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The optic chiasm, or optic chiasma, is the part of the brain where the optic nerves cross. It is located at the bottom of the brain immediately inferior to the hypothalamus. The optic chiasm is found in all vertebrates, although in cyclostomes, it is located within the brain.
The optic nerve, also known as cranial nerve II, or simply as CN II, is a paired cranial nerve that transmits visual information from the retina to the brain. In humans, the optic nerve is derived from optic stalks during the seventh week of development and is composed of retinal ganglion cell axons and glial cells; it extends from the optic disc to the optic chiasma and continues as the optic tract to the lateral geniculate nucleus, pretectal nuclei, and superior colliculus.
The vitreous body is the clear gel that fills the space between the lens and the retina of the eyeball in humans and other vertebrates. It is often referred to as the vitreous humor or simply "the vitreous". Vitreous fluid or "liquid vitreous" is the liquid component of the vitreous gel, found after a vitreous detachment. It is not to be confused with the aqueous humor, the other fluid in the eye that is found between the cornea and lens.
Optic nerve hypoplasia (ONH) is a medical condition arising from the underdevelopment of the optic nerve(s). This condition is the most common congenital optic nerve anomaly. The optic disc appears abnormally small, because not all the optic nerve axons have developed properly. It is often associated with endocrinopathies, developmental delay, and brain malformations. The optic nerve, which is responsible for transmitting visual signals from the retina to the brain, has approximately 1.2 million nerve fibers in the average person. In those diagnosed with ONH, however, there are noticeably fewer nerves.
Fluorescein angiography (FA), fluorescent angiography (FAG), or fundus fluorescein angiography (FFA) is a technique for examining the circulation of the retina and choroid using a fluorescent dye and a specialized camera. Sodium fluorescein is added into the systemic circulation, the retina is illuminated with blue light at a wavelength of 490 nanometers, and an angiogram is obtained by photographing the fluorescent green light that is emitted by the dye. The fluorescein is administered intravenously in intravenous fluorescein angiography (IVFA) and orally in oral fluorescein angiography (OFA). The test is a dye tracing method.
The optic disc or optic nerve head is the point of exit for ganglion cell axons leaving the eye. Because there are no rods or cones overlying the optic disc, it corresponds to a small blind spot in each eye.
Meridian is used in perimetry and in specifying visual fields. According to IPS Perimetry Standards 1978 (2002): "Perimetry is the measurement of [an observer's] visual functions ... at topographically defined loci in the visual field. The visual field is that portion of the external environment of the observer [in which when he or she is] steadily fixating ...[he or she] can detect visual stimuli."
A cone dystrophy is an inherited ocular disorder characterized by the loss of cone cells, the photoreceptors responsible for both central and color vision.
Codocytes, also known as target cells, are red blood cells that have the appearance of a shooting target with a bullseye. In optical microscopy these cells appear to have a dark center surrounded by a white ring, followed by dark outer (peripheral) second ring containing a band of hemoglobin. However, in electron microscopy they appear very thin and bell shaped. Because of their thinness they are referred to as leptocytes. On routine smear morphology, some people like to make a distinction between leptocytes and codocytes- suggesting that in leptocytes the central spot is not completely detached from the peripheral ring, i.e. the pallor is in a C shape rather than a full ring.
Julius Hirschberg was a German ophthalmologist and medical historian. He was of Jewish ancestry.
Toxic and nutritional optic neuropathy is a group of medical disorders defined by visual impairment due to optic nerve damage secondary to a toxic substance and/or nutritional deficiency. The causes of these disorders are various, but they are linked by shared signs and symptoms, which this article will describe. In several of these disorders, both toxic and nutritional factors play a role, acting synergistically.
1p36 deletion syndrome is a congenital genetic disorder characterized by moderate to severe intellectual disability, delayed growth, hypotonia, seizures, limited speech ability, malformations, hearing and vision impairment, and distinct facial features. The symptoms may vary, depending on the exact location of the chromosomal deletion.
The fundus of the eye is the interior surface of the eye opposite the lens and includes the retina, optic disc, macula, fovea, and posterior pole. The fundus can be examined by ophthalmoscopy and/or fundus photography.
Optic neuropathy is damage to the optic nerve from any cause. Damage and death of these nerve cells, or neurons, leads to characteristic features of optic neuropathy. The main symptom is loss of vision, with colors appearing subtly washed out in the affected eye. On medical examination, the optic nerve head can be visualised by an ophthalmoscope. A pale disc is characteristic of long-standing optic neuropathy. In many cases, only one eye is affected and patients may not be aware of the loss of color vision until the doctor asks them to cover the healthy eye.
Papillorenal syndrome, is an autosomal dominant genetic disorder marked by underdevelopment (hypoplasia) of the kidney and colobomas of the optic nerve.
Fundus photography involves photographing the rear of an eye, also known as the fundus. Specialized fundus cameras consisting of an intricate microscope attached to a flash enabled camera are used in fundus photography. The main structures that can be visualized on a fundus photo are the central and peripheral retina, optic disc and macula. Fundus photography can be performed with colored filters, or with specialized dyes including fluorescein and indocyanine green.
A mouth assessment is performed as part of a patient's health assessment. The mouth is the beginning of the digestive system and a substantial part of the respiratory tract. Before an assessment of the mouth, patient is sometimes advised to remove any dentures. The assessment begins with a dental-health questionnaire, including questions about toothache, hoarseness, dysphagia(difficulty swallowing), altered taste or a frequent sore throat, current and previous tobacco use and alcohol consumption and any sores, lesions or bleeding of the gums.
Haab's striae, or Descemet's tears, are horizontal breaks in the Descemet membrane associated with congenital glaucoma. It is named after Otto Haab. These occur because descemet's membrane is less elastic than the corneal stroma. Tears are usually peripheral, concentric with limbus and appear as line with double contour.
Hutchinson's patch is a dull orangish-pink area on the cornea, most often found at the periphery of the cornea. The sign is an indication of interstitial keratitis, causing corneal neovascularisation.
Blood vessels derived from the ciliary vessels are thickly set in the layers of the cornea and produce a dull red color—"the salmon patch of Hutchinson." These patches may be small and crescent-shaped, or large and sector-like.
Descemet membrane endothelial keratoplasty (DMEK) is a method of corneal transplantation. The DMEK technique involves the removal of a very thin sheet of tissue from the posterior side of a person's cornea, replacing it with the two innermost layers of corneal tissue from a donor's eyeball. The two corneal layers which are exchanged are the Descemet's membrane and the corneal endothelium. The person's corneal tissue is gently excised and replaced with the donor tissue via small 'clear corneal incisions' (small corneal incisions just anterior to the corneal limbus. The donor tissue is tamponaded against the person's exposed posterior corneal stroma by injecting a small air bubble into the anterior chamber. To ensure the air tamponade is effective, it is necessary for people to strictly posture so that they are looking up at the ceiling during the recovery period and until the air bubble has fully resorbed.
References
- ↑ "Optic disc pallor. COMS Grading". Webeye.ophth.uiowa.edu. 2006-06-27. Retrieved 2012-02-15.
- ↑ "Chapter 4 – Optic Nerve Compression: Vascular – Ophthalmic Artery Aneurysm". Oph.ucsd.edu. Archived from the original on 2012-07-12. Retrieved 2012-02-15.
- ↑ "EyeRounds.org: Dominant Optic Atrophy: 47 year-old female with chronic, mildly subnormal vision". Webeye.ophth.uiowa.edu. Retrieved 2012-02-15.
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