Fundus photography involves photographing the rear of an eye. 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; the models and technology of fundus photography has advanced and evolved over the last century. Since the equipments are sophisticated and challenging to manufacture to clinical standards, only a few manufacturers/brands are available in the market: Welch Allyn, Volk, Zeiss, Nidek, Kowa, CSO, CenterVue, Ezer are some example of fundus camera manufacturers; the concept of fundus photography was first introduced in the mid 19th century, after the introduction of photography in 1839. The goal of photographing the human ocular fundus was but becoming more achievable.
In 1851, Hermann von Helmholtz introduced the Ophthalmoscope, James Clerk Maxwell presented a colour photography method in 1861. In the early 1860s, Henry Noyes and Abner Mulholland Rosebrugh both assembled fundus cameras and tried fundus photography on animals. Although the news was encouraging and showed promise, the vision of capturing a satisfactory photo of a human ocular fundus was still far from reach. Early fundus photos were limited by insufficient light, long exposures, eye movement, prominent corneal reflexes that reduced the clarity detail, it would be several decades. There has been some controversy regarding the first successful human fundus photo. Most accounts state William Thomas Jackman and J. D. Webster since they published their technique along with a reproduction of a fundus image in two photography periodicals in 1886. Three other names played a prominent role in early fundus photography. According to some historical accounts, Elmer Starr and Lucien Howe may have been first to photograph the human retina.
Lucien Howe is a well-known name in Ophthalmology, together with his assistant Elmer Starr, they collaborated on the fundus photography project in 1886-88. Howe described their results as the first "recognizable” fundus photograph a nod to Jackman & Webster being the first to "publish” a fundus photograph. Based on the written accounts and Starr's image was more "recognizable” as a fundus. Efforts to photograph the fundus have been ongoing for 75 years. Hundreds of specialists worked to overcome the problem, achieved in the early 20th century by Friedrich Dimmer, who published his photographs in 1921. Dimmer’s fundus camera, developed about 1904, was a complicated and sophisticated research tool and it was not until 1926 that Stockholm’s Johan Nordenson and the Zeiss Camera Company were able to market a commercial device for use by practitioners, the first modern Fundus camera. Since the features of fundus cameras have improved drastically to include non-mydriatic imaging, electronic illumination control, automated eye alignment, high-resolution digital image capture.
These improvements have helped make modern fundus photography a standard ophthalmic practice for documenting retinal disease. Following the development of fundus photography, David Alvis, Harold Novotny, performed the first fluorescein angiography in 1959, using the Zeiss fundus camera with electronic flash; this development was huge feat in the world of Ophthalmology. Several countries began large-scale teleophthalmology programs using digital fundus photography around 2008; the optical design of fundus cameras is based on the principle of monocular indirect ophthalmoscopy. A fundus camera provides an upright, magnified view of the fundus. A typical camera views 30 to 50° of retinal area, with a magnification of 2.5x, allows some modification of this relationship through zoom or auxiliary lenses from 15°, which provides 5x magnification, to 140° with a wide angle lens, which minifies the image by half. The optics of a fundus camera are similar to those of an indirect ophthalmoscope in that the observation and illumination systems follow dissimilar paths.
The observation light is focused via a series of lenses through a doughnut shaped aperture, which passes through a central aperture to form an annulus, before passing through the camera objective lens and through the cornea onto the retina. The light reflected from the retina passes through the un-illuminated hole in the doughnut formed by the illumination system; as the light paths of the two systems are independent, there are minimal reflections of the light source captured in the formed image. The image forming rays continue towards the low powered telescopic eyepiece; when the button is pressed to take a picture, a mirror interrupts the path of the illumination system allow the light from the flash bulb to pass into the eye. A mirror falls in front of the observation telescope, which redirects the light onto the capturing medium, whether it is film or a digital CCD; because of the eye’s tendency to accommodate while looking though a telescope, it is imperative that the exiting vergence is parallel in order for an in focus image to be formed on the capturing medium.
