What’s wrong with RGPs?

Why I only fit soft lenses…

I took the decision a while back not to fit RGP lenses at all to keratoconics. I will gladly assess RGP fits and monitor patients wearing them - but I will not fit RGP lenses from scratch unless there are very strong reasons to do so. This is due to issues with badly fitting lenses causing scarring of the type shown below. The problem is, even if you fit RGPs really well – and I used to fit a lot of them – if keratoconus progresses, then a good fit can rapidly become a “bad” fit – that is a flat fitting lens that rubs on the cone. As this actually tends to improve vision in the short term (a flat fitting lens resting on the cone will give very good vision!!) the wearer is not really aware there is a problem at first.

Click pictures for larger images


Combination of Hydrops and corneal abrasion		Typical RGP “scuff” type scar		RE 3 months KeraSoft wear		LE 3 months KeraSoft wear

Although these scars will reduce once out of RGPs – if corneas are left long enough in badly fitting RGPs, then vision will be permanently affected and grafting may be necessary. Of course, there are people who wear RGPs successfully for 20 years or more without any scarring, as their lenses are very well fitting but, to my mind – why even risk this? How can we predict which corneas will scar and which will not?

Incidentally, scarring from Hydrops often strengthens the cornea and reshapes it naturally. Because Hydrops scars tend to be patchy, vision is often quite good through them, once settled.


Natural scar from hydrops		RGP round scar		RGP induced scar		Post CXL scar from RGP

Mechanical Effects of RGP lenses

RGP lenses can exert physical pressure on the surface of the cornea very similar to that experienced in eye rubbing – below is an
abstract of an article that explains this in more detail:

The bio mechanics of keratoconus and rigid contact lenses
Charles McMonnies
Eye & Contact Lens: Science & Clinical Practice: March 2005 – Volume 31 – Issue 2 – pp 80-92

	PURPOSE: To examine aspects of the genesis and progression of keratoconus through an analysis of the biomechanical forces associated with this condition, including those generated by rigid contact lenses. METHODS: The biomechanics of applanation tonometry and rigid contact lenses serve as a basis for examining contact lens adherence and the potential for contact lens induced mid peripheral corneal applanation and apical molding with apical clearance fittings. DISCUSSION: Some physiologic and pathologic mechanisms for increases in intraocular pressure are reviewed. The possibility is raised that hard squeeze blinks, for example, could significantly increase the distending forces that bear on the corneal apex in keratoconus and that some apical clearance contact lens fittings could increase the risk of progressive ectasia. Support for these hypotheses is found among healthy eyes and eyes with keratoconus that show increased curvature when apical clearance fittings are worn. CONCLUSIONS: The known risk of scarring responses to excessively flat fitting rigid contact lenses must be balanced against the possible risk of molding and ectasia advancement responses to tight definite apical clearance lenses. Fittings within the range of minimal apical clearance and minimal apical contact (divided support) may be the most appropriate. The appearance and performance of these fittings may be difficult to distinguish clinically. Because some patients may develop pathologic levels of intraocular pressure with vigorous eye rubbing, strong squeeze blinks, inverted body positions, and strenuous muscular effort, patients with, or at risk for, keratoconus, glaucoma, or progressive myopia should be advised of the possible adverse significance of these activities.

	Effect of fitting apical clearance rigid lenses
	Most practitioners would agree that fitting RGP lenses flat so that they bear down hard on the cone is not a good idea. Although this will give good vision, it does have adverse effects on the cone. Most fitting techniques for rigid lenses now advise a “just apical clearance fit” – i.e. so that the apex of the lens is just clearing the cone with a “feather touch”. However, this is difficult to achieve exactly and often lenses are fitted a little steeper than this. However, steep fitting lenses can cause their own particular problems: lenses that are fitted steep can create a vacuum under the lens during blinking. The lens flattens slightly on blink and then suction pulls the cornea under the lens as the eye opens again. Stagnation of tears under the lens can also contribute to corneal oedema, which in turn can increase the steepness of the cone. Thus it is not unusual for keratoconics newly fitted with RGPs to find their lenses need steepenign after around 6 months of wear.

	Apical clearance rigid contact lenses induce corneal steepening Swarbrick Helen A; Hiew Ross; Kee Ai Vy; Peterson Sophia; Tahhan Nina Optometry and vision science : official publication of the American Academy of Optometry 2004;81(6):427-35

	Cascade Theory of Keratoconus Christopher Kerr, past President of the BCLA, gave a lecture at the Royal Society of Medicine called “First do no harm: a modern approach to the holistic management of keratoconus” which explains the cascade theory of keratoconus and describes how RGP lenses are possibly implicated in the progression of keratoconus