Article

CLINICAL: CORNEA

FRONT AND CENTER

AS-OCT aids in identifying and monitoring an array of conditions

Anterior segment (AS)-OCT provides quantitative and qualitative data on the front section of the eye, namely the anterior chamber angle, cornea, crystalline lens and iris, via a cross-sectional view.

Here, I review the common uses for this technology.

GLAUCOMA

AS-OCT is advantageous in assisting in both the diagnosis and monitoring of glaucoma. Specifically it:

  • is non-contact, making it ideal for use on patients uncooperative with gonioscopy. That said, the technology should be used with gonioscopy, as gonioscopy enables you to see trabecular meshwork pigmentation, among other items that AS-OCT does not.
  • is not circumvented by corneal pathology, unlike gonioscopy.
  • enhances your visualization of the anatomy of the iris, so you can look for plateau iris, which often precedes chronic angle closure glaucoma, and discover rare pathologies, such as tumors, affecting the iris.
  • helps you look for narrow anterior chamber angles, particularly during physiological mydriasis, as the device can be used in dark environments, and aids you in the consistent monitoring of the angle because its video imaging feature allows its user to note the exact positioning of conjunctival blood vessels, iridotomies, iris, nevi and more during scan acquisition.
  • provides an enhanced view of peripheral iridotomies (PI), so you can see whether the PI is fully patent or assess whether the laser did, in fact, create a full-thickness PI.
  • aids in your detection of pupillary block, as it reveals the presence of a convex iris configuration.
  • measures lens thickness and crystalline lens rise.

A patient‘s Descemet’s membrane endothelial keratopathy graft, behind a corneal transplant, became detached and was visible with AS-OCT.

Gross detachment of a graft in a patient who had a previous Descemet’s stripping automated endothelial keratoplasty, via AS-OCT.

SCLERAL LENS FITS

Knowledge of scleral shape is essential to the proper fit of a scleral contact lens. AS-OCT provides assistance here in that it enables the measurement of corneal, limbal and scleral angles. (Keep in mind that corneal topography provides shape and elevation data, alone.) Further, slit lamps are prone to error in providing accurate apical clearance measurements of scleral lenses, and AS-OCT is not.

CORNEAL PATHOLOGY/SURGERIES

In conditions, such as Fuchs’ corneal dystrophy, in which central corneal thickness measurements are needed to assess corneal edema, AS-OCT provides this data.

In addition, the device aids in the planning and management of pre and post corneal surgeries, respectively.

For example, you can use it to monitor corneal health before and after procedures, such as corneal collagen crosslinking and modern keratoplasties, such as Descemet’s membrane endothelial keratoplasty, Descemet’s stripping endothelial keratoplasty and Descemet’s stripping automated endothelial keratoplasty. In the case of the latter procedures, the device can help you detect proper graft adhesion. Also, you can monitor corneal thickness to see whether edema is occurring, and watch for graft rejection as well as scar formation. A Descemet’s membrane endothelial keratoplasty graft is 10 μm to 15 μm thick, so it’s hard to visualize via slit lamp.

Further, you can utilize the device to detect non-obvious forme fruste keratoconus prior to performing refractive surgery and, perhaps, proceed with corneal collagen crosslinking if the keratoconus is progressing. (Some patients might not have obvious corneal steepening, but might have corneal thinning, which can indicate a risk factor for keratoconus.)

Finally, AS-OCT has the ability to perform corneal pachymetry mapping, which can be useful in detecting ectasia and corneal steepening.

CATARACTS

When it comes to cataract surgery and phakic IOL implantation, AS-OCT can provide measurements of the axial length of the eye and other useful biometrics, such as anterior chamber depth, the anterior chamber angle, lens meridian parameter and posterior lens thickness. This ability enables you to get reliable data to correctly select IOL lens powers and better calculate effective lens position to enhance the prediction of proper refractive outcomes.

These newer biometrics are being used in recent IOL formulas to help reduce residual refractive error. This same data also helps you determine proper lens selection used during phakic IOL procedures by measuring anterior chamber width and corneal vault.

A fully reattached Descemet’s membrane endothelial keratopathy graft, via AS-OCT, after air bubble injection to re-attach the graft.
All Images courtesy of Dr. Josh Johnston

ADVANCING CARE

Further advancement of our profession relies primarily on two things: (1) expanded scope laws that allow us to provide more medically driven optometric care and (2) advancements in the diagnostic and treatment technologies we use in our clinics. AS-OCT is one such advancement that is becoming a vital tool in our diagnostic armamentarium.

FINAL WORD

CPT Code 92132 is the code for common optometric uses of the AS-OCT. That said, not all insurance carriers will reimburse for this code. OM