Gas-permeable contact lenses are a blessing to the many wearers who would not otherwise have adequate vision. But, they are not without flaws. These contact lenses may cause a number of corneal issues, the most common of which is probably 3/9 staining. The name derives from the location of the corneal staining in the peripheral cornea at the 3 o’clock and 9 o’clock positions.
3/9 staining is also known as peripheral corneal staining (PCS). Virtually all types of contact lens wear can cause this type of staining. Hydrogel lenses tend to produce less staining, while extended wear GP lenses may induce the most. This is why it is important to stain all corneas prior to beginning the fitting process. It must be noted that not all 3/9 staining is contact lens-related. Dry eye patients will frequently exhibit this type of staining, and obviously, staining that exists prior to lens fitting is not caused by contact lenses. Significant staining caused by dry eye syndrome should be cleared up before beginning the fitting process.
There are many products that can help to clear up staining caused by dry eye syndrome. I typically begin with the instillation of quality artificial tears a minimum of four times per day for a period of at least two weeks. If this is not successful in minimizing or eliminating the staining, I may insert punctal plugs and proceed to Restasis (Allergan), if necessary.
Which Dye is Best?
Corneal staining is most commonly graded on a zero to four scale. The following is how I learned to grade staining:
• Zero is no staining and no subjective symptoms.
• One is a few punctuate stains (less than 40) that are not coalesced; usually, there will be no symptoms.
• Two means mild amount of punctuate staining (greater than 40) that has not coalesced. Symptoms may include burning and/or dry sensations.
• Three means the punctuate staining has begun to coalesce, and the conjunctiva may become injected. The patient may decrease their wearing time.
• Four will have a large area of coalesced staining usually with conjunctival injection. Patients may be intolerant to their lenses, as well as complain of burning, itching and conjunctival injection. At this grade, the symptoms may be present even after the lenses are removed.
Sodium fluorescein is the most common stain used to evaluate corneal integrity. Fluorescein will not readily penetrate intact corneal cells; however, it will penetrate damaged corneal epithelial cells. Fluorescein staining is best viewed using cobalt blue light and a yellow Wratten filter. Remember to evaluate the cornea three to five minutes after instillation of the fluorescein dye, which allows the dye time to absorb into the affected cells. If you view the cornea immediately after dye instillation, you may overlook significant staining.
Potential GP Lens Causes
It is easy to determine that 3/9 corneal staining exists—the tough part is figuring out the cause or causes and solving the problem. Various GP lens parameters can be a factor in 3/9 corneal staining. These include: lens material; lens centration; peripheral curve system, which includes edge lift, thickness and profile as well as width and radius of intermediate and peripheral curves; lens wearing time; and lens-to-cornea relationship (i.e., sagittal depth of the lens).
Eliminate Staining For Successful Lens Wear
Not all peripheral corneal staining is dangerous, but it is never a good sign. It creates an avenue for bacteria to enter the cornea, which could lead to potentially serious infections, neovascularization and corneal scarring. This is why contact lens practitioners should make every attempt to discover and minimize or eliminate all corneal staining. Next month, I will review how various lens characteristics can induce peripheral corneal staining and suggest possible solutions to these problems.