Glaucomas are a group of eye disorders characterized by progressive optic nerve damage in which an important part is a relative increase in intraocular pressure (IOP).
Glaucoma is the 2nd most common cause of blindness worldwide. According to the World Health Organization, about 64 million people worldwide have glaucoma, but only half are aware of it.
Many forms of glaucoma have no pronounced symptoms and, therefore, you may not notice a change in vision until the condition is at an advanced stage. It’s very important to have regular eye examination so a diagnosis can be made in its early stages and treated appropriately. The sooner glaucoma is recognized, the higher the chances of preventing vision loss.
Glaucoma can occur at any age, however it’s six times more common among people over 60.
Glaucomas are categorized as
- Open-angle glaucoma
- Closed-angle glaucoma
The signs and symptoms of glaucoma vary depending on the type and stage of your condition.
The most common sings of open-angle glaucoma are characteristic visual field defects. Early primary open-angle glaucoma symptoms nevertheless are uncommon. Usually, the patient becomes aware of visual field loss only when optic nerve atrophy is marked. Intraocular pressure might be normal or high but is almost always higher in the eye with more optic nerve damage.
Patients with acute angle-closure glaucoma have severe ocular pain and redness, decreased vision, colored halos around lights, headache, nausea, and vomiting. The systemic complaints may be so severe that patients are misdiagnosed as having a neurologic or gastrointestinal problem. Examination typically reveals conjunctival hyperemia, a hazy cornea, a fixed mid-dilated pupil, and anterior chamber inflammation. Intraocular pressure is usually 40 to 80 mm Hg.
When to see a doctor
Promptly go to a doctor if you note some of the symptoms of acute angle-closure glaucoma. Treatment must be initiated immediately because vision can be lost quickly and permanently.
Glaucoma is the result of damage to the optic nerve. As this nerve gradually deteriorates, blind spots develop in your visual field. For reasons that doctors don’t fully understand, this nerve damage is usually related to increased pressure in the eye.
Elevated eye pressure is due to a buildup of a fluid (aqueous humor) that flows throughout the inside of your eye.
In healthy eye more than 98 per cent of the aqueous humor exits the eye via either the trabecular meshwork and the Schlemm canal which are located in the angle formed by the junction of the iris and cornea at the periphery of the anterior chamber.
Because glaucoma can lead to blindness before any signs or symptoms are apparent, it is necessary to be aware of the following risk factors:
- Older age
- Family history of glaucoma
- African ethnicity
- Thinner central corneal thickness
- Systemic hypertension
In people of African ethnicity, glaucoma is more severe and develops at an earlier age, and blindness is 6 to 8 times more likely.
Patients with symptoms that may indicate glaucoma should be referred to an ophthalmologist for a comprehensive examination that includes a thorough history, family history, examination of the optic disk, visual field examination, tonometry (measurement of intraocular pressure), measurement of central corneal thickness, optic nerve imaging using optical coherence tomography, and gonioscopy.
Glaucoma is diagnosed when characteristic findings of optic nerve damage are present and other causes have been excluded. Elevated intraocular pressure makes the diagnosis more likely, but elevated IOP can occur in the absence of glaucoma and is not essential for making the diagnosis.
Lowering the intraocular pressure is the only clinically proven treatment of glaucoma. Nevertheless, patients with characteristic optic nerve and corresponding visual field changes are treated regardless of IOP measurement.
Three methods of glaucoma treatment are available: drugs, laser surgery, and incisional surgery. The type of glaucoma determines the appropriate method.
Drugs and most laser surgeries (eg, argon laser trabeculoplasty) modify the existing aqueous secretion and drainage system. Traditional incisional surgeries create a new drainage pathway between the anterior chamber and subconjunctival space.
Canaloplasty is a nonpenetrating surgery using microcatheter technology. To perform a canaloplasty, an incision is made into the eye to gain access to the Schlemm’s canal. A microcatheter will circumnavigate the canal around the iris, enlarging the main drainage channel and its smaller collector channels through the injection of a sterile, gel-like material called viscoelastic. The catheter is then removed and a suture is placed within the canal and tightened.
The most common conventional antiglaucomatous surgery is the trabeculectomy. In trabeculectomy the surgeon makes a partial thickness flap in the scleral wall of the eye and a window opening under the flap to remove a portion of the trabecular meshwork. The scleral flap is then sutured loosely back in place to allow fluid to flow out of the eye through this opening, resulting in lowered intraocular pressure and the formation of a bleb or fluid bubble on the surface of the eye.
Argon laser trabeculoplasty (ALT) may be used to treat open-angle glaucoma, but this is a temporary solution, not a cure. During the procedure, a 50-μm argon laser spot is aimed at the trabecular meshwork to stimulate the opening of the mesh to allow more outflow of aqueous fluid.
Selective laser trabeculoplasty (SLT) uses a Q-switched 532 Nd:YAG laser to selectively target pigmented cells of the trabecular meshwork in a nonthermal manner, increasing fluid outflow and thereby lowering intraocular pressure. It has been shown in trials to be as effective as the older ALT. However, because SLT is performed using a much lower power laser, it does not appear to affect the structure of the trabecular meshwork (based on electron microscopy) to the same extent, so retreatment may be possible if the effects from the original treatment should begin wear off.
Nd:YAG laser peripheral iridotomy (LPI) may be used in patients susceptible to or affected by angle closure glaucoma or pigment dispersion syndrome. During laser iridotomy, laser energy is used to make a small, full-thickness opening in the iris to equalize the pressure between the front and back of the iris, thus correcting any abnormal bulging of the iris. In people with narrow angles, this can uncover the trabecular meshwork. In some cases of intermittent or short-term angle closure, this may lower the eye pressure. Laser iridotomy reduces the risk of developing an attack of acute angle closure. In most cases, it also reduces the risk of developing chronic angle closure or of adhesions of the iris to the trabecular meshwork.
Nonpenetrating deep sclerectomy
Nonpenetrating deep sclerectomy surgery is a similar, but modified, procedure, in which instead of puncturing the scleral bed and trabecular meshwork under a scleral flap, a second deep scleral flap is created, excised, with further procedures of deroofing the Schlemm’s canal, upon which, percolation of liquid from the inner eye is achieved and thus alleviating intraocular pressure, without penetrating the eye. NPDS is demonstrated to have significantly fewer side effects than trabeculectomy. However, NPDS is performed manually and requires higher level of skills that may be assisted with instruments.