Physiology of the lens Flashcards
What are the main contents of the lens?
The lens contains 65% water, 34% proteins, and 1% lipids, cholesterol, and trace elements.
What is the primary source of nutrient supply for the lens?
The aqueous humor.
What is the primary site for ATP synthesis in the lens?
The epithelium.
What are the factors that maintain lens transparency?
Thin epithelium, regular arrangement of lens fibers, few cellular organelles, little extracellular space, orderly arrangement of lens proteins, relative dehydration, semipermeable character of lens capsule, avascularity, and antioxidants
What is accommodation in the context of eye physiology?
Accommodation is the process by which the eye increases its optical power to maintain a clear image (focus) on an object as it draws near the eye.
What changes occur in the eye during accommodation?
Contraction of the ciliary muscle releases tension on the zonular fibers, the elastic lens capsule increases its curvature, lens thickness increases, and equatorial diameter decreases.
What additional changes occur during accommodation to enhance focus?
Reduction in pupil size in both eyes and convergence of both eyes.
What is presbyopia?
Presbyopia is the physiological insufficiency of accommodation associated with the aging of the lens, resulting in progressively worsening ability to focus clearly on close objects.
How does the lens change with age in presbyopia?
The lens becomes stiffer and less flexible as it accumulates more proteins over time, reducing its ability to increase curvature when tension is released on the zonular fibers.
What are the symptoms of presbyopia?
Difficulty reading small print, needing to hold reading material farther away, headaches, and eyestrain.
What is the treatment for presbyopia?
Convex (plus) lenses, which provide additional power for focusing on near objects (“reading glasses”)
