Sodium chloride eye drops are an over-the-counter ophthalmic product formulated as a hypertonic saline solution, meaning they contain a higher-than-normal concentration of salt. These drops are designed to address the collection of excess fluid within the cornea, the clear, dome-shaped front surface of the eye. By introducing a concentrated salt environment, these drops temporarily help restore the proper fluid balance.
How Sodium Chloride Eye Drops Work
The effectiveness of these drops relies on osmosis, the natural process where water moves across a semipermeable membrane, like the corneal tissue. Water moves from an area of lower solute concentration to an area of higher solute concentration. The typical concentration of sodium chloride in these drops is either 2% or 5%, significantly higher than the natural salt level within the eye’s fluids.
When the hypertonic drops are applied, they create a strong osmotic gradient. This gradient pulls excess water molecules out of the swollen corneal tissue and into the tear film on the eye’s surface.
This extraction reduces the overall fluid volume in the cornea, shrinking the tissue and clarifying the front of the eye. The water drawn out mixes with the tear film and is flushed away with normal blinking. The mechanism is purely physical, using concentration differences to achieve a therapeutic effect.
Treating Corneal Swelling
The primary application for sodium chloride eye drops is the temporary management of corneal edema, the medical term for swelling of the cornea. This swelling occurs when endothelial cells, which maintain the cornea’s fluid balance, are damaged or fail to function correctly. When these cells fail, fluid accumulates, causing the clear corneal tissue to become hazy or cloudy.
This haziness affects vision, causing blurring, decreased sharpness, and the appearance of halos or rainbow rings around light sources, especially at night. The drops are used for conditions causing chronic endothelial dysfunction, such as Fuch’s dystrophy, or following eye surgeries like cataract removal, which can cause short-term post-operative edema.
By drawing out the fluid, the hypertonic solution temporarily reverses the swelling, improving visual acuity and reducing symptoms like cloudiness and halos. The drops manage the physical symptom of fluid retention but do not correct the underlying eye condition. The 5% concentration solution or ointment is often prescribed for more pronounced swelling due to its increased osmotic strength.
Safe Use and Application Guidelines
Sodium chloride eye drops are available in solution (typically used during the day) and ointment forms (often reserved for overnight application). To maintain sterility, users must wash their hands thoroughly before application and avoid touching the dropper tip to any surface, including the eye. One or two drops are placed into the pocket created by pulling down the lower eyelid, followed by gently closing the eye for a minute or two.
The high salt content can cause a temporary stinging or burning sensation immediately after use, which is a common side effect. If using the drops alongside other ophthalmic medications, observe a waiting period of at least five to ten minutes between applications. This prevents the sodium chloride from washing out the other medication.
Patients who wear soft contact lenses must remove them before applying the drops, as the lens material can absorb the salt, leading to irritation or damage. Wait at least 15 minutes after instillation before reinserting the contacts. If severe eye pain, changes in vision, or if swelling and redness persist or worsen for more than three days, stop use and immediately consult an eye care professional.