During ophthalmoscopy, I noticed that a lot of light was shining back out through the iris of my 30-year-old White patient? Pupil reactions are normal and the patient is otherwise healthy. What is going on?

This sounds like iris transillumination. The pigment in the iris is too thin in parts or missing and this allows the light from your ophthalmoscope that is reflected from the patient’s retina to pass through the iris and for you to see it.

Iris transillumination can occur in people with ocular albinism, oculocutaneous albinism and pigment dispersion syndrome. From the description of the patient, it sounds to me as if this is a case of pigment dispersion syndrome.

This can lead to a condition called pigmentary glaucoma. Pigment cells are rubbed off the back of the iris by the fibres that support the crystalline lens. There is an anatomical abnormality which brings these fibres into contact with the iris and as the iris contracts and dilates through the normal process of controlling the amount of light that goes into the eye pigment is removed.

The pigment floats around the aqueous humor and eventually accumulates in the anterior chamber angle where it can clog the trabecular meshwork. The clogging of this meshwork prevents aqueous from draining out of the eye causing an increase in intraocular pressure. Spikes in intraocular pressure can occur and exercise is known to contribute to these. Eventually, the pressure spike damages the nerve fibre layer in the retina causing visual field defects. This is pigmentary glaucoma.

Somewhere between 30 and 50% of people with pigment dispersion syndrome convert to pigmentary glaucoma.

Pigmentary glaucoma can be treated with eye drops that lower the intraocular pressure or with drops that constrict the pupil causing it to move away from the lens fibres. But, these drugs can cause blurred and/or dim vision.

In some patients, laser trabeculoplasty is used to open up the drainage system in the eye to increase fluid flow, which lowers eye pressure.

Another treatment for is laser iridotomy. A laser is used to make a small hole in the iris, causing the iris to move away from the lens of the eye. This prevents the lens fibres from scraping the pigment from the iris and clogging the eye’s fluid flow. However, it has limitations and does not always achieve its desired effect.