Glaucoma: Types, Causes, Symptoms and Treatment

Definition

Glaucoma is an eye disease that causes damage to the optic nerve. it can lead to loss of vision and eventual blindness. It usually occurs in the presence of high intraocular pressure. However, glaucoma can occur with normal or even below normal ocular pressure, such as damage to nerves due to poor blood supply or weakness of some structures around the eye.

Epidemiology

• Worldwide, 66.8 million of persons suffer from vision impairment, if not complete blindness due to Glaucoma.
• Incidence in USA of 300,000 new cases each year o Expert estimate that half of those affected may not know they have it because symptoms may not occur during early stages of the disease.

Pathophysiology

 

 

• Aqueous humor is secreted by the cells of ciliary process into the posterior chamber and through pupil.
• The aqueous humor then leaves the eye by flowing through the trabecular network in the anterior chamber angle, entering Schlemm’s canal and passing through it into the venous system.
• A second pathway is via the ciliary muscle into the supra chorodial space and then though the sclera.
• Glaucoma can occur as a result of a blockade in the normal outflow of aqueous humor.

Types of Glaucoma

1. Primary open-angle glaucoma
2. Primary closed-glaucoma (angle-closure)
3. Secondary glaucoma
4. Congenital glaucoma

Primary Open-Angle Glaucoma

• Primary open-angle glaucoma is chronic, and slowly progressing
•  It is an asymptomatic multifactorial disorder
• It is the most common form of glaucoma
• Usually, the asymptomatic patients exhibit markedly diurnal variations in the intra ocular pressure
• High risk factors include being black, age over 40 yrs, having a family history of the disease, being very near sighted, having history of diabetes, hypertension, previous eye injury or eye surgery, prolonged use of steroid.
• Treatment is medical except refractory cases were surgery is needed

Primary Closed-Angle Glaucoma (Acute Glaucoma)

• • This type of glaucoma results from a sudden complete blocking of fluid flowing out of the eye.
  • Its symptoms include-pain, nausea, vomitting, blurred vision, and seeing a halo (rainbow) around lights. o A medical emergency and must be treated immediately or blindness could result in 1 or 2 days.
  • Eyes predisposed to closed -angle glaucoma have shallow anterior chambers and narrow angles.
  • Dilation of the pupil by drugs, emotional stress or darkness may precipitate an acute attack.
  • Age and female gender are predisposing factor.
  • The priority is to use medical means (eye drops, tablets, injections) to reduce the amount of fluid produced into the eye to lower pressure on the optic nerve.
  • Following this, a small hole is made in the iris by laser or surgery to connect the posterior and anterior chamber. This permits the fluid to pass through and allow the forward bulging iris to fall back, which usually opens the angel of the anterior chamber.

Secondary Glaucoma

Causes

1. Abnormal deposits in the eye fluid.
2. Uveitis – an inflammation of the pigmented tissues inside the eye.
3. Lens changes may give rise to secondary increase in eye pressure
4. Physical trauma to the eye
5. Drug treatment with corticosteroids for prolonged time (by increasing production of aqueous fluid)
6. Tumors
7. Haemorrhage inside the eye

Treatment

• Treatment depends on potential for useful vision.
• If there is, then treatment should lower intraocular pressure and reduce any associated inflammation
• Treatment of underlying cause(s) e.g. removal of hyphaema or hypermature lens
• Long term treatment to control the intraocular pressure may be required before surgery is considered.
• If no potential for useful vision (e.g. Secondary Glaucoma due to diabetic retinopathy), then management should aim at symptomatic pain relief with mydiatrics and steroids

Congenital Glaucoma

• Congenital glaucoma is usually hereditary
• Inherited as a recessive trait
• Both eyes are usually involved in a greater percentage of the patients but often not to the same extent.
• Children born with this problem have obvious symptoms such as cloudy eyes, sensitivity to light and excessive tearing.
• Surgery is usually recommended especially as medicines may have unknown effects in infants and may be difficult to administer.

Symptoms

• Congenital glaucoma is asymptomatic
• Vision stays normal, no pain
• However, although patients see things in front of them, they miss objects to the side and out of the corner of their eye.
• Without treatment, patient notice they suddenly do not have side vision. It seems to them as though they are looking through a tunnel.
• Over time, the remaining forward vision may decrease until there is no vision left.

