About 60% of PXE sufferers develop eye problems, many of which lose central vision. No-one ever goes completely blind because of PXE, some peripheral vision is always retained.

How the eye works

The eye is like a camera. When you take a picture, the lenses in front of the camera allow light through and focus that light on the film that covers the back wall of the camera. When the light hits the film, the picture is taken. The eyes work in much the same manner. The front parts of the eye (the cornea, the pupil and the lens) are clear and allow light through. The cornea and lens focus light on the back inside wall of the eye. A thin layer of tissue called the retina covers this wall. The retina is like the film in the camera. It is the seeing tissue. When the focused light hits the retina, a picture is taken and messages about this picture are sent to the brain through the optic nerve.

This is how we see. The retina has two parts: the peripheral retina and the macula. If you imagine the retina as a circle with a bull's-eye at the centre, the macula is like the bull's-eye: it is very small and is located near the optic nerve. The large area of retina that surrounds the macula and makes up 95% of the retina is called the peripheral retina. The peripheral retina gives us vision to the side, which is called "peripheral" vision. This is what we refer to when we say, "I saw something out of the corner of my eye." Because the peripheral retina cannot see detail clearly, we cannot use peripheral vision to read, thread a needle, drive, or even recognise a face. If I see someone "out of the corner of my eye," I can tell who the person is by his or her general shape, but I won't be able to see the expression on that person's face.

PXE affects the macula and not the peripheral vision. If the macula in only one eye is affected, you will still be able to see detail with the other eye but if the macula in both eyes is severely affected then it will become impossible to do work that requires detail vision. A person who has lost the ability to see detail with each eye will still be able to get along fairly well. Almost all people can see well enough to take care of themselves and continue those activities that do not require detail vision. People learn to make use of the areas just outside the macula to see detail better. Once the macula has been severely damaged, treatment is usually no longer possible. Therefore, everyone should test the vision in each eye, separately, each day if they have a problem, by using the Amsler grid.

The Amsler Grid

The Amsler Grid is a square drawn on paper of approximately 3 inches side, divided into smaller squares of approximately one eighth of an inch side forming a grid. At the centre of the grid a black dot of approximately one eighth of an inch in diameter is drawn. Test the vision in each eye by looking at the dot in the centre with each eye separately.You may notice distortion of the grid pattern such as bent lines and irregular box shapes or a grey shaded area. If this is the first time of noticing such irregularities you should see your ophthalmologist as soon as possible. Again, if you see any changes from the previous time of checking you should also see your ophthalmologist.

The eyes and PXE

The effect of PXE on the eye is directly on the microscopically thin layer of elastic tissue in the back of the eye. This tissue, which is directly underneath the retina and which supports the retina, develops cracks called angiod streaks. The streaks themselves cause no problems but with time (10 to 30 years), and often following trauma or heavy straining, the angiod streaks may cause slight bleeding. Such retinal haemorrhages readily heal but commonly leave a scar which, if it interferes with the macula, will lead to loss of central vision leaving only the less sharp peripheral vision.

These abnormal blood vessels are called SubRetinal NeoVascularization (SRNV). An eye when leaking will lose its ability to see detail unless treatment is done promptly even though treatment does not guarantee that vision won't be lost. In addition, if SRNV occurs in one eye, there is about a one in ten chance per year that it will occur in the other eye. The earlier that SRNV can be discovered, the more likely that vision can be saved or at least loss of central vision delayed. In other words, pay close attention to your eyesight and see your eye doctor if there is any type of change in your vision.

Fluorscein Angiography

If your doctor suspects SRNV, he will do a special test called fluorescein angiography. To do the test, dye is injected into a vein in the patient's arm. The dye travels throughout the body, including the eyes. With a special camera and a flash, not an X-ray machine, a series of photographs of the retina are taken as the dye passes through it. The photographs will show the kind of changes that have occurred in the retina and where those changes are located. This is necessary to determine what treatment, if any, should be given.

The photographs provide a kind of map that the doctor uses during treatment. There is another photographic test called indocyanine green angiography that is done the same way as fluorescein angiography. This test may give additional information that may be helpful if laser treatment is to be done.