Sarah Ali Hasan, Dr. Mandeep Singh, “Automatic Diagnosis of Astigmatism for Pentacam Sagittal Maps”, Third International Workshop on Recent Advances in Medical Informatics (RAMI-2014) (Accepted to be published on (27-29Sep). IEEE conference.

1. Automatic Diagnosis of
Astigmatism for Pentacam
Sagittal maps
By: Sarah Ali Hasan & Dr. M.D Singh

2. Outline:
 Background
 Human Eye & facts about Cornea
 Astigmatism physics & types
 Tools
 Corneal Topography & PENTACAM
 Characterizing Astigmatic Corneas
 Methodology
 Results
 Comparison to Related previous work
 Future work

3. Anatomy of human eye
 Spheroid structure with an average diameter of 24mm.
 External structures:
eyelids, eyelashes, tears
and fat glands, extra ocular
muscles, conjunctiva.
 Internal structures:
cornea, sclera, iris, ciliary
body, choroid, retina, lens,
anterior and compartment,
optic nerve.

4. Facts about Cornea
 Cornea scatters almost
10% of the incident light.
 Cornea’s average of
curvature is 7.8 mm.
 Cornea is accounting for
about 43-44 diopters at
corneal Apex (that is: 2/3 of
total dioptric power of
human eye).
 Corneal Geography:
 Apex: central zone
(4mm), overlies the pupil &
responsible For HD vision.
Paracentral Zone:
Where the cornea begins
to flatten.
 Peripheral zone.
 Limbal zone.

5. Astigmatism physics & types
 Either both or one surface of
the cornea or the lenses is
not spherical, but cylindrical
Which results in no distinct
point of focus inside the eye;
rather a smeared or spread
out foci.
 Astigmatism is of two types;
regular & irregular.

6. Continued..
 One eye can has two
refractive errors in the
perpendicular meridians;
each one is a resultant of
spherical error + astigmatic
error.
 Steep meridian is the one of
higher degree of curvature
and the flat meridian is the
one with less degree of
curvature
 Position of meridians
decides the type of regular
astigmatism case.

7. Corneal Topography & PENTACAM
 A non-invasive medical
imaging technique for
mapping the surface
curvature of the cornea.
 The corneal topography
and color coded maps
derived from quantitative
analysis of numerous
surface points.
 Physicians interpret the
color coded images to
diagnose & treat patients
with eye refracting issues.

8. Continued..
 Corneal topographers is of two types:
 Projection based corneal
topography, from which Curvature
maps like Saggital maps are driven.
 Reflection Based corneal
topography, from which Elevation
maps are driven.
 PENTACAM is a combined device
consisting of a slit illumination system
and a Scheimpflug camera which
rotates around the eye.
 This camera rotates around the
camera 360° in 2seconds to capture 50
images for the surface of cornea, all
are centered at the cornea center.

9. Characterizing Corneas

10. Continued..

11. Methodology
 The aim is to suggest a computerized technique to help
making this decision on diagnosing Astigmatic corneas.

12. Sample image

13. Data &Results
 Data base is a selected
group of (84) PETACAM
topographic images.
 All the samples are for
patients of Dr.G.S
Randhawa Eye Hospital.

14. Continued..
 Correctly diagnosed &
missed cases were
distributed over
confusion matrix for
accuracy calculation.
 Classification accuracy
is approximately 80%.

15. Comparison to Related previous work
 Neural Networks classification.
 Zernike polynomials analysis .
 Also many ophthalmologists provided similar criterion
for keratoconus detection.
 We used image processing techniques such as
morphological operations and cross correlation to
classify and identify the cases.
 Astigmatism diagnosis and classification is not
discussed as much as Astigmatism treatment in the
literature , it is still done manually by interpreting the
corneal topographic and tomographic images.
 The algorithm presented in this paper is novel.

16. Future work
 Pixel values can be included as they represent the
diopter values at the specific meridians and the last have
such an important rule on deciding the diagnosis of the
refractive error.
 Performing all the image processing techniques on the
colored images.
 Including the scale provided beside the color coded
topographic image.

17. THANK YOU !
