What is the test for determining whether a plaintiff has a thin skull?

In Zacharias v. Leys (2005), 219 B.C.A.C. 88, 2005 BCCA 560, Esson J.A. considered the application of the principles in Athey v. Leonati, 1996 CanLII 183 (SCC), [1996] 3 S.C.R. 458, where a plaintiff has a pre-existing condition that would, on the evidence, support a finding of a measurable risk that this condition would have detrimentally affected the plaintiff in the future. In Athey, supra, two scenarios were considered: 1. Where the injuries are unexpectedly severe owing to a pre-existing condition (thin skull). Here, a negligent defendant is liable for all damages even though the plaintiff’s losses are greater than they would be for the average person; 2. Where the pre-existing condition was inherent in the plaintiff’s “original position” (crumbling skull). Here, a defendant will be liable for the injuries caused, but not for the effects of the pre-existing condition which the plaintiff would have experienced anyway.