A short description on corneal topography, instruments , keratoconus and the corneal topographic reports

1. CORNEAL
TOPOGRAPHIC
REPORTS
PRESENTED BY -
AL AMIN, GAURAB NARZARY,
JYOTISHMOY BORAH, NILIMESH SARMA,
RUHUL AMIN BARBHUIYA.
B.OPTOM 2ndYEAR

2. CORNEAL TOPOGRAPHY
HISTORY-
* The word topography is derived from greek word “TOPOS”
(place) and “GRAPHEIN” (to draw).
DEFINATION-
* Corneal topography refers to the study of the shape of the corneal
surface by graphical representation. It helps in determining the
refractive status of the eye. Since the anterior surface of the cornea
along with the tear film layers forms the major refractive element of
the eye.
DIMENSIONS OF CORNEA-
* Diameter -
Anterior Surface - Dh – 11.75mm
Dv – 11.00mm
Posterior Surface –

3. * Thickness –
Centre – 0.52mm
Periphery – 0.67mm
* Radii of curvature –
Human corneal surface is ashperic
Anterior – 7.8mm
Posterior – 6.5mm.
LAYERS OF CORNEA-
There were mainly 5 layers of cornea –
1. A nterior Epithelium.
2. B owman’s membrane.
3. C entral Stroma.
4. D ecemet’s membrane.
5. E ndothelium.
6. Dua’s layer.

4. INSTRUMENTS OF MEASUREMENT-
* KERATOSCOPE:-
a) Placido disc.- Placido disc is also known as keratoscope which is
used to access the shape of anterior surface of the cornea.
b) Photokeratoscopy.- When a photographic flim camera is attached
to keratoscope the instrument is called photokeratoscopy.
c) Videokeratoscopy.- When a TV camera is attached to keratoscope
it is called as videokeratoscopy.

5. PLACIDO DISC
TOPOGRAPHY
About-
* This system imply placido disc projection device. Historically the
placido disc based system were the first to be developed and thus are
mostly used and understood. Most placido disc based system project
around 8-32 concentric rings on the cornea. The rings are numbered
from inside out.
A specific ring in different instrument may cover different
areas , therefore it is important to mention the diameter of the
projected ring along with the number.
PRINCIPLE-
* Use of 1st Purkinge’s image.
Methods of measurement-
* Consists of equally spaced alternating black and white lines.
* A luminous object (target of rings) is placed infront of patient’s
cornea.
* Image size produced in the corneal reflection is measured.

6. Clinical interpretation-
* Circular ring : Spherical cornea
* Oval rings : Regular astigmatism
* WTR astigmatism
* ATR astigmatism
Disadvantages-
* Small degrees of abnormalities of corneal shape are not
easily identifiable .
* Not used in corneas with epithelial defects and stromal
ulcers.
* Clinically signifacnt amounts of corneal cylinder(upto
3.00D) may not be diagnosed.
* Subtle irregularities cannot be detected.

7. INDICATIONS & USES-
1) Pre operative and post operative assessment of refractive patient.
2) Pre operative and post operative assessment of Keratoplasty.
3) Irregular astigmatism.
4) Corneal dystrophy and bullous Keratopathy.
5) Keratoconus(diagnostic and follow up).
6) Follow up of corneal ulceration and abscess.
7) Contact lens fitting .
8) Evaluation of tear film quality.
9) To study unexplained low visual acuity after any
surgicalprocedure(Trabeculectomy, extra capsular lens extraction).
10) Post traumatic corneal scaring .
11) Reference instrument for IOL implants to see the corneal
difference before and after surgery.

8. COMMERCIALLY AVAILABLE
PLACIDO DISC TOPOGRAPHY
SYSTEM
1. LSUCTS - It projects 11 rings. Display 4 basic type of diagrams.
2. CMS - It projects 32 rings covering cornea from apex to limbus,
with 1400 data points.
3. Computerised corneal topography EX270 - Zoom magnification
upto 8 times, & shows corneal contour map of whole of the cornea.
4. Eyesys 2000 corneal analysis system - It projects 16 rings,
& analyses 6000-6500 data points.
5. TMS 1 topographic modelling system - It projects 31rings providing
7000 data points.

