Why Do Scleral Lenses Get Foggy?

Why Do Scleral Lenses Get Foggy?

by Brian Chou, OD, FAAO, FSLS

  • September 4, 2020

Why do scleral lenses get foggy?  Scleral contact lenses can restore vision for keratoconus and other conditions where the front eye surface is not smooth.  But 25-50% of scleral lens wearers report their vision gets hazy, cloudy, or foggy.  If you are reading this article, you are probably experiencing these symptoms and seek a fix.  Resolution requires your eye doctor to correctly identify the cause. There are three major causes of these “midday fogging” symptoms.

Foggy due to white blood cells and debris

White blood cells (leukocytes) and tear debris can get in the tear fluid between the cornea and the scleral lens. The accumulated debris scatters light, causing foggy, cloudy, and hazy vision.  A study from 2019 found that fogging symptoms are more common with thicker tear volumes underneath scleral contact lenses.  Removing the scleral lens and then reapplying it with fresh non-preserved saline solves the problem, although only temporarily.  Frequent removal and reapplication multiple times a day is a burden and not practical.

To help, some practitioners advocate mixing a thick non-preserved artificial tear, like Refresh Celluvisc (Allergan), into the scleral lens to displace debris. Yet a more desirable and enduring answer involves an experienced scleral lens prescriber to reduce the amount of tear fluid between the cornea and contact lens.  It is important the tear volume is reduced in an unmeasured manner.  Otherwise, the lens may rub on the sensitive corneal surface leading to discomfort and related complications.  Accurate measurement requires use of an instrument called ocular coherence tomography (OCT), available to patients undergoing scleral lens prescribing at ReVision Optometry.  The practitioner can also reduce tears pumping and stagnating material underneath.  In other cases, a customized scleral shell made from an imprint of the eye can mitigate visual symptoms caused by debris accumulation.  All these strategies can minimize, but not always eliminate, midday fogging symptoms.

Foggy due to swelling of the cornea

Swelling of the cornea, or “corneal edema”, results when the cornea does not get enough oxygen to support its ability to pump fluid out and prevent swelling. This is more common in patients with a condition called Fuch’s endothelial corneal dystrophy and in eyes that have undergone corneal transplantation.  When the outer layer of the cornea swells up, the bubbled outer skin of the cornea, or epithelium, scatters light causing foggy, cloudy, and hazy vision.

Your eye doctor can reduce contact lens thickness, use a more oxygen-permeable material, and reduce the tear thickness underneath the lens.  Each of these factors can increase oxygen flux to the cornea, facilitating fluid removal from the cornea.  Unfortunately, foggy vision due to corneal edema does not go away with removal and rapid reapplication of the contact lens.  Instead, corneal edema usually takes 30 to 90 minutes for it to go away after contact lens removal.  Even a skilled scleral lens prescriber is not always able to eliminate corneal edema.

Foggy due to poor lens surface wettability

If fluid on the front of the scleral lens beads up like water on a newly waxed car, the vision can suffer.  Good vision requires that the tear fluid spreads out smoothly and evenly over the front lens surface.  Poor lens wetting causes foggy, cloudy, and hazy vision symptoms which fluctuates with blinking.  Some are particularly prone to poor lens surface wetting due to their unique tear chemistry.  In other cases, poor lens wetting is caused by accidentally getting an oily substance onto the lens such as lanolin.  Lanolin is in certain types of moisturizing lotion and soap.  Proper lens care tailored to your tear chemistry to help.  Special contact lens surface treatments like plasma treatment and Tangible Hydra-PEG, can solve wetting problems.  By default, all scleral lenses from ReVision Optometry come with a plasma treatment or Tangible Hydra-PEG, at no additional cost.


If you wear scleral contact lenses and experience foggy, cloudy, or hazy vision, request an appointment at ReVision Optometry today for proper diagnosis to set your best path to reclaim good vision.