| Tunnel vision | |
|---|---|
 | |
| Simulation of tunnel vision | |
| Specialty | Ophthalmology |
Tunnel vision is the loss of peripheral vision with retention of central vision, resulting in a constricted circular tunnel-like field of vision. [1]
| Tunnel vision | |
|---|---|
| | |
| Simulation of tunnel vision | |
| Specialty | Ophthalmology |
Tunnel vision is the loss of peripheral vision with retention of central vision, resulting in a constricted circular tunnel-like field of vision. [1]
Tunnel vision can be caused by:
Eyeglass users experience tunnel vision to varying degrees due to the corrective lens only providing a small area of proper focus, with the rest of the field of view beyond the lenses being unfocused and blurry. Where a naturally sighted person only needs to move their eyes to see an object far to the side or far down, the eyeglass wearer may need to move their whole head to point the eyeglasses towards the target object.[ citation needed ]
The eyeglass frame also blocks the view of the world with a thin opaque boundary separating the lens area from the rest of the field of view. The eyeglass frame is capable of obscuring small objects and details in the peripheral field.[ citation needed ]
Activities which require a protective mask, safety goggles, or fully enclosing protective helmet can also result in an experience approximating tunnel vision. Underwater diving masks using a single flat transparent lens usually have the lens surface several centimeters from the eyes. The lens is typically enclosed with an opaque black rubber sealing shell to keep out water. For this type of mask the peripheral field of the diver is extremely limited. Generally, the peripheral field of a diving mask is improved if the lenses are as close to the eye as possible, or if the lenses are large, multi-window, or is a curved wrap-around design.[ citation needed ]
Binoculars, telescopes, and microscopes induce an experience of extreme tunnel vision due to the design of the optical components.
A wide field microscope or telescope generally requires much larger diameter and thicker lenses, or complex parabolic mirror assemblies, either of which results in significantly greater cost for construction of the optical device.[ citation needed ]
Wide-field binoculars are possible, but require bulkier, heavier, and more complex eyepieces. The diameter of the objective lenses is unimportant for field of view. [10] The widest-angle eyepieces used in telescopes are so large that two would not fit side-by-side for use in binoculars.[ citation needed ]
Glaucoma is the leading cause for irreversible blindness globally. [11] Glaucoma usually starts with no symptoms to start losing peripheral vision, and if untreated, it can leads to a complete loss of peripheral vision, which is tunnel vision, and eventually, central vision will be affected leading to complete blindness. Central vision refers to the range people see that's straight ahead of them, and it's characterized with fine details and better ability to detect color. And peripheral vision is the range outside of fixation. The mechanism underlying this procedure starts with an imbalance between aqueous humor secretion and aqueous humor drainage. In the eyes, the ciliary body secrets liquids in the eye, called aqueous humor, after the secretion, the liquid arrives at posterior chamber, which is the space between lens and iris. Then the liquid goes past the pupil to arrive at the anterior chamber, the space between iris and cornea, and eventually goes out of the eye through the connective tissue called trabecular meshwork. In healthy eyes, the drainage and the secretion of aqueous humor is balanced, but in glaucoma, the drainage is either partially or completely blocked, causing an increased pressure in the eye. The excess aqueous humor will eventually push on the optic nerves at the back of the eye. Peripheral vision loss is often the first symptom in the process since the nerves in the surroundings are the first to be damaged. If untreated, a complete loss of peripheral vision, tunnel vision, occurs.
Because of constant motion, the visual field of a driver is usually not stable. To monitor changes in our environment, peripheral vision plays a big role in signalling us when it will be safe to change lanes, whether a pedestrian is crossing the street, which direction the car in front is turning, and how fast the car is running. [12] Since drivers have expectations of these possible collisional cues to appear in their peripheral vision, they tend to drive safer when these cues are presented peripherally than at fixation. In patients with glaucoma, they have more difficulties in lane maintenance, scanning and vehicle control. [13] In addition, compared to individuals without field defects, people with impaired peripheral visual require longer search time, more fixations with shorter durations, and more errors while driving, influencing their ability to maintain a steady lane and increasing their risks of collision. [14]
Similar to driving, walking requires information from peripheral vision as well. When going up or down a staircase, people tend to use their central vision to mark the shift from a level surface to the stairs, but peripheral vision is usually used for filling in detail about the intermediate steps. [15] When the staircase is following a predictable pattern, e.g., the staircase in school, people can walk up and down successfully with their central vision restricted, and when the staircase is less predictable, e.g., some steps on the trials in the mountain, people need to use their central vision to fixate on each step. [12] For people with tunnel vision, fixating on each step and stairs climbing up or down stairs is necessary, no matter how predictable the staircase is, and this will result in slower speed climbing the stairs and increased risk to fall [12] .
