Guidelines for recommending topographic or tomographic scans for Keratoconus suspects

Keratoconus is an ectatic collagen disease in which a person’s corneal stromal collagens are affected so that anterior eye is bulged out, particularly prominent in one point of cornea, that is slightly infero-nasal to central cornea. The prevalence of cornea is reported lowest in Denmark, 4 per 10K population and is highest in Middle East, more in rural Iran, where it is 40 per 10K population. Due to the increased number of competent optometrists and rising level of consumer’s consciousness about Keratoconus, many refractive camps are being organized in the schools, colleges, sport clubs and focused communities that also incorporate keratoconus screening. In the screening program of Keratoconus, we can have the following tools:

    1.   A variant of Snellen’s charts to determine the visual acuity (first presenting and later best corrected) whether it is normal or subnormal (<6/6)

    2.   Retinoscopy for objective refraction and to judge the quality of vitreo-retinal reflex

    3.   A subjective refraction set (phoropter or trial box/frame) for conforming the best corrected visual acuity

    4.   Keratometer (portable for mobile camps) for determining the anterior corneal curvature

With the above mentioned tools we can arrest the keratoconus suspects and look for other features like: Scissor;s reflex, Munson’s sign, Rizutti’s sign, Charlleux sign through the torchlight, direct ophthalmoscope or retinoscope. Other signs like Fleischer’s ring, stromal nerves prominence, localized corneal thinning and bulging can be seen through slit lamps after patients are taken to the hospital. 

Despite the presence of various above sign, a topographic, more specifically tomographic scan is a must for the diagnostic confirmation of keratoconus so as to move on to determining the most appropriate treatment option. Since, topographic/tomographic scans are expensive, these tests should only be advised to the patients between 10 - 35 years of age who meet any one of the three criteria as outline below:

Criteria for recommending topographic/tomographic scans of Keratoconus suspects

   1.   Refractive Astigmatism

i)                 All cases of refractive astigmatism >2.50 Diopters

ii)             All cases of refractive astigmatism >1Diopters the axis of which lies between 20⁰ – 70⁰ or 110⁰ – 160⁰.

   2.   Corneal power

If at least one of the k-reading (K_max) > 47.2 Diopter (or steeper radius of curvature, r_min<7.15mm)

    3.   Quality of Vision and refraction

If retinscopy shows sign of scissor’s reflex with no obvious pathology (e.g, trauma or healed ulcer) and BCVA does not improve to 6/6 (BCVA<6/6)

 

 

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