Eye drops are the most common form of medication for your eyes. There are also ointments (aka salves), pills and injectable medicines. The eye is unique in the many ways. It can be treated directly with medicines. Eye drops and ointments are the most common. Medications given by mouth or intravenous usually don’t get into the eye well, due to the blood brain barrier. Direct injection of medicine into the eye is probably the best for treating problems inside the eye (e.g. the retina).
The skin is the only other organ in the body where the medication is placed directly upon it. We use lotions and creams to treat ailments and diseases of the skin.
Eye drops, too, are placed right where we want them. These drops commonly treat infections, fight glaucoma, lubricate, reduce inflammation, etc. Eye drops are best suited for problems that develop outside, that is, on the surface, of the eye. They aren’t so useful for treating diseases in side the eye as the drops do not penetrate the eye very well.
Each eye drop has a volume of about 32 microliters. The volume of the surface of the eye is about 28 microliters. These are approximations, but my point is that for most eye drop medications, the volume of one drop exceeds the amount of liquid that can be “held” by the surface of the eye.
This means that whatever the medication, never use more than one drop, or, the excess will roll down your cheek…it is a waste. I have always recommended that if the directions recommend the use of more than one drop at a time, don’t buy it. The manufacturer knowingly advises you waste a portion of the product.
A more practical view? Often patients are directed to use more than one different type of eye drop. Separate the drops by a minute or two to prevent the first being washed away (and down your cheek) by the second drop. Give the first drop time to be absorbed.
There are fewer medications available in ointment form. The advantage of an ointment, or salve, is the effects may last a bit longer. Once applied, the ointment heats up. As it nears body temperature, the ointment melts and releases the medicine over the ocular surface.
Ointments; however, are somewhat greasy, difficult to apply and, most of all, generally blur the vision. Patients don’t like to use them, they are messy and they can’t see.
Eye ointments are great for eye lid problems and for cases where lubricating the eye requires more than just drops (e.g. just before you go to bed).
Rarely used in the office setting, intravenous medications can be used when there are eye and systemic complications that need to be treated. Beyond the scope of this article, intravenous medications may be used to treat certain infections, bacterial and viral, that are out of control (e.g. herpes, CMV, syphilis). Still not much drug finds its way into the eye even whe given I.V. The “blood-brain-barrier” prevents many drugs from getting inside the eye. This is a unique problem of the eye and the brain.
Tablets and pills are sometimes used to treat certain types of inflammation, occasionally eye pressure and only a few types of infections. This route, too, fails to get large quantities of medicine inside the eye, again, due to the blood brain barrier.
Most of the advances in treatment for macular degeneration and diabetic retinopathy involve intravitreal injections. Injecting anti-VEGF medications and steroids have given us new ways to treat these two common retinal diseases. This circumvents the the “blood brain barrier.”
This category is really a subset of intravitreal injections. These devices will be injected into the eye and release drug over many months (bypasses the blood brain barrier). Right now, Ozurdex, is the only FDA approved system. It releases steroid for the treatment of retinal vascular occlusions. Other sustained release systems are in the pipeline.
What Does This Mean?
Depending on the malady, topical eye drops and ointments are probably best suited to treat disease outside the eye. They have the advantage of being applied directly to the target tissue.
Similarly, by directly injecting medicine into the eye to treat retinal disease, intravitreal injections share the same advantage; namely, directly applying the medication to the target.
While the main thrust of this web site focuses on retinal disease, don’t forget that eye drops were really the first time we could apply medicine directly to the eye. History has taught us that this is a very effective method. This makes for an exciting future for the treatment of retinal disease.