Scleral lenses are large-diameter gas permeable contact lenses that rest on the sclera, the white part of the eye. This design creates a fluid-filled reservoir that vaults completely over the sensitive corneal surface, benefiting those with conditions like keratoconus or severe dry eye. Despite the comfort and improved vision, a common and frustrating experience known as Midday Fogging (MFD) can occur. MFD causes the lens to become hazy or cloudy after several hours of wear, reducing visual clarity and often requiring temporary removal to restore sharp sight.
The Primary Causes of Scleral Lens Fogging
The root cause of scleral lens fogging is the accumulation of microscopic particulate matter within the fluid reservoir between the lens and the cornea. This debris is primarily composed of components from the eye’s natural tear film, including mucin, epithelial cells, and lipids. Tear film instability is a significant contributor, especially in wearers with underlying ocular surface conditions like Meibomian Gland Dysfunction (MGD) or chronic dry eye. These conditions introduce excessive oils and inflammatory components that migrate under the lens. A lens fit that is slightly too loose or features excessive peripheral edge lift can also exacerbate the issue by acting as a pump, drawing in contaminated tears and trapping them within the vault.
User-Controlled Strategies for Prevention and Clearing
Immediate Clearing and Solution Choice
Wearers can employ several preventative measures and immediate actions to manage midday fogging. The most direct response to MFD is to safely remove the lens, thoroughly rinse both surfaces, and then re-insert it with a fresh fill of solution. This process temporarily flushes the accumulated particulate matter from the reservoir, instantly restoring clear vision. The type of solution used to fill the lens before insertion can also influence the speed of debris accumulation. Experts often recommend using preservative-free saline solutions, or incorporating a high-viscosity, preservative-free artificial tear into the filling solution to help slow debris movement.
Hygiene and Insertion Technique
Careful attention to hygiene is beneficial in reducing the debris load. Before handling the lenses, hands should be washed with mild soap, and oil-based lotions or makeup should be avoided near the eyelids. Ensuring the internal surface of the lens is completely clean before adding the filling solution prevents the initial introduction of residue. Proper insertion technique is also important to prevent fogging caused by air bubbles trapped beneath the lens. The lens must be filled completely with solution and inserted without excessive tilting to avoid trapping air, which causes immediate and distinct blur.
When the Lens Fit Requires Professional Adjustment
Vault and Peripheral Adjustments
When midday fogging is persistent and requires repeated cleaning, it signals an underlying issue with the lens design that requires an eye care professional (ECP). The depth of the fluid reservoir, or the vault, is a critical parameter that influences debris accumulation. If the vault is excessively thick, it creates a larger space for particles to congregate, and the ECP may need to reduce this depth. The fit of the lens periphery, where the lens rests on the sclera, also plays a significant role in debris ingress. A peripheral edge that is too tight or too loose can allow contaminated tears to be pumped under the lens with every blink, so the ECP can adjust the peripheral curves to optimize the seal.
Advanced Modifications
In cases where standard adjustments are insufficient, the ECP may explore more advanced modifications to the lens design. This can include implementing a customized back surface design to achieve a more precise alignment with the eye. In rare instances, the ECP may consider adding a microscopic vent hole, or fenestration, to the lens. This vent facilitates a slow, controlled exchange of fluid, which can help flush out trapped debris. Addressing these structural fit issues requires specialized diagnostic equipment and professional expertise.