Pentacam Scheimpflug Imaging

How the Pentacam works

A Scheimpflug camera is angled so that a thin slice of the cornea is in focus from front to back. The Pentacam rotates this camera around the eye's axis, capturing dozens of slices in about two seconds, and reconstructs the whole cornea and anterior chamber in three dimensions. Because it images the cornea's back surface directly, rather than inferring it, it detects changes there that a front-surface topographer cannot see.

What it measures

• Front and back surface curvature maps
• Elevation maps of both surfaces against a reference sphere, which reveal early cones
• A thickness map of the entire cornea, with the thinnest point located
• Indices that combine these into a keratoconus probability and a screening score for refractive surgery
• Anterior chamber depth and angle, relevant to the EVO ICL and to glaucoma
• Lens density, which grades a cataract objectively

Why the back surface matters

Keratoconus often begins on the back surface of the cornea before the front surface or the vision changes. Elevation of the back surface, and thinning matched to it, are the earliest reliable signs, and they are why tomography rather than topography alone is used to screen laser vision correction candidates. Operating on an eye with undetected early keratoconus risks ectasia, so tomography is an important safeguard before refractive surgery.

When it is used

LASIK, PRK, SMILE and ICL consultations; keratoconus evaluation and monitoring; before cataract and lens surgery to plan astigmatism correction and detect irregularity that affects lens choice; in the assessment of corneal dystrophies, scars and grafts; and in the design of specialty contact lenses. All four of our offices have Pentacam corneal tomography, and it is part of your consultation where it helps answer the question for your eyes.

Preparation

Soft contact lenses out for a few days and rigid or scleral lenses for two to three weeks before scanning. A stable tear film gives the cleanest scan.