(FIGURE 1) Conjunctival UV autofluorescence (CUVAF) photograph showing the area of CUVAF outlined.

(Figure 2) Comparison of central corneal thickness measurement of twin 1 with twin 2 for monozygotic (MZ) twin pairs on the left compared with twin 1 with twin 2 for dizygotic (DZ) twin pairs on the right. The large difference between the two groups of twins suggests a high heritability.

(FIGURE 3) Comparison of CUVAF measurement of twin 1 with twin 2 for monozygotic (MZ) twin pairs on the left compared with twin 1 with twin 2 for dizygotic (DZ) twin pairs on the right. The similar correlation for the two groups of twins suggests a shared environment.