Glaucoma refers to a group of eye diseases that damage the optic nerves due to gradually increasing pressure within the eye, the intraocular pressure (IOP). Glaucoma can develop in one or both eyes. Glaucoma is one of the leading causes of blindness, yet many people are unaware that they have this condition since the vision impairment may be painless as well as insidious. For this reason, a regular eye examination is extremely important, particularly if there is a family history of glaucoma, since early diagnosis and treatment can often help to preserve vision.
There are different types of glaucoma, such as :
- Open-angle or chronic glaucoma
- Angle-closure or acute glaucoma
- Congenital glaucoma, which is present at birth, and usually runs in families.
- Secondary glaucoma, which may be caused by drugs such as corticosteroids or systemic diseases.
Angle-closure glaucoma may be associated with a red, painful eye, blurred vision, nausea, and vomiting, which will demand immediate attention.
A comprehensive eye examination should be done for detection of glaucoma, which may include the following :
- Indirect fundoscopy – examination of the eye after dilating the pupil.
- Tonometry – to measure IOP. Tonometry may not always be diagnostic of glaucoma since some people with glaucoma may have normal IOP.
- Visual acuity test – an eye chart is used to measure how well a person can see, so as to be able to assess how far his vision has been affected by the disease.
- Visual field test – to measure the peripheral or side vision, loss of which is one of the main signs of glaucoma.
- Pachymetry – following the application of anesthetic drops in the eye, an ultrasonic wave instrument is used to measure the thickness of the cornea.
- Gonioscopy – a special type of contact lens with mirrors is used to examine the outflow channels of the angle.
- Ophthalmoscopy – a hand-held device, known as the ophthalmoscope, is used to look directly through the pupil into the eye. Damage to the optic nerve or cupping of the optic disc, which may be caused by increased IOP, can be detected if present.
- Optic nerve imaging – photographs may be taken of the optic nerve and the inside of the eye by means of special cameras.
- Pupillary reflex response – this is the change in the diameter of pupil size in response to any stimuli, such as constriction of the pupil caused by light. This response depends on the normal functioning of the optic nerve.
- Retinal examination – a slit-lamp or ophthalmoscope is used to examine the retina, after the pupil has been dilated with eye drops. Signs of glaucoma, as well as signs of cataract, and other problems related to the retina and optic nerves are looked for.
- Slit-lamp examination – the slit-lamp projects a thin, intense beam of light into the eye which allows a magnified view of the interior of the eye.
Treatment cannot cure open-angle glaucoma but it can halt further progression of the condition. The main aim of treatment is to preserve vision, primarily by reducing the IOP.
Eye drops that lower the IOP, either by helping fluid leave the eye or by decreasing fluid production in the eye, are usually the first line of treatment in open-angle glaucoma.
- Beta-adrenergic antagonists, such as timolol, levobunolol, carteolol, and metipranolol act by reducing fluid production in the eye.
- Prostaglandin analogs, such as latanoprost, travoprost, and bimatoprost act by increasing the outflow of fluid from the eye.
- Adrenergic agonists, such as brimonidine, epinephrine, and apraclonidine act by reducing fluid production as well as by increasing drainage.
- Carbonic anhydrase inhibitors, such as dorzolamide, brinzolamide, acetazolamide, and methazolamide act by reducing fluid production.
- Parasympathomimetic agents or miotics, such as pilocarpine, demecarium, echothiophate, and isoflurophate act by increasing outflow.
- Osmotic agents, such as isosorbide and mannitol may be used with caution to treat angle-closure glaucoma where the IOP remains high in spite of other treatments.
A combination of eye drops may be necessary for effective treatment, or eye drops plus oral drugs may be prescribed. In case of angle-closure glaucoma, which is a medical emergency, medication may need to be given intravenously to lower the IOP.
Laser treatment is considered when eye drops and medication cannot be used or fail to give the desired results. Laser treatment may be considered for open-angle glaucoma. Laser trabeculoplasty is a painless procedure which works by helping to open the fluid outflow channels.
Laser treatment in angle-closure glaucoma is usually done to prevent an acute attack by relieving pressure within the eye. This may be done as an emergency procedure by doing an iridotomy, which involves opening a new channel in the iris. Laser cyclo-ablation is another form of laser treatment.
Surgery is indicated when both medication and laser treatment fails to yield the desired results. Filtration surgery (trabeculectomy) involves making a new opening for fluid to be drained from the eye. Surgery to open the outflow channels of the angle is the treatment of choice in most cases of congenital glaucoma. The other types of surgery make use of aqueous shunt devices to lower IOP, and viscocanalostomy.