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This Is What You Need to Know About Culturing Ocular Bacteria


Every soon-to-be optometrist in every optometry school knows that bacteria and the eye can make for an unfortunate mix.

Typically, when a patient presents with an out-of-control bug, we start them on our favorite antibiotic drop, bring them back in a few days, and watch them heal like nothing happened.

But what about those patients that come in with something that just doesn’t look quite right or the ones who take their drops exactly like you prescribed but still aren’t getting better?

These are the patients you should consider culturing.

Whether your practice has invested in its own culturing materials or you use a local lab, knowing which patients need to be examined, when to collect your bacteria, and which testing materials should be utilized is key to successfully managing these difficult cases.

This article will give new grads a quick review of these key points of ocular culturing.

1. What presentations should be cultured?

Culturing can be performed on any patient that you wish; however, the following ocular infections should warrant strong consideration for testing:

  • Central corneal ulcers
  • Ulcers that have significantly thinned the stroma (“significant thinning” can be different from clinician to clinician. I would strongly recommend  culturing anytime thinning reaches 50% or more due to risk of progression to perforation)
  • Large K ulcers – the American Academy of Ophthalmology’s EyeNet article “Confronting Corneal Ulcers” recommends culturing any ulcer 2mm or larger
  • Unresponsive conjunctivitis, K ulcers, or blepharitis
  • Atypical K ulcers – extreme pain with minimal clinical signs, possible fungal etiology, etc.
  • Suspected endophthalmitis – this will require a referral for an aqueous humor and/or vitreous tap; typically, these referrals are to a retinal specialist

2. When should cultures be taken?

One of the most important things to remember when culturing is that once a medication is applied to the eye, the chances of obtaining a good, pure sample are diminished.

If you suspect that your patient may have an atypical or particularly sight-threatening condition, it’s best to go ahead and culture at first presentation.

If you do not have full culturing abilities at your office, you should connect with a local lab and make sure you stock their preferred means of collection. This way, you’re always prepared for anything that lands in your exam chair.

Remember: Do not wait for the results of your culture to begin treatment. After gathering your sample, go ahead and start your patient on whichever therapy you feel is most appropriate. Be sure to educate him or her that your treatment plan may be altered after the results are obtained.

In some cases, an infection initially seems ordinary but does not respond to treatment in the manner you expected. If this is the case, go ahead and culture anyways. While it will not be the ideal scrape, there may be enough bacteria remaining to create a successful culture and help with your patient’s management.

3. Which tools and medium should be used for testing?

The tools you use should be tailored to the location you are scraping.

Corneal cultures should be performed with a spatula, blade, forceps, or moistened applicator.

Conjunctival and lid margin specimens may be taken with moistened applicators. Some labs will equip you with specific broth to wet the applicator with, though sterile saline will work as well. In addition, most labs will provide collection culturettes which will allow for sterile transport from your office to theirs.

The medium on which to culture will depend on which bacteria you suspect to be present. It is best to inoculate multiple different types of plates to get the best likelihood of growth and identification.

The three most common plates used are Sabouraud, chocolate, and blood, and you should make sure you know which types your local lab utilizes.

Whether you choose to work with a local lab in your area or would like to culture within your own office, it is important to remember to utilize this diagnostic tool.

Severe bacterial infections can be daunting, but proper ID of the culprit will mean faster resolution for your patient and less risk of permanent vision loss.

We at always encourage our readers to ask questions and let us know when there’s a topic they’d like us to cover on the site. Some may wonder if we actually pay attention to those comments and requests… the answer: ABSOLUTELY! This article is one example of you asking and us making it happen! Shortly after our Antibiotic and Antiviral Guide was released, one reader requested information regarding ocular bacteria culturing. So, dear reader, here you go! Enjoy!
  1. American Academy of Ophthalmology EyeNet “Confronting Corneal Ulcers.”
  2. The Charles T. Campbell Eye Microbiology Lab “Lab Diagnostic Testing: Bacteria.” Bacteria.htm
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About Patricia Fulmer O.D.

Patricia Fulmer O.D.
Patricia is a 2012 graduate of The University of Alabama at Birmingham School of Optometry and former AOSA National Liaison to the AAO. After graduation, she moved to Amarillo, TX, to complete her residency in Ocular Disease and Primary Care at the Thomas E. Creek VA Hospital. Patricia is the current Center Director for VisionAmerica of Huntsville, a co-management practice specializing in secondary and tertiary care, cataract surgery, strabismus, and oculoplastics in Huntsville, AL. She recently earned her Fellowship in the American Academy of Optometry at the 2015 meeting in New Orleans. In her free time, she enjoys traveling, attending concerts, art, and Alabama football.

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