9. Scales used-
* Absolute scale - In it each colour represents the 1.5D intervals
between 35-60D whereas above & below the range colours
represents 5D intervals.
* Normalised scale – In it cornea is divided into 11 equal colours
spanning that eyes total dioptric power.
COLOUR CODES-
* Cool colours – Black, Blue, Azure – Flatter surfaces.
* Warm colours – orange, red, white – Steeper surfaces.
* Normal – green, yellow – Normal surfaces.

10. KERATOCONUS
*What is keratoconus?
- Keratoconus is a progresssive eye disease in which the normally round cornea thins and
bulges into a cone like shape.
- Patients with keratoconus often report decreasing vision, distortion, glare/flare,
monocular diplopia or ghost images.
- Keratoconus is differtiated into mild , moderate and advanced disease as well as by
shape.
* Signs of keratoconus-
- oil droplet reflex, prominent corneal nerves, fleischer ring and scaring, bulging of lower
lids on downgaze(Munson sign), acute hydrops.
*Treatment –
1.Eye glasses- for visual improvement and astigmatism management.
2.Contact lenses- usually RGP contact lenses, may be recommended, with mild cases to
neutralize the irregular corneal astigmatism.
3. Corneal collagen cross linking- it involves administering riboflavin (vit. B2) eye drops
and UVA light in carefully selected parameters that strengthen the front layers of the
cornea and avoid damage to the back part of the eye.
4.Cornea transplant-
A) Deep anterior lamellar keratoplasty(DALK)- it involves replacements of the central
anterior cornea, leaving the patient’s endothelium intact. DALK is the treatment of
choice for keratoconus or corneal scars.
B) Penetrating keratoplasty(PK)- it is the traditional full thickness transplant where all
layers of the cornea are removed and replaced with donor tissue.

11. CORNEAL TOPOGRAPHIC
PATTERNS
* The normal cornea flattens progressively from the centre to the
periphery by 2.00 to 4.00D with the nasal area flattening more than the
temporal area. Depending upon corneal curvature 10 different
topographic patterns in normal eyes can be seen in colour coded
absolute maps –
1.Round, 2.Oval, 3.Superior Steepening, 4.Inferior Steepening,
5.Symmetric Bowtie, 6.Irregular, 7.Symmetric bowtie with skewed
radial axis, 8.Asymmetric bowtie with inferior steepening,
9.Asymmetric bowtie with superior steepening, 10.Asymmetric bowtie
with skewed radial axis.

12. PSBT= Prolate symmetric bow tie
PABT= Prolate asymmetric bow tie
OSBT= Oblate symmetric bow tie
OABT= Oblate asymmetric bow tie
PI= Prolate irregular OI= Oblate irregular
SF= Steep/flat LS= Localised steep

13. 1- Demographic data – Name, ID no., DOB, Sex.
2. Eye – OD/OS
3. Date, Time, Exam no.
4. Ks- steep keratometric value,
Kf- flat keratometric value,
AveK- Average keratometric value,
MinK- Mean keratometric value,
Cyl- Cylindrical value, Em- elevation map,
SRI- surface regularity index,
PVA- present visual acuity,
SAI- surface asymmetry index.
KCI- keratoconus index, KSI- keratoconus severity index,
SK1 & SK2- subclinical keratoconus, DSI- differential sector index,
OSI- opposite sector index, CSI- coherrence scanning
interferometry,
SDP- standard deviation of power, IAI- irregular astigmatism index,
KPI- keratoconus prediction index, AA- analysed area.

19. OU- Asymmetric skewed bowtie with
superior steepening

22. OU-Asymmetric bowtie with inferior
steepening

25. OD- Asymmetric skewed with
superior steepening

27. OD- Symmetric skewed bowtie
OS- Asymmetric skewed bowtie with
inferior steepening

30. OD- Irregular astigmatism
(Triple)

32. END OF SLIDE.
THANK YOU...