Retinial Degeneration
by Renato Meduri
Effects of early ageing on cells.
Degenerative retinopathies are
important pathologies since severe visual impairments are possible. Even if they
are well observed and described in medical texts since the nineteeth century,
only in the past decade, thanks most of all to molecular medicine, important
knowledge was acquired concerning their causes and, therefore, on prevention and
treatment.
The eye can be compared to a camera. The anterior portion, which
is the part we see when we look into our eyes (cornea, sclera, crystalline),
corresponds to the objective. The film corresponds to the retina.
It
is formed of many layers of cells linked together in a highly precise manner. It
has the most particular characteristic of transforming the light impulse that
reaches it through the pupil in a nerve stimulus which is sent to the brain
through the optical nerve.
This function of transfer is however extremely
demanding on the cells and requires an important level of energy. There are no
problems for a young cell, but when it begins to mature this demanding work is
more severe, the cell becomes older and dies. The cells are devoid of
regenerative capacity and their number substantially diminishes.
From a
hundred million cells during teenage years, they diminish to 75 millions at
the age of 70. If the cell is constitutionally weak, ageing happens
early.
This process of early ageing limited to the retina is substantially at
the basis of all forms of retinial degeneration which are characterized by the
more or less precocious death of a higher number of cells and therefore, of a
proportional reduced sight.
Of course the phenomenon is limited to the retina since the
subject can maintain a wonderful physical and mental health.
Retinitis
pigmentosa is a disease caused by genetic alterations, in other words the DNA.
Even the ageing process is genetic: if one has parents who have a good
longevity, chances are this person will live a long time: it's a matter of
DNA.
If we imagine the cells of the retina like houses where the inside room
has engineers and technicians working on planning and preparing every aspect of
a house from the brick to the windows which are then assembled to build a home,
we have a good exemple of what genes do: they design and build every detail used
in building a home.
If one of the engineers or technicians doesn't plan or
assemble properly one of the particular pieces for construction, the walls,
windows, roof and plumbing of the house will have weak points.
These weak points will entail more or less important
downfalls which can create unreliability and unstability for the home.
This
is exactly what happens in a cell when one or more genes are no longer able to
build proteinaceous enzymes or a structure necessary to the
cell.
It is now known that genetic
destiny cannot be changed; vice versa, external agents contribute significantly
to lengthen or shorten the life of a home with construction
defects.
In fact, if the home is
exposed to rain, wind, sun or humidity, damage will happen earlier to the
structural partitionings; if, on the contrary, negative treatment is avoided on
the home, it will last longer.
Even
for the cells of the retina, life will be longer if exposure to risk factors is
avoided: light and the well-known free radicals or if useful substances and
nutrients have been given to the cell for its stability.
For exemple, in specific forms of retinitis
pigmentosa, in which are lacking the genes responsible for bringing and using
vitamin A, it is therefore useful to take some of this vitamin taking care to
verify dosage in the blood in order to avoid overdosage.
It is also appropriate to use determined molecules
which improve the cell's oxidation capacity (such as Levocarnitina commonly
adopted to improve muscular performances). A sort of revolution derives from the
possibility of clinical use of particular molecules: the growth
factors.
It is a wide class of
proteins which action has been detected by Levi di Montalcini; we could define
them as the molecules of life because they efficiently prevent the death of
cells in crisis. In technical terms they are called anti-apoptotic molecules.
Cardialogists, dermatologists and neurologists are making an increasing use of
them: infarcted hearts, damaged epidermis, brains with degenerative pathologies
have been benefitting from them for only a few years.
At the experimental level, if they are administered in
eyes with retinitis pigmentosa, they can block its evolution. Stem cells
represent potential therapies also for other degenerative diseases, but for the
retina, however, applications are not yet without constraint.
It will certainly not be possible to heal from genetic
trouble as it is not possible to cure diabetes by taking insulin, but the
evolution of the disease can be slowed down more or less significantly. In fact
the decisive therapy will only be genetic.
Molecular genetic is particularly
important as it allows today to find the exact location of the anomalous gene
and therefore the precise defect in its make up in about 85% of patients. It is
an important step towards the eventual substitution of the affected
gene.
Already, the identification of
the gene allows in a certain percentage of cases the implementation of more
interesting therapies. The simple medical genetics, that is the study of the
genealogical tree, is also useful. Finally, it is necessary to emphasize how the
risk of affected descendants is greater when parents have married between blood
relations.
There exist numerous forms
of retinitis pigmentosa and even within the same family it is possible to have
various symptomatologies. The most characterized symptom is however HEMERALOPIA,
that is a reduced visual capacity in bright lights: children who stop playing at
sunset; orientation difficulties when entering dim environments, for exemple in
a movie theatre, etc.