Objective Structured Practical Question (OSPE)Topic: Corneal Topography

According to the course curriculum of BCPS

AUTHOR:Dr Md Anisur Rahman Anjum.MBBS (Dhaka Medical College). DO (Dhaka University) FCPS (EYE)Associate ProfessorNational Institute of OphthalmologyDhaka, Bangladesh. Chamber: Mojibunnessa Eye HospitalHouse: 18 Road: 6. Dhanmondi, Dhaka, 1205. Bangladesh.Email: anjumk38dmc@gmail.comCell: 01711-832397

OSPE: 1

Question

QuestionThis is the corneal topography of a patient awaiting

cataract surgery. a. What does the corneal topography show? = 3 b. What is the effect on the corneal topography if the

patient had an extracapsular cataract extraction through the superior corneal approach and all the tension of the sutures are evenly distributed and not tightened? = 4

c. What is the effect on the corneal topography if the patient had phacoemulsification through a temporal corneal approach using a foldable lens? = 3

Answera) The corneal topography shows with-the-rule astigmatism. 

    (The astigmatism is shown by the typical bow-tie appearance and since the steepest part of the cornea is at 90 degrees the astigmatism is with-the-rule)

b) Cutting the cornea superiorly will flatten the cornea and therefore reduced the astigmatism. (provided the tension of the sutures are equally distributed and not tighten)

c) A temporal cornea approach with small incision surgery has minimal effect on the corneal topography. (Due to the small incision and the further distance between the temporal peripheral cornea and the centre of the cornea).

OSPE: 2

Corneal topography of a patient awaiting cataract surgery.

• a. What does the corneal topography show?• b. What is the effect on the corneal topography if the patient had an

extracapsular cataract extraction through the superior corneal approach and all the tension of the sutures are evenly distributed and not tightened?

• c. What is the effect on the corneal topography if the patient had phacoemulsification through a temporal corneal approach using a foldable lens?

ANSWER The corneal topography shows with-the-rule astigmatism.

(The astigmatism is shown by the typical bow-tie appearance and since the steepest part of the cornea is at 90 degrees the astigmatism is with-the-rule)

Cutting the cornea superiorly will flatten the cornea and therefore reduced the astigmatism. (provided the tension of the sutures are equally distributed and not tighten)

A temporal cornea approach with small incision surgery has minimal effect on the corneal topography. (Due to the small incision and the further distance between the temporal peripheral cornea and the centre of the cornea).

OSPE:3

CORNEAL TOPOGRAPHY

QUESTION This is the corneal topography of a patient pre-cataract

surgery. a. What does the picture show? = 2 b. The patient's refraction can be corrected with -3.00DS to 6/6.

Give a reason why he does not require cylindrical correction. = 4

c. A temporal clear corneal incision was performed because the patient has deep set eye. What is the effect on:

• i. the cornea tissue = 2 ii. the cornea astigmatism = 2

ANSWER With the rule astigmatism.• There is a vertical bow tie appearance of the cornea which

corresponds to that part of cornea with the steepest meridian. The patient may have against the rule lenticular astigmatism

which exactly neutralize the corneal astigmatism.• The refraction of the eye is contributed by the cornea & the

lens. The astigmatism of the cornea can be neutralized by lenticular astigmatism if its axis is opposite to that of the cornea. For this reason, astigmatic keratometry reading during cataract surgery should be based on the corneal topography and not on the glass prescription.

A temporal clear corneal incision will flatten the cornea in the meridian of the incision.

Because of the “coupling” the cornea will be steepened at 90 degree away. In this case, the with-the-rule-astigmatism will increased.

OSPE: 4

QUESTION This is the corneal topography of a patient pre-cataract

surgery. a. What does the picture show? = 2 b. The patient's refraction can be corrected with -3.00DS to 6/6.

Give a reason why he does not require cylindrical correction. = 4

c. A temporal clear corneal incision was performed because the patient has deep set eye. What is the effect on:

• i. the cornea tissue = 2 ii. the cornea astigmatism = 2

ANSWER With the rule astigmatism.• There is a vertical bow tie appearance of the cornea which

corresponds to that part of cornea with the steepest meridian. The patient may have against the rule lenticular astigmatism

which exactly neutralize the corneal astigmatism.• The refraction of the eye is contributed by the cornea & the

lens. The astigmatism of the cornea can be neutralized by lenticular astigmatism if its axis is opposite to that of the cornea. For this reason, astigmatic keratometry reading during cataract surgery should be based on the corneal topography and not on the glass prescription.

A temporal clear corneal incision will flatten the cornea in the meridian of the incision.

Because of the “coupling” the cornea will be steepened at 90 degree away. In this case, the with-the-rule-astigmatism will increased.

OSPE: 5

Picture of the corneal topography.

Question

1) What does the above picture show? 2) What is the most likely diagnosis? 3) What is the hall mark sign of the disease?4) Write down the staging of the disease5) Write 2 physical signs may be seen on slit-

lamp?

Answer1) The corneal topography shows corneal steepening

with downward displacement of the apex. =22) Early keratoconus (the maximum power of cone is

only 47.50 D) =13) The hallmark of keratoconus is central or paracentral

stromal thinning, (accompanied by apical protrusion and irregular astigmatism.) =2

4) It can be graded by keratometry according to severity as mild (<48 D), moderate (48–54 D) and severe (>54 D).=3

Answer5) The following signs may be present in this

patient: =2Corneal thinning and steepening of the apexVertical striaeFleischer's ring below the cone(Source: Kanski = P: 210)