“Pink Eye” can be due to various causes. The most common to the least common are listed below. When people say “I have ‘Pink Eye’, they generally mean the very contagious Viral version discussed below. 


1. Blepharitis due to Staphlococcus bacteria (which is most cases is the normal kind of bacteria naturally on our bodies) on eyelashes is the most common cause of a Red Eye/”Pink Eye”: this type of pink eye usually resolves in a couple of days if treated appropriately with lid hygiene, diluted tea tree oil. 
https://drcremers.com/2015/11/the-best-way-to-clean-your-face-and.html

If severe (or a more aggressive bacteria), or if patient wants a faster healing time, antibiotic (+/- steroid) ointment and drops are sometimes given. In the case below, the severe bacterial infection of they eyelids and lashes have caused a Staph Marginal Ulcer to form above the inflamed Panus or new blood vessels creeping onto the cornea. 

2. Blepharitis due to Demodex mites: this usually a non-dangerous, common organism that lives on our bodies from time to time. It can cause “pink eye,” though if on eyelashes or burrowing into the meibomian gland orifices at the base of the eyelashes. This usually resolves in less than a week with proper lid hygiene with warm compresses and diluted tea tree oil.  

3. Contact Lens Overwear: too little oxygen getting to the cornea can cause a “pink eye” effect. This resolves usually within a few hours to days if not severe once the contact lens is removed and re-fitted for a higher oxygen permeable type or daily disposable type. 

4. Viral Conjunctivitis: “True pink eye” generally refers to a Pink Eye from a Virus. This is very common especially among children who have a little cough due to a virus but then contaminate their eyes with their hands.


A virus can stick around in the eye for weeks depending on a patient’s immune system and/or if patient has been using steroid drops or pills to help decrease symptoms.


Most often Viral Conjunctivitis lasts 2 weeks.
However, a more dangerous virus 


However, a more nasty version due to adenovirus serotypes 8, 19, 37 can cause Epidemic Keratoconjunctivitis which can last for weeks and can cause debilitating scars on the cornea and conjunctiva that can last for years.


5. Severe Dry Eye: such as in patients with severe Sjogren’s syndrome or Rheumatoid Arthritis or Lupus can cause severe eye redness.


6. Iritis or Uveitis: inflammation inside the eye can cause redness. Iritis can be due to:
a. Blunt trauma to they eye.
b. Nontraumatic iritis can be due to:
  i. Non-infectious causes:
1) Ankyosing Spondylitis
2) Reiter syndrome, 
3) Sarcoidosis
4) Inflammatory bowel disease, 
5) Psoriasis
6) Tight contact lens
  ii. Infectious Causes: 
1) Lyme disease, 
2) Herpes Simplex
3) Herpes Zoster
4) Toxoplasmosis,
5) Tuberculosis,
6) Syphilis
7) Other rarer infections bacteria or viruses

More on Demodex Blepharitis:

DEMODEX BLEPHARITIS

There remains a great deal of controversy in treating Demodex only for the fact that there are not many randomized, double blinded controlled trials on how best to treat Demodex that are not written or sponsored by someone who has a financial interest in the treatment options (ie, Tea Tree Oil works, but a key author in most of the Demodex Blepharitis papers has a company that makes Tea Tree Oil towelettes: they work but many eyeMDs remain suspicious).

Also it is not clear if all sheets have to be cleaned, all make up has to be thrown out: they likely just come right back in patients that are susceptible to them such as patients with Rosacea. 

A recent journal article noted a variety of pathologic features together with conjunctival inflammation can be found in patients with Demodex infestation of the eyelids. These same kinds of pathologies are commonly found in ocular rosacea, said Scheffer C.G. Tseng, M.D., director of the Ocular Surface Center and medical director, Ocular Surface Research & Education Foundation at TissueTech, Miami. “When conventional treatments for rosacea fail, tea tree oil lid scrubs seem to eradicate the mites,” Dr. Tseng said. “In any type of ocular inflammation where the condition is refractory, doctors need to consider Demodex as a causative agent,” he said. “For instance, recurrent pterygia may be the result of an inflammatory disease, and it may be Demodex that hasn’t been well treated. That would explain the pterygia’s recurrence.”

