Keratoconus

Corneal scar from previous hydrops Fleischer's ring (arrowed) around the cone Vogt's striaes in keratoconus Enlarged corneal nerves in  keratoconus

. This is a favourite corneal case in slit-lamp examination. In early keratoconus, the signs may be subtle. The following  signs should may you suspect that the patient has keratoconus: presence of periocular eczema or Down's syndrome wearing of hard contact lenses corneal graft in the contralateral eye. Some candidates have been asked to examine the corneal reflexes with a direct ophthalmoscope, there are often abnromal  reflexes some of which may resemble subluxation of the lens. In early cases, the only signs may be thinning of the cornea apex with striation of the stroma and Descemet's membrane  (Vogt's striaes). There is Fleischer's ring surronding the cone (blue light on the slit-lamp can improve its visualization). The  corneal nerves are prominent. In advanced cases, there are cornea scars from previous hydrop. Other examination: remember to examine the fellow eye which may show a different stage of progression or corneal graft mention tot he examiner that you like to demonstrate the Munson's sign (which is distortion of the lower lid on  down-gaze) and Rizzuti's sign (conical reflection on the nasal cornea when a penlight is shone from the temporal side). look for associated featrues such as Down's syndrome, atopic eczema, connective tissue disorders such as Marfan's  syndrome

Questions:

1. What is an acute hydrop and is it an indication for urgent corneal graft?

Answer
Acute hydrop develops from a break in the Descemet's membrane leading to the entry of aqueous into the stroma causing stromal oedema. The condition is painful and the cornea appears opaque.
It is not an indication for urgent corneal graft because the oedema tends to resolve over weeks and months when the endothelium cells enlarge and grow over the Descemet's break. Cycloplegic and topical steroid are often used because of the pain and photophobia. 5% sodium chloride can be used to reduce the oedema.

2. What is the histological feature of keratoconus?

Answer
There is fragmentation of Bowman's layer, thinning of the stroma and overlying epithelium. The Descemet's membrane shows folds and breaks. Diffuse scarring is often present in the stroma.

3. How would you treat a patient with keratoconus?

Answer
The main problem is high astimgatism which is irregular and often progressive. Glasses can initially correct the astigmatism and when these become ineffective hard contact lens is used. When the vision can not be corrected with the contact lens or when the cornea becomes too steep for the contact lens, corneal graft is indicated.

4. The following are the corneal topographies of two patients with irregular astigmatism. Which one belongs to the patient with keratoconus and which one to patient with pellucidal marginal degeneration?
 

Answer The topography belongs to a patient with keratoconus which shows the typical inferior steepening of the  cornea.

Answer The topography belongs to a patient with pellucidal marginal degeneration. There is inferior steepening  of the cornea but the cornea also shows flattening  of the central cornea which is typical of this condition.

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