Red Eye – 1

Simplest of complaints to evaluate in a primary care setting, since the main goal is to decide who needs to see an ophthalmologist & who doesn’t.  And that can be summed up in one word…

OW !!!  i.e., PAIN.  Painful red eyes are caused by a variety of sight-threatening conditions, some of which require truly emergent attention.  But just don’t send anyone to an E.D. without phoning first, because if there’s no ophthalmologist on-call, the patient will have traveled from Square 1 to Square 0.

Acute Visual Impairment is another parameter requiring urgent ophthalmologic attention.  But for now, let’s eyeball our differential for the non-traumatic Red Eye.


No Eye Pain


Less Common


Painful  !!!

First, a word about Pain.  There’s a big difference between frank eye pain on the one hand, and an uncomfortable, foreign-body, scratchy, gritty sensation on the other.  It’s important to distinguish — all the entities in the second column above cause true unequivocal pain, and (except for the simple corneal abrasion) garner an immediate trip to ophthalmology.  If the patient’s descriptors seem ambiguous, it’s unlikely to warrant such a referral.

Also, a word about Visual Loss.  Evaluate visual acuity in one way or another for anyone with a primary eye complaint.  At least have the patient cover each eye at a time to see what they can read around the exam room.  The ideal is to do it formally with a Snellen chart at a distance.  This is imperative if you’re going to refer them; it’s real embarrassing to call an ophthalmologist and not have acuity numbers to recite.

What if the patient’s one symptomatic eye has worse acuity than the other?  How can you tell if it’s due to organic eye disease [potentially serious], or simple refractive error (i.e. that eye needs glasses, completely benign)?  It’s not uncommon for people to be quite myopic in one eye & never notice it.  This is an absolutely crucial difference to distinguish, & if you don’t remember the simple, easy way to do so (we covered it under “Acute Headache – 2”), click here please.  It’s one of the most important eye tests you can ever learn.

A red eye with organic visual loss (doesn’t pinhole), painful or painless, should have a complete exam by ophthalmology.  The exception might be if you find a chronic cataract the patient never knew about, & suspect that the visual deficit is also chronic.


Let’s start with the less common, but more exciting, conditions.  Again, “Pain” means true pain that might even warrant narcotics, not just an uncomfortable, scratchy, foreign-body sensation.

**  CORNEAL ABRASION  —  This is obviously traumatic, and that’s the key.  But I’ve seen several patients present with, “Something scratched my eye,” simply because they guessed that something must have.  One had a sight-threatening corneal ulcer!  So always ask, “What were you doing when it happened?”  If they’d been hiking and a branch snapped in their face, fine.  But if no convincing injury obviously occurred, be very suspicious that it’s something more.

Also ask, “When?”  Corneal abrasions heal completely in 24 hours (rarely by 48).  If the pain has lasted over a day without diminishing significantly, it’s either a deeper injury, or different disease.  The only other possibility, especially if you see vertical abrasions, is that a foreign body is stuck under the upper lid, scratching the cornea with every blink.

Oftentimes you can see corneal abrasions with a simple penlight, or with an ophthalmoscope on positive diopters [the “black” numbers;  “zero” focuses on the retina if both you and patient have 20/20 vision, negative “red” numbers take you further in, positives focus on out to the lens, iris, cornea].  But you often have to do fluorescein staining to see the scratches.

Addendum:  Maybe the “got something in my eye” happened in a metal workshop, or any place people were cutting or hammering metal.  This raises the possibility of intraocular penetration by a tiny high-velocity foreign body.  May not even have red eye or pain.  History alone, of the specific setting, generates an Ophtho referral, even if there’s no treatment warranted.  This is what’s behind the screening question before MRIs, lest the magnet whip that tiny occult piece of metal back & forth [I’ve always wondered if the possibility got thought out ahead of time, or if it took a couple of bad outcomes to raise the query].

**  KERATITIS / CORNEAL ULCER  —   The cornea hurts like crazy.  Corneal ulcers are usually roundish, but can look just like abrasions, sometimes seen by simple penlight, or with an ophthalmoscope on the positive diopters, and certainly by fluorescein staining.  On the one hand, they can progress fast and destroy the cornea.  Also, any scar they happen to leave will permanently interfere with vision.  They usually require scraping for microbiologic diagnosis and systemic or maybe subconjunctival antibiotics in addition to topical.  Refer stat.

[NOTE:  In all pictures below, the bright pure-white spots in pupils are reflections from flash cameras, not eye lesions].


Corneal ulcer on Left is green fluorescein uptake around 5:00.
Ulcer on Right is large cloudy defect at 3:00.

**  SCLERITIS  —  Very painful, in contrast to the benign episcleritis we’ll mention later.  Pain may radiate to face or present as a retro-orbital headache, exacerbated by extra-ocular movements.  Look beneath the conjunctival injection, as the sclera assumes a telltale bluish hue.  Gentle wiggling of the globe, through the closed eyelid, is quite tender.  Requires work-up of potential collagen-vascular causes, but first requires aggress treatment to prevent blindness.


Note the bluish hue to the sclera, underneath the conjunctival injection.

**  IRITIS / UVEITIS  —  The main way to distinguish this from conjunctivitis is, as we said, pain.  Iritis hurts, no doubt about it.  Sometimes the iris goes into spasm, so there’s a fixed, usually constricted, pupil.  You may see a “ciliary flush,” i.e. concentrated injection primarily right around the iris.  But maybe not.

