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| Glaucoma: The treatment perspective |
Treatment is usually begun with a topical drug. If necessary, other topical or systemic drugs are added. When drugs fail to control the intraocular pressure, laser energy applied to the trabecular meshwork (laser trabeculoplasty) may be used to increase aqueous outflow. When drugs and laser trabeculoplasty fail to control the intraocular pressure, a new route for aqueous egress can be created surgically.
MEDICAL TREATMENT is both, an art and a science. The goal of treatment is to preserve visual function. Lowering the IOP is only a secondary goal . It is necessary to tailor the treatment to the needs of the patient and when doing so, the following need to be kept in mind -
A) The target tissues of topically applied ocular hypotensive medication are within the eye. Ocular conditions which can limit bio availability such as tear film deficiency, corneal scarring, chronic non-specific blepharoconjunctivitis and intra ocular inflammation and may co-exist.
B ) Patient's compliance with instructions for instilling eye drops can be improved by
- Educating patient about nature of the disease
- Emphasizing need for life long treatment.
- Assessing patient's ability to instill eye drops correctly and in accordance to dosage schedule.
- Educating patient about possible side effects
- Avoiding eye drops with specific side effects, on individual patients.
- Use drops which affect patients daily routine minimally.
- Can the treatment regimen maintain the desired target IOP for 24 hours in a day
- Is the patient amenable to follow up to assess the reponse to treatment .
- Simpler the treatment regimen , better the compliance.
- Fewer side effects mean better patient compliance
- Topical preparations contain preservatives which may cause conjunctival inflammation and cytotoxic effects on the ocular surface . Preservative free preparations would be ideal , particularly when multiple drugs are being used . However no such drugs are available in India .
Most drugs for glaucoma are applied topically. Because of the brief contact time and the strong protective barrier of the eye, the drug solutions need to be concentrated. Excess drug drains through the nasolacrimal duct into the nose, where it may be absorbed into the systemic circulation. For example, Timolol administered to one eye enters the bloodstream in a concentration sufficient to cause a measurable decrease in intraocular pressure in the opposite eye . Those who use topical drugs should occlude the nasolacrimal duct with either digital pressure or simple eyelid closure for about five minutes, this maneuver increases intraocular drug concentrations and decreases systemic concentrations.
There is no single accepted drug of choice in glaucoma therapy . The initial drug of choice could vary depending on the likely compliance with treatment , socioeconomic and health status of the patient, efficacy of the drug and the geographical location of the treating physcian . The drug given initially to patients with most types of glaucoma is a non selective, topical beta adrenergic-antagonist drug, such as Timolol maleate ( in the absence of any contraindication ), because of the pressure lowering efficacy, long duration of action, and few ocular side effects of this class of drugs. A second drug, if needed, might be a prostaglandin analogue (such as Latanoprost / Bimatoprost /Ttravtoprost ) or an alpha 2 adrenergic agonist ( Brimonidine). However the choice of the initiating drug could also be prostaglandin analogue or selective alpha 2 adrenergic agonists.
Topical carbonic anhydrase inhibitors (such as Dorzolamide) constitute the third choice . Cholinergics like Pilocarpine, have often been relegated to the last because of their ocular and visual side effects . However in the Indian context they provide effective IOP lowering which is cost effective. It is important to select the right candidates - aphakes and pseudophakes who are not high myopes .
When therapy with a topical drug is instituted, it may be applied to one eye, with the opposite, untreated eye used as a control. This method makes it possible to determine whether any change in intraocular pressure is due to the drug or to the normal variation of intraocular pressure. However this is usually not possible in the Indian scenario.
If there is no response, the drug is discontinued in order to avoid unnecessary costs and side effects. If there is a substantial decrease in intraocular pressure but the eye pressure remains high, another drug should be added. Different classes of drug have additive effects on intraocular pressure. Exceptions are nonselective beta adrenergic-antagonist drugs and nonselective adrenergic agonist drugs, which have little additive effect when given together. Cholinergic drugs and Prostaglandins with adequate spacing can also be used together .
- Multiple drops are less likely to be instilled correctly as compared to single preparations.
- Combination drops and more likely to be instilled correctly than drops from multiple bottles.
- Fixed drug combinations offer the advantage of less toxicity by preservatives and lower costs, than fixed preparations
- Combination therapy with identical mechanism of action should be avoided.
Although there are numerous medications available with different modes of action, about 2/3 of patients require combination treatment . With monotherapy a 25 % reduction can be expected in the relative IOP. From combination therapy 35% and from maximal medical therapy 40% of IOP reduction from baseline.
A golden rule of treatment is to always use the least amount of drug, in the lowest concentration, least number of times such that one effectively gets the highest efficacy with the least possible side effects.
Other terms commonly used in the medical treatment of glaucoma are :-
Maximal Medical Therapy ( MMT ) : When a patient is on representative medication from each of the available groups of antiglaucoma medication .
Maximal Tolerable Medical Therapy ( MTMT ) : Maximal Medical Therapy where drugs to which the patient is intolerant , have been excluded , in an effort to achieve medical control of IOP .
Systemic carbonic anhydrase inhibitors may be added if the IOP remains uncontrolled with MMT or in situations where the IOP is extremely elevated .The patient's tolerance may dictate whether these medications are used for a short or long time . Because of the potential for side effects they are not used on a long term basis
Excerpts from the lecture "Recent Advances in the Medical Management of Glaucoma " by Dr. Devindra Sood at the annual meeting organized by the Kerala State Ophthalmological Society, Cochin, Kerala November 2008 |
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