Ocular Discharge – Part 1
Where do you start?
Ocular discharge is a common presenting sign, but contrary to what you might think, it is rarely due to a primary bacterial infection. With a logical, thorough and systematic approach to your history gathering and ocular examination, you can usually make a diagnosis, and the specific cause can be treated.
History:
Ask the right questions
What is the nature of the discharge and has it changed?
- Clear discharge suggests tear overflow either due to increased tear production (indicative of pain) or tear overflow (indicative of a drainage issue).
- Grey to white to cream discharge suggests increased mucin and/or pus (indicative of chronic irritation and/or infection)
Unilateral or bilateral?
- Ocular trauma, foreign bodies are rarely bilateral
- Infections and immune-mediated disease are often bilateral
Is the discharge acute or chronic?
Unilateral purulent ocular discharge of several weeks discharge.
A grass seed was removed from the lacrimal sac.
- Acute suggests a recent change such as trauma, foreign body, development of a lid abnormality
- Chronic suggests a long-term issue that may include the above but may also be something less obvious
Is there associated blepharospasm and/or pawing at the eye?
- Indicates painful eye(s)
Has there been a response to any previous medications/treatments?
- A response to a topical agents may be to any of its components, not necessarily the ‘active’ ingredient. The classic example is dry eye (keratoconjunctivitis sicca) often misdiagnosed as ‘recurrent conjunctivitis’ – any topical agent (including antibiotic drops/ ointments) will act as a lubricant and tend to improve or even temporarily resolve signs, only for them to return when medications stop.
Ocular examination:
Concentrate on ruling out potential causes
Confirm the nature of the discharge
- Tear staining – suggests excess lacrimation associated with pain, or normal lacrimation combined with poor drainage
- Mucoid – may be within normal limits but can suggest some level of chronic irritation leading to increased mucin production by conjunctival goblet cells
- Mucopurulent – suggests chronic irritation with some degree of secondary infection leading to white cell production and exudate
- Purulent – suggests infection and/or foreign body reaction with associated white cell exudate
Check for eyelid abnormalities
Distichiasis
- Entropion, distichiasis, ectopic cilia, trichiasis, trauma, iatrogenic (lid margin malunions, suture rubs, etc), tear duct and/or drainage abnormalities – this may be easier to assess after topical anaesthesia (see below)
Check for conjunctival and nictitans abnormalities
- Non-specific inflammation/conjunctivitis, lymphoid follicular conjunctivitis, atypical pannus, nictitans gland/cartilage anomalies
Assess the cornea
- Look for signs of ulceration, vascularization, granulation (fluorescein stain if indicated – see below)
Check for foreign bodies
- Particularly with an unexplained unilateral discharge
- Look behind the nictitans, the upper and lower conjunctival fornices (will need topical anaesthesia – see below)
Assess intraocular structures
- Looks for signs of uveitis and/or glaucoma, foreign body, etc
Relevant ancillary procedures:
The order is important
Schirmer Tear Test (STT) BEFORE any drops or stain put in the eyes
- Any eye with unexplained conjunctival inflammation and/or mucopurulent to purulent discharge
Schirmer tear test – use before any drops
MUST have a STT to rule dry eye in or out – dry eye is extremely common in dogs
- If you have already used drops in the eye its too late and you will need to wait a few hours or schedule another appointment (oops…)!
Topical anaesthetic drops if blepharospasm is present
- If blepharospasm is eliminated or markedly reduce it suggests ocular surface pain; if no effect it suggests intraocular/deep pain
Fluorescein staining to rule corneal ulceration in or out (can be combined with topical anaesthesia ‘flushing’ of the eye)
- Remember stain uptake by granulation tissue and healed ‘facets’ from previous ulcers can lead to misinterpretation of staining.
Swab for culture and sensitivity typically not needed
- Consider for melting ulcers (but don’t wait for a result)
- Only culture for a primary infection when all other causes ruled out!
https://www.voreyevet.com.au/tonys-top-10/ophthalmic-examination-equipment-essentials/
