The cause of myopia (short-sightedness) has puzzled researchers for many years ? is it nature or nurture?
Shedding some light on the cause of short-sightedness is recent PhD graduate, Mohamed Dirani (Vision Cooperative Research Centre), who has undertaken the largest twin study in the world to investigate myopia and other eye conditions.
The resuls were presented at the 2007 CRCA Conference.
?For many years researchers have suggested that environmental risk factors such as urbanisation, increased near work such as reading, and higher educational levels may play a significant role in the development of myopia,? Mohamed said.
?But it is not the whole story, in fact it only explains a small part of the development of myopia. The results of our twin study support a strong genetic basis to myopia.
?We have found that an identical twin has an 80% chance of developing myopia if their twin has myopia, versus a 40% chance if you are a non-identical twin.?
The study has examined more than 1,200 identical and non-identical twins of both genders aged between 18 to 86 years.
Studies of twins are particularly useful for understanding myopia, as they allow researchers to look at the interaction between heredity and environmental influences. Identical twins share 100% of their genes, as well as much of their early childhood environment. Non-identical twins also share a similar childhood environment but are not genetically alike. Comparing these two groups allows researchers to assess the relative influence and interaction of genes and environment for complex diseases.
Currently one in five Australians suffer from myopia, which is rapidly increasing throughout the world. By 2020, it is estimated the number of people with myopia will grow to one third of the world?s population (2.5 billion). For example in Singapore, a series of studies have shown an myopia increase in males aged 15-25, from 26% of this group in the late 1970s, to 83% in the late 1990s.
The large number of participants and wide age range in the Vision CRC Twin Study will allow better examination of the role of genetic and non-genetic factors in the development of refractive errors, particularly myopia.
All individuals involved undertook a questionnaire, had a full eye examination and provided a blood sample for DNA analysis. Additional family history was also taken and immediate family members are to be assessed for further heritability analysis.
?We will also use our twin data for genetic linkage analysis, which will help in identifying the gene(s) responsible for myopia development,? says Mohamed.