الفهرس 
PHYSICS, TECHNOLOGY AND SOFTWARE OF PENTACAMOnly 14 pages are availabe for public view
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Abstract
T
he Pentacam is the first instrument to use a rotating Scheimpflug camera to take multiple images of the anterior segment and use these to generate three-dimensional images and calculate measurements of the eye. It provides:
• Detailed Scheimpflug images of the anterior segment from anterior corneal surface to the posterior surface of the crystalline lens
• Three-dimensional visualization and animation of the anterior segment.
• Measurements of anterior chamber angle, chamber volume, chamber depth, pupil diameter and corneal characteristics such as eccentricity, central radius and astigmatism.
• Pachymetry (limbus to limbus, accurate to ±5 μm). We can locate any point on the cornea manually, on screen, and see the thickness at that point. The map notes the thinnest region.
• Densitometry data for the cornea and the crystalline lens, including the subcapsular layer, shown both graphically and quantitatively. The quantitative data make it easy to identify a developing cataract, categorize existing cataracts, and document their development.
• Topographic maps of the anterior and posterior corneal surfaces, based on measurement of 25, 000 elevation points (when using the two-second scan), including tangential and sagittal (axial) curvature and limbus-to-limbus elevation, with freely selectable reference bodies.
• A “true net power map” that shows the refractive power of the cornea at any given point. (The instrument calculates the refractive power of both surfaces and adds them together.)
Because the Pentacam only measures to the posterior capsule of the crystalline lens, it can’t provide a measure of axial length. Also, because it’s optically based, it can’t measure from sulcus to sulcus. However, it can usually capture data behind an opacity because the camera images the eye from so many angles.
The Pentacam features automatic Keratoconus detection. Progression of keratoconus and following treatment with newer technologies like corneal collagen crosslinking and Intacs¨ can be monitored.
The Pentacam provides a comprehensive, precise and valid measurement of corneal power and optical aberrations that allows the ophthalmologist to make better decisions regarding the IOL design and power, particularly in cases with abnormal corneas, either from ectatic conditions or previous keratorefractive surgery. The measurement obtained from the Pentacam in abnormal corneas should be used in combination with formulas designed for this particular instrument.
The Pentacam Tomography calculates a virtual model of the anterior segment of the eye including the cornea. It is possible to move, zoom and rotate it to detect the depth and the size of any opacity in the cornea.
The Pentacam is useful in managing post-PKP patients especially in decision making with respect to suture removal. Another interesting application is in diagnosing Capsular Bag Distension Syndrome. Also the Pentacam identify subtle corneal opacities and follow the changes over time such as in adenoviral keratoconjunctivits.
The Pentacam illustrates the location of implantable phakic IOL’s positioning in relation to crystalline lens as well as cornea, AC angle during the pre-op assessment. This allows the ophthalmologist to follow up these patients with ICL for monitoring their risk for developing cataract.
For glaucoma screening, Anterior Chamber Volume has been found to be a good screening tool for diagnosing eyes with narrow angles. The software provides a colored map of the anterior chamber depth-both central and peripheral. Also the software allows for IOP modification taking into consideration the corneal thickness.
However it is limited in its evaluation of the anterior chamber angle. Direct angle visualization of the scleral spur, ciliary body, and ciliary sulcus is possible only with the Anterior Segment OCT and UBM; not the Pentacam.
Opacification of the crystalline lens can be quantitatively imaged and analyzed using the Pentacam. The grading of lens density through Scheimpflug images has been found to correlate well with the LOCS III grading system for cataracts. This densitometry helps in choosing the power modality during pacoemulsification.It is also excellent tool for identifying intralenticular foreign bodies.
The key advantages of the rotating imaging process are the precise measurement of the central cornea, the correction of eye movements, the easy fixation for the patients and the extremely short examination time.