الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 217 |  |  |
| | | from | 217 | | |
Abstract
The retina is a circular disc with a diameter of 30–40 mm and a thickness of 0.5 mm. It is the light-sensitive area composed of millions of densely packed cells.
The cells of the retina are classified into:
I. Retinal pigment epithelium (RPE)
II. Neurons:
1) Photoreceptor neurons (Rods and Cones cells)
2) Conducting neurons (Bipolar cells and Ganglion cells)
3) Associating neurons (Horizontal cells and Amacrine cells)
III. Glial cells (Müller cells, Astroglia and Microglia)
There are ten distinguishable layers (from superficial to profound) within these cells:
1. Retinal pigment epithelium (RPE).
2. Photoreceptor layer (PRL): consists of the outer segments of rods and cones.
3. Outer limiting membrane (OLM): it is the junctional complexes made between the processes of different Müller cells or between the processes of Müller cells and photoreceptors.
4. Outer nuclear layer (ONL): it consists of the cell bodies of photoreceptors. Its thickness is an important biomarker for retinal degeneration.
5. Outer plexiform layer (OPL): it is the first synapse in the retina between processes of photoreceptors, bipolar cells, horizontal cells, and some amacrine cell types.
6. Inner nuclear layer (INL): it consists of the cell bodies of bipolar cells, Horizontal cells, Amacrine and Muller cells.
7. Inner plexiform layer (IPL): it is the synapse between processes of Bipolar, Ganglion and Amacrine cells.
8. Ganglion cell layer (GCL): its the cell bodies of Ganglion and Amacrine cells.
9. Nerve fiber layer (NFL): it is the Optic nerve fibers.
10. Inner limiting membrane (ILM): it is the fusion of Müller cell feet.
Tamoxifen is regarded as a pioneering medicine due to its application in breast cancer treatment, chemoprevention, and research as a selective estrogen receptor modulator (SERM). According to its concentration, it is well known that tamoxifen has a two-stage influence on cell growth control. Tamoxifen is cytostatic on estrogen receptor-positive cell lines at low concentrations (0.1 mM), close to its affinity for the estrogen receptors (ER). This effect can be reversed by the addition of 17b-estradiol (E2), which competes with Tamoxifen on the ER and stimulates the proliferation of tumor cells by acting as an ER agonist. At pharmacologically relevant concentrations (1–10 mM), tamoxifen is cytotoxic, but E2 does not reverse this cytotoxicity, indicating that the ER is not implicated in this effect.
Tamoxifen can cause crystalline deposits and pseudo-cystic foveal cavitations. These findings have been compared to macular telangiectasia type 2, indicating a similar pathogenesis involving Muller cell dysfunction. The pseudo-cystic foveal cavitations noted in tamoxifen retinopathy can be differentiated from cystic macular edema by the absence of leakage noted on the fluorescein angiogram and normal-to-reduced retinal thickness.
Melatonin (N-acetyl-5-methoxytryptamine) is a potent free radical scavenger with antioxidant and anti-inflammatory properties. In addition to the pineal gland, melatonin is produced in the retina, where it functions as an endogenous neuromodulator. Melatonin may serve as a protective agent in ocular conditions including photokeratitis, cataracts, retinopathy of prematurity, ischemia/reperfusion injury, and human refractory central serous chorioretinopathy.
Lutein is one of the few xanthophyll carotenoids present in high concentration in the macula of the human retina. As de novo synthesis of lutein is impossible within the human body, lutein can only be obtained through diet. It is a naturally occurring substance abundant in egg yolks and dark green leafy vegetables. Many basic and clinical studies have reported lutein’s anti-oxidative and antiinflammatory properties in the eye, suggesting its beneficial effects on the protection and alleviation of ocular diseases such as agerelated macular degeneration, diabetic retinopathy, retinopathy of prematurity, myopia, and cataract.