Optical nerve

Vision is vital for human activities, and eyes are very sensitive to a number of toxic insults induced by chemical compounds. The most serious outcome is permanent eye damage which may be so severe as to cause loss of vision. The eye consists of the cornea and conjunctiva, the choroid, the iris, and the ciliary body. It also contains the retina, which is of neural origin, and the optic nerve. The retina contains photoreceptors, a highly specific light-sensitive type of neural tissue. The eye also contains the lens and a small cerebrospinal fluid system, the aqueous humor system, that is important for the maintenance of the steady state of hydration of the lens and thus the transparency of the eye. 

The eye has its own hydraulic system, and disturbances in it may cau.se serious damage to the eye. The normal eye pressure is 22 mm Hg, but when the pressure increases to 28-30 mm Hg, the optic nerve is squeezed and becomes hypoxic. This increase in the eye pressure may be due to acids or alkali causing inflammation in the anterior chamber of the eye, blocking the outflow of aqueous humor back into the systemic circulation. 

Augen-hornhaut,/. cornea, -kammerwasser, n. aqueous humor, -licht, n. eyesight, -lid, n. e3 elid. -linse, /. crystalline lens eye lens. e3 epiece. -marmor, m. eye-spotted marble, -mass, n. measure by eye. -merk, n. object in view, aim. -nerv, m. optic nerve, -nichts,... 

Sehnepuddeln, n. puddling of fibrous iron. Sehnerv, m. optic nerve. 

Methanol is a dangerous fire hazard when exposed to heat or flame, and a moderate expl hazard when exposed to flame. It is a dangerous disaster hazard upon exposure to heat or flame, and can react vigorously with oxidizing materials. Methanol possesses distinct narcotic props, and is also a slight irritant to the mucous membranes. Its main toxic effect is exerted upon the nervous system, particularly the optic nerves and possibly the retinae. In the body the products formed by its oxidn are formaldehyde and formic acid, both of which are toxic. Because of the slowness with which it is eliminated, methanol should be regarded as a cumulative poison (Ref 5)... 

Adverse reactions associated with administration of the corticosteroid ophthalmic preparations include elevated IOP with optic nerve damage, loss of visual acuity, cataract formation, delayed wound healing, secondary ocular infection, exacerbation of comeal infections, dry eyes, ptosis, blurred vision, discharge, ocular pain, foreign body sensation, and pruritus. 

Figure 33. Proposed interface between an electronic component (video camera) and a nerve (optical nerve) that could transduce electronic signals from the equipment to ionic signals that can be understood by dendrites.

At its most fundamental level, the circadian cycle rests on the influence of so-called clock genes . These genes have been studied most extensively in insects but they have also been found in humans. Their protein products enter the cell nucleus and regulate their own transcription. This feedback process is linked to exposure to light and so it is not surprising that visual inputs are important for maintenance of circadian rhythms. However, it is not the reception of specific visual information, transmitted in the optic nerve to the lateral geniculate nucleus (LGN) and visual cortex (i.e. visual discrimination), that is responsible for the rhythm but the more simple, almost subconscious, reception of light. 

Figure 22.3 Possible links in the induction of circadian rhythm between daylight, the suprachiasmatic nucleus and melatonin release from the pineal gland. Some fibres in the optic nerve, projecting from the eye to the lateral geniculate nucleus (LGN) in the thalamus, innervate the suprachiasmatic nucleus (SCN) in the anterior hypothalamus, via the retinohypothalamic tract (RHT). Others project to the SCN from the LGN in the geniculohypothalamic tract (GHT). The release of melatonin into the circulation from the pineal gland (PG) is maximal at night and appears to be controlled partly by noradrenaline released from sympathetic nerves originating in the superior cervical ganglion (SCG). Melatonin receptors are found in the SCN, the removal of which dampens melatonin secretion...

The HunterLab system (1958) was the hrst to use the opponent color theory stating that the red, green, and blue cone responses are re-mixed into opponent coders as they move up the optic nerve to the brain.Based on that theory, the HunterLab color space is three-dimensional and rectangular (see Figure 1.6). 

At about four months gestation, mesenchymal cells emanating from the central hyaloid vessel at the optic disc invade the inner layers of the retina. These endothelial complexes develop into capillaries as vascularization proceeds anteriorly in all directions towards the ora serrata from the optic nerve. As this progresses, so the embryonic hyaloid vessels in the vitreous undeigo regression. These retinal vessels do not, however, reach the most anterior portion of the retina until 8 months gestation and the anterior temporal retinal periphery, ferthest removed from the optic nerve, is not vascularized until about full term (Flower and Patz, 1971). 

Witkin J.W. (1987). Immunocytochemical demonstration of luteinizing-hormone-releasing hormone in optic nerve and nasal region of fetal rhesus macaque. Neurosci Lett 79, 73-77. 

The goals of therapy are to prevent further loss of visual function minimize adverse effects of therapy and its impact on the patient s vision, general health, and quality of life control intraocular pressure in order to reduce or prevent further optic nerve damage and educate and involve the patient in the management of their disease. 

The posterior segment of the eye contains vitreous humor (a clear jelly-like substance), the retina, the retinal vasculature, and the optic nerve head. The retina transforms light energy... 

Optic nerve head (optic disc) cupping. 

Diffuse thinning, focal narrowing, or notching of the optic nerve head rim. 

Optic nerve head and nerve fiber layer changes occur before visual field changes can be detected. 

Evaluate diagnostic tests (e.g., IOP, visual fields, and optic nerve evaluations) to determine if the patient s current glaucoma therapy is effective. 

Geniculate nucleus The portion of the brain that processes visual information from the optic nerve and relays it to the cerebral cortex. 

Lamina cribrosa A series of perforated sheets of connective tissue that the optic nerve passes through as it exits the eye. 

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