Age-related macular degeneration (AMD)
leading cause of vision loss among the elderly. This is a progressive condition
which attacks the macula of the eye. This is the area of central vision which
we use to read, write, drive, recognize and carry on daily activities. It has a
high concentration of photoreceptor cells called cones, which are responsible
for color vision. Since the macula is highly sensitive, any damage results in
the brain receiving distorted, unclear images. AMD does not affect peripheral
AMD has an unknown etiology wherein the causes
are still unclear. The major risk factors include age, ethnicity, family
medical history of AMD and smoking. However, according to a recent study
published in BMC Medicine
researchers Layal Chakar, Gabriëlle HS Buitendijk, Abbas Dehghan, Marco Medici
and Albert Hofman et al
., found a
link between the thyroid hormone and AMD. In animal studies, it had been proved
that inducing hypothyroidism
in mice with retinal
degeneration preserves cone photoreceptors while hyperthyroidism worsens the
deterioration. The researchers investigated this correlation in human
The researchers studied data collected from
5,573 participants from the Rotterdam Study in the age range of 55 years or
older. The Rotterdam Study is a population-based cohort study to examine
factors that determine the occurrence of cardiovascular, neurological,
ophthalmologic, psychiatric, and endocrine diseases in the elderly population
residing in Ommoord, a suburb of Rotterdam. The study began in 1989.
In the current study, the researchers explored
correlations between free thyroxine (FT4), thyroid-stimulating hormone (TSH)
and development of AMD. TSH is a
regulatory hormone that controls the release of thyroid hormone. A low level of
TSH is seen in hyperthyroidism while a high level is seen in hyperthyroidism.
The aim of the study was to find an association between FT4, TSH with retinal
pigment alterations (RPA), which act as an early warning for retinal damages.
The researchers were able to demonstrate a
positive correlate between elevated levels of FT4 and increased risk of AMD.
They discovered an association between higher thyroid levels and RPA. This
suggests an important role played by the thyroid hormone in the development of
AMD. However, the study did not indicate a link between TSH and AMD.
The study has significant implications for
clinical practice in terms of treating hypothyroidism with thyroid hormone. The
researchers suggest a cautious approach to treating subclinical hypothyroidism,
a condition where FT4 levels are normal but TSH levels are high. The
researchers also suggest that treatment of thyroid cancer
which involves suppressing TSH, could possibly lead to development of AMD.
However, further studies are required to establish the same.
The researchers believe that more studies are
needed to validate the existing findings and correlations to evolve better
treatment protocols for hypothyroidism and thyroid cancer without increasing
the possible risk of AMD
1. Chakar, L., Buitendijk, G., Dehghan, A., Medici,
M., Hofman, A. et al. (2015). Thyroid function and age-related macular
degeneration: a prospective population-based cohort study - the Rotterdam
Study. BMC Medicine, 13:94, doi:10.1186/s12916-015-0329-0. Accessed on 5 August
2015 from http://www.biomedcentral.com/1741-7015/13/94
2. Ittermann, T. & Jürgens, C. (2015).
Thyroid function: a new road to understanding age-related macular degeneration?
BMC Medicine, 2015; 13:95, doi: 10.1186/s12916-015-0343-2. Accessed on 5 August
2015 from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4407388/