Orthokeratology uses rigid gas permeable contact lenses worn overnight to temporarily reshape the cornea and reduce or eliminate low to moderate degrees of myopia and astigmatism. The lenses have a molding effect on the cornea through epithelial redistribution, allowing patients to be correction-free during the day. However, the effect is not permanent and vision returns to the pre-treatment level if lenses are not worn. Ortho-k treatment generally takes one month for effects to stabilize and is most effective for prescriptions between -1.00 to -4.50 diopters of myopia and up to -1.50 diopters of astigmatism.

1. SLIDES PREPARED BY
OPTOM FASLU MUHAMMED

2.  Orthokeratology (often abbreviated to ortho-k) is the use of
specifically designed rigid gas permeable contact lenses to alter
the shape of the cornea in order to reduce or eliminate low to
moderate degrees of myopia and astigmatism. Ortho-k lenses are
worn at night and then removed in the morning. This makes them
especially suitable for people working in dusty atmospheres or
taking part in activities such as water or contact sports. There is
also increasing interest in the potential use of the technique in
reducing myopic progression in young patients.
 The lenses have a moulding effect on the cornea by a process of
epithelial redistribution. This is not permanent, hence the need for
nightly wear. If the lenses are left out, typically for two or three
consecutive nights depending on the original refractive error, the
original prescription returns.

3.  It can take up to seven nights for the lenses to fully correct the refraction
and up to a month before the correction is stable for a useful period of
time. On average, 60-70 per cent of the correction is achieved after the
first night of wear; however, some people are more successful
 with ortho-k lenses than others.
 As the effects of ortho-k lenses are fully reversible, they are a good
compromise for people considering corrective laser eye surgery but who
have reservations about the permanent change in corneal shape and
thickness. The patient is correction-free during the day and only wears
the lenses when sleeping, reducing the possible discomfort of dry eyes or
variable vision during the day. Most successful prescriptions tend to be
between -1.00DS and -4.50DS and up to -1.50DC, but it is also possible
to correct up to -6.00DS and, with specialist toric periphery ortho-k
lenses, up to -2.50DC.


4.  Ortho-k patients tend to be loyal customers
because you are the eye care professional
who enabled them to have correction-free,
comfortable, clear vision during the day.
Furthermore, as a planned replacement
programme, practitioner and patient develop
a good rapport early on in the treatment

5.  Ortho-k lenses are RGP lenses with a flat
central zone and a reverse geometry curve.
They have a similar shape to a post-Lasik
cornea (Figure 2).


6.  The fitting and aftercare of ortho-k lenses requires a significant amount of chair
time, which the patient and practitioner must be prepared for. The patient must
understand what happens to their eyes while wearing the lenses and confirm full
compliance with the fitting and aftercare procedure. It is only through regular
wear of the lenses and reliable attendance of aftercare appointments that they
will achieve their desired freedom from correction during the day. You cannot
have part-time correction with ortho-k lenses – it is all or nothing. When the
lenses are not worn, the myopia will return.
 Myopia is corrected during the night-time wearing of the lenses but, in the first
few days or weeks, the full correction may not be maintained for the whole day. It
is important that the patient does not have too high an expectation of the lenses
in the early days. However, there is usually a very positive response from the
patient when, after a few nights, they no longer have to wear an optical correction
for most of the day. The ‘wow’ effect may not be the same as an initial response
after Lasik, as the end point is reached in progressive steps. A 60-70 per cent
reduction in correction might be expected after the first night of wear, meaning a
-3.00DS myope may only require a -1.00DS correction after one night. During
these early days, the residual correction can easily be corrected with daily
disposable lenses.

7.  The first fitting appointment should include a full history and symptoms (including medical, ocular and contact
lens wearing history), refraction, corneal radius measurements, topography and a slit lamp examination (with
obvious particular emphasis on the front surface of the eye with and without fluorescein). If the patient is
currently an RGP wearer, they should leave their lenses out for 10-15 days before the fitting appointment to
ensure the cornea has returned to its ‘original’ shape. Most practitioners recommend less so for soft lens
wearers.
 The information from this initial appointment and the data collected should help to decide upon the suitability
of the patient for ortho-k fitting. It is also a useful time to make an initial judgement about how realistic the
patient expectations are and it is important at this stage to keep the patient informed of the exact nature of
the process and likely outcome – all supported with careful record-keeping of what has been recommended.
 Below we outline the ideal fitting profile:
 A 4-5mm diameter centrally flattened zone that is centred on the pupil to give good visual acuity and contrast
sensitivity in normal lighting conditions
 A concentric, regular steep ring zone in the mid-peripheral cornea around the central zone. The more regular
the ring, the better the lens centration
 A peripheral cornea whose geometry is unchanged
 After the fitting appointment the following criteria should be considered as likely to be suitable for ortho-k:
 Spherical prescription of between -0.75DS and -4.50DS.
 Cylindrical prescription up to -1.25DC ‘with the rule’ or -0.75DC ‘against the rule’.
 Astigmatic spectacle refraction should be the same as the corneal astigmatism. Like fitting RGP lenses, any
lenticular astigmatism may reduce the visual acuity and quality.

8.  Higher levels of myopia might not be easily corrected
due to the initial corneal eccentricity and required
epithelial reformation requirement.
 Larger pupils (notably with higher refractive error).
 Very flat corneas (flatter than radii of 8.20mm).
 Corneal irregularities – as might be caused by, for
example, keratoconus, dystrophies, pterygia.
 Very dry eyes – keratoconjunctivitis sicca (rheumatoid
arthritis is a contraindication, as might be some tear-
affecting medications).
 Poor re-epithelialisation rates (for example in diabetes
or with some medications).

9.  High motivation to be correction-free (professional or
occupation demands, sport, leisure).
 Requirements to take part in activities that are
affected by wearing glasses or contact lenses.
 An interest in, but concerns about, refractive surgery.
 Myopic progression, especially in younger children.
 Success may also be improved if the patient has a full
understanding about how ortho-k works, shows good
compliance, and is willing to attend the frequent
aftercare appointments in the first few weeks and
later attend half-yearly aftercares. They should also
be familiar with the expectation of changing their
lenses at least once a year.

10.  The lenses are individually made to the specifications required by each patient. When all the
required information has been received by the supplier they will calculate the parameters and
produce the lenses. In about 80 per cent of patients, the first lenses will be the correct fit and
provide the correction required. If the patient has been correctly selected and all the
measurements accurately taken, it is only necessary in a minority of cases that the lenses need
changing.
 To order the lenses the following information is required:
 Refraction.
 Back vertex distance.
 Central corneal radii.
 Total eccentricity at 30 degrees.
 Eccentricity in the four meridians at 30 degrees.
 Horizontal and vertical corneal diameter.
 Topography picture and the make and model of the keratographer used. Now you just need to
wait for the lenses to arrive.
 Once the contact lens is delivered the patient is asked to take an appointment.
 After the initial fit consecutive three reviews in a time period of two months is given.
 Also the patient is asked to follow proper care for the contact lenses.
 And the patient is advised to visit if there are any complications further.