Practical instruments for fundus photography perform the following modes of examination: Colour, where the retina is illuminated by white light and examined in full colour. Red free fundus photography utilises a filter in order to better observe superficial lesions and some vascular abnormalities within the retina and surrounding tissue. A green filter ~; this allows a better contrast for viewing retinal blood ve
Cranial nerves are the nerves that emerge directly from the brain, in contrast to spinal nerves. 10 of the cranial nerves originate in the brainstem. Cranial nerves relay information between the brain and parts of the body to and from regions of the head and neck. Spinal nerves emerge sequentially from the spinal cord with the spinal nerve closest to the head emerging in the space above the first cervical vertebra; the cranial nerves, emerge from the central nervous system above this level. Each cranial nerve is present on both sides. Depending on definition in humans there are twelve or thirteen cranial nerves pairs, which are assigned Roman numerals I–XII, sometimes including cranial nerve zero; the numbering of the cranial nerves is based on the order in which they emerge from the brain, front to back. The terminal nerves, olfactory nerves and optic nerves emerge from the cerebrum or forebrain, the remaining ten pairs arise from the brainstem, the lower part of the brain; the cranial nerves are considered components of the peripheral nervous system, although on a structural level the olfactory and trigeminal nerves are more considered part of the central nervous system.
Most humans are considered to have twelve pairs of cranial nerves, with the terminal nerve more canonized. They are: the olfactory nerve, the optic nerve, oculomotor nerve, trochlear nerve, trigeminal nerve, abducens nerve, facial nerve, vestibulocochlear nerve, glossopharyngeal nerve, vagus nerve, accessory nerve, hypoglossal nerve. Cranial nerves are named according to their structure or function. For example, the olfactory nerve supplies smell, the facial nerve supplies motor innervation to the face; because Latin was the lingua franca of the study of anatomy when the nerves were first documented and discussed, many nerves maintain Latin or Greek names, including the trochlear nerve, named according to its structure, as it supplies a muscle that attaches to a pulley. The trigeminal nerve is named in accordance with its three components, the vagus nerve is named for its wandering course. Cranial nerves are numbered based on their rostral-caudal position. If the brain is removed from the skull the nerves are visible in their numeric order, with the exception of the last, CN XII, which appears to emerge rostrally to CN XI.
Cranial nerves have paths outside the skull. The paths within the skull are called "intracranial" and the paths outside the skull are called "extracranial". There are many holes in the skull called "foramina" by. All cranial nerves are paired, which means that they occur on both the right and left sides of the body; the muscle, skin, or additional function supplied by a nerve on the same side of the body as the side it originates from, is referred to an ipsilateral function. If the function is on the opposite side to the origin of the nerve, this is known as a contralateral function. Intracranial course of cranial nerves is important regarding diagnosis of various intracranial lesions like brain tumors and intracranial arterial aneurysms. Dysfunction of one or more cranial nerves indicates stimulation by some lesion. For example an acoustic schwanoma may cause disturbance in hearing but with further growth of tumor it may involve other cranial nerves and the patient may present with pain resembling trigeminal neuralgia when the tumor involves trigeminal nerve or diplopia due to abducent nerve involvement facial palsy with facial nerve compression.
These findings along with cerebellar signs will suggest the diagnosis of a cerebellopontine angle lesion. A patient presenting with ptosis may have a posterior communicating artery aneurysm compressing the oculomotor nerve during its intracranial course. Facial pain in the distribution of any one or all divisions of trigeminal nerve suggests stimulation of trigeminal nerve roots by a near by vessel; the cell bodies of many of the neurons of most of the cranial nerves are contained in one or more nuclei in the brainstem. These nuclei are important relative to cranial nerve dysfunction because damage to these nuclei such as from a stroke or trauma can mimic damage to one or more branches of a cranial nerve. In terms of specific cranial nerve nuclei, the midbrain of the brainstem has the nuclei of the oculomotor nerve and trochlear nerve; the fibers of these cranial nerves exit the brainstem from these nuclei. Some of the cranial nerves have sensory or parasympathetic ganglia of neurons, which are located outside the brain.
The sensory ganglia are directly correspondent to dorsal root ganglia of spinal nerves and are known as cranial sensory ganglia. Sensory ganglia exist for nerves with sensory function: V, VII, VIII, IX, X. There are parasympathetic ganglia, which are part of the autonomic nervous system for cranial nerves III, VII, IX and X; the trigeminal ganglia of the trigeminal nerve occupies a space in the dura mater called Trigeminal cave. This ganglion contains the cell bodies of the sensory fibers of the three branches of the trig
The optic tract is a part of the visual system in the brain. It is a continuation of the optic nerve that relays information from the optic chiasm to the ipsilateral lateral geniculate nucleus, pretectal nuclei, superior colliculus, it is composed of two individual tracts, the left optic tract and the right optic tract, each of which conveys visual information exclusive to its respective contralateral half of the visual field. Each of these tracts is derived from a combination of temporal and nasal retinal fibers from each eye that corresponds to one half of the visual field. In more specific terms, the optic tract contains fibers from the ipsilateral temporal hemiretina and contralateral nasal hemiretina; the optic tract carries retinal information relating to the whole visual field. The left optic tract corresponds to the right visual field, while the right optic tract corresponds to the left visual field. To form the right visual field, temporal retinal fibers from the left eye and nasal retinal fibers from the right eye form the left optic tract, to form the left visual field, temporal retinal fibers from the right eye and nasal retinal fibers from the left eye form the right optic tract.
