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Interpretation of corneal shape.

This visual recognition feature tests the ability to interpret corneal topography and tomography and using this information to help to decide on contact lens fitting.

Optometrists [??]

Contact lens [??] opticians

The topography images above were taken from the same cornea at the same time.

01 What possible sign of corneal ectasia can be seen?

a) Placido ring distortion

b) There appears to be inferior steepening

c) The steepest meridian is outside normal limits

d) The axis of the steepest meridian is vertical 02 If the keratometry readings are 7.65mm and 7.59mm, with an eccentricity value of 0.8, based on this topography, which corneal rigid gas permeable lens should provide the best fit?

a) A spherical design with back optic zone radius (BOZR) of 7.75 and total diameter (TD) of 10mm

b) An aspherical design with BOZR of 7.65 and a TD of 10.4mm

c) A spherical design with a BOZR of 7.65 and a TD of 8.5mm

d) An aspherical design with a BOZR of 7.75 and a TD of 8.5mm

03 What is seen in the image?

a) Keratoconus

b) Poor image due to incorrect centration of the Placido rings

c) Pellucid marginal degeneration

d) Poor image due to tear film break up

These are the right and left eye topographies of the same patient.

04 Which of the following is true regarding the corneal astigmatism shown in the topographies?

a) It is apical

b) It is against-the-rule

c) It is limbus-to-limbus

d) It is compound myopic

05 What kind of fluorescein pattern would you expect to see under a corneal rigid gas permeable lens fitted to either of these corneas?

a) Vertical touch with a small edge clearance, and horizontal pooling with a large edge clearance

b) Vertical pooling with a small edge clearance, and horizontal touch with a large edge clearance

c) Vertical pooling with a large edge clearance, and horizontal touch with a small edge clearance

d) Vertical touch with a large edge clearance, and horizontal pooling with a small edge clearance

06 Which cornea is likely to be abnormal?

a) The left eye

b) The right eye

c) Both because their central astigmatism is asymmetrical

d) Neither because they show enantiomorphism

07 Which of the following findings could indicate corneal ectasia based on the Pentacam images shown?

a) The inferior-superior asymmetry

b) The steepest power reading on the anterior cornea

c) The pachymetry measurement at the thinnest point

d) The position of the steepest point on the cornea

08 Where is the thinnest point on the cornea?

a) Precisely in the centre

b) Superotemporal of centre

c) Inferonasal of centre

d) Inferotemporal of centre

09 Which of the following is true?

a) The eye would have to be fitted with a scleral lens

b) The eye is unsuitable for contact lenses

c) Based on the pachymetry map, the eye would be unsuitable for corneal cross-linking

d) The cornea has with-the-rule astigmatism

10 Which of the following is true?

a) This cornea has against-the-rule astigmatism

b) The eye is unsuitable for contact lenses

c) The thinnest point on this cornea corresponds with the steepest point

d) There is inferior-superior asymmetry

11 This cornea shows:

a) Superotemporal steepening

b) Inferotemporal flattening

c) Thicker than average pachymetry readings

d) Cyclotorsion

12 What is the most likely diagnosis here?

a) Keratoconus

b) Pellucid marginal degeneration

c) Contact lens induced corneal war-page

d) Previous laser surgery

Exam questions

Under the enhanced CET rules of the GOC, MCQs for this exam appear online at www.optometry.co.uk. Please complete online by midnight on 23 August 2019. You will be unable to submit exams after this date.

* Claire McDonnell is a qualified optometrist and an optometry lecturer at the Technological University Dublin. Her specialist areas are contact lenses and paediatric optometry.

Course code: C-71016

Deadline: 23 August 2019

Learning objectives

* Be able to interpret corneal shape plots (Group 3.1.1)

* Be able to interpret corneal shape plots (Group 3.2.1)

Claire McDonnell FAOI, MSc

Caption: Image A

Caption: Image B

Caption: Image C

Caption: Image D
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Title Annotation:Corneal mapping
Author:McDonnell, Claire
Publication:Optometry Today
Date:Jul 1, 2019
Words:686
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