Unilateral contact lens discomfort (CLD) occurs when a contact lens feels irritating, scratchy, or uncomfortable in only one eye. This localized irritation suggests the cause is not systemic, such as general tear film quality or widespread environmental allergens, but rather a problem affecting the lens or the surface of that single eye. Pinpointing the source often involves examining three categories: issues with the lens itself, the introduction of external debris, or a pre-existing physiological condition unique to that eye.
Lens Integrity and Fit Problems
The physical properties of the contact lens in the uncomfortable eye can be the direct source of irritation. Microscopic damage, such as a small tear, chip, or rough edge, causes persistent friction against the corneal or conjunctival tissue. This structural compromise often results from improper handling or damage within the lens case, leading to a sharp, localized scratchiness.
Surface deposits are another common issue, often occurring unevenly between the two lenses. Proteins, lipids, and calcium from the tear film adhere to the lens surface, creating a rough texture that cleaning solutions may not fully remove. This buildup reduces the lens’s wettability, leading to dryness and a gritty feeling that intensifies with blinking.
Discomfort can also stem from an incorrect lens fit, as eyes are rarely symmetrical. The lens base curve must closely match the cornea’s shape. A lens that is too steep fits too tightly, restricting tear and oxygen exchange, which causes irritation and redness. Conversely, a lens that is too flat moves excessively, causing constant awareness and unstable vision. The lens may also be inside-out, causing the edges to flare out and rub against the eye until it is properly flipped.
External Contaminants and Handling Issues
Transient irritants introduced during handling or from the environment frequently explain why discomfort appears suddenly in only one eye. A common scenario involves a foreign body, such as a speck of dust, an eyelash, or a fiber, becoming trapped between the lens and the cornea. The lens presses the particulate matter against the eye, causing acute pain or a persistent foreign body sensation until the lens is removed and cleaned.
Chemical contamination is another source of localized irritation, often traced back to residue on the hands or in the storage case. Handling the lens after using soap, lotion, or perfume can transfer trace chemicals that sting or burn the eye upon insertion. Similarly, an incomplete rinse after cleaning with a hydrogen peroxide solution can leave residual peroxide, causing an immediate burning sensation in the affected eye.
Environmental factors can also contribute to unilateral discomfort. Localized exposure to irritants, such as smoke, wind, or harsh air conditioning blowing directly on one side of the face, can cause one lens to dry out more quickly. This desiccation makes the lens adhere more firmly to the eye, reducing its smooth movement and resulting in dryness and friction confined to the exposed eye.
Underlying Eye Health Conditions
Sometimes, the lens itself is not the problem, but rather a change in the eye that makes it intolerant to lens wear. Dry eye syndrome can present asymmetrically, where the tear film in one eye is less stable due to factors like meibomian gland dysfunction or uneven tear production. This localized dryness causes the lens to lose moisture and frictionally irritate the ocular surface, resulting in unilateral discomfort.
A physical injury to the corneal surface is another frequent cause of acute, one-sided pain. A corneal abrasion, which is a scratch on the cornea’s outer layer, can occur during rough lens insertion or removal, or from debris trapped under the lens. This damage leaves the nerve endings exposed, causing severe pain and light sensitivity in the affected eye.
The onset of an infection or inflammation can also begin in a single eye, making lens wear painful. Early-stage infectious keratitis, often linked to poor lens hygiene, or a localized case of conjunctivitis may cause inflammation, redness, and a gritty feeling before becoming bilateral. Allergic reactions, such as Giant Papillary Conjunctivitis (GPC), can sometimes affect one eye more severely due to a hypersensitivity reaction to lens deposits or the lens material itself.
Urgent Symptoms Requiring Professional Care
Certain symptoms signal a deeper issue requiring immediate attention from an eye care professional, necessitating the removal of the contact lens and a cease of wear. These indicators suggest a serious condition, such as a severe infection or deep corneal injury, that poses a threat to vision.
Seek prompt consultation if you experience any of the following symptoms:
- Sudden, severe, or escalating eye pain that persists after removing the lens.
- Significant, dense redness in the white of the eye that does not subside.
- A noticeable decrease in vision that remains blurred even when wearing glasses.
- Sensitivity to light (photophobia), especially when accompanied by pain.
- Unusual discharge, swelling of the eyelids, or the appearance of a white or gray spot on the cornea.