Orthokeratology alias corneal refractive therapy
is the use of specialized lenses for temporary
correction of mild-to-moderate myopia. Modern
orthokeratology involves the overnight use of
reverse-geometry gas-permeable lenses as an alternative
to refractive surgery and spectacle wear.
Orthokeratology is also often referred to
as OK, ortho-k, corneal reshaping and colloquially
rigid contacts. Modern orthokeratology or commonly
overnight orthokeratology is now established
worldwide as a viable alternative to refractive
Historical analysis of orthokeratology
The history of orthokeratology can be traced
as far back as to the Chinese myth of the use
of small weights or sandbags on eyelids during
sleep to reduce myopia. This can be considered
the basic principle behind orthokeratology.
This was followed by another precursor to modern
orthokeratology in the concept of flat-fitting
glass scleral lenses. In 1888, the French ophthalmologist,
Eugene Kalt, implemented these lenses to flatten
the cone in keratoconus cases and hence reduce
Modern orthokeratology took its first step
in 1962, when George Jessen, made an accidental
discovery. While working on his application
of the “orthofocus” method for
fitting polymethylmethacrylate (PMMA) lenses,
he chanced upon improvements in uncorrected
vision once the lenses were removed. The 1960s
and 1970s saw various researches on the conventional
In 1971, the International Orthokeratology
Section of the National Eye Research Foundation
defined orthokeratology as “the reduction,
modification, or elimination of refractive
anomalies by the programmed application of
contact lenses.” However, this definition
became redundant with time.
Problems in stabilizing flat-fitting lenses
on the cornea led to various experiments to
modify lens designs. Meanwhile, four studies
on the effectiveness of orthokeratology continued
using different lens designs and theories.
There were four such studies with identical
reports of modest success in reductions in
myopia (averaging an estimated 1.00 D) but
with erratic and individually variable patterns.
Thereafter, orthokeratology took a backseat
in refractive concepts until its resurgence
in the mid 1990s.
Renewed interest occurred due to advancement
in technology and a new concept of accelerated
orthokeratology. This was triggered by production
of reverse-geometry lens designs by Wlodyga
and Stoyan; the invention of appliances for
corneal topographic analysis; and the availability
of high-Dk gas-permeable materials that made
overnight lens use possible.
orthokeratology came about overnight, which
is now the standard practice worldwide.
In 2003, the Food and Drug Administration
approved the Paragon CRT, the first of
its kind, for use in overnight orthokeratology
in the US.
The methodology behind overnight orthokeratology
In overnight orthokeratology, the specialized
lenses are used during night sleep and taken
off on awakening. This ensures clear vision
without the help of spectacle or contact lenses
all through the day.
In modern orthokeratology, the specialized
lenses used are reverse-geometry gas-permeable
lenses. The effect of the use of these lenses
is noticeable almost instantly and the constancy
of the therapy after 7 to 10 days of its use.
The procedure is also totally reversible once
the lens is discontinued.
The result of the process occurs through a
fine reshaping of the anterior corneal layers.
This results in thinning of the central corneal
epithelium and thickening of the mid peripheral
stroma. However, the cellular biology of these
changes is still being investigated further.
Effectiveness of orthokeratology
Various clinical researches on overnight orthokeratology
have been conducted by the application of various
reverse-geometry lens designs. They have ascertained
the process to be an effective corrective technique
for myopia, to a maximum of around 4.00 D.
Though the procedure has been tried on patients
with higher myopia (mainly in Asia), there
have been alarms about its safety and standard
of vision in such cases.
The ability of orthokeratology to correct
astigmatism, hyperopia and possibly presbyopia
is still undergoing extensive research. The
toric reverse-geometry lenses that are specialized
to correct astigmatism are currently under
Pros and cons of overnight orthokeratology
The benefits of this process are its ease
of use and non-invasive nature and its reversible
potential. Moreover, once the lenses are removed
after nightwear, it almost instantly removes
any left over edema and a tear film fragment
build up. This also ensures insignificant lens
uneasiness generally associated with open-eye
gas-permeable lens use. Hazards associated
with daily wear for instance 3-and 9-o’clock
staining or ocular dryness is also minimal.
Among its disadvantages is the lesser issue
of the temporary nature of the therapy. If
night uses of lenses are discontinued, the
cornea reverts to its original shape soon.
The biggest and very serious concern is the
complication of overnight hypoxia. Though there
is an antidote in the use of high-Dk materials,
there has been a high incidence of severe corneal
infections due to a lack of proper clinical
standards. There has been a higher incidence
of such infections in East Asia compared to
Western nations. Worse still, many of the cases
have been children below 15. Such cases have
reported noticeable decrease in best-corrected
visual clarity and have had to undergo keratoplasty
to bring back eyesight.