Several autonomic ocular motor responses are consensual. The optic tract is responsible for relaying visual information to the LGN, but it is peripherally responsible for transducing these bilateral autonomic reflexes, including the pupillary light reflex and pupillary dark reflex; the pupillary light reflex is an autonomic reflex that controls pupil diameter to accommodate for increases in illumination as perceived by the retina. Higher light intensity causes pupil constriction, the increase of light stimulation of one eye will cause pupillary constriction of both eyes; the neural circuitry of the pupillary light reflex includes the optic tract which joins the optic nerve to the brachium of the superior colliculus. To the pupillary light reflex, the pupillary dark reflex is an autonomic reflex that controls pupil diameter to accommodate for decreases in illumination as perceived by the retina. Lower light intensity causes pupil dilation, the decrease of light stimulation of one eye will cause pupillary dilation of both eyes.
The neural circuitry of the pupillary dark reflex includes the optic tract which joins the optic nerve to the hypothalamus. Lesions in the optic tract correspond to visual field loss on the left or right half of the vertical midline known as homonymous hemianopsia. A lesion in the left optic tract will cause right-sided homonymous hemianopsia, while a lesion in the right optic tract will cause left-sided homonymous hemianopsia. Stroke, congenital defects, tumors and surgery are all possible causes of optic tract damage. Peripheral prism expanders and vision restitution therapy are employed in patients with visual field loss resultant of permanent optic tract damage. In certain split-brain patients who have undergone a corpus callosotomy to treat severe epilepsy, the information from one optic tract does not get transmitted to both hemispheres. For instance, a split-brain patient shown an image in the left visual field will be unable to vocally name what has been seen as the speech-control center is in the left hemisphere of the brain.
Pupillary reflexes the pupillary light reflex, are a powerful diagnostic tool employed in clinical and emergency medical practice. A lack of equal consensual pupillary constriction to a light stimulus a Marcus Gunn pupil, can be indicative of optic nerve damage, brainstem death, or optic tract damage in between
The hypoglossal nerve is the twelfth cranial nerve, innervates all the extrinsic and intrinsic muscles of the tongue, except for the palatoglossus, innervated by the vagus nerve. It is a nerve with a motor function; the nerve arises from the hypoglossal nucleus in the brain stem as a number of small rootlets, passes through the hypoglossal canal and down through the neck, passes up again over the tongue muscles it supplies into the tongue. There are two hypoglossal nerves in the body: one on the left, one on the right; the nerve is involved in controlling tongue movements required for speech and swallowing, including sticking out the tongue and moving it from side to side. Damage to the nerve or the neural pathways which control it can affect the ability of the tongue to move and its appearance, with the most common sources of damage being injury from trauma or surgery, motor neuron disease; the first recorded description of the nerve is by Herophilos in the third century BC. The name hypoglossus springs from the fact that its passage is below the tongue, from hypo and glossa.
The hypoglossal nerve arises as a number of small rootlets from the front of the medulla, the bottom part of the brainstem, in the preolivary sulcus, which separates the olive and the pyramid. The nerve passes through the subarachnoid space and pierces the dura mater near the hypoglossal canal, an opening in the occipital bone of the skull. After emerging from the hypoglossal canal, the hypoglossal nerve gives off a meningeal branch and picks up a branch from the anterior ramus of C1, it travels close to the vagus nerve and spinal division of the accessory nerve, spirals downwards behind the vagus nerve and passes between the internal carotid artery and internal jugular vein lying on the carotid sheath. At a point at the level of the angle of the mandible, the hypoglossal nerve emerges from behind the posterior belly of the digastric muscle, it loops around a branch of the occipital artery and travels forward into the region beneath the mandible. The hypoglossal nerve moves forward lateral to the hyoglossus and medial to the stylohyoid muscles and lingual nerve.
