A 76-year-old female presents with complaints of difficulty reading. Ophthalmologic examination is remarkable for bilateral, white opacifications in her eyes, consistent with cataract formation. In which of the following structures are the opacifications located?

Cataracts are lens opacifications. It is not known whether senile cataracts represent disease or normal opacification with age. Cataracts may occur as a consequence of diabetes mellitus, long-term steroids, or congenital infections. They are successfully treated at present with lens extractions and implantation of prosthetic lenses. Note: Aqueous humor is continually replaced due to active secretion by the ciliary body. As such, it does not undergo opacification; it is in constant flux. Corneal opacification is generally a consequence of squamous metaplasia, in which the transparent, non-keratinized, squamous cells are replaced by opaque, keratinized, squamous cells. Squamous metaplasia is a reparative process, usually due to friction injury to the cornea or vitamin A deficiency. The optic nerve is not transparent, and it does not undergo opacification injury. It may, however, atrophy due to ischemic, traumatic, infective, or metabolic insults. Ref: Harper R.A., Shock J.P. (2011). Chapter 8. Lens. In P. Riordan-Eva, E.T. Cunningham, Jr. (Eds), Vaughan & Asbury's General Ophthalmology, 18e.