I. AMLEI classification (by type of deficiency)
which may be cumulative:
The first 3 are directly related to the
composition of tears
The mucin layer - the innermost layer in
direct contact with the eye surface is notably produced by conjonctival and
goblet cells. Its composition seems to be very complex and may be subdivided in
several layers. This layer acts as a surfactant, which means that it enables the
uniform distribution of the other layers upon the eye surface. Without it, the
tears are unable to spread evenly over the surface and thus creating dry spots.
The aqueous layer - the central layer and
certainly thickest and most abuundant one in healthy eyes
The lipid layer - a greasy layer in
direct contact with the eye to limit evaporation and which is mainly produced by
the meibomian glands situated in the edge of the lids. Certains pathologies such
as meibomianitis or meibomitis (inflammation of the said glands), rosacea,
blepharitis (inflammation of the lids), some hormonal deficiency, particularly
affect this layer. A recent study by doctor Tseng has demonstrated that the
lipid deficiency due to the meibomius glands is the predominent cause of dry
eyes in post lasik dry eye.
Most studies, however, indicate that
LASIK-induced dry eye is due to the severed corneal nerves in the cornea.
Thus confirming the theory of neuro-lachrymal unit as well. Nevertheless, the lipid
deficiency may be cause the severed nerves and loss of corneal sensitivity.
II. Other older classifications exist, such
as Sjögren (and sometimes autoimmune dry eye) and non-Sjögren dry eye was very
commun a few years ago but has progressively been abandonned because, the vast
majority of dry eyes is non-Sjögren, which makes that category not very
specific.
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Preserve our Eyes not our Drops!
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