Is glaucoma eye-drops compliance that difficult?
A patient's perspective
By Sam Fong, Alpha-C Support Group, Glaucoma Society (Singapore)
Far too many glaucoma patients have lost too much of their sight, much too early and unnecessarily, due to non-compliance on the use of their eye-drops. The correct use of eye-drops is surprising low even among the educated population. What are the reasons?
We take our medicine by habit. Traditionally, eye-drops have been primarily seen as lubricants for dry eyes and to be used as and when required. Very few instructions are given to the user other than the drops should get into the eye. Even if it overflows the eye lids, it is acceptable. After the application, the user feels almost immediate relief from the discomfort. So, the feedback is that eye-drops produce good results and when eye is better, the drops are no longer required. It is also the same with pills. A 3-times-a-day medicine does not mean an 8-hourly cycle - you would often take it after breakfast, after lunch and after dinner, or at your leisure. In most common ailments, medication relieves the symptoms of pain or discomfort while the body's immune-system performs its own auto-healing process. Thus, you can get well, with or without medicine, albeit with a little more suffering along the way. Therefore, a patient's views of medicine are gathered through their common experiences. And, however you take your medicine, you usually do get well eventually!
Glaucoma Eye-drops - a pressure regulator
However, with glaucoma, it is not quite the same story. It is not a common experience and the normal technique does not apply. This is because, when you have glaucoma, your eye’s auto-regulation system has failed. Eye-drops are no longer a symptom-reliever but now acts as a regulator of intra-ocular pressures (IOP) in the eye. You can say it is like the pace-maker used to regulate the heart beat and stopping the pace-maker will cause the faulty heart to function erratically. So it is with the eye. When your application of IOP-lowering eye-drops are stopped or not regular, the unregulated glaucomatous eye pressure may fluctuate diurnally by as much as +10 mmHg from its low.
First, we need to try to understand how glaucoma is treated with the use of eye-drops. Currently, the only available treatment for glaucoma is by lowering the IOP. We can do this by taking medicine in the form of tablets, using eye-drops or by surgery where an alternate drainage path is created for AH (aqueous humor) outflow. It is quite obvious that tablet intake is probably the least effective means for lowering IOP in the eye because the medicine is not directly applied to the eye and that surgery is the most effective because it directly and physically creates a vent in the eye for pressure relief.
No feedback indication
What makes it difficult for the patient to understand the usefulness of the eye-drops is that the pressure in the eye is awfully low. Take a drinking straw and fill it with water to 150mm height and hold it against your arm and you will feel nothing; double it to 300mm water height and again you will feel nothing pressure-wise. This represents the limits of the range of pressures between 11 and 22mmHg. The eye-drops in most instances are trying to regulate the IOP in the patient*s eye within this range and to find a "safe" level required by the patient. And because the patient cannot feel the effects physically, the patient cannot appreciate the usefulness of the eye-drops. The process is unable to provide a system of positive feedback that can be measured by the patient. In the case of diabetes, the patient is able to measure daily his blood-sugar level and gauge his compliance but this is not quite the case with glaucoma. With glaucoma, the patient can only get the performance-feedback at his next clinic visit, which may be 5 to 6 months later.
There are various causes of non-compliance in the use of eye-drops. Broadly we may classify them into two groups:-
1) failing to take prescribed doses at recommended intervals
2) failing to dispense the correct dosage due to wrong techniques
Unclear Prescription Convention
It is traditional in medicine prescription to use the day to represent the interval of dosage and then specify the number of times they have to be taken, often before or after food. Thus this practice is also applied to glaucoma eye-drops - do you apply nightly, twice a day, three times a day, or four times a day? The day is taken as the yardstick. What then about the night? Does one sleep through it without medication? If the patient sleeps 10 hours a day, what happens to the 3 or 4 times a day dosage interval? It is possible in such instances that the eye-drops would have over-regulated the IOP during the wake-hours and under regulated the IOP during the sleep-hours. This can only lead to undesirable results for patients with "spiked-up" IOPs during the night.
If the traditional prescription methods are confusing, then change them. Perhaps it may be better to base the application times on a 24-hour day (inclusive of the night) - applying eye-drops 12 hourly, 8 hourly, or 6 hourly - instead of the 2x, 3x or 4x per day convention. In this way, the time of dosage each day will be the same and much easier to remember. This makes the exact dosage times clearer and helps the patient to be more disciplined. The patient will also have a better idea of the dosage interval and plan ahead. Thus, if adherence to a 6-hourly dosage schedule is not possible for the patient because his work, age, health etc, it would be better that the ophthalmologist prescribe eye-drops which have longer effectiveness. Studies show that greater compliance is seen with lower-dose frequency and falls sharply as the frequency is increased. With once-a-day dosage, 75% of patients use their drops regularly. But, the patients' compliance falls to 40% when the dosage ís increased to a 6-hourly schedule.
