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JESÚS PINTOR AN. R. ACAD. NAC. FARM.

ciliary body, iris, trabecular meshwork, lens, and the retina (11, 12).
Not all the structures previously mentioned have been fully
investigated; nevertheless it has been possible to understand the role
of nucleotides and dinucleotides on corneal surface and intraocular
pressure (IOP).

THE OCULAR SURFACE

There are two main pathological states regarding the ocular
surface. On the one hand dry eye, and on the other hand corneal
wound healing that occurs after superficial injuries. None of them
have efficacious treatments and are lacking of the discovery of new
substances for their care.

Dry eye and tear secretion

Tear secretion is an important physiological process because tear
forms the interface between the air and the ocular tissues. Tears
protect the corneal surface with antibacterial systems, such as
lysozyme and lactoferrin, provide the epithelium with nutrients, and
lubricate the eyelids. Also, they wash away those particles that may
damage the cornea. There are situations in which some problems
in the volume or in the quality of tears occur, and therefore may
produce several negative effects such as corneal function failures,
discomfort, and even pain (a sandy feeling that may be accompanied
by irritation). If the problem is related to a reduction in the total
volume, the mucin layer of the corneal epithelium will not guarantee
a uniform film, thus shortening the tear break-up time. Specialists
such as optometrists and ophthalmologists, by means of dyes such
as fluorescein, Bengal pink, or lissamine green, can follow these
changes of the normal tear film to a pathological state. Tear film
stability is particularly important for contact lens wearing, because
a deficient volume or a poor quality will make the adaptation of
contact lenses difficult. Between 20% and 30% of contact lens
wearers develop ocular dryness. Extreme conditions such as air
conditioning, wind, heaters, or a prolonged read without a regular
blinking frequency will facilitate an increase of tear evaporation.

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