Rigid gas permeable contact lenses: out in the cold.
BACKGROUND
Rigid gas permeable (RGP) contact lens wearers may experience episodes of lens fracture during handling. In this paper, we report the case of a keratoconic contact lens wearer whose lens fractured whilst being handled at sub-zero temperatures. Subsequent studies illustrate how PMMA and RGP contact lenses behave when exposed to sub-zero temperatures.


METHODS
Using a previously validated custom-built strain gauge we have measured the force required to invert RGP contact lenses (Fluroperm, DK30-DK151, PMMA and Aquasil; dioptric power -2.00DS) under different temperature conditions.


RESULTS
It was found that RGP lenses, frozen to -7 degrees C, required on average 15% less force to cause inversion than when stored at room temperature, regardless of material. It was also found that without due care, lenses of all materials fractured more easily after having been frozen, than lenses kept at room temperature. Fracture rates rose from 8% to 83% if lenses were stored wet (at -7 degrees C) as opposed to dry.


CONCLUSIONS
The authors conclude that practitioners should consider inappropriate contact lens storage and handling as a possible reason for otherwise unexplained acute RGP contact lens fracture.
Jackson
A Jonathan
AJ
Department of Ophthalmology, Contact Lens & Low Vision Unit, Royal Victoria Hospital/Queen's University of Belfast, Northern Ireland, United Kingdom. jonathan.jackson@belfasttrust.hscni.net
Wolsley
Clive J
CJ
D003261:Contact Lenses; D004868:Equipment Failure; D019544:Equipment Failure Analysis; D005615:Freezing; D005740:Gases; D010539:Permeability; D013314:Stress, Mechanical
D005740:Gases