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CORNEAL PACHYMETRY
Dr Cesar Carrillo
May, 2014
Vien9ane/NOC **Disclaimer** The images contained in this presenta5on are not
my own, they can be found on the web
Corneal Pachymetry Outline
• Indica5ons • Contact methods:
o Ultrasonic pachymetry o Op5cal pachymetry (confocal microscopy)
• Non-‐contact methods: o Op5cal biometry (OCT,OLCR, ORBSCAN, Pentacam)
Corneal Pachymetry Indica9ons • Measurement of corneal thickness • Used to gauge endothelial status • Refrac5ve surgery candidates • Central corneal thickness (CCT) as indicator of glaucoma risk (OHTS)
• Evalua5on and management of ocular hypertension & glaucoma
• Rou5ne part of ophthalmic evalua5on
Corneal Thickness
Corneal Pachymetry
Contact pachymeytry
1. Ultrasonic
2. Op5cal (confocal microscopy)
Ultrasound Pachymetry • Henderson and Kremer (1980) • Measure the amount of 5me (transit 5me) needed, for ultrasound pulse, to pass the cornea and return to the transducer
• Speed of sound in cornea is 1640m/sec
Corneal Pachymetry
Ultrasound biomicroscopy (40 -‐ 50 MHz) Very-‐high frequency ultrasound (70MHz) • Require water bath • Allow determina5on of corneal sublayer detail and pachymetry
Eye Cubed
• A/B ultrasound scan • 40 MHz UBM wide-‐field anterior segment mode
• Allows view of anterior structures: cornea , iris, ciliar body, lens an IOL
Corneal Pachymetry
Tradi9onal Ultrasound (10 – 20 MHz) • Dry contact systems • Simple • Portable • Cost-‐effec5ve • Accuracy relies on precise probe placement
Ultrasound Pachymetry Probe: • Piezoelectric crystal-‐geometrical design • Emits an ultrasonic beam of 20 MHz • Hand held • Straight probe handle difficult to use • Angled probe handle is easier
Ultrasound Pachymetry
Measurements: • Average series of thickness measurements in a frac5on of sec. • Record all readings within 5 -‐10° • Record all readings within 5 -‐10 μ • Reject readings outside the range • If the probe is not perpendicular or the readings are too disparate, is rejected
Ultrasound Pachymetry Accuracy: • ± 5 – 10 μ • Measure thickness range 200 -‐ 2000μ • Selected speed of 1640m/sec • Some units allow adjustments of sound speed (faster speed will produce a thicker corneal reading)
Ultrasound Pachymetry
Addi5onal features: • Built-‐in glaucoma risk calculator • Iden5fy a pa5ent’s 5-‐y risk of progression in glaucoma (OHTS) • OHTS based on 6 risk factors: Age, Race, IOP, Pagern Standard Devia5on, Cup to Disk ra5o, and CCT
Ultrasonic Pachymeters
1. PachPen® 2. Pachmate® 3. Tomey®
4. PalmScan P2000 FastPach®
PachPen®
• Ergonomic hand held, body angled
• Portable, LCD screen • Allows entry IOP = corrected IOP
• User segable speed of sound • Capture and store up to 9 measurements plus average
Tomey®
• Compact, portable • Built-‐in printer • Simple, quick & easy • 8 readings with Average • Pa5ent data imput • Measurement data export • Large data LED display
Pachmate® • Automa5c measurement mode, portable
• Up to 25 meas. of a single loca5on • Displays current, average, & Std dv • Mapping mode up to 33 measurements • Configura5on memory • Built-‐in IOP correc5on Calcula5on • Probe: 30,45,60,75 & 90°
PalmScan P2000 FastPach®
Corneal Pachymetry CONTACT PACHYMETRY • Ultrasound • Op5cal (Confocal Microscopy)
NON-‐CONTACT PACHYMETRY • OPTICAL (ORBSCAN-‐ OCT-‐OLCR-‐Pentacam)
Confocal Microscopy • Contact technique (high mag 20-‐500x) • Focus through cornea thickness (in vivo) • Display & allow measurements of detailed sublayer cellular structure
• Iden5fica5on of corneal microbial pathology
• Limited use in corneal opaci5es • Data acquisi5on & interpreta5on 5mely
ConfoScan 4®
OPTICAL PACHYMETRY • Original method using slit lamp • Non Contact Method • Thickness is es5mated using an equa5on
(refrac5ve index & ant. Radius of curvature) • Major problem in clinical, prac5cal use of
this instrument is repeatability of measurements, par5cularly among observers
Non-‐contact Pachymetry
Op5cal Pachymetry
Orbscan • Op5cal coherence
pachymetry • Provides pachymetry +
topography • Non contact op5cal
scanning • Underes5mates corneal
thickness in post refrac5ve surgery & haze
Op5cal Coherence Tomography (OCT)
• And op5cal low-‐coherence reflectometry (OLCR) are based on op5cal interferometry
• Discern sublayer detail and pachymetry • Perform measurements on corneas with pathology
• OCLR provides con5nuous measurements during corneal abla5on procedures
OLCR • Op5cal low-‐coherence reflectometry • Non-‐invasive, non-‐contact • Biometer with a huge specifica5on o • Axial eye length
• Corneal thickness • Anterior chamber depth • Aqueous depth • Lens thickness • Radii of corneal curvature of flat and steep meridian • Axis of the flat meridian • White-‐to-‐white distance • Pupil diameter
Visante OCT
Visante OCT
PentaCam® • Comprehensive anterior segment analyser • 3-‐D rota5ng Scheimpflug camera • Perform 5 func5ons in 2 sec 1. Scheimpflug image of anterior segment 2. 3-‐D anterior chamber analyser 3. Pachymetry 4. Corneal topography 5. Cataract analyser
PentaCam®
• Pachymetry displayed as a color image over its en5re area from limbus to limbus
• Actual thickness measured individually by a mouse click at any loca5ons
PentaCam®
PentaCam®
• Applica5ons: 1. Corneal refrac5ve surgery evalua5on 2. Glaucoma screening 3. IOP modifica5on (CCT) 4. Ketatoconus detec5on & quan5fica5on
Corneal Pachymetry Report