Although the fixation is a more important component in one's ability to read with visual acuity, patients with tunnel vision loss are associated with impairment in reading performance, resulting in slower reading speed, more errors, and slower progression to the next line. [13] In people with glaucoma, the size of their visual span is limited due to the loss of peripheral vision, and the number of words they can see is also less. When measuring a smaller visual span in the central 10° in the visual field, people with glaucoma on average identified 2.3 less words at one glance than people with healthy eye conditions around the same age. Given reading is a crucial skill to understand one's surrounding, e.g., reading directions in the airport, about 60% of patients mentioned reading difficulty as the reason for their referral to the low vision care, and reading problem is a major source of anxiety for Glaucoma patients with slower reading speed, more errors, and slower progression to the next line of text. [13]
The parahippocampal place area in the brain is related to scene recognition, and in individuals with normal vision, the processes of recognizing scenes and navigating through them involve distinct cortical neural pathways. The peripheral visual field is associated with magnocellular pathways, processing low spatial frequency information, which encompasses broad details, and the central visual field is linked with parvocellular pathways, responsible for the high spatial frequency information, which captures finer details within a scene. In neuroimaging, peripheral vision is shown to be more important than central vision for categorizing different natural scenes, since the activation of the parahippocampal place area is more significant when scene categorization tasks are shown in the peripheral visual field. [13] In addition, vision is an important part for balancing while interacting with different scenes. Patients with tunnel vision, peripheral vision loss, report implication in postural instability, increasing their chances of falling. [13]
Occipital lobe is the area in mammal's brains responsible for processing visual inputs. Specifically, the ventral occipital temporal cortex is responsible for face recognition. Although central vision loss is linked with impaired face recognition ability, and little research has focused on face recognition in peripheral vision, a review article mentioned increases in activity in the ventral occipital temporal cortex on fMRI when a facial image is presented in the ipsilateral peripheral visual field, indicating the peripheral vision may play a more important role in face recognition than previously believed. [13] Furthermore, studies examined that Glaucoma patients, who have peripheral vision loss, need shorter distance to recognize faces and gender. [16] Individuals with good central vision but peripheral vision loss performed worse in the Cambridge face memory test, which tests face recognition ability, than control, and they reported more problems in face recognition in a self-report. [17]
Glaucoma is a group of eye diseases that lead to damage of the optic nerve, which transmits visual information from the eye to the brain. Glaucoma may cause vision loss if left untreated. It has been called the "silent thief of sight" because the loss of vision usually occurs slowly over a long period of time. A major risk factor for glaucoma is increased pressure within the eye, known as intraocular pressure (IOP). It is associated with old age, a family history of glaucoma, and certain medical conditions or medications. The word glaucoma comes from the Ancient Greek word γλαυκός, meaning 'gleaming, blue-green, gray'.
In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply 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.
Peripheral vision, or indirect vision, is vision as it occurs outside the point of fixation, i.e. away from the center of gaze or, when viewed at large angles, in the "corner of one's eye". The vast majority of the area in the visual field is included in the notion of peripheral vision. "Far peripheral" vision refers to the area at the edges of the visual field, "mid-peripheral" vision refers to medium eccentricities, and "near-peripheral", sometimes referred to as "para-central" vision, exists adjacent to the center of gaze.
The visual field is "that portion of space in which objects are visible at the same moment during steady fixation of the gaze in one direction"; in ophthalmology and neurology the emphasis is mostly on the structure inside the visual field and it is then considered “the field of functional capacity obtained and recorded by means of perimetry”.
The ciliary body is a part of the eye that includes the ciliary muscle, which controls the shape of the lens, and the ciliary epithelium, which produces the aqueous humor. The aqueous humor is produced in the non-pigmented portion of the ciliary body. The ciliary body is part of the uvea, the layer of tissue that delivers oxygen and nutrients to the eye tissues. The ciliary body joins the ora serrata of the choroid to the root of the iris.
An eye examination is a series of tests performed to assess vision and ability to focus on and discern objects. It also includes other tests and examinations pertaining to the eyes. Eye examinations are primarily performed by an optometrist, ophthalmologist, or an orthoptist. Health care professionals often recommend that all people should have periodic and thorough eye examinations as part of routine primary care, especially since many eye diseases are asymptomatic.
Fuchs dystrophy, also referred to as Fuchs endothelial corneal dystrophy (FECD) and Fuchs endothelial dystrophy (FED), is a slowly progressing corneal dystrophy that usually affects both eyes and is slightly more common in women than in men. Although early signs of Fuchs dystrophy are sometimes seen in people in their 30s and 40s, the disease rarely affects vision until people reach their 50s and 60s.
