Familial Adenomatous Polyposis
John Parker, MD - Ophthalmologist
It is a curious fact that half of the people with FAP have spots in the back of their eyes (retina) which look like freckles and may signal the disease years before polyps (adenomas) develop in the colon. These are not tumours but harmless or benign patches of pigment which exist at birth and do not grow. They do not affect the eyes and how we see. For this reason, patients and their families should not be worried about having an eye test, even though it may seem like just one more investigation.
There is a tendency for affected family members to have similar amounts of eye freckling. Some may have a great many while others have none at all. These spots are not visible to the naked eye but must be diagnosed by an eye specialist or ophthalmologist who uses eyedrops to dilate the opening at the centre of the eye (pupil) along with a mirror attached to a scope for examining the retina. Nothing is placed inside the eyes and the effect of the drops wears off after several hours. Driving is not permitted and close reading is discouraged during this period.
Patients need to know that an eye examination for glasses, cataracts, or glaucoma will not necessarily pick up these spots which are easily missed. Some freckles may be less than 1/10 mm. Since FAP is a rare disease, the ophthalmologist, unlike the optometrist, will recognize the association with FAP and freckles. Other types of spots in the retina can be confused with these freckles, emphasizing the need for an experienced observer. Some patients may see their eye doctor for other problems and are told there is nothing "wrong" but the correct testing may not have been done. Part of the Famlial GI Cancer Registry's role is to refer patients and their children or siblings to ophthalmologists across Canada who are interested in FAP.
One very important benefit of this research is that an eye test can help families better understand their risk for FAP. Although genetic testing with blood samples can often be used successfully in large families, sometimes the test does not work well, for example, when there is only one affected person in a family or paternity is uncertain. However, when combined with the results of the DNA analysis of the blood samples, it may be possible to reduce much of the anxiety facing parents about the risk to their children. Sometimes, it can be extremely difficult to adapt to FAP when there is no family history to fall back on and counselling can make a difference.
Parents should be aware that a child who has no eye freckles may still have FAP. Bowel screening or Sigmoidoscopy is recommended until the risk is clarified. One can have FAP with or without associated growths such as skin cysts, bony growths, and eye freckles. The age of the child must be considered before having the eye test since no bowel investigation is undertaken before puberty, unless the child has bowel symptoms such as bleeding or change in bowel habit. It has been noticed that children with eye freckles tend to develop adenomas earlier than affected youngsters without such spots in their eyes. Finding out about new research and what it means to your family will allow you to gain valuable information about your child's risk.