Keratoconus PDF

Keratoconus is a common disorder and most GPs will have several keratoconic patients in their practice. The majority of these patients will already know of their condition and be under the care of an optometrist or ophthalmologist. It is rare for GPs to make the diagnosis; indeed this can be difficu...

Keratoconus is a common disorder and most GPs will have several keratoconic patients in their practice. The majority of these patients will already know of their condition and be under the care of an optometrist or ophthalmologist. It is rare for GPs to make the diagnosis; indeed this can be difficult in mild forms, even with specialised equipment. Because the condition can have profound implications for the patient and GPs have a very important supportive role, a brief understanding of the disease and its management is useful. Included in this document What is keratoconus? Symptoms Signs Management Key points What is keratoconus? Fig. 1. Keratoconus or ‘conical cornea’. The cornea in profile is obviously cone-shaped. (Courtesy Assoc. Prof. R. Clemett.) Keratoconus is a disease in which the cornea develops an irregular conical shape (Fig. 1). The exact cause is not known. In mild to moderate keratoconus the vision is relatively good but in more severe cases the cornea becomes very thin and distorted and the vision can be very poor even with correcting lenses. Most patients develop the disease between the ages of 12 and 20 and have ongoing corneal steepening until their third or fourth decade. The disease is bilateral but usually one eye is more severely affected than the other. Keratoconus is more common in patients with Down’s and Marfan’s syndromes and in atopic individuals. Symptoms Most patients complain of the slow onset of blurred or distorted vision. This is obviously a very non specific symptom but the diagnosis should be considered in all young adults who develop blurred vision and refractive errors, particularly if unilateral and of slow onset. Often patients have glasses but are still unhappy with their vision, even when the glasses are new. This is because spectacles cannot fully compensate for the irregular changes in the shape of the cornea. Even if the vision is good with glasses the progressive nature of the disease often necessitates frequent spectacle changes. Signs Vision The vision is usually reduced but still improves with a pinhole. In more severe cases the pinhole vision may be reduced due to severe central corneal distortion and scarring. Red reflex Observing the red reflex is one of the best ways to detect keratoconus. The reflex is distorted (Fig. 2) and the dark circular areas appear to ‘swirl’ particularly if the patient keeps their eye still and the examiner moves slowly from side to side as they observe the reflex. The cornea In advanced cases the cornea is obviously conical if viewed from the side (Fig. 1). A clever way to determine the shape of  the cornea in more subtle cases is by looking for Munson’s sign, which is simply observing that the conical cornea indents the lower eyelid as the patient gazes downward (Fig. 3). In advanced keratoconus, the posterior endothelial layer of the cornea can ‘fracture’ leading to the rapid influx of aqueous fluid into the cornea, a condition known as corneal hydrops. This results in the sudden appearance of a circular white lesion in the central cornea. The vision is profoundly affected and the eye is uncomfortable and watery. It takes 6-10 weeks for the corneal oedema to resolve and vision is usually permanently affected by secondary corneal scarring. Fig. 1. Keratoconus or ‘conical Fig. 2. The red reflex in a keratoconic Fig. 3. Munson’s sign. The right cornea’. The cornea in profile is patient. The steep and irregular cornea is conical and the profile of the obviously cone-shaped. (Courtesy central cone distorts and darkens the lower eyelid is moulded by the cone. Assoc. Prof. R. Clemett.) red reflex. Like most sufferers, this patient has asymmetrical disease. Management If you suspect that a patient has keratoconus refer them to an optometrist in the first instance. In mild cases spectacles will restore normal vision. In mild to moderate cases hard contact lenses can overlay the irregular corneal surface and the vision may be good. In some areas, patients with a community services card qualify for a contact lens subsidy. In advanced cases, the cornea becomes so conical that contact lenses are unstable and cannot be tolerated. In such cases corneal grafting may be necessary. Key points Keratoconus is a common disease. Like all patients presenting with slow onset visual loss, the initial referral should be to an optometrist. Mild forms can be treated with spectacles and contact lenses. More severe cases need corneal grafts. The role of the GP is primarily supportive. © GP Eyes - Dr Malcolm McKellar 2011