Diagnosis

• Persons over 40 yrs and with family history of Glaucoma require 3 tests which together provide the best probability of detection. These tests are:
  • Ophthalmoscopy – This is viewing the appearance of the optic nerve (optic disc) by using an ophthalmoscope.
  • Tonometry – This is measuring the pressure within the eye
  • Perimetry – This is checking the ‘all round’ vision i.e. the visual field by lights flashed on in different positions away from the center

Medical Treatment

1. Miotic drops are used. They increase the outflow of fluid from the eye.Miotic drops include:
   1. Pilocarpine HCL (1%, 2%, 3%, 4%). A direct cholinergic agent, which causes constriction of the
   2. pupil, contraction of the ciliary muscle and fall in intraocular pressure (IOP). NB: Gel and Ocusert system (20, 40)
   3. Carbachol: this is slightly longer acting. It produces less papillary constriction but increases accomodation spasm, conjuctivial hyperemia and headache. Usually 1 to 2 drops of 0.5 to 0.75% are instilled in each eye every 8 hours.
   4. Physostigmine: this is an anticholinesterase miotic. It is also considered stronger than pilocarpine and has longer duration of action. 0.25 to 0.5% solution of physostigmine is given every 4 to 6 hours.
   5. Potent cholinesterase inhibitors such as demecarium, echothiophate iodide and disisopropyl phosphorofluoridate (DEP) are powerful miotics used to treat open angle glaucoma when short acting agents prove inadequate.
2. Beta adrenoceptor blocking drops: Beta adrenoceptor receptors are primarily found in the ciliary muscles, and together with alpha adrenoceptors in the Iris. B-adrenoceptor blockers lower the production of aqueous humor and this effect is obtained with both topical and systemic administration. ß-adrenergic blockers have been the most commonly prescribed first-line agents for the treatment of Open angle glaucoma. Examples:
   1. Timolol
   2. Levobunolol
   3. Cartelol
   4. Betaxolol
   5. Timoptic XE the gel-forming solution, administered once daily.
   6. Because of possible systemic absorption, Beta adrenoceptor blocking drops are used with caution in patient with sinus bradycardia.
3. Carbonic anhydrase inhibitor drops e.g. Dorzolamide is commonly used to reduce the production of fluid into the eye by blocking ocular carbonic anhydrase.
4. Prostaglandin drops – PG analogues, which increase uveoscleral outflow, have had the most significant impact in terms of compliance and convenience. E.g Latanoprost (Xalatan), Unoprostone (Rescula), Bimatoprost (Lumigan), Travoprost (Travatan). They are often prescribed as 1st line because: they are as effective as beta adrenergic blockers, administered once daily, and have minimal side effect.
5. Alpha 2 agonist drops– Examples include brimonidine (Alphagan) and Apraclonidine (Iopidine). They decrease production of aqueous humour and increase uveoscleral outflow.
6. Adrenaline drops – B-adrenergic stimulation increases aqueous humor outflow e.g. dipevalylepinephrine (Propine)

Each of these medications may be used alone or in combination with one another.

• In case of timolol and dorzolamide (Timoptol & Trusopt) these drops are produced ready mixed in one bottle under the trade name Cosopt.
• Also Timolol and Latanoprost under the tradename Xalacom.
• Sometimes tablets may be used such as acetazolamide (Diamox) or dichlorphenamide (Daranide).
• The tablets reduce fluid production

 

Antiglaucoma Drugs

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Patient Education on Administration

• Hold the inverted bottle between the thumb and middle finger
• Rest this hand on the forehead to minimize the risk of inadvertent eye injury caused by sudden unexpected movement of the hand.
• The index finger is left free of the container, releasing one drop for the dose.
• The lower eyelid should be drawn downwards to depress the bottom with the index finger of the opposite hand
• The patient should look up and administer the drug into the pouch of the eye.

Laser Treatment

• Laser treatment is indicated in case of deterioration in the field of vision
• The procedure is called trabeculoplasty – this opens the pores in the trabecular meshwork.
• It is an outpatient procedure.
• Its results are variable but often effective, although the eye pressure may slowly rise again later.

Surgical Treatment

• If laser treatment fails, an operation called trabeculectomy is carried out to reduce eye pressure.
• It is achieved by forming a small safety valve in the region of the trabecular meshwork for fluid to escape into the loose tissue under the conjunctiva which covers the white of the eye.
• From there it is absorbed back into the blood stream.
• The drainage site can usually be seen after raising the upper lid and appears as a semitransparent blister just above the margin of the cornea in the white of the eye.