CORNEAL TOPOGRAPHY
Is Your Practice Ready for a Corneal Topographer
A corneal topographer can help advance your
lens practice with custom fits, corneal reshaping and more.
By Dianne M. Anderson, OD
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Figure 1.(top) Oval Keratoconus (middle) Pellucid
Marginal Degeneration, (bottom) Oblique Astigmatism. It is difficult to determine the
diagnosis with refraction and
keratometry values. The topography maps clearly
show the differences.
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Corneal
topography plays an integral part in the decision-making process when managing
challenging contact lens fits as well as in the diagnosis and management of corneal
disorders.
Without topography, choices are limited to ordering
and dispensing numerous pairs of diagnostic contact lenses or attempting to refer
the patient to another practice. This can be time-consuming for both practitioner
and patient. And the results may be less than favorable if the patient chooses not
to return to your practice. Your decision to purchase a topographer should be motivated
by the desire to provide patients with the most comprehensive eye care possible
— as well as the desire to expand your knowledge and fitting skills with specialty
contact lens designs.
Access
to topography also opens up the world of corneal reshaping or orthokeratology. The
return on investment with corneal reshaping can be spectacular, and so can patient
satisfaction.
Many people view this modality
as an attractive alternative to LASIK. And because the FDA has placed no age restriction
on corneal reshaping, it's a great alternative to glasses or daytime contact lenses
for adolescents.
The future of corneal reshaping also
looks promising as new lens designs such as hyperopic/presbyopic, toric and possibly
hybrid lenses come to market. Ongoing research shows the potential for myopia control
with corneal reshaping. So there's great promise for both practitioner and consumer
that this modality may establish future trends in correcting refractive errors with
contact lenses.
Evaluating Your Lens Practice
The decision to purchase a corneal topographer
is very individualized. What is imperative to one practitioner may be meaningless
to another. If you fit into one or more of the following scenarios, a topographer
could be a significant asset to your practice.
You refer patients to other practices
for topography. If questionable astigmatic refractions and irregular
keratometry mires send you directly to the referral pad, think again. You could
be servicing these patients with your own topographer.
Patients
will be impressed with the technology and convenience. You can collect the service
fee and proceed to schedule the patient for a specialty lens fitting. Keep in mind
that referring patients out may give them the impression that you're not fully capable
of meeting their needs.
You enjoy working with
GPs such as keratoconic and toric designs. These specialty GPs are best
fit via diagnostic lenses from fitting sets. The initial diagnostic lens choice
is best calculated from evaluation of corneal topography. It's helpful to know if
the patient has keratoconus, pellucid marginal degeneration (PMD) or highly oblique
astigmatism (Figure 1). The dynamics of the GP will be more physiologically compliant
with the underlying cornea if you consider the peripheral contours of the cornea.
Many new GP designs allow unique manipulations of the optic zone, peripheral curves
and eccentricity to customize the fit for improved visual performance and comfort.
You
manage difficult astigmatic soft contact lens fits. Some astigmatic
refractions give great results with spectacles, but unsatisfactory results with
soft toric lenses. Corneal topography can reveal some reasons for this trouble.
The astigmatism may be irregular, oblique, lenticular or limbal-to-limbal (Figure
2). These cases may require custom toric, soft lens designs. Accurate measurement
of HVID with the topographer is key to successful lens diameter and base curve selection.
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Figure
2. Limbal-to-limbal astigmatism. These patients can experience poor quality of vision
with standard lens designs. Spectacle correction, however, is usually excellent. |
You rehabilitate patients
who have contact lens-induced corneal warpage. Many patients overextend
the life of their soft lenses or wear traditional hydrogels on a continuous schedule.
Some are wearing tight lenses. GP wearers can be guilty of overwear and excessive
protein deposits, or may be wearing old, poorly fit lenses. The result may be transient
visual impairment secondary to corneal edema and warpage. This usually presents
as a significant change in the refractive astigmatism that correlates to a significant
change in corneal astigmatism.
The practitioner may find irregular
keratometry mires which make it difficult to differentiate corneal warpage from
early keratoconus. However, you can better evaluate the problem from a topographic
map.
Discontinuing lens wear and repeating
topography in three to four weeks may show a significant difference map (Figure
3). These maps are an impressive way to explain this problem and prevent its recurrence.
You have an interest in corneal
reshaping. With advanced lens designs and solid FDA results on file, the
time is ripe to expand your services to include corneal reshaping. There is a great
potential for patient retention and profit within this specialty. However, there's
also a great deal of apprehension linked to this decision. The initial investment
required may seem overwhelming and you may have questions about your potential success
with soliciting patients or with your clinical fitting skills.
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Figure 3. Difference
map of lens-induced corneal warpage. Notice the change in corneal appearance and
refraction over three weeks time. This patient had been wearing a large diameter,
tight-fitting soft toric lens. |
Becoming
certified in corneal reshaping is straightforward. And learning the dynamics of
reverse-geometry lenses will set you apart from the average contact lens practitioner.
Certification courses cost nothing but a few hours of well-spent time.
