Best disease, also termed vitelliform macular dystrophy, is an autosomal dominant disorder, which classically presents in childhood with the striking appearance of a yellow or orange yolklike lesion in the macula. Dr Franz Best, a German ophthalmologist, described the first pedigree in 1905.
The lesion evolves through several stages over many years, with increasing potential for adverse visual outcome. A hallmark of the disease is a markedly abnormal electro-oculogram (EOG) in all stages of progression and in phenotypically normal carriers
To understand the causes of astigmatism, it is useful to understand how the eye works.
The eye works in a similar way to a conventional camera and is made up of three parts:
Astigmatism usually occurs as a result of problems with the cornea.
The cornea is a transparent layer of tissue that covers the front of the eye. It helps to protect the eye from damage and infection. The cornea and lens are also responsible for focusing incoming light onto the retina to create a clear image.
To work properly, the cornea needs to be perfectly curved – like the top half of a football. However, in cases of astigmatism, the curve of the cornea is imperfect, with one half either being steeper or flatter than the other part.
When light hits an imperfectly curved cornea, the retina does not receive a perfectly sharp image of light. Instead, the light is slightly ‘smeared’, resulting in blurred vision.
The reasons why some people are born with an imperfectly curved cornea are unknown. However, there is some limited evidence that the condition can run in families.
Being born prematurely, and/or with a low birth weight, may also increase the risk of a child developing astigmatism. This may be because the eye does not have time to fully develop in the womb.
Injuries to the cornea can also result in astigmatism, as can damage to the cornea caused by eye surgery.
As most people who have astigmatism are born with the condition it is very important that your children receive regular eye tests.
If your child has been born with astigmatism they are unlikely to realise that there is anything wrong with their vision, so if their vision is not regularly tested, conditions like astigmatism could remain undiagnosed for many years. Undiagnosed astigmatism can affect a child’s learning and development because they may have problems reading and concentrating at school.
Your child will receive an eye test shortly after they are born, and a follow-up test six weeks later.
A comprehensive eye test is also recommended once your child reaches the age of four. By this age, if they have an eye condition, it should be able to be diagnosed through testing.
Children should then have an annual eye test until they are 16 years of age.
Adults over the age of 16 usually only require an eye test every two years, unless advised otherwise by their optician.
There are a number of tests that can be used to diagnosis astigmatism. One test, known as a visual acuity test, can be used to assess your, or your child’s, ability to focus on objects at different distances.
The visual acuity test usually involves reading letters on a chart, where the letters become progressively smaller on each line.
Another test uses a piece of equipment called an astigmatic dial. This is a chart, or panel, that shows a series of lines making up a semi-circle. People with astigmatism will usually see some lines more clearly than others.
A device called a keratometer can be used to measure the degree of astigmatism. It can measure how light is being focused by the cornea and detect any imperfections in the curve of the cornea.
The symptoms of astigmatism include: