A 27-year-old man with asthma complains of increasing distortion of vision in both eyes over six months. What is going on?
Even with this limited information (young age, asthma, and progressive distortion of vision), I would suspect that the condition was keratoconus. I would confirm by checking the appearance of the retinoscopy reflex (split reflex), the presence of astigmatic refractive correction, and low values of keratometry readings (indicating steep corneal curvature) and any distortion of the keratometry mires.
In keratoconus the cornea thins. Intraocular pressure pushes on the cornea and it bulges outwards in a cone shape. It is a progressive condition although the rate of change and severity varies. The cone is astigmatic and the vision is blurred often even with optimum refractive correction (glasses or rigid contact lenses).
It seems to be common in the Middle East. I remember having a meal with around twelve people in Jordan and everyone had keratoconus or had a close family member with keratoconus. There are many eye specialists in the Middle East with a vast amount of experience in managing keratoconus.
People often write that it is due to living in hot and dry conditions. I don’t think Jordan is any hotter or drier than the centre of Spain in the summer months and there isn’t much keratoconus in Spain.
People often write that it is due to eye rubbing distorting the cornea. I’ve had hay-fever since I was 18 years old and have done my fair share of eye rubbing. I don’t have keratoconus.
What causes keratoconus is unknown. It may be genetic and it occurs more in people who have allergies like asthma or eczema. It could be related to the mechanism that causes these atopic conditions. Atopy is the genetic tendency to develop allergic diseases such as hay fever, asthma and eczema. Atopy is typically associated with heightened immune responses to common allergens, especially inhaled allergens and food allergens.
Levels of vision can be improved in the early stages with glasses and or contact lenses. It is important to consider referral to an ophthalmologist specialising in corneal disease as cross-linking can stop cone progression. It is effective in around 94% of patients with a single 30-minute outpatient procedure. It is also important to remember if the referral is delayed, the cornea may become too thin, and the procedure becomes unsafe. In addition, cross-linking is only suitable where the corneal shape is continuing to deteriorate.
Interestingly, n people in their late 30s, the cornea naturally stiffens and cross-linking is generally not required. However, an extensive and much-curved cone may have developed by then, warranting a corneal transplant.