corneal pachymetry

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® • 
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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® Non-­‐contact Pachymetry 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 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 • 
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Op5cal low-­‐coherence reflectometry Non-­‐invasive, non-­‐contact Biometer with a huge specifica5on • 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