The
human eye is an amazing organ comprised of fifteen parts, all working together
so we can experience vision. Over time, our eyes start to age showing signs of
lost efficiency of various functionalities. One of the main parts of the eye,
the cornea, is a fascinating piece of tissue. It is comprised of five layers,
all of which are designed to be optically transparent.
The
cornea provides a surface for the tear film, the layer of moisture with
multiple functions, to cling to. Light is bent by the greatest degree when
passing through these structures so it can be focused on point with the retina.
The crystalline lens accounts for the remaining third of refractive
power.
Refractive
issues appear when the power of these anatomical components – the cornea and
crystalline lens is not well coordinated with the physical length of the
eyeball. In hyperopia (long-sightedness), the eyeball is too short for its
refractive power, and in myopia (short-sightedness), it is too long.
Common
surgeries such as LASIK and PRK have addressed this imbalance of refractive power
to eyeball length by reshaping the cornea. Thin corneas can be treated with
refractive procedures, and treatment suitability is also subject to other
eligibility criteria such as pre-existing corneal disease and even lifestyle
factors. Therefore, it is important to choose the appropriate candidates for
each type of procedure.
The
minimum corneal thickness required for refractive surgery is dependent on the
degree of refractive error that needs to be corrected. The higher the
refractive error, the higher the prescription required, and usually, the more
tissue that needs to be removed.
LASIK
procedures require the creation of
a flap of corneal tissue and, for those with thin corneas, make it challenging
for reshaping. PRK surgery solves this issue by removing the very top layer,
known as the epithelium, which leaves the rest of the corneal matter available
for sculpting by laser. However, there are still requirements for patients
considering PRK surgery, and sometimes other options must be considered that do
not involve a laser to reshape the cornea.
Some
options include intraocular contact lenses, or implantable contact lenses
(ICL). These lenses are artificial and are made of biosynthetic material that
goes between the iris and the crystalline lens. However, not everyone may
benefit from these lenses, and LASIK or PRK treatments may be more suitable to
those who could benefit from a more permanent solution.
