ORTHOKERATOLOGY
A Successful
Combination for Ortho-K
This
approach can provide winning outcomes for your patients and practice.
By Deepa Chandrasekaran, OD, MS
Bausch
& Lomb's Vision Shaping Treatment (VST) program is a non-surgical process that
utilizes custom-designed lenses to gently reshape the front surface of the eye and
reduce nearsightedness. VST can be performed with a number of lens designs including
the BE Retainer lens (Precision Technology Services, Ltd.). In this article we'll
examine how the straightforward lens fitting provides successful clinical outcomes
— even for practitioners who are just getting started in offering this vision
correction option to their patients.
The BE Retainer lens, manufactured in the
Equalens II material (Dk = 85; Bausch & Lomb) is available through authorized
distributors in North America. The lens, according to its designer John Mountford,
Dip. App. Sc, FAAO, FCLSA. has a unique back surface geometry and is not a true
reverse geometry lens design.
A scientifically validated program
determines the appropriate BE Retainer lens design that will control the fluid forces
in the tear layer to create predictable corneal shape and refractive change.
The lens acts like a platform that
produces a required tear layer profile for an individual corneal shape. The tear
layer will apply negative force (pull) where it is the thickest and a positive force
(push), where it is thinnest to achieve equilibrium across the entire surface of
the fluid layer. It is this "squeeze film pressure" that we use in orthokeratology
to shift the epithelium, which causes the desired refractive change.
The Fitting Technique
Fitting of the lens begins with appropriate patient
selection. Rule out patients who have pupils larger than 6.00mm in normal light
or who have irregular astigmatism because of keratoconus or any corneal disorder.
Myopes up to –5.00D and low astigmats (up to –1.50D with-the-rule and
–0.75D against-the-rule) are generally good candidates. Juvenile to adult
myopes also are considered the best candidates for vision correction with orthokeratology.
After you deem a patient to be a good candidate,
determine his or her potential for optimal orthokeratology therapy from the required
refractive change and corneal topographic data of eccentricity value (e-value) and
apical radius.
The E300 Corneal Topographer (Medmont,
medmont.com) is particularly suited to the BE Retainer software because of integration
between the two systems. You may use other brands of topographers instead, but you
must enter the topography data into the software program.
Once you enter the data into the BE
Retainer program, the software determines the precise refractive potential of a
specific cornea. This potential is compared to the required refractive change to
determine the potential success of optimal orthokeratology therapy for the patient.
After entering the patient's data into
the BE program and determining the desired refractive change, the system calculates
both the patient's ideal BE Retainer design and the closest diagnostic trial lens
in the fitting set.
A Different Technique
In contrast to other orthokeratology techniques,
this one requires no detailed evaluation of the lens on the eye at the fitting visit.
Once fit with the BE Retainer lens from the trial set, advise the patient to sleep
while wearing the lenses overnight and to return the next day for follow-up.
The success of the initial lens fit on the
eye is gauged by the one day post-VST response. At that follow-up visit, either
tell the patient to continue with the current lenses or initiate a retrial using
a steeper or flatter base curve. The BE software provides guidance for this step
after you input the patient's topographical data.
Follow-up
visits should include an evaluation of the lens on-eye performance with fluorescein
pattern assessment, where you can best view subtleties of tear clearances and lens
fit by observing the fluorescein pattern through a yellow Wratten filter.
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Figure 1. Corneal topographies of patient AB,
top) Pre-VST; middle) One day Post-VST; bottom) One week Post-VST.
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Two Successful Fits
The following is a brief reporting of two patients
interested in orthokeratology who we fit with the BE Retainer lenses with good results.
Case #1 A 36-year-old female
patient, AB, presented wearing Frequency 55 Aspheric (CooperVision) contact lenses:
OD –1.00 DS (20/20); OS –1.75 DS (20/20). She had never worn GP lenses.
Figure 1a shows her corneal topographies.
The simulated K readings from the corneal
topography maps were OD 42.37 (7.965)/43.25 (7.803) @ 102 and OS 42.62 (7.918)/43.25
(7.803) @ 054.
Per the fitting protocol, we calculated
the base curve based on corneal plane refraction and corneal topography with the
help of BE Retainer software. We used trial lenses, provided through Essilor Laboratories,
of 8.80mm base curve and 11.0mm diameter for each eye. Visual acuity was 20/20-2
monocularly and 20/20 binocularly with the lenses.
We taught AB how to apply and remove
the lens and advised her to return the following day without having removed the
lenses. At the follow-up visit, AB's vision with lenses was 20/20-2 monocularly,
over-refraction was plano and the lenses centered with a faint bull's eye fluorescein
pattern.
The treatment provided the desired
visual effect of 20/20 monocularly without lenses and the expected associated corneal
topographic change of central flattening (Figure 1b).
We advised AB to continue wearing the
lenses throughout each night while sleeping and to return in one week for a follow-up
evaluation.
At the one-week follow-up visit, AB
was very pleased with the daytime vision of each eye without lenses. She reported
clear vision for computer work and reading. The clear vision was stable until 7
p.m. after which time she had some difficulty with glare. However, she reported
her vision was still good enough to function, including driving a car, without supplemental
correction.
The lenses were centered with a faint
bull's eye fluorescein pattern evident and an over-refraction of plano in both eyes.
We removed the lenses, and corneal topography again demonstrated the bull's eye
topographic patterns (Figure 1c).
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Figure 2. Corneal topographies of patient CD
a) Pre-VST; b) One day Post-VST; c) One week Post-VST |
AB's vision without lenses was 20/20
monocularly and 20/15 binocularly. We asked her to try wearing the lenses for one
night only to see if she would have clear vision for up to two days. She telephoned
the office to say that wearing the lenses for one night and seeing for two days
works very well for her. She continued to wear her lenses every alternate night,
routinely enjoying good clear vision through the late evening hours.
Case #2 A 29-year-old
female patient, CD, wore Acuvue Advance (Vistakon) contact lenses [OD –1.75
DS (20/20) and OS –2.00 DS (20/20)] and was interested in orthokeratology.
As with patient AB, this patient had a similar experience with the BE Retainer lens
fit per the recommended protocol.
Patient
CD wears her lenses every other night and enjoys clear vision throughout the day.
Figure 2 shows the topographical findings. Her 11.0mm diameter lens base curves
were OD 8.50mm and OS 8.46mm.
Both of the cases presented
here demonstrate that low myopic patients fit with BE Retainer lenses guided by
the software program can enjoy good vision throughout the day and into the evening
hours without the need for supplemental vision correction.
Successful Outcomes
Orthokeratology is a valid choice for some patients
who would like to see clearly without spectacles or contact lenses during the day.
The advantages of the BE Retainer lenses and the Vision Shaping Treatment program
are straightforward lens fitting and successful clinical outcomes.
Dr. Chandrasekaran is working as a Clinical
Assistant professor at UAB School of Optometry and at two private practices in Montgomery,
Alabama.
Contact Lens Spectrum, Issue: October 2006