treatment plan
Dellen and Dimple Veiling
BY TIMOTHY T. MCMAHON, OD, FAAO

Are dellen and dimple veiling the same thing? Nope. One condition is caused by desiccation as well as some additional factors, while the other is mechanically induced.

Dellen

Dellen represent a characteristic phenomenon involving the cornea. Clinical features include a round or oval depression in the cornea, typically located in the periphery or mid periphery. Fluorescein pools in the depression, and at times there is overlying staining. The epithelium within the depression can be either clear or opalescent in appearance.

Dellen with contact lenses. Courtesy The University of Illinois at Chicago Department of Ophthalmology & Visual Sciences

Dellen are caused by a cascade of events, incited by a focal absence of the mucin layer over the epithelium. This is caused by an obstruction that prevents the eyelid (or equivalent) from wiping over an area of the cornea. The corneal epithelium is hydrophobic and, in the absence of mucin, will repel water and produce a dry spot. The dry epithelial surface then allows for a local deturgesence of the underlying anterior stroma, giving the appearance of corneal thinning. Over time the overlying epithelium erodes and leaves a defect.

Dellen are found with rigid contact lenses (rarely) when the region adjacent to the contact lens edge is not wiped by either the eyelid due to a potential space forming or because the lens fails to translate laterally. This process is equivalent to the causes of 3 and 9 o'clock staining and secondary peripheral inflammatory responses in rigid contact lens wearers. In these two cases, the problem is diffuse, whereas dellen are local.

Treatment involves re-establishing the normal mucin layer and a hydrophilic surface. Once this happens, the epithelium repairs itself, and the stroma swells to normal proportions again. If the epithelium is intact, this process can occur within hours. In rigid lens wearers, thinning the edge taper is important. Also, it is usually better to increase the size of the lens rather than decrease it. If the lens is made smaller, often dellen move more centrally rather than disappear.

	Dimple veiling in an RGP lens. Note the bubble at the bottom of the lens

Dimple Veiling

Dimple veiling is a different animal. This phenomena occurs in rigid contact lens wearers almost exclusively. Due to the fitting relationship, in some eyes small bubbles form at the lens edge (frothing), get sucked under the lens and land under the base curve. These small bubbles are then mechanically compressed by the lens and indent the corneal epithelium. The compression produces a transient depression or divot. These divots and bubbles, if sufficient in number, will interfere with vision, producing glare, hazy vision and a loss of contrast sensitivity.

In my experience, I see this most often in eyes with corneal transplants. Removing the lenses for a few hours leads to resolution of the dimple veiling and the associated symptoms. Longer term, the treatment of choice is to decrease the optical zone size. Adjusting this parameter has worked the best for me.

Dr. McMahon is a professor and Director of the Contact Lens Service at the University of Illinois at Chicago Dept. of Ophthalmology & Visual Sciences.