Scleral lenses are large-diameter contact lenses designed to vault entirely over the cornea, resting instead on the white part of the eye, known as the sclera. This design creates a fluid-filled space, or tear reservoir, between the back surface of the lens and the front of the eye, which helps correct vision and provides therapeutic moisture. A common frustration for wearers is “Midday Fogging” (MFD), where vision becomes hazy or cloudy after several hours of wear. This visual blur affects up to 30% of scleral lens users and typically requires immediate intervention to restore clear vision. This article explores the mechanisms behind this clouding, the steps for immediate relief, and strategies for preventing its recurrence.
Identifying the Cause of Midday Fogging
Midday fogging is caused by the accumulation of particulate matter within the tear reservoir between the lens and the cornea. Under normal circumstances, the natural blinking process helps mechanically remove sloughed-off epithelial cells and other debris from the ocular surface. However, the scleral lens acts as a barrier, preventing normal tear exchange and debris clearance, leading to a build-up of waste materials.
The debris often consists of fine, white particulate matter, including sloughed corneal epithelial cells and inflammatory cells like neutrophils. Other components frequently found are mucin, a cloudy, gelatinous material from the tears, and lipids or meibomian oil droplets, which appear as yellowish or brown deposits from the eyelids. The presence of these materials suggests that fogging is often tied to an inflammatory response, especially in patients with pre-existing conditions like severe dry eye, blepharitis, or ocular allergies.
A poor lens fit can also contribute significantly to this issue, particularly if the lens does not conform properly to the scleral surface. If the edge of the lens, known as the haptic or landing zone, has excessive lift, it can allow a greater flow of debris-laden tears from the outer eye to enter the reservoir. Conversely, a lens that is too tight can create a suction effect, which may irritate the conjunctiva and generate more debris. This accumulation, trapped by the closed-system nature of the lens, ultimately leads to hazy vision.
Immediate Steps to Clear Fogging
When vision suddenly becomes hazy due to fogging, the only reliable immediate solution is to remove the lens, clean it thoroughly, and reapply it with fresh solution. The process begins with carefully removing the lens using the prescribed suction device and inspecting the front surface for any protein or lipid deposits. If deposits are visible on the outside, gently rub the lens with a recommended daily cleaner before rinsing it completely with sterile, preservative-free saline.
The next step is to completely empty the lens bowl and refill it with a fresh, preservative-free saline solution. To help slow the recurrence of fogging, some wearers may benefit from adding a few drops of a high-viscosity, preservative-free artificial tear drop into the bowl before topping it off with saline. Products like single-use vials of carboxymethylcellulose or similar ingredients can create a more viscous fluid that acts as a temporary barrier against debris inflow.
Once the lens is filled, it must be reinserted promptly, paying careful attention to proper technique to prevent air bubbles from being trapped beneath the lens. A trapped bubble can cause immediate discomfort and vision blur that mimics fogging. This process of removal, cleaning, refilling, and reinsertion (RRR) provides immediate clarity by physically flushing the accumulated debris from the reservoir. Wearers should always carry their lens removal and reinsertion supplies with them to manage unexpected fogging episodes.
Preventative Strategies and Long-Term Care
For long-term management, the most significant preventative strategy involves a professional evaluation of the lens fit by the prescribing eye care specialist. Minor adjustments to the fit can significantly reduce the problem, as poor alignment is often a primary contributor to fogging. The doctor may modify the peripheral edge lift or haptic design to better align with the scleral contour, which minimizes the amount of debris-laden tear fluid flowing into the reservoir.
Another effective long-term strategy is to change the lens cleaning and disinfection regimen. Switching from a multipurpose solution to a hydrogen peroxide-based cleaning system is often recommended, as it provides a deep, preservative-free clean that can better manage protein and lipid build-up on the lens surface. For heavy depositors, the doctor may suggest using an enzymatic cleaner, such as Menicon Progent, for bi-weekly deep cleaning to break down stubborn deposits.
Addressing underlying ocular surface disease is a preventative measure that reduces the source of the debris. Conditions like meibomian gland dysfunction (MGD), blepharitis, or ocular allergies increase inflammation and the production of debris and oils that feed into the tear reservoir. Treating these with prescribed drops, eyelid hygiene routines, or targeted therapies can significantly decrease the frequency and severity of midday fogging. Some patients also find that changing the type of filling solution, perhaps from an unbuffered to a buffered saline, may help minimize epithelial cell sloughing and reduce fogging.