Where should you place the lens?

Where should you place the lens?

• A. on conjunctiva
• B. on iris
• C. on cornea or inferotemporal scleral
• D. on the eyelid margin

Answer: (C)

The essential idea is that a contact lens must rest on the eye where the lens is designed to sit for proper vision and comfort. Soft contact lenses are intended to sit on the cornea, the smooth, curved front surface that provides the main refractive power. That positioning keeps the lens centered over the pupil and uses the tear film to help with oxygen delivery to the cornea. Some lens designs, like scleral or certain specialty fits, vault over the cornea and rest on the sclera (the white part of the eye). In these cases, the landing zone can be in a region such as the inferotemporal sclera, where the sclera provides a stable, non-tissular surface and helps minimize lid interaction. Placing a lens on the eyelid margin or directly on the iris would not be appropriate: the eyelid margin is not a stable, protective surface for a lens, and the iris would obstruct vision and cause distortion. The conjunctiva is a vascular, mobile surface that isn’t the intended bearing surface for a corrective lens. So, the correct placement is on the cornea, or on the sclera in the inferotemporal area for scleral-type designs.

The essential idea is that a contact lens must rest on the eye where the lens is designed to sit for proper vision and comfort. Soft contact lenses are intended to sit on the cornea, the smooth, curved front surface that provides the main refractive power. That positioning keeps the lens centered over the pupil and uses the tear film to help with oxygen delivery to the cornea.

Some lens designs, like scleral or certain specialty fits, vault over the cornea and rest on the sclera (the white part of the eye). In these cases, the landing zone can be in a region such as the inferotemporal sclera, where the sclera provides a stable, non-tissular surface and helps minimize lid interaction.

Placing a lens on the eyelid margin or directly on the iris would not be appropriate: the eyelid margin is not a stable, protective surface for a lens, and the iris would obstruct vision and cause distortion. The conjunctiva is a vascular, mobile surface that isn’t the intended bearing surface for a corrective lens.

So, the correct placement is on the cornea, or on the sclera in the inferotemporal area for scleral-type designs.