Wednesday, April 10, 2019

itchy allergy eyes

Photo by Jeremy Gilchrist, capturing the yellowish-green cloud of pine pollen in Durham, NC

Spring has sprung here in North Carolina, and, as you can see in the photo, we're in the thick of Pollenpocalypse. This is around the time of year that I start to see a large influx of patients with red, watery, itchy eyes. The tree and grass pollen that come with spring can often cause allergies to flare, and the eyes are a common site for such allergic reactions.

What is allergic conjunctivitis?
Allergic conjunctivitis is inflammation (-itis) of the eye (specifically, the conjunctiva) caused by an allergic reaction. Probably didn't need me to figure that one out, right? The sequence of events that occur, in a nutshell (1):
  1. The surface of the eye is exposed to an allergen (pollen, animal dander, ragweed, etc).
  2. The immune system responds by producing immunoglobulin E (IgE), which binds to mast cells. Mast cells are found on the conjunctiva, which is the transparent tissue covering the white part of the eye as well as the inner eyelids.
  3. This causes the mast cell to degranulate and release chemical mediators, one of which is histamine.
  4. Histamine binds to receptors on cells in the conjunctiva, which causes itching, redness, tearing, and swelling.
  5. Allergy eyedrops work by stabilizing the mast cells and/or binding to the histamine receptors (thus blocking histamine from binding), which interrupts the cycle and reduces the allergic response. 

Are there different forms of allergic conjunctivitis?
Yes, though it may be more of a spectrum of inflammation rather than distinct entities. The most common forms of allergic conjunctivitis (seasonal or perennial allergic conjunctivitis) are type 1 hypersensitivity reactions, and generally only exhibit what's referred to as the early phase response. This involves the acute symptoms of itching, redness, tearing, swelling, etc. The more chronic types of inflammation (vernal or atopic keratoconjunctivitis) are thought to have both type 1 and type IV hypersensitivity reactions, exhibiting the late phase response that often comes with tissue damage (2).

What should I use to get rid of my allergic conjunctivitis?
First, I would discourage the use of any "redness relief" drops; more on why in this previous blog post. You want to treat the cause, not just mask a symptom.

My go-to over-the-counter recommendation would be ketotifen fumerate (available generic and branded as Alaway, Zaditor, etc). Ketotifen is an H1-receptor antagonist (aka antihistamine) and a mast cell stabilizer, meaning it prevents the release of histamine and other mediators from mast cells. Translation: less itching and redness and swelling! This drug is dosed 1 drop in each eye twice a day as needed. You should instill the drop without contact lenses, and wait about 10 minutes before putting the contacts in. Ketotifen is approved for children age 3 and up.

It's not a bad idea to keep allergy eyedrops in the refrigerator; the cooling effect upon use can help sooth the inflamed ocular surface.

This may be all you need in mild cases of acute allergic conjunctivitis. But if your symptoms continue or worsen, make an appointment to see your eye doctor ASAP! There are numerous prescription options to pursue, from anti-histamines to steroids, depending on the level of inflammation present. There are a handful of prescription medications that are approved for children as young as 2, as well as options for convenient once-a-day dosing.

There's also the chance that what you suspect are allergies could be something else, or a combination of multiple things (dry eye, uveitis, infection, contact lens complications- the list goes on). For instance, oral antihistamines frequently taken for allergies can dry the eye, which can cause further inflammation of the ocular surface. Our tears are helpful for flushing away allergens, so dry eyes can make allergic conjunctivitis symptoms worse. It's a bit of a catch 22, but your eye doctor can devise an effective treatment strategy. Something as simple as switching to daily disposable contact lenses can help alleviate your symptoms considerably. When in doubt, see an optometrist!

--> CliffsNotes: If your eyes are itchy, watery, and red, you may have allergic conjunctivitis. There are effective over-the-counter options (like Alaway or Zaditor) as well as many prescription options. See your optometrist to make sure what you're experiencing is in fact allergic conjunctivitis, and discuss what treatment option is best for you.