Eye drops are a common medication for various eye conditions, from dryness and allergies to glaucoma. While applied locally, they can cause unexpected systemic side effects, including nausea. This is possible because the body absorbs the medication beyond the eye itself. This article explores the mechanisms behind this effect and provides guidance on managing such reactions.
How Eye Drops Can Cause Nausea
Despite being administered directly into the eye, active ingredients in eye drops can enter the bloodstream and affect other body systems, including the digestive system. This process is known as systemic absorption. The primary route for this absorption is through the nasolacrimal duct, often called the tear duct, which connects the eye to the nasal cavity.
Excess eye drop solution, not absorbed by the eye’s surface, flows through small openings in the eyelids (puncta) into this duct system. From the nasolacrimal duct, the medication drains into the back of the throat and is then swallowed. Once ingested, these active ingredients can bypass the liver’s initial filtering process, known as first-pass metabolism, allowing them to enter the bloodstream more rapidly and in higher concentrations than if taken orally.
The highly vascularized mucous membranes of the nasal cavity and throat also contribute to this systemic uptake. Studies indicate that topical ocular drugs can achieve systemic absorption rates ranging from 20% to 80%. Once in the bloodstream, certain drug compounds can interact with receptors or systems outside the eye, leading to side effects like nausea.
Specific Eye Drops Linked to Nausea
Certain types of eye drops are more commonly associated with systemic side effects, including nausea. Pilocarpine, often prescribed for glaucoma and some age-related vision problems, is known to frequently cause nausea as a side effect. This medication can also lead to vomiting, diarrhea, and increased sweating due to its effect on the parasympathetic nervous system. Nausea from pilocarpine can sometimes be reduced by taking the medication with food or adjusting the dosage.
Eye drops used to dilate pupils, such as atropine and cyclopentolate, can also induce nausea if absorbed systemically. Atropine ophthalmic drops may cause vomiting and giddiness if they enter the bloodstream. Cyclopentolate, another dilating agent, can also cause nausea and vomiting, particularly in sensitive individuals or children. These effects are linked to the medication’s anticholinergic properties. Additionally, some beta-blocker eye drops, used for glaucoma, can have significant systemic absorption, potentially leading to side effects like fatigue or a slow heart rate, though nausea is less frequently highlighted as a primary symptom.
Managing Nausea and When to Seek Help
Several practical steps can help minimize the systemic absorption of eye drops and reduce the likelihood of experiencing nausea. After applying eye drops, gently close your eyes for a few minutes and press a finger against the inner corner of your eye, near the nose. This technique, called nasolacrimal occlusion, helps block the tear duct, preventing the medication from draining into the throat and entering the bloodstream. Holding this pressure for one to five minutes can significantly reduce systemic absorption.
It is also important to use only one drop per eye, as the eye can only hold a limited volume, and excess drops are more likely to be systemically absorbed. If multiple eye drops are prescribed, wait at least five minutes between applications to prevent one drop from washing out the other and to allow for better absorption.
If nausea or other concerning symptoms occur, it is important to contact your eye care professional. Seek immediate medical attention if you experience severe or persistent nausea, vomiting, dizziness, or signs of an allergic reaction such as hives, swelling, or difficulty breathing.