No Filter?

Let’s revisit the use of an often overlooked and helpful tool

Ask a crowd full of optometrists whether they use vital dyes to evaluate the health of the ocular surface, and almost every hand will shoot up in affirmation. Ask the same crowd about their use of other dyes, such as lissamine green and Rose bengal, and fewer hands go up, appearing in a half-hearted fashion as if to say, “sometimes, but not always.”

Anyone who knows me professionally knows I appreciate lissamine green’s capacity to reveal dry eye disease (DED) early by highlighting conjunctival defects. But, for those who are stalwart supporters of sodium fluorescein, I recommend using a Wratten filter to optimize your view of the ocular surface.


While some contact lens fitters regularly use a Wratten filter, many of us haven’t laid hands on one since a lab session in optometry school. I was one of these folks, until I had a conversation with Mike Christensen, O.D., Ph.D., F.A.A.O., a professor at Southern College of Optometry.

Dr. Christensen knew I had a special interest in DED, so we spent a lot of time talking about the disease and all the nuances that go along with its diagnosis. What he said changed the way I looked at my DED suspects.

Specifically, he said, “If you see a great photo in a journal, the odds are a Wratten 12 filter was used to take the picture.” Not long after that conversation, he brought a filter to my dry eye clinic, and I couldn’t believe the difference in the staining pattern detail. While I struggled to see conjunctival staining with fluorescein and the cobalt filter alone, when paired with the yellow Wratten filter, it popped.

Mike Christensen, O.D., Ph.D., and director of Research at Southern College of Optometry, in Memphis.
Photo courtesy of Ramon Gomez.


Wratten 12 and 15 are standard barrier filters that provide a deep yellow or orange color. They work by eliminating all the reflected blue light. Many new slit lamps feature a Wratten filter, but they also can be added to existing slit lamps manually and provide the same effect. The filter can aid in the early diagnosis of ocular surface disease, and it may help with staining related to contact lenses and solutions and RGP fluorescein patters.

My suggestions for using a Wratten filter:

  • Instill NaFL dye, and select the cobalt blue filter to view the cornea through the slit lamp.
  • Place a Wratten 12 filter over the slit lamp light source.
  • Watch the image take on a brighter, crisper view.


Often in DED, doctors find there is a discordance between signs and symptoms. They see patients who complain of irritation, epiphora and foreign body sensation without any significant clinical signs to corroborate their feelings. Those patients are often at risk for being dismissed by their optometrists.

Let’s consider that the disease’s signs may be present, but practitioners are unable to identify the subtle corneal defects. With the use of a simple filter, O.D.s may be able to connect the dots for their patients and nail the diagnosis.

Dr. Christensen changed the way I practice in a small, but meaningful, way. Sometimes, it’s the little things that make the biggest impact on our patients and our practices. OM