Demodex tails around the root of the lash

Demodex

Demodex head close-up

Identifying symptoms of Demodex

Symptoms can vary per patient but the most common symptoms are:

1. Foreign body sensation especially in the morning

2. Itching and early morning itching specifically.

3. Early morning itching and irritation is common with these mites because of their aversion to light, Dr. Safran said. 

4. Crusting of eyelashes/eyelids especially in the morning.

5. Burning of eyes during day

6. Redness

7. Tearing chronically.

8. Poor response to anti-allergy drops

Tea tree oil treatment

1. Use 50% Tea Tree Oil from Trader Joes, Amazon, local Healthfood store:

a. Dilute TTO to 50% in Macadamia nut oil, Coconut Oil or Water. 

b. Use a cuetip or tip of clean towel to aggressively try to get the oil into the lash roots and along the lashes to kill any eggs: cuetip should be moist enough to see oil getting onto the skin when touched. 

c. Treat eyebrows also if a very severe case or symptoms not improving in a couple of days when only eyelashes are treated. Depending on the severity of the case, some patients need to use tea tree shampoo for the hair and eye lashes every day and use tea tree soap or face wash every day.

d. For severe cases, I usually give Tobradex (tobramycin 0.3% and dexamethasone 0.1% sterile ophthalmic suspension and ointment, Alcon) till tube runs out and replace it with bacitracin or erythromycin after one-two weeks depending on severity, to suffocate mites at night when they usually reproduce. 

e. You can treat the brow first, then the lid to get rid of the excess oil 

f. Some MD offices will do applications at a visit: about 10 minutes apart, and then finish with a tea tree ointment at 20%, which has to be ordered from a compounding pharmacy.

g. Full strength tea tree oil can burn terribly even if it does fully enter into the eye. Avoid.

• h. For women: consider throwing out makeup and not use any new makeup for a week: this depends on severity. I have had many patients that used the Tea Tree Oil every day & did not need to throw out their make up. If you are not improving though, throw it out & avoid make up for a week.
• 
  
• i. Some patients do not need to buy new pillows & sheets. If not improving, though, buy new bedding.
• 
  
• j. Have your spouse checked if also having symptoms. 
• k. Have any pets that sleep on the bed checked
• for the first few weeks, patients should use tea tree ointment at night after the shampoo scrub at home

Other Options:

BlephClean From http://www.eyeworld.org/article.php?sid=4381

Note: Demodex come out at night and mate, lay their eggs on the lashes, and then crawl back into the follicle in the morning, causing the patient to itch.

BlephClean: In-Office Lid Hygiene BlephClean is a painless in-office procedure performed by your eyecare professional. A revolving handpiece is used to carefully spin a cotton tip along the edge of your eyelids and lashes, removing scurf and debris and exfoliating your eyelids. The soaked cotton-tip is disposable and a clean one is used for each individual eyelid The procedure lasts about 5 minutes and is well tolerated. Most patients simply report a vibration sensation. A freezing drop is usually placed in each eye prior to treatment for increased comfort. After the procedure, the patient is instructed on how to maintain their clean eyelids with regular twice daily lid hygiene. The procedure is typically repeated at 3-6 month intervals. More frquently if needed due to the collection of the debris again. Demodex usually needs this treatment every week for 3 week using tea-tree oil (TTO) to control the demodex infestation.

“If there’s a lot of inflammation, I like Tobradex (tobramycin 0.3% and dexamethasone 0.1% sterile ophthalmic suspension and ointment, Alcon) that’s replaced by bacitracin or erythromycin after one week,” Dr. Safran said. Anecdotal stories from Dr. Safran’s patients indicate that upon presentation, on a scale of 1 to 10, most patients stated, “Red eyes are associated with not feeling well, lack of sleep, those sorts of things. When their eyes burn and are red, patients are very aware of it. After they have the tea tree oil treatment, patients’ scores go from a 9 to a 2, or an 8 to a 1.” Surprising asides “A surprising finding was that once we got rid of the mites, some patients’ vision improved,” Dr. Tseng said. “Originally we thought this was a coincidence. Because mites affect the oil glands, the tear film is not doing well. If the tear film is unstable, it will cause a blur when the eye opens quickly. Once the mites are gone, the tear film stabilizes, and the vision improves.” He did note that not all patients’ vision will improve; the fact that some did was a pleasant surprise. “The tea tree oil is probably not the last word on killing [Demodex], but it’s better than anything else we have right now,” Dr. Safran said.

From http://www.eyeworld.org/article.php?sid=4381