It continues forward to the tip of the tongue. It distributes branches to the intrinsic and extrinsic muscle of the tongue innervates as it passes in this direction, supplies several muscles that it passes; the rootlets of the hypoglossal nerve arise from the hypoglossal nucleus near the bottom of the brain stem. The hypoglossal nucleus receives input from both the motor cortices but the contralateral input is dominant. Signals from muscle spindles on the tongue travel through the hypoglossal nerve, moving onto the lingual nerve which synapses on the trigeminal mesencephalic nucleus; the hypoglossal nerve is derived from the first pair of occipital somites, collections of mesoderm that form next to the main axis of an embryo during development. The musculature it supplies develop as the hypoglossal cord from the myotomes of the first four pairs of occipital somites; the nerve is first visible as a series of roots in the fourth week of development, which have formed a single nerve and link to the tongue by the fifth week.
The hypoglossal nucleus is derived from the basal plate of the embryonic medulla oblongata. The hypoglossal nerve provides motor control of the extrinsic muscles of the tongue: genioglossus, hyoglossus and the intrinsic muscles of the tongue; these represent all muscles of the tongue except the palatoglossus muscle. The hypoglossal nerve is of a general somatic efferent type; these muscles are involved in manipulating the tongue. The left and right genioglossus muscles in particular are responsible for protruding the tongue; the muscles, attached to the underside of the top and back parts of the tongue, cause the tongue to protrude and deviate towards the opposite side. The hypoglossal nerve supplies movements including clearing the mouth of saliva and other involuntary activities; the hypoglossal nucleus interacts with the reticular formation, involved in the control of several reflexive or automatic motions, several corticonuclear originating fibers supply innervation aiding in unconscious movements relating to speech and articulation.
Reports of damage to the hypoglossal nerve are rare. The most common causes of injury in one case series were compression by tumours and gunshot wounds. A wide variety of other causes can lead to damage of the nerve; these include surgical damage, medullary stroke, multiple sclerosis, Guillain-Barre syndrome, infection and presence of an ectatic vessel in the hypoglossal canal. Damage can be on both sides, which will affect symptoms that the damage causes; because of the close proximity of the nerve to other structures including nerves and veins, it is rare for the nerve to be damaged in isolation. For example, damage to the left and right hypoglossal nerves may occur with damage to the facial and trigeminal nerves as a result of damage from a clot following arteriosclerosis of the vertebrobasilar artery; such a stroke may result in tight oral musculature, difficulty speaking and chewing. Progressive bulbar palsy, a form of motor neuron disease, is associated with combined lesions of the hypoglossal nucleus and nucleus ambiguus with wasting of the motor nerves of the pons and medulla.
This may cause difficulty with tongue movements, speech and swallowing caused by dysfunction of several cranial nerve nuclei. Motor neuron disease is the most common disease affecting the hypoglossal nerve; the hypoglossal nerve is tested by examining its movements. At rest, if the
Anatomical terms of neuroanatomy
This article describes anatomical terminology, used to describe the central and peripheral nervous systems - including the brain, spinal cord, nerves. Neuroanatomy, like other aspects of anatomy, uses specific terminology to describe anatomical structures; this terminology helps ensure that a structure is described with minimal ambiguity. Terms help ensure that structures are described depending on their structure or function. Terms are derived from Latin and Greek, like other areas of anatomy are standardised based on internationally accepted lexicons such as Terminologia Anatomica. To help with consistency and other species are assumed when described to be in standard anatomical position, with the body standing erect and facing observer, arms at sides, palms forward. Anatomical terms of location depend on the location and species, being described. To understand the terms used for anatomical localisation, consider an animal with a straight CNS, such as a fish or lizard. In such animals the terms "rostral", "caudal", "ventral" and "dorsal" mean towards the rostrum, towards the tail, towards the belly and towards the back.
For a full discussion of those terms, see anatomical terms of location. For many purposes of anatomical description and directions are relative to the standard anatomical planes and axes; such reference to the anatomical planes and axes is called the stereotactic approach. Standard terms used throughout anatomy include anterior / posterior for the front and back of a structure, superior / inferior for above and below, medial / lateral for structures close to and away from the midline and proximal / distal for structures close to and far away from a set point; some terms are used more in neuroanatomy, particularly: Rostral and caudal: In animals with linear nervous systems, the term rostral is synonymous with anterior and the term caudal is synonymous with posterior. Due to humans having an upright posture, their nervous system is considered to bend about 90°; this is considered to occur at the junction of the diencephalon. Thus, the terminology changes at either side of the midbrain-diencephalic junction.
