Understanding the Tear Drainage System
To understand how eye drops can go from eye to throat, it is essential to first know how the eye's natural drainage system works. The body's tear production system, called the lacrimal apparatus, continuously produces tears to lubricate and protect the eye's surface. These tears are produced by the lacrimal glands and then drained away through a specific pathway:
- Puncta: Located on the inner corners of the upper and lower eyelids are two tiny openings, called puncta. Tears that have bathed the eye's surface collect here.
- Canaliculi: The puncta lead into small, tube-like canals called canaliculi.
- Lacrimal Sac: The canaliculi drain into the lacrimal sac, which is positioned on the side of the nose.
- Nasolacrimal Duct: From the lacrimal sac, tears travel down the nasolacrimal duct, which empties into the nasal cavity.
Once the fluid is in the nasal cavity, it flows back into the throat, where it is swallowed along with saliva. This explains why you can often taste or feel eye drops running down your throat shortly after application. This drainage is a completely normal bodily function for excess tears and is what allows eye drops to follow the same path.
The Importance of Proper Eye Drop Application
While tasting eye drops is a common occurrence, improper application can have consequences beyond an unpleasant flavor. When a drop drains into the throat, the medication can be absorbed by the vascular-rich mucous membranes in the nasopharynx and enter the bloodstream. This is known as systemic absorption.
For many over-the-counter (OTC) eye drops, this systemic absorption is harmless, causing nothing more than the taste. However, for certain medicated drops, particularly prescription drops for conditions like glaucoma, systemic absorption can be a significant issue. Medications like beta-blockers, used to treat glaucoma, can affect the cardiovascular system and breathing if they are absorbed systemically in large enough quantities.
Techniques to Prevent Systemic Absorption
To maximize the effectiveness of the medication in the eye and minimize unwanted systemic absorption and side effects, proper application technique is crucial. Medical professionals recommend a method called punctal occlusion.
Steps for Proper Eye Drop Application with Punctal Occlusion:
- Wash Your Hands: Always start with clean hands to prevent introducing germs into your eye.
- Tilt Your Head: Tilt your head back slightly and gently pull your lower eyelid down to create a small pocket.
- Apply the Drop: Squeeze the bottle to release one drop into the pocket. Avoid touching your eye or any other surface with the bottle tip.
- Close Your Eyes Gently: Close your eyes and avoid squeezing them shut, as this can force the drop out.
- Press the Inner Corner: Gently press your index finger on the inner corner of your eye, where the eyelids meet the nose. This is where the tear ducts are located.
- Hold for 1–3 Minutes: Maintain pressure for at least 1–3 minutes. This blocks the tear ducts and keeps the medication in the eye where it can be properly absorbed.
For patients who have difficulty with this technique, lying down during application can make it easier.
Comparing Application Methods
| Feature | Standard Application (Without Occlusion) | Proper Application (With Punctal Occlusion) |
|---|---|---|
| Drainage to Throat | Common, as the drop quickly follows the natural tear drainage pathway. | Minimal, as the tear duct is temporarily blocked, preventing drainage. |
| Taste | Frequently experienced due to medication draining down the throat. | Unpleasant taste is avoided or significantly reduced. |
| Effectiveness | Potentially reduced, as a portion of the medication is lost to systemic drainage. | Enhanced, as the medication is held on the ocular surface for better absorption. |
| Systemic Side Effects | Higher risk, especially with certain prescription drugs like beta-blockers. | Lower risk, as systemic absorption is significantly reduced. |
| Recommended For | OTC comfort drops where systemic absorption isn't a concern. | All medicated eye drops, especially prescriptions for serious conditions like glaucoma. |
What About the Safety of Ingested Eye Drops?
For most individuals using eye drops as directed, the small amount that drains into the throat is safe. However, there are important exceptions, particularly for certain OTC anti-redness eye drops containing decongestants like tetrahydrozoline. When swallowed, these can be toxic, causing symptoms such as low blood pressure, slowed heart rate, and sleepiness. This is especially dangerous for young children, and the FDA has issued warnings regarding accidental ingestion. Always store eye drops out of reach of children. For accidental ingestion of any eye drops, immediately contact a poison control center.
Conclusion
It is an anatomical fact of pharmacology that can eye drops go from eye to throat via the nasolacrimal duct. While the sensation of tasting a bitter or metallic flavor after using eye drops is common, it signifies that some of the medication is being absorbed systemically rather than locally. For OTC products, this is usually just an annoyance. However, for prescription medication, this can lead to reduced efficacy and potential side effects. By consistently practicing proper application techniques like punctal occlusion, patients can ensure they receive the full therapeutic benefit of their eye drops while minimizing any risk of systemic side effects.
For more detailed information on proper application, based on advice from the UCI Office of Undergraduate Admissions, consult your doctor or pharmacist.
