Epithelial Microcysts

Case reports

As many as 10 microcysts can be observed in the corneal epithelium of about 50% of non–contact lens wearers. Thus, the appearance of a small number of microcysts in a contact lens wearer should be considered a normal occurrence.

A number of authors have published estimates of the prevalence of a significant microcyst response in association with various types and modalities of lens wear ; these estimates are summarised in Table 19.1 . Bearing in mind the different methodologies, lens types and study durations employed by the various authors, the concordance of estimates of prevalence is good. In general, a lower prevalence of microcysts is associated with daily wear of contact lenses compared with extended wear of hydrogel lenses. The prevalence of microcysts associated with both hydrogel lens extended-wear and low-Dk rigid lens extended wear approaches 100% and is zero with silicone hydrogel lenses.

Toshida and Murakami reported an atypical case of microcysts associated with silicone hydrogel contact lens wear based on observations with an in vivo confocal laser microscope. They reported that treatment with betamethasone phosphate and levofloxacin eye drops (both five times daily) resulted in alleviation of the condition after 10 days. Since microcysts usually take up to 3 months to resolve (see ‘Prognosis’ ), the formations observed by these authors may have been a different form of pathological entity to the microcyst response described in this chapter.

Hospital surveys

In 1992, Stapleton et al. reported that of 1,104 patients with contact lens–related disorders presenting to an eye clinic, only 11 (1.0%) displayed epithelial microcysts. Of the extensive hospital-based surveys of contact lens complications conducted between 2009 and 2018 – carried out in China, India, Nepal, Singapore, the USA and UK – only one study reported the observation of epithelial microcysts. This was in the UK survey of Radford et al., where one case of epithelial microcysts was observed among 877 contact lens wearers (0.1%) attending Moorfields Eye Hospital with contact lens–related disorders other than microbial keratitis.

Slit lamp biomicroscope appearance

Microcysts can be seen in the central and paracentral cornea at low magnification (× 15). They appear as minute, scattered, grey, opaque dots with focal illumination and as transparent refractile inclusions with indirect retro-illumination ( Fig. 19.2 ). Microcysts are often said to be irregular in shape, but all of the photomicrographs of microcysts which I have examined suggest that they are generally of a uniform spherical or ovoid shape. Zantos suggested that they can vary in size from 15 to 50 μm ³ ; however, microcysts as large as the full thickness of the epithelium (50–75 μm) have not been reported, so it is likely that microcysts are in the order of 5 to 30 μm in diameter.

Careful observation at high magnification (× 40) is required to differentiate epithelial microcysts from other epithelial inclusions, such as vacuoles or bullae, which take on a superficially similar appearance. The preferred observation technique is marginal retro-illumination. The observation and illumination arms should be set at least 45° apart. A 2-mm-wide beam should be directed to one of the lateral margins of the pupil so that, when focused on the cornea, the background is evenly split between the illuminated iris and the black pupil. Microcysts are then readily observed in the region of the epithelium lying in front of the border of the iris and the pupil. It is important to consider the internal illumination characteristics with respect to the background (pupil and iris) and to ignore the directly illuminated corneal section that may be adjacent to the corneal region of interest. By slowly scanning laterally from side to side, an overall estimate of the number of microcysts can be derived.

The greater the number of microcysts, the greater is the probability of detecting slight superficial punctate staining, which represents a breaking open of the anterior epithelial surface as microcysts emerge from the deeper layers and are expunged from the cornea.

Once it has been established under high magnification (× 40) that the inclusions being observed are, indeed, microcysts (see ‘Differential Diagnosis’ ), the severity of the overall response can be quantified by once again observing the cornea at a low enough magnification so that it fills the field of view (perhaps × 10 magnification). By scanning back and forth with a 1-mm vertical beam, it is possible to view the microcysts in direct focal illumination. Holden et al. advocated quantifying the severity of a microcyst response by counting the number of microcysts, which, at this low level of magnification, appear as minute, grey dots. An alternative strategy is to grade the response using a grading scale for epithelial microcysts, such as that provided in Appendix A .