Superior to the junction, the terminology is the same as in animals with linear nervous systems. Inferior to the midbrain-diencephalic junction the term rostral is synonymous with superior and caudal is synonymous with inferior. Dorsal and ventral: In animals with linear nervous systems, the term dorsal is synonymous with superior and the term ventral is synonymous with inferior. In humans, however the terminology differs on either side of the midbrain-diencephalic junction. Superior to the junction, the terminology is the same as in animals with linear nervous systems. However, inferior to the midbrain-diencephalic junction the term dorsal is synonymous with posterior and ventral is synonymous with anterior. Contralateral and ipsilateral referring to a corresponding position on the opposite left or right side and on the same side respectively. Standard anatomical planes and anatomical axes are used to describe structures in animals. In humans and most other primates the axis of the central nervous system is not bent.
This means that there are certain major differences that reflect the distortion of the brains of the Hominidae. For example, to describe the human brain, "rostral" still means "towards the face", or at any rate, the interior of the cranial cavity just behind the face. However, in the brain "caudal" means not "towards the tail", but "towards the back of the cranial cavity". Alternative terms for this rostro-caudal axis of the brain include antero-posterior axis. "Dorsal" means "in the direction away from the spinal cord i.e. in the direction of the roof of the cranial cavity". "Ventral" means downwards towards floor of the cranial cavity and thence to the body. They lie on the superior-inferior or Dorsoventral axis; the third axis passes through the ears, is called the left-right, or lateral axis. These three axes of the human brain match the three planes within which they lie though the terms for the planes have not been changed from the terms for the bodily planes; the most used reference planes are: Axial, the plane, horizontal and parallel to the axial plane of the body in the standard anatomical position.
It contains the medial axes of the brain. Coronal, a vertical plane that passes through both ears, contains the lateral and dorsoventral axes. Sagittal, a vertical plane that passes from between the nostrils, between the cerebral hemispheres, dividing the brain into left and right halves, it contains the medial axes of the brain. A parasagittal plane is any plane parallel to the sagittal plane. Specific terms are used for peripheral nerves. An afferent nerve fiber is a fibre originating at the present point. For example, a striatal afferent is an afferent originating at the striatum. An efferent nerve fiber is one. For example, a cortical efferent is a fibre coming from elsewhere, arriving to the cortex. Note that, the opposite of the direction in which the nerve fibre conducts signals. Specific terms are used to describe the route of a nerve or nerve fibre: A chiasm i
The terminal nerve, or cranial nerve zero, was discovered by German scientist Gustav Fritsch in 1878 in the brains of sharks. It was first found in humans in 1913. A 1990 study has indicated; the nerve has been called by other names, including cranial nerve XIII, Zero Nerve, Nerve N, NT. The terminal nerve appears just anterior of the other cranial nerves bilaterally as a microscopic plexus of unmyelinated peripheral nerve fascicles in the subarachnoid space covering the gyrus rectus; this plexus appears near the cribriform plate and travels posteriorly toward the olfactory trigone, medial olfactory gyrus, lamina terminalis. The nerve is overlooked in autopsies because it is unusually thin for a cranial nerve, is torn out upon exposing the brain. Careful dissection is necessary to visualize the nerve, its purpose and mechanism of function is still open to debate. The zebrafish was used as a developmental model in research from 2004; the connections between the terminal nerve and the olfactory system have been extensively studied in human embryos.
It was found to enter the brain at stages 18 from olfactory origins. Although close to the olfactory nerve, the terminal nerve is not connected to the olfactory bulb, where smells are analyzed; this fact suggests that the nerve is either vestigial or may be related to the sensing of pheromones. This hypothesis is further supported by the fact that the terminal nerve projects to the medial and lateral septal nuclei and the preoptic areas, all of which are involved in regulating sexual behavior in mammals, as well as a 1987 study finding that mating in hamsters is reduced when the terminal nerve is severed. Vomeronasal organ Vilensky JA. "The neglected cranial nerve: nervus terminalis". Clinical Anatomy. 27: 46–53. Doi:10.1002/ca.22130. PMID 22836597. Fuller GN, Burger PC. "Nervus terminalis in the adult human". Clinical Neuropathology. 9: 279–83. PMID 2286018