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.

Monday, January 28, 2019

get the red out

How do "redness relief" eye drops work?

Short answer: "Redness relief" drops contain an ingredient that causes the superficial blood vessels of the eye to constrict, or narrow

Long answer: Brace yourself- it's about to get real nerdy up in here. Our blood vessel walls are made up of smooth muscle tissue. There are receptors in that smooth muscle tissue called alpha-adrenergic receptors. These receptors are activated by alpha-adrenergic agonists, which are agents that essentially stimulate the sympathetic (ie: fight or flight) response in the blood vessels. So when an alpha-adrenergic agonist binds to these receptors, it causes the muscle to contract, which constricts the blood vessels

Vascular smooth muscle has two types of alpha-adrenergic receptors: alpha 1 and alpha 2. The active ingredients in many of the redness relief drops on the market work by affecting only alpha 1 receptors, or both alpha 1 and alpha 2 receptors. File that away in your mind; we'll return to that shortly. Some common examples of drugs that behave this way: phenylephrine and tetrahydrozoline (alpha 1 only), and naphazoline and oxymetazoline (alpha 1 and alpha 2) (1). These are the ingredients commonly found in over-the-counter "redness relief" eye drops.

What is the active "redness-relieving" ingredient in some common eyedrops?

  • Naphcon-A (Alcon): Naphazoline hydrochloride 0.025%
  • Visine
    • Visine Original Redness Relief: Tetrahydrozoline hydrochloride 0.05%
    • Visine Advanced Redness and Irritation Relief: Tetrahydrozoline hydrochloride 0.05%
    • Visine Maximum Strength Redness Relief: Tetrahydrozoline hydrochloride 0.05%
    • Visine Totality: Tetrahydrozoline hydrochloride 0.05%
    • Visine AC Ultra Itchy Eye Relief: Tetrahydrozoline hydrochloride 0.05%
    • Visine A Multi-Action Eye Allergy Relief: Naphazoline hydrochloride 0.025%
  • Rohto
    • Rohto Digi Eye: Tetrahydrozoline hydrochloride 0.05%
    • Rohto Ice: Tetrahydrozoline hydrochloride 0.05%
    • Rohto Cool: Naphazoline hydrochloride 0.012% 
    • Rohto Cool Max: Naphazoline hydrochloride 0.03%
  • Clear Eyes
    • Clear Eyes Redness Relief: Naphazoline hydrochloride 0.012%
    • Clear Eyes Maximum Itchy Eye Relief: Naphazoline hydrochloride 0.012% 
    • Clear Eyes Cooling Comfort Itchy Eye: Naphazoline hydrochloride 0.012%
    • Clear Eyes Complete 7 Symptom Relief: Naphazoline hydrochloride 0.025%
    • Clear Eyes Maximum Redness Relief: Naphazoline hydrochloride 0.03% 
    • Clear Eyes Cooling Comfort Redness Relief: Naphazoline hydrochloride 0.03%
    • Clear Eyes Triple Action: Tetrahydrozoline hydrochloride 0.05%
    • Clear Eyes Traveler's Eye Relief: Tetrahydrozoline hydrochloride 0.05% 
    • Clear Eyes Pure Relief Multi-Symptom: Phenylephrine hydrochloride 0.10%
  • Bausch and Lomb
    • Opcon-ANaphazoline hydrochloride 0.02675%
    • B&L Advanced Eye Relief Redness Reliever: Naphazoline hydrochloride 0.012%
    • B&L Advanced Eye Relief Maximum Redness Reliever: Naphazoline hydrochloride 0.03%
    • Lumify Redness Reliever: Brimonidine tartrate 0.025%

I personally do not recommend the majority of these redness relief drops. Why not?

Drops that affect alpha 1 receptors can lead to rebound hyperemia (translation: eyes become more red when you stop using the drop), and tachyphylaxis (translation: loss of effectiveness over time). 

Arteries carry oxygenated blood away from the heart to the body's tissues. Since alpha 1 receptors are predominantly in arteries, the drugs that act on these receptors cause constriction of the arteries, which decreases blood flow and thus oxygen flow to the tissue. Over time, the body adjusts to this lack of oxygen by down-regulating, or producing less of, the alpha 1 receptors. So this lessens the body's response to the drop (tachyphylaxis). With loss of effectiveness comes more frequent use, and more frequent use can possibly lead to toxicity from the preservatives in the drop (2). Overusing these drops can even cause your pupils to dilate!

When the drop is discontinued after a long period of use, the body's attempt to deliver more oxygen to the oxygen-deprived eye tissue is to dilate the blood vessels, which makes the eyes appear redder (rebound hyperemia). This can then cause a person to return to using the eye drop, and the vicious cycle goes on. 

What is Lumify?

Lumify is an over-the-counter eye drop that has been FDA approved for the relief of ocular redness due to minor eye irritations. It is approved for age 5 and older, begins working within 1 minute of instillation, and provides up to 8 hours of redness relief. 

The active ingredient in Lumify is brimonidine tartrate (0.025%). Brimonidine tartrate (in higher concentrations) has long been used as a medication to lower eye pressure. It is also used in ocular surgery to control bleeding. In gel form, it is used to treat facial redness due to rosacae in adults. 

How is Lumify different than all of the other redness relief drops out there?

Brimonidine tartrate is a selective alpha-2 adrenergic receptor agonist. Recall that all of the other drops mentioned above work on either alpha 1 only or both alpha 1 and alpha 2. Because of Lumify's selectivity, its effect is primarily on the veins and not the arteries. Thus, Lumify does not have as significant of an effect on oxygen flow, which reduces the oxygen-deprivation that triggers those negative side effects. In Phase 3 clinical trials, Lumify showed no evidence of tachyphylaxis and minimal rebound hyperemia (3)

But WHY are your eyes red?

There are numerous conditions/factors that can make eyes red: dryness, allergies, contact lens overwear, uveitis, infection, foreign body, exposure to smoke or other irritants, fatigue, etc. Don't just buy a drop to mask the symptom; see an optometrist to determine and address the source.

--> CliffsNotes: Redness relief drops can have unwanted side effects, so I don't recommend frequent use of drops like Visine, Clear Eyes, Rohto, etc. Lumify's unique mechanism of action avoids these unwanted side effects. If your eyes are red, it's best to start by seeing your optometrist to figure out why they're red.

*Dr. H has no financial interests in any of the products mentioned*