We sometimes use footballs as an analogy for the eye. A football is filled with air to give it the needed firmness to play the world’s favourite sport. In a similar way in the eye, a watery substance called the aqueous gives it the needed firmness (between 10 and 21 mm Hg in most people) required for its function. Indeed this aqueous does much more than keeping the shape of your eye; it helps to nourish the inner structures of the eye, and provides oxygen to those parts that are not close to blood vessels.

The aqueous is produced by the ciliary body, located on the inner side of the eye, just opposite to the junction between the cornea and sclera. When not enough fluid is produced, the eye feels soft, the vision drops, and the eye may even become a little smaller. We then speak of hypotony (a decrese of intraocular pressure). When this pressure drops to 1 or 2 mm Hg, we suffer from severe hypotony and our eyes at greatest risk!.

Hypotony has several causes but in general it results from a lack of aqueous production in the ciliary body as a result of inflammation, scarring or detachment.

What are the symptoms a patient with hypotony experiences?

A mild hypotony gives usually no symptoms but if the pressure drop is more severe, a vision drop is often the first change you will notice. If this vision loos follows a trauma, an extensive eye surgery (for instance a retinal detachment surgery, particularly involving the use of silicone oil), or some situations where a lot of scars are formed in the eye, the resultant hypotony can lead to shrinkage of the eye (Phthisis bulbi). This is often accompanied by pain and if allowed to progress, the eye is lost without a chance of recovering vision.

What can be done for hypotony?

A patient suffering from hypotony need a careful and personalized clinical exam in order to identify the cause of his problem. This complete eye exam will often required specialized diagnostic tools such a UBM (ultrasound biomicroscopy). The cause of your hypotony will determine your treatment:

If the cause is inflammatory, you will be given anti-inflammatory medications and these will generally increase the intraocular pressure. However, if your hypotony is due to scarring or to a ciliary body detachment, you will probably need surgery (stripping of membranes above the ciliary processes or the reparation of the cyliary body detachment) in order to normalize the intraocular pressure and to recover your vision.

A small increase in intraocular pressure (even just 2 or 3 mm Hg) can lead to a significant improvement in the eye: folds present in the retina normally disappear, vision improves and the eye often becomes a little more normal in size.