Because there are now several
corneal reshaping lenses on the market, choosing the designs to fit can also be
overwhelming. Consulting with the vendors and distributing labs of corneal reshaping
lenses will help you choose the designs that will best fit into your practice.
Your patients are inquiring about
LASIK. If you're in a successful contact lens practice, rarely will a day
go by without several patients inquiring about their candidacy for LASIK. You may
be prepared to answer their questions or to refer them out for further evaluation.
With a topographer, you are able to
begin the LASIK evaluation in your office. There may be some interesting, unexpected
patterns on the topography map that could disqualify the patient. Even if the topography
map shows everything is normal, the patient may wish to try corneal reshaping as
a safer alternative to LASIK.
Choosing a Topographer
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Figure 4. (top) Paragon CRT Images. Inferior
decentered lens needs reduced LZA, (middle) laterally decentered lens needs increased
RZD (bottom) well-centered CRT lens |
There are numerous manufacturers and models of
topographers. Basic features include axial and refractive maps, tangential maps,
difference or subtractive maps,
elevation maps and contact lens fitting analysis.
More advanced features include video imaging, detailed map analysis and/or Zernike
analysis/wavefront aberrometry. Some models combine autorefraction and keratometry
with corneal mapping software. Combined features may be a good choice if you're
just getting started with topography and don't own an autorefractor or autokeratometer.
These models save space, and perform the duties of three instruments in one.
Each model differs in the quality and detail
of images produced. Models with high resolution, numerous rings and large number
of data points will generate more detailed maps. Some topography-based ortho-k designs
require a topographer with high resolution capabilities for precise measurements
of apical radius, sagittal depth and HVID. Prices vary according to features and
detail. Some manufacturers price their topographers with or without the required
laptop or desktop computer. You may need additional software to perform functions
such as ortho-k predictability and specific GP lens design. It's also important
that you understand the applications and limitations of the different models before
you make a decision.
You
can also gather more information from the manufacturer Web sites and instrument
buying guides.
Applying Topography to Your Lens Practice
Performing topography saves chair time by allowing
you to accurately diagnose corneal disorders and efficiently fit or design the appropriate
contact lenses for each patient. In each case, the best treatment is determined
by diagnosis, patient needs and lenses available to best meet those needs (Table
1).
It's imperative to perform topography on patients
undergoing corneal reshaping. A baseline map is saved and used as a comparison to
monitor the patient's progress. Difference maps are helpful in determining which
changes in lens parameters, if any, are necessary (Figure 4).
Axial or refractive maps help you monitor
refractive changes and tangential maps help determine the orientation of those changes
on the cornea.
Summary
Utilizing corneal topography to its full potential
can advance your fitting skills and success with a variety of specialty contact
lens designs. The right combination of instruments and self-motivation will have
you well on your way to creating a profitable and rewarding specialty contact lens
practice.
To obtain references for this article,
please visit http://www.clspectrum.com/references.asp and click on document #129.
Dr. Anderson is a graduate of Indiana University
School of Optometry. She practices in the western suburbs of Chicago, specializing
in orthokeratology, keratoconus and post-surgical lens fits and anterior segment
disease. She may be reached at Dianne.Anderson@comcast.net
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TABLE 1 |
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Applicable
Diagnostic and Procedural Codes
ICD
-9 CODES
367.22 Irregular Astigmatism
371.50 Corneal Dystrophy, unspecified
371.52 Other Anterior Corneal Dystrophies
371.61 Keratoconus, stable
371.62 Keratoconus, acute hydrops
371.20 Corneal Edema, unspecified
371.24 Corneal Edema Secondary to CL Wear
371.82 Disorder Secondary to CL Wear (not edema)
CPT CODES
92015 Refraction, Refractive Visit
92070 CL Fit for Treatment of Disease/Lenses
Supplied
92310 CL Design, Fit and Follow-up (non-aphakic)
92325 CL Modification/Supervision of Adaptation
92326 Replacement of Contact Lens
92499 Corneal Topography
CONTACT LENS MATERIALS
V2510 GP Spherical
V2520 Soft
Spherical
V2511 GP Toric
V2521 Soft Toric
V2513 GP Ext Wear
V2531 Soft
Ext Wear
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Internet
Resources
Paragoncrt.com.
User-friendly online CRT tutorial and certification exam. Offers monthly online
interactive Web seminars, numerous practice-management guidelines available.
BERetainer.com.
This site provides a detailed explanation of topography features needed to successfully
fit this version of Bausch & Lomb's Vision Shaping Treatment (VST). Access articles
on pre- and post-fitting topography analysis. VST and BE Retainer certification
available online.
SynergEyes.com.
Detailed, interactive site geared toward informing practitioners and patients about
this new family of hybrid lenses.
Clspectrum.com.
Use the keywords "corneal topography" to access a wealth of archived articles on
various applications of topography.
Contemporary Orthokeratology
— This is an ortho-k overview written by Ed Bennett, OD, MSEd. Listed under
Vision Care CE on clspectrum.com. COPE-approved for 1 credit hour.
Contact Lens Spectrum, Issue: August 2006