Contact lenses offer clear vision directly on the eye’s surface. They must be positioned correctly before insertion for both comfort and effective vision correction. An inverted lens causes discomfort and vision issues, but discerning the correct orientation can be challenging due to the lens’s thin, clear nature.
Visualizing the Correct Lens Orientation
A correctly positioned contact lens should resemble a smooth, perfect bowl or a gentle “U” shape when resting on a fingertip. When viewed from the side, the edges should curve softly upward without any outward flaring. This smooth, continuous curvature is engineered to match the natural dome of the cornea, allowing the lens to sit securely and comfortably on the eye.
Identifying the Inside-Out Lens
An improperly oriented lens will not maintain the ideal bowl shape, instead appearing like a shallow saucer or a rimmed plate. When the lens is inverted, the edges visibly flare outward, creating a noticeable lip around the circumference. This outward bend prevents the lens from conforming to the eye’s surface curvature. Flipping the lens disrupts its optical alignment, causing immediate discomfort upon insertion.
Practical Methods for Checking Orientation
To verify orientation, the “Taco Test” can be performed. Gently place the lens between the tips of your thumb and index finger, then lightly squeeze the sides together. If the lens is correctly oriented, the edges will meet cleanly and curve inward, forming a defined “taco” shape. If the lens is inside out, the edges will resist meeting and flare outward toward your fingertips.
Some contact lenses also include small laser-etched markings, often the numbers “123,” near the edge to aid in orientation. Hold the lens on your fingertip up to a bright light and look for these markings. If the numbers or letters read correctly from left to right, the lens is properly oriented. If they appear backward or inverted, the lens is inside out and needs to be flipped.
Immediate Effects of Improper Insertion
If a lens is inserted inside out, the wearer will typically feel immediate and distinct discomfort. This sensation often feels like something is scratching or rubbing against the eye, which is caused by the flared edge creating friction against the sensitive corneal surface. An inverted lens will not adhere properly to the cornea, leading to excessive movement or sliding across the eye’s surface, particularly when blinking. This unstable fit can also result in noticeably blurry or distorted vision, as the lens’s optics are not correctly positioned to focus light on the retina.