03 November 2017
It used to be that the vision journey for people with progressing keratoconus was that they would wear glasses until their vision wasn’t good enough in them and then wear rigid gas permeable (RGP) contact lenses until they became too uncomfortable. Once RGPs could no longer be tolerated then the final option was a corneal graft to reduce the steepness so that an RGP lens could again be worn over the graft. Now we have two new treatments - corneal crosslinking to attempt to halt the progression of keratoconus and also scleral contact lenses which are able to fit much more extremely steep corneas comfortably and with good vision.
These changes to the journey was highlighted by a recent interaction I had with a lady with severe, progressing keratoconus but corneas already too thin for crosslinking.
She has been successfully wearing 17.5mm diameter sclerals achieving 6/7.5+ vision.
Her concern was the prognosis for this eye and its very, very steep and thin, 77D cone as it seems to be progressing. She understood that the cornea is thinning and she was worried about perforation, more so because she is a frequent traveller and can not always access medical care urgently. I could tell her about my experience with hydrops but had to do some research to be able to give her the facts she needed about perforation of the cornea.
So while hydrops is common and well documented, occurring in ~2-3% of patients with keratoconus, either spontaneously or secondary to ocular trauma, perforation is exceedingly rare. Hydrops happens most commonly with vigorous eye rubbing and it causes clouding of the cornea which in most cases resolves without any treatment or with only steroid drops over 6-10 weeks. It is only if the eye fails to heal on its own that surgery is needed and this happens about 20% of the time. It’s not an eye emergency and is no cause to restrict her travelling lifestyle but it is a reason to discuss managing the risk of trauma to the eye and eye rubbing.
Perforation on the other hand, has not generally been described in textbooks as a consequence of keratoconus: It is exceptionally rare. It has been reported in english language medical journals only a handful of times worldwide, in the last 30 odd years. It has severe consequences and is an eye emergency, but given the very low incidence it is unlikely to be a need to restrict the lifestyle of someone with keratoconus beyond managing the risk of eye trauma.
Scleral lenses have allowed this lady and many like her to comfortably wear her scleral lenses with good vision long after her corneas are too steep and thin for RGPs to fit suitably. I was able to tell her that historically, perforation is an exceptionally rare occurrence. However, with scleral lenses allowing for steeper and thinner corneas before requiring grafting, it is possible that the incidence of perforation due to keratoconus may increase. At this stage there has been no documented change in the incidence of perforation.
Mostafavi, S, David ; Chu, S, David. Two Cases of Keratoconus Associated With Spontaneous Corneal Perforation. Cornea, 2010, Vol.29(7), p.825-827 Lam FC1, Bhatt PR, Ramaesh K. Spontaneous perforation of the cornea in mild keratoconus. Cornea. 2011 Jan;30(1):103-4.