OCULUS Pentacam Interpretation Guide

58
10.9 Pellucid marginal degeneration
These are pictures of classic pellucid marginal degeneration (PMD). The pachymetry map
(Figure 69) shows the band of thinning located 1 - 2 mm from the inferior limbus. This is an area
that cannot be imaged on a Placido system, which is limited to imaging the central 9.0 mm.
The Scheimpflug images (Figure 67, Figure 89) show a relatively normal appearance when the
cornea is viewed through a horizontal cut and the pathognomonic appearance when viewed
through a vertical cross-section, revealing severe flattening over most of the cornea, an inferior
band of thinning and a sharp change in corneal contour over the area of thinning. PMD is one
of the most misdiagnosed conditions when the diagnosis is based on Placido imaging. A Placido
system cannot reach to the area of the pathology. Descriptive curvature terms such as "lobster
claw" pattern, etc. are fraught with problems and are associated with a very high false positive
rate.
DIAGNOSIS - pellucid marginal degeneration
Figure 69: Corneal thickness in a case of PMD
Figure 67: Scheimpflug image 180°
showing PMD
Figure 68: Scheimpflug image 90°
showing PMD
10 Screening for refractive surgery

OCULUS Pentacam Specifications

General

Measurement Time	Less than 2 seconds
Corneal Coverage	Up to 12 mm
Software	Pentacam Software
Data Transfer	USB
Corneal Topography	Yes
Display	External monitor required
Measurement Principle	Scheimpflug imaging
Camera	Rotating Scheimpflug camera
Light Source	Blue LED
Pachymetry	Yes
Anterior Chamber Analysis	Yes
Imaging Principle	Scheimpflug imaging
Fixation	Internal
Power Supply	100-240 V, 50/60 Hz
Resolution	High resolution
Lens Density Measurement	Yes
Dimensions	Varies depending on model and configuration
Weight	Varies by model, check manufacturer specifications
Number of Images	25 or 50