At least two explanations for the lower vulnerability of cones than rods
(Fig. 4)warrant consideration. First, earlier maturation may protect the cones. It is the immature photoreceptors that appear particularly vulnerable to retinal oxygen levels that are too high or too low.
8 Second, cones appear more resistant to pathologic processes. Compared with rods, cones have twice as many mitochondria and approximately three times the surface area of mitochondrial cristae.
17 Thus, the cones are equipped for greater aerobic ATP production, and this, Perkins et al.
17 theorize, protects against metabolic insults and apoptosis. As a corollary, they postulate that therapeutic interventions that support mitochondrial energy production may be beneficial in many photoreceptor diseases.
17 Furthermore, cones, in contrast to rods, have the capability of using endogenous glycogen, affording protection against the adverse effects of hypoxia and attendant hypoglycemia.
50 The data from the subjects represented in
Figure 4and from additional subjects
2 indicate that ROP affects the rods, and it is known that in some patients, ROP has a progressive, degenerative course.
51 Thus, therapies that support mitochondrial energy production may be beneficial in ROP and may even have a role in preventing ROP, because it is rod sensitivity that predicts the vascular abnormalities in rat models of ROP.
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