Presentation is loading. Please wait.

Presentation is loading. Please wait.

TOPOGRAPHY ORBSCAN S.A.A. Mortazavi MD. Associate Professor of Ophthalmology Isfahan University of Medical Sciences 2/22/20131.

Similar presentations


Presentation on theme: "TOPOGRAPHY ORBSCAN S.A.A. Mortazavi MD. Associate Professor of Ophthalmology Isfahan University of Medical Sciences 2/22/20131."— Presentation transcript:

1 TOPOGRAPHY ORBSCAN S.A.A. Mortazavi MD. Associate Professor of Ophthalmology Isfahan University of Medical Sciences 2/22/20131

2 Use the principle of projection Use the principle of projection Forty scanning slit beams (20 from the left and 20 from the right with up to 240 data points per slit ) to scan the cornea and measure independently the X,Y & Z locations Forty scanning slit beams (20 from the left and 20 from the right with up to 240 data points per slit ) to scan the cornea and measure independently the X,Y & Z locations 2 ORBSCAN SYSTEM 2/22/2013

3 Forty slit images are acquired in two 0.7 second periods Forty slit images are acquired in two 0.7 second periods Each of the 40 slit images triangulates one slice of ocular surface Each of the 40 slit images triangulates one slice of ocular surface Distance between data slices average 250 microns Distance between data slices average 250 microns Orbscan imaging 2/22/20133

4 4

5 Orbscan I only slit scan topography Orbscan I only slit scan topography Orbscan II the placidodisc added in orbscan I Orbscan II the placidodisc added in orbscan I ORBSCAN 2/22/20135

6 6

7 The images used to construct the anterior corneal surface,posterior corneal surface,anterior iris and anterior lens surfaces The images used to construct the anterior corneal surface,posterior corneal surface,anterior iris and anterior lens surfaces Data regarding the corneal pachymetry and anterior chamber depth Data regarding the corneal pachymetry and anterior chamber depth 7 ORBSCAN 2/22/2013

8 The computer calculates a hypothetical sphere that matches as close as possible to the actual corneal shape being measured The computer calculates a hypothetical sphere that matches as close as possible to the actual corneal shape being measured Compares the real surface to the hypothetical sphere showing areas above the surface of the sphere in warm colours and areas below the surface in cool colours Compares the real surface to the hypothetical sphere showing areas above the surface of the sphere in warm colours and areas below the surface in cool colours 8 BEST FIT SPHERE (BFS) 2/22/2013

9 9

10 Highlights the abnormal areas in the cornea in orange to red colors Highlights the abnormal areas in the cornea in orange to red colors The normal areas are all shown in green The normal areas are all shown in green Helpful in generalized screening in preoperative examination Helpful in generalized screening in preoperative examination NORMAL BAND SCALE 2/22/201310

11 112/22/2013

12 To create a good quality corneal flap in LASIK if either extremes (too steep or too flat) is the case, this can lead to surgical flap complications To create a good quality corneal flap in LASIK if either extremes (too steep or too flat) is the case, this can lead to surgical flap complications K readings of more than 48 D are an indication of potential keratoconus K readings of more than 48 D are an indication of potential keratoconus 12 AXIAL MAP 2/22/2013

13 132/22/2013

14 142/22/2013

15 152/22/2013

16 The orbscan measures thickness from the tear film layer to descemet’s membrane and is thicker than that obtained with ultrasound The orbscan measures thickness from the tear film layer to descemet’s membrane and is thicker than that obtained with ultrasound Adjustment factor (acoustic factor),the default setting is 92% Adjustment factor (acoustic factor),the default setting is 92% Provides a reading showing the thinnest point of the cornea that may not necessarily be the central reading Provides a reading showing the thinnest point of the cornea that may not necessarily be the central reading PACHYMETRY MAP 2/22/201316

17 Thinnest point <470 micron Thinnest point <470 micron In pathological corneas, thinnest point is often displaced inferotemporal In pathological corneas, thinnest point is often displaced inferotemporal Difference of >100 microns from the thinnest point to the values at 7mm optical zone Difference of >100 microns from the thinnest point to the values at 7mm optical zone 17 PACHYMETRY MAP 2/22/2013

18 The green colour is referred as refrence sphere (at sea level ) The green colour is referred as refrence sphere (at sea level ) The warmer colours are above this level and the cooler colours are below The warmer colours are above this level and the cooler colours are below 18 ELEVATION MAP 2/22/2013

19 192/22/2013

20 The difference between the highest and lowest points is a potential keratoconus indicator if over 100 microns (Rousch criteria) The difference between the highest and lowest points is a potential keratoconus indicator if over 100 microns (Rousch criteria) 20 ELEVATION DATA 2/22/2013

21 Many surgeons think the first sign of keratoconus appears on the posterior surface of the cornea Many surgeons think the first sign of keratoconus appears on the posterior surface of the cornea 3.13% of population screened for laser surgery had posterior ectasia criteria by orbscan, despite having axial topography classified as normal 3.13% of population screened for laser surgery had posterior ectasia criteria by orbscan, despite having axial topography classified as normal 21 POSTERIOR ELEVATION MAP 2/22/2013

22 222/22/2013

23 A best fit sphere (BFS) >55D on the posterior profile, indicative of posterior ectasia A best fit sphere (BFS) >55D on the posterior profile, indicative of posterior ectasia Greater than 50 micron generally accepted as abnormal Greater than 50 micron generally accepted as abnormal In corneas thinner than normal over 40 as abnormal In corneas thinner than normal over 40 as abnormal 23 POSTERIOR ELEVATION MAP 2/22/2013

24 Post BFS >55D Difference pachymetry between thinest point & thickest point in 7 mm zone >100 µ Diff >45µ Mean k >47 D I-S index >1.5D Distance from corneal apex to thinest point >0.9 mm Thinest point <470 µ Orbscan diagnostic parameters for K.C 2/22/201324

25 252/22/2013

26 Number of abnormal maps Posterior float difference > mm & 5mm irregularity Peripheral thickness changes Astigmatism variance between eyes Steep k’s –mean power map Risks of ectasia indices 2/22/201326

27 272/22/2013

28 One abnormal map ; perform with caution One abnormal map ; perform with caution Two abnormal map ; with concern Two abnormal map ; with concern Three abnormal map ;contraindicated Three abnormal map ;contraindicated Three step rule 2/22/201328

29 ضمن عرض پوزش بدلیل حجم بالای LECTUER ادامه اسلایدها امکان پذیر نمیباشد در صورت نیاز به ادامه لطفا به واحد سمعی و بصری مرکز آموزشی درمانی فیض مراجعه و یا با شماره تلفن داخلی 392 تماس حاصل نمائید با تشکر


Download ppt "TOPOGRAPHY ORBSCAN S.A.A. Mortazavi MD. Associate Professor of Ophthalmology Isfahan University of Medical Sciences 2/22/20131."

Similar presentations


Ads by Google