Cone dystrophy

Now the standard of care, topographers soon pay for themselves.

In the early 1990s, corneal mapping was considered an academic research tool - expensive and difficult to interpret and understand. In the decade since, the use of corneal topography has risen exponentially - approximately 10 companies offer various methodologies. Today, topography is the standard of care for clinical practice and is mandatory for proper patient care in surgical comanagement and advanced contact lens care.

Count the ways . . .

Topography makes pretty pictures and impresses patients but what does it mean? Approach topography not as an "extra test" but as a "clinical monitor or surveillance" system. Let's look at some diagnoses or "rule outs" that you can use it to determine and gauge with.

* "I've never seen clearly with spectacles." When you can't refract an individual to 20/20, there's a reason that you must find: You need to rule out a variant astigmatism, irregular astigmatism, corneal anomaly and higher-order aberrations.

Topography can be particularly useful in pediatric cases; keeping children still for keratometry is an exasperating task.

* "I can't see with the new contact lenses you gave me." Sometimes the slit lamp doesn't see everything. Topography is the most appropriate method to determine if there's been contact lens induced corneal warpage or wrinkling, apical vault, corneal molding or corneal bearing.

Hydrophilic lenses or newer designs whose materials have "stiffness" can induce subclinical (not recognizable on biomicroscope) corneal/refractive anomalies. You may miss this during a refit but pick up on it with surveillance topography (as seen in the figure on page 50).

* "My son wants contact lenses." The keratometer reads only 1.5 mm of the central cornea while topography measures 8,000 to 10,000 discrete radii of curvature over the entire corneal surface. This is a no brainer: To fit a contact lens in the most efficient manner, topography is essential. The entry question is, "What does this cornea look like before the placement of a contact lens?"

As medical devices, contact lenses require periodic surveillance by a licensed, educated eye-care provider; topography is part of the medical device monitoring process. (1-800 Contacts and friends don't offer such services. Bring the level of care to a higher standard and third parties become less of an issue).

* "I wake up with irritated eyes." You perform a slit lamp exam and observe corneal staining and possibly an epithelial scalloping consistent with a basement membrane dystrophy. You must treat and monitor. You should use topography to complement your slit lamp exam. If there's a corneal anomaly, you can map it (turn off the extrapolation mode of the topographer; otherwise, it will hide the subtle defects).

Corneal mapping allows you to use the various indices and differential mapping to discern the benefit of therapy. Use of the differential mapping and documentation of the "regularity values" will assist in determining the proper therapy. Repeat topography for wound healing surveillance at each follow-up visit.

* "Doc, I'm ready for LASIK." The case of early diagnosis and surgical co-management. If you don't use a topographer in surgical comanagement - well, as Clint Eastwood might say, "I think you have a healthy, regular cornea to have LASIK - Do you feel lucky? Well, do you?"

If you don't have some form of corneal imaging as well as pachymetry available, you shouldn't co-manage a refractive surgical case. You need not spend $15,000 on equipment; however, ask yourself how many surgical referrals will be rejected because of undiagnosed corneal anomalies or a thin central corneal measurement. Topography can detect corneal anomalies that you can't visualize with the best biomicroscopic exam nor determine via the best refraction.

In screening patients for LASIK, I've found early or form-fruste keratoconus, a form of ectasia that lacks the visible corneal anomalies yet demonstrates an inferior displacement of the apical cornea and lack of topographic symmetry.

Another case wanted LASIK to rid herself of the inconvenience of spectacles and contacts lenses. Five exams left her at 20/25 vision with a moderate level of myopic astigmatism. Keratometry was documented as stable without variances and visual acuity was always best corrected to only 20/25 +. Even when I performed retinoscopy, it was sharp and clear.

Other than the acuity, this was an excellent LASIK candidate. Until the topography, which exhibited a subtle inferior apical displacement with significant variance in her regularity indices. I showed the topography to two O.D.s and three M.D.s five different responses. Ultimately, the patient didn't have LASIK and she was refit to a specialty design gas permeable lens.

What about the police officer who refracts post LASIK to 20/20, yet the subtle undercorrection that he has is making him unhappy? In this case, topography will demonstrate abnormalities of the postoperative cornea such as decentration of the ablation or central islands. It will assist in determining the cause of "less than optimal" results and assist in advising the patient.

* "Doc, I got a piece of metal in my eye." The case of wound healing management. How do you document and determine wound healing on a patient who has a foreign body (FB), abrasion or comanagement of a postoperative patient?

Medicare likes drawings, but I didn't go to art school. Photos mean a thousand words. Topography should be complemented with 35 mm or digital photodocumentation. The topographer captures a picture that documents the location and size of the FB, defect or surgical wound. More importantly, it will document the defect or wound at 24 hours, seven days and until complete wound healing.

If a patient enters the office (CPT 99214 or 92150) with an abrasion (ICD 918.10) or wound, you should take a topography (CPT 92499 or 92285 [anterior segment photo]) before and after FB removal. Why? The epithelial defect created by the removal of the FB (ICD 65222) will differ significantly from the original wound.

The initial topography documents the location and size; the second documents the epithelial defect and the subsequent (CPT modifier -76) determines healing. If you've never seen this patient nor have baseline topography of each eye, take a baseline topography of the fellow eye for comparison.

* Specialty contact lens designs. Feel uncomfortable with designing a bitoric, keratoconic, post graft or even a spherical gas permeable (GP) contact lens? Most topographers have some form of contact lens design software to assist. The software allows you to use various materials and to manipulate the fit and fluorescein pattern on screen as many times as desired to establish just the right fit.

Send the information to your lab for a "custom fit lens." It's a lot more efficient than calling in a refraction and keratometric reading. Chair time and overhead are reduced because of a decrease in lens reorders.

In a study conducted by Daniels, Silbert and Jedlicka, the topographic software enabled the fitter to create a GP design that yielded a comparable fitting rate of approximately 90% comparable to diagnostically fit and better than empirically fit GP lenses (see figure at left).

* Keratoconus identification and management. Recognition of the disease has been increasing simply by the use of topography in LASIK screening. However, frank ectasia of the cornea, noted on retinoscopy and slit lamp exam, is best confirmed by topography. It will assist the practitioner in determining the position of the cone and differentiate the form of ectasia (i.e., keratoconus or pellucid).

If the keratoconic patient requires a graft, topography is an essential part in monitoring the postoperative eye; it will assist in the peri-operative suture adjustment as well as postoperative suture removal and subsequent contact lens fit.

Make room in your practice

While topography is not new, it's still highly under-used in clinical practice. As the standards of care change, topography or corneal imaging will become an essential part of patient care. Keratometry still has its place, and so does schiotz tonometry. But as we evaluate its multiple uses and benefits in patient care, the value of a topographer will quickly become evident.

KEN DANIELS, O.D., F.A.A.O.

Author's note: The author has no financial interest in any company that makes or develops corneal imaging systems. He has, however, been a research consultant for Tomey Corp.

Dr. Daniels is adjunct assistant clinical professor at the Pennsylvania College of Optometry and is an NEI Investigator. He's also in private practice at Hopewell-Lambertville Eye Associates in New Jersey. You can reach him at (609) 466-0055.

Copyright Boucher Communications, Inc. Jun 2003
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