Dear Dr Judy,

I suppose the uncertain area is:

How capable is the emmetropisation process if all
environmentally/behaviourally negative factors were altered to be
posative factors?

It appears that those who are aware of genetic and environmental
influences can be divided into essentially two opposites camps

1. Myopia cannot be improved - possibly it can be halted for some forms
of myopia.  It can vary up or down but generally it varies down until
middle age, improves slightly for several decades and then varies down
again.

2. Myopia can be improved if environmentally/behaviourally  negative
effects are changed to environmentally/behaviourally posative effects.

So then we come to Twin studies to decide this one way or another.

In the context of these studies I am interested in the relationship of
family habits, family anxiety,  twin dominance/rivalry/birth order,
loneliness etc etc etc in the development of myopia.

If these influences are very important in myopia we would expect the
most *similar* refractions in the following order when studying MZ and
DZ twins.

1. MZ  Raised together in the same family who are treated *most*
identically by care givers (inside the family and at school ect) and
other family members **and** who have the most supportive relationship
with each other **and** who are most alike physically.    These twins
may be so alike that outsiders particularly could not treat each twin
as a different person because they could not tell the difference
between them.

2. Then some kind of confusion in ordering of differently treated (MZ
twins who are *not* supportive of each other) and similarly treated (DZ
twins who *are* supportive of each other)

3. Finally the *most* differently treated DZ twins who are not
supportive of each other and most unalike physically.

To my knowledge this has never been tested in this manner.

Genetic studies of twins assume environment/behaviour is not relevant,
and yet a test of environmental/behavioural factors in a twin study
would produce the same statistical results in favour of
environmental/behavioural factors.

Similarly "Familial high myopia" is said to be inherited in a
"Mendelian" manner.   This is assumed because it occurs in 3
generations with some members having high myopia over -6D.

Meanwhile environmentally/behaviourally we can conclude that "family
habits, family anxiety,dominance/rivalry etc etc etc"
are likely to be passed from generation to generation.

In conclusion:

1. If we are in the genetic camp the 'Classical twin study' method and
"familial high myopia" are concrete 'very scientific evidence' that
myopia has a very strong genetic component influencing it so that
emmetropisation is unable to restore normal sight.

2. If we are in the environmental/behavioural camp we notice that
current gene studies are concluding that "different genes seem to be
the cause of high myopia in different families"  (but still no genes
yet found for these families)

I have written to the British Twin study group to ask them if they are
prepared to examine the most refractively different set of MZ twins for
behavioural differences.  These twins seem to have the capability of
providing some very useful data on the environmental/behavioural
reasons why myopia developes.

Andrew