August 2012

 

CORNEA

 

Device focus

More knowledge yields better diagnoses


by Michelle Dalton EyeWorld Contributing Writer
   

Epithelial ingrowth in a LASIK flap with overlying epithelial modeling

Epithelium downgrowth around a DSAEK graft; the same cornea identifies the source of the ingrowth as a venting incision

Narrow angles before and after laser peripheral iridotomy

A partially detached DSAEK graft Source (all): Steven G. Safran, M.D.

How anterior segment optical coherence tomography is making it easier to plan treatment strategies

There is no doubt in most clinicians' minds that the technological advances witnessed in imaging devices has made diagnosing some abnormalities a bit easier for the anterior segment surgeon. "There's so much more information we can have at our fingertips now, it's incredible," said Steven G. Safran, M.D., in private practice, Lawrenceville, N.J. Among the pathologies more easily identified with anterior segment optical coherence tomography (OCT) are epithelial ingrowth under LASIK flaps, determining residual stromal bed thickness, etc. "Anterior segment OCT is incredibly important for evaluation of Descemet's stripping automated endothelial keratoplasty (DSAEK) and Descemet's membrane endothelial keratoplasty (DMEK) grafts," Dr. Safran said. "I think it will be necessary for any cornea surgeon doing this kind of work to have this technology."

Liliana Werner, M.D., Department of Ophthalmology and Visual Sciences, John A. Moran Eye Center, Salt Lake City, and her group recently published a study1 showing anterior segment OCT "can be useful in assessing intraoptic changes (which in turn may avoid a misdiagnosis of IOL opacification and help avoid unnecessary procedures such as posterior capsulotomy or vitrectomy)," she said. Anterior segment OCT is either time domain or spectral domain (sometimes referred to as Fourier domain); the former uses a moving reference mirror for measuring the time it takes for light to be reflected while the latter uses faster, non-mechanical technology to measure multiple wavelengths of reflected light across a spectrum, according to information on the Heidelberg Engineering (Carlsbad, Calif.) website.

"It's a very specific way of looking at small pieces of the anterior segment anatomy," Dr. Safran said. Time domain machines such as the Visante (Carl Zeiss Meditec [CZM], Dublin, Calif.) "are relatively easy to use," Dr. Werner said. "The examination of a non-contact, non-immersion technique and images at different meridians can be obtained relatively fast."

Dr. Safran prefers spectral domain systems, which include the RTVue (Optovue, Fremont, Calif.), which proclaims imaging speed unmatched by other spectral domain systems, the Cirrus HD-OCT (CZM), and the Spectralis (Heidelberg). The Cirrus is able to image a 4 mm section of the cornea, the RTVue 7 mm, and the Spectralis angle-to-angle, Dr. Safran said. "In my opinion, spectral domain is to time domain what computers are to slide rules," he said, citing better image quality potential from the spectral domain systems. Dr. Werner said clinically speaking, ophthalmologists can use these systems to "confirm a diagnosis of different conditions leading to opacification of IOLs, which include calcification of hydrophilic acrylic lenses, snowflake degeneration of PMMA lenses, among others."

Advantages of anterior segment OCT

Both physicians agreed, however, that a major benefit of anterior segment OCT is to confirm what the slit lamp cannot. "The slit lamp is still an incredibly important piece of equipment," Dr. Safran said. "But when you see something that needs clarification, OCT can provide very detailed information about things that can't be visualized optically. The OCT images are guided, however, by slit lamp examination and then can be used to bring out details about specific things seen on exam. When looking at the posterior segment we know where the macula and optic nerve are, so we can automatically go there to scan. But with anterior segment OCT, the pathology that needs examination is almost completely guided by the slit lamp evaluation." For instance, if a patient's corneal transplant graft is failing and the endothelium doesn't look healthy, "I can look at the posterior surface of the cornea to the host-graft junction," Dr. Safran said. "If the junction is small, you can plan on a DSAEK instead of a repeat graft." And because the diagnostic tool is helping plan a (potentially) safer surgery, using anterior segment OCT is reimbursable, he said. For more common pathologies, this type of OCT can help clinicians differentiate between posterior or anterior astigmatism, he added.

Dr. Werner said while IOL opacification and glistenings can generally be confirmed under the slit lamp, "some ophthalmologists not familiar with these conditions may be in doubt," she said. Since IOL calcification or snowflake degeneration can only be treated by explantation, an OCT scan can help confirm the location of the opacificationIOL, posterior capsule, vitreous, etc. "If unnecessary procedures such as Nd:YAG laser posterior capsulotomy or vitrectomy are avoided in these cases, the surgeon explanting/exchanging the opacified IOL will have the best conditions and will be able to place the new lens within the capsular bag," she said.

Anterior segment OCT is being used to measure corneal flaps, anterior chamber diameter, and crystalline lens thickness, and can be used to evaluate phakic IOL vaulting, epithelial ingrowth in post-LASIK eyes, or residual stromal bed thickness, or even help determine where to place sutures in a corneal transplant, the surgeons said.

"If my OCT could do what the IOLMaster [CZM] can do, I'd have to have two OCTs in the office," Dr. Safran joked.

Reference

1. Werner L, Michelson J, Ollerton A, Leishman L, Bodnar Z. Anterior segment optical coherence tomography in the assessment of postoperative intraocular lens optic changes. J Cataract Refract Surg. 2012;38:1077-1085.

Editors' note: Dr. Safran is a non-paid consultant for Heidelberg. Dr. Werner has no financial interests related to this article.

Contact information

Safran: 215-962 5177, safran12@comcast.net
Werner: 801-581-6586, liliana.werner@hsc.utah.edu

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