Consumption rates of common dosing schedules are around 80% when the drops are taken by patients who are on a once-a-day dose; and falls to 50% when patients are placed on 6-hourly dosages.
Though the consumption rate looks better, the time interval of application has often been compromised. Often non-compliance may be due to:-
- 1) Lack of planning
2) Forgetfulness
3) Change of daily schedule
4) Confusion about instructions
5) Cost of the medicine
However, getting the correct timing for dosing is only one aspect of compliance. The other, which is more difficult to manage, is getting the necessary dosage into the eye where it is required. Here, tablets have the advantage over eye-drops for compliance because the former can be counted but the latter is difficult to measure. An eye-drops dispensing bottle is designed to release one drop-size at a time into the eye. Most eyes are capable of receiving at least 0.8 of a drop-size. Three things can happen to a drop when instilled:-
1) some over-flow the rim of the eye
2) some gets drain out through the tear duct
3) some gets absorbed by the eye - the only useful portion
Depends on Patient, his Patience and Persistence
The objective is to allow as little of (1) and (2) to happen and as much of (3), which is the only useful portion of the eye-drop, to take place. The eye-drop must get to the eye to do its job. How much of the drop is going to be effective depends on the patient, his patience and his persistence. Too little of (3) would result in partial compliance or lack of efficacy. How much of the drop should do useful work i.e. (3) is a chicken-and-egg issue. The test is, if by maximizing the usefulness of the drop will maximize the IOP lowering, the maximum usefulness should logically be targeted. It saves money, it gives less side effects.
Consider a Case Study. Let us say that a control patient needs a 35% IOP reduction to reach the target pressure. Assuming that, with this patient, the prescribed eye-drop is capable of lowering the IOP by 40% if optimal efficacy is practiced but only 20% was obtained due to poor but consistent application. As a result, on examination of the optic nerves and visual field results, the ophthalmologist prescribes to add on another eye-drop so as to lower the IOP further by another 20% and the target IOP was met. Note that this could actually be achieved with the first drop if there was good compliance. Thus, with good compliance, it is possible to reach the target pressure with less cost, a less frequent dosing regime and less side effects. Trying to get everyone to achieve the maximum benefit from the drop may not be practical but some good practices may yield better results than haphazard applications.
Some Good Techniques for Good Compliance
Let us consider some of the better techniques adopted for good compliance. In a workshop study of 20 patients some good practices were introduced and the performance gauged after the next visit. The results of the initial visit and subsequent visit are tabled: The results showed that wit
Let us try to understand how each of these steps helps to improve the procedure of application. Getting the eye-drops properly absorbed by the eye requires time and it varies with different eye-drops and from person to person. Generally, 5 minutes would be sufficient but with the carbonic anhydrase inhibitors (CAI) they might take as much as 10 minutes because of their more waxy and viscous nature. Keeping still for 5 minutes in the tilted head back and the eye gently closed position will keep the drop at optimum instilment mode. Closing the eye gently without blinking and squeezing will improve the dosage. The action of blinking will cause fluid to drain down the tear ducts and together with some of the medicine. Applied pressure-lacrimal puntae, a procedure of applying slight pressure to the inner corner of the eye with the finger, will physically close the tear duct blocking drainage through this channel temporarily. The patient should try to apply drops to one eye at a time instead of both eyes simultaneously if difficulties are experienced in preventing over-flowing. A delay of 1 or 2 minutes between instilment of drops to each eye often helps. Similarly, if more than 1 drop is instilled to the same eye at close interval, a minimum of 5 to 10 minutes between applications will ensure that the second drop does not wash out the first drop.
Even the most conscientious patient forgets or misses the time to take a medication occasionally. But, immediately upon realizing it, he should take the medicine as soon as possible unless the time is so close to the next scheduled medication, that he should skip the dose and carry on according to his normal schedule.
One must safeguard against the folly of being fully compliant just before the next clinic review with the objective of obtaining good IOP readings, with the hope that the ophthalmologist would not increase the dosage of eye-drops and thus save cost. This will not work, as the optic nerves and visual field results will reveal the long-term consistency or inconsistency of eye-drops compliance. But it is only when the patient understands the importance of being consistent, that the patient would want to be compliant.
Conclusion
Finally, the patient should remember that the IOP-lowering eye-drop acts as an IOP regulator. In order that it can function in this role, the interval of application should be regular, as prescribed, and consistently maintained over long periods of time. The ability to apply each dose with maximum effectiveness to the eye will enable maximum benefit to be obtained from each drop and avoid additional medicine. By being compliant the benefits to the patient are:-
- It will require less eye-drop dosage
- It will have fewer side-effects
- It will save you money
- Most importantly, it will save your SIGHT!