The one test that’s 100% specific for iritis (dare I say that) is “Cross Photophobia.”  Shine a light into the opposite pupil, and the involved eye feels pain!  The only structure you will have manipulated is the iris (by consensual pupillary reaction).

Most iritis is idiopathic, but a fair bit is due to other diseases such as syphilis, tuberculosis, rheumatologic disorders, etc.

Ciliary Flush:


**  OPTIC NEURITIS  —  Idiopathic 50% of the time, and due to Multiple Sclerosis (or a harbinger of eventual M.S.) the other 50%.  Pain may overshadow redness; there’s invariably some visual impairment, which may be subtle.

Fundoscopic exam may reveal an acute swollen disk; if long-standing, a pale white disk (optic atrophy).  But maybe not.

Key Test:  the Swinging Flashlight, for an Afferent Pupillary Defect (APD) [a.k.a. Marcus-Gunn pupil].  In a completely dark room, shine a light in the uninvolved eye — Pupil Constricts.

  • Shine it quickly over to the involved side, Pupil Dilates!
  • Swing back to the uninvolved, Pupil Constricts.
  • Back to the involved eye, Pupil Dilates!
  • etc.

This is another key element of every eye exam that should always be performed (and almost never is).  It evaluates optic nerve function.  Click here for a simple explanation of neuroanatomy; click there for a fascinating case.

**  NARROW-ANGLE GLAUCOMA  —  Nothing subtle; abrupt onset of severe eye and retro-orbital pain, often with vomiting.  The cornea appears cloudy.  Immediate surgery can save the eye.  The main reason this gets missed is that the clinician thinks “migraine” (unilateral headache with vomiting) & forgets to examine the eye.

**  RECURRENT CORNEAL ABRASION  —  Some corneal abrasions never heal completely, and can recur spontaneously, even during sleep.  The onset is abrupt, they feel just like the original, but there’s no trauma.

On exam, you may note a round corneal lesion, easily visible when stained with fluorescein.  It’s round because the abrasion widens out radially from the persistent defect at its center.  Since there’s no trauma, it looks just like an infectious corneal ulcer, so you send them stat to Ophtho, probably via an E.D.  Diagnosis will be made by slit lamp.

**  CONTACT LENS WEARER  —  The rate of sight-threatening corneal infections with extended-wear lenses may be as high as 0.1% per year [which is 5% with 50 years of use!)].  Assuming the lens has been removed, & pain has persisted, presume it’s a corneal ulcer until proved otherwise.


Next posting we’ll cover the much more common case of the Non-Painful Red Eye(s).  But to review briefly, the very FIRST STEP in evaluating “Red Eye” is to carefully determine — Is there Pain?  Let’s say, yes, it’s…


Unless it’s a simple corneal abrasion (with a convincing history of compatible trauma), they’ll be headed for ophtho, maybe to an ER.  Document visual acuity.  Check out the following parameters:

Vomiting, Severe Eye Pain, Cloudy Cornea ???
  • Think Acute Narrow Angle Glaucoma:  send straight to E.D. for surgery.
 Corneal opacities (may need fluorescein staining) ???
  • If so, it’s Keratitis.  Send to ophtho stat, maybe via an E.D.
Severe pain, worse with extra-ocular movements ???
Bluish hue to sclera ???  Tender globe (by gently wiggling it through the closed eyelid) ???
  • Scleritis.  Send to ophtho stat.
Ciliary flush???  Fixed-pupil (usually constricted) ???
Cross-Photophobia ???
  • Gotta be Iritis / Uveitis.  Call ophtho.
Swollen Optic Disk?  Pale Optic Disk?
Afferent Pupillary Deficit (Marcus-Gunn Pupil) by Swinging Flashlight Test ???
  • Suspect Optic Neuritis.  Call ophtho.
Contact Lens Wearer with new eye pain ???  Beware an early sight-threatening Corneal Ulcer
  • If lens has been out for a day, & still painful, send to Ophtho stat
  • If lens recently out, and pain progressive or unremitting, send to Ophtho stat
  • If corneal opacity, send to Ophtho, maybe via E.D. !!!
  • If lens still in, question sanity
To be complete, what do you do when there’s a history of same-day trauma, and you see a lesion, fully compatible with a Corneal Abrasion?
  • Examine for Cross-Photophobia.  If present, the injury is deeper (traumatic iritis).  Send to Ophtho.
  • If a topical anesthetic didn’t relieve the pain for a few minutes, the injury is also deeper than the cornea
If there’s No Cross Photophobia, & temporary pain relief obtained by topical anesthetic:
  • Don’t Patch (found to delay healing)
  • DO Rx analgesia, even narcotics (these things hurt!!!)
  • If not all better in 24 hours, send to Ophtho (this is rare)

Next Posting: the much more common condition: Non-Painful Red Eye.

2 responses to “Red Eye – 1

  1. I had optic neuritis. The ophthalmologist I tried to make an appointment with told me over the phone that I was just having ‘allergy problems’. I kept telling him that I couldn’t see much out of my right eye, that it felt like a big blob of Vaseline had been smeared in my eye and it hurt….thank God for my local optometrist who fit me in that very day.

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