From an evolutionary perspective, a more complex structure such as the inverted retina can generally come about as a consequence of two alternate processes: (a) an advantageous "good" compromise between competing functional limitations, or (b) as a historical maladaptive relic of the convoluted path of organ evolution and transformation. Vision is an important adaptation in higher vertebrates. A third view of the "inverted" vertebrate eye is that it combines two benefits: the maintenance of the photoreceptors mentioned above, and the reduction in light intensity necessary to avoid blinding the photoreceptors, which are based on the extremely sensitive eyes of the ancestors of modern hagfishes (a fish that lives in very deep, dark water). Retinal layers
The vertebrate retina has ten distinct layers. From closest to farthest from the vitreous body:

Inner limiting membrane – basement membrane elaborated by Müller cells. Nerve fibre layer – axons of the ganglion cell bodies (note that a thin layer of Müller cell footplates exists between this layer and the inner limiting membrane). Ganglion cell layer – contains nuclei of ganglion cells, the axons of which become the optic nerve fibres, and some displaced amacrine cells. Inner plexiform layer – contains the synapse between the bipolar cell axons and the dendrites of the ganglion and amacrine cells. Inner nuclear layer – contains the nuclei and surrounding cell bodies (perikarya) of the amacrine cells, bipolar cells, and horizontal cells. Outer plexiform layer – projections of rods and cones ending in the rod spherule and cone pedicle, respectively.
It has recently been shown that the oxidative stress associated with cigarette smoke can inhibit the activity of HDAC2, thereby blocking the anti-inflammatory effects of corticosteroids.) Pharmacokinetics
Absorption
When theophylline is administered intravenously, bioavailability is 100%. Distribution
Theophylline is distributed in the extracellular fluid, in the placenta, in the mothers milk and in the central nervous system. The volume of distribution is 0.5 L/kg. The protein binding is 40%. The volume of distribution may increase in neonates and those suffering from cirrhosis or malnutrition, whereas the volume of distribution may decrease in those who are obese. Metabolism
Theophylline is metabolized extensively in the liver (up to 70%). It undergoes N-demethylation via cytochrome P450 1A2. It is metabolized by parallel first order and Michaelis-Menten pathways. Metabolism may become saturated (non-linear), even within the therapeutic range. Small dose increases may result in disproportionately large increases in serum concentration. Methylation to caffeine is also important in the infant population. Smokers and people with hepatic (liver) impairment metabolize it differently. Both THC and nicotine have been shown to increase the rate of theophylline metabolism. Excretion
Theophylline is excreted unchanged in the urine (up to 10%). Clearance of the drug is increased in children (age 1 to 12), teenagers (12 to 16), adult smokers, elderly smokers, as well as in cystic fibrosis, and hyperthyroidism.