Visual or vision impairment is the partial or total inability of visual perception. In the absence of treatment such as corrective eyewear, assistive devices, and medical treatment – visual impairment may cause the individual difficulties with normal daily tasks including reading and walking. The terms low vision and blindness are often used for levels of impairment which are difficult or impossible to correct and significantly impact daily life. In addition to the various permanent conditions, fleeting temporary vision impairment, amaurosis fugax, may occur, and may indicate serious medical problems.
A visual field test is an eye examination that can detect dysfunction in central and peripheral vision which may be caused by various medical conditions such as glaucoma, stroke, pituitary disease, brain tumours or other neurological deficits. Visual field testing can be performed clinically by keeping the subject's gaze fixed while presenting objects at various places within their visual field. Simple manual equipment can be used such as in the tangent screen test or the Amsler grid. When dedicated machinery is used it is called a perimeter.
Ocular hypertension is the presence of elevated fluid pressure inside the eye, usually with no optic nerve damage or visual field loss.
Dominant optic atrophy (DOA), or autosomal dominant optic atrophy (ADOA), (Kjer's type) is an autosomally inherited disease that affects the optic nerves, causing reduced visual acuity and blindness beginning in childhood. However, the disease can seem to re-present a second time with further vision loss due to the early onset of presbyopia symptoms (i.e., difficulty in viewing objects up close). DOA is characterized as affecting neurons called retinal ganglion cells (RGCs). This condition is due to mitochondrial dysfunction mediating the death of optic nerve fibers. The RGCs axons form the optic nerve. Therefore, the disease can be considered of the central nervous system. Dominant optic atrophy was first described clinically by Batten in 1896 and named Kjer’s optic neuropathy in 1959 after Danish ophthalmologist Poul Kjer, who studied 19 families with the disease. Although dominant optic atrophy is the most common autosomally inherited optic neuropathy (i.e., disease of the optic nerves), it is often misdiagnosed.
Pigment dispersion syndrome (PDS) is an eye disorder that can lead to a form of glaucoma known as pigmentary glaucoma. It takes place when pigment cells slough off from the back of the iris and float around in the aqueous humor. Over time, these pigment cells can accumulate in the anterior chamber in such a way that they begin to clog the trabecular meshwork, which can in turn prevent the aqueous humour from draining and therefore increases the pressure inside the eye. A common finding in PDS are central, vertical corneal endothelial pigment deposits, known as Krukenberg spindle. With PDS, the intraocular pressure tends to spike at times and then can return to normal. Exercise has been shown to contribute to spikes in pressure as well. When the pressure is great enough to cause damage to the optic nerve, this is called pigmentary glaucoma. As with all types of glaucoma, when damage happens to the optic nerve fibers, the vision loss that occurs is irreversible and painless.
Glaucoma is a group of diseases affecting the optic nerve that results in vision loss and is frequently characterized by raised intraocular pressure (IOP). There are many glaucoma surgeries, and variations or combinations of those surgeries, that facilitate the escape of excess aqueous humor from the eye to lower intraocular pressure, and a few that lower IOP by decreasing the production of aqueous humor.
Hemianopsia, or hemianopia, is a visual field loss on the left or right side of the vertical midline. It can affect one eye but usually affects both eyes.
Pseudoexfoliation syndrome, often abbreviated as PEX and sometimes as PES or PXS, is an aging-related systemic disease manifesting itself primarily in the eyes which is characterized by the accumulation of microscopic granular amyloid-like protein fibers. Its cause is unknown, although there is speculation that there may be a genetic basis. It is more prevalent in women than men, and in persons past the age of seventy. Its prevalence in different human populations varies; for example, it is prevalent in Scandinavia. The buildup of protein clumps can block normal drainage of the eye fluid called the aqueous humor and can cause, in turn, a buildup of pressure leading to glaucoma and loss of vision. As worldwide populations become older because of shifts in demography, PEX may become a matter of greater concern.
Cerebral diplopia or polyopia describes seeing two or more images arranged in ordered rows, columns, or diagonals after fixation on a stimulus. The polyopic images occur monocular bilaterally and binocularly, differentiating it from ocular diplopia or polyopia. The number of duplicated images can range from one to hundreds. Some patients report difficulty in distinguishing the replicated images from the real images, while others report that the false images differ in size, intensity, or color. Cerebral polyopia is sometimes confused with palinopsia, in which multiple images appear while watching an object. However, in cerebral polyopia, the duplicated images are of a stationary object which are perceived even after the object is removed from the visual field. Movement of the original object causes all of the duplicated images to move, or the polyopic images disappear during motion. In palinoptic polyopia, movement causes each polyopