fortunately, preventing acute angle-closure glaucoma with the YAG laser peripheral iridotomy is, in most cases, fast, easy and risk free. Small holes are made in at-risk eyes that allow an alternative passage for aqueous humor.
