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These are tiny cystic vesicles present on the outer (epithelial) surface of the cornea. They can arise in a number of different conditions:
- Associated with certain types of contact lens.
- Associated with recurrent corneal erosion syndrome.
- In the presence of vapours of certain industrial chemicals, eg aliphatic, alicyclic and heterocyclic amines.
- Associated with certain corneal dystrophies (epithelial basement membrane dystrophy (EBMD) or Cogan's microcystic corneal dystrophy and Meesmann's dystrophy).
- They have been more recently associated with interferon therapy and exemestane.
- They may be found in pre-invasive carcinoma of the cornea.
This varies with the aetiology, the most common being microcysts associated with contact lens wear.
Some may be asymptomatic. Others may cause ocular irritation or transient blurred vision and - if they rupture - cause painful corneal erosions which show up as punctate epithelial erosions (there will be scattered pinpoints of fluorescein uptake across the corneal surface).
This depends on the underlying cause but, generally, these patients are managed in an ophthalmology clinic. The source is removed where possible (such as in the case of contact lenses) and intensive lubrication with the aim to limit cyst formation and rupture is the mainstay of treatment.
If they persist and repeatedly rupture, they may be treated as would a case of recurrent corneal erosion syndrome, ie topical chloramphenicol, lubricants and - if there is no improvement - a period wearing a bandage contact lens (a soft lens with no refractive power that sits over the cornea and protects it from the shearing forces of the blinking lids). In severe cases, focal debridement may be required.
If they fail to heal adequately, the patient may go on to develop the self-perpetuating condition of recurrent corneal erosion syndrome, whereby there is an ongoing cycle of cyst formation and rupture as the epithelium does not have the time to heal fully.
This depends on the cause. Microcysts associated with wearing contact lenses should settle when the lenses are removed. Microcysts associated with corneal erosion syndrome, as are found in dry eye, should settle with intensive (and ongoing prophylactic) lubrication. Cysts arising as a result of industrial chemical vapour exposure settle over a few hours after vacation of the vapour, with no long-term sequelae. Corneal dystrophies are generally progressive disorders which worsen over time.
Good patient education with regards to wearing contact lenses, and lubrication.
Further reading and references
The Wills Eye Manual (4th ed) 2004
Ballantyne B; Glaucopsia: an occupational ophthalmic hazard. Toxicol Rev. 200423(2):83-90.
Clinical Ophthalmology: A Systematic Approach
Fracht HU, Harvey TJ, Bennett TJ; Transient corneal microcysts associated with interferon therapy. Cornea. 2005 May24(4):480-1.
Papathanassiou M, Nikita E, Theodossiadis P, et al; Exemestane-induced corneal epithelial changes. Cutan Ocul Toxicol. 2010 Sep29(3):209-11.
Dark AJ, Streeten BW; Preinvasive carcinoma of the cornea and conjunctiva. BJO 1980 (64): 506-514 [abstract].
Moorfields Manual of Ophthalmology