Professor Adèle Ehongo – Dr Noélie Bacq | Shedding Light on PICC: A Condition Associated with Visual Defects in People with Short-sightedness

In their review, Ehongo and Bacq recommend optical coherence tomography – or OCT – as a screening tool for PICC. This non-invasive imaging technique uses light to acquire cross-sectional images of the eye, allowing clinicians to distinguish between neighbouring layers.

The choroid layer is made up of blood vessels, and is neighboured by two other layers: the sclera on the outside and Bruch’s membrane on the inside. In addition to visual field defects, the researchers cover other complications of short-sightedness that are associated with PICC, among them peripapillary staphyloma, which involves thinning and protrusion of the sclera. Studies show that peripapillary staphyloma occurs in 40 to 100% of eyes with PICC.

To better define PICC, Ehongo and Bacq documented and established in a previous study that PICC is a cleavage between the choroid and sclera. The exact mechanisms that allow PICC to arise are not fully understood, but several hypotheses are discussed in detail in the team’s review.

One involves the idea that the sheath enclosing the optic nerve is more prone to traction in a short-sighted eye. This traction applies to the entire thickness of the wall of the eye, including the sclera, choroid and Bruch’s membrane. It creates a protrusion of the sclera at the back of the eye. Bruch’s membrane, thanks to its resistance, maintains its position. The choroid layer between the two then thickens and eventually retracts from the sclera, leading to PICC.

Using OCT, the researchers showed how this same traction also promotes the appearance of peripapillary staphyloma. The presence of a staphyloma in a short-sighted eye is important, because it worsens the visual prognosis.

The concept that a protrusion of the eyeball around the optic disc is promoted by traction of the optic nerve sheaths is crucial. It opens perspectives in the understanding of other types of staphylomas, whose cause remains unknown. Indeed, the muscles that control eye movement could promote local protrusions of the eyeball, corresponding to other types of staphylomas.

The team’s review has shed much-needed light on PICC, and will help to demystify the condition for clinicians and researchers, leading to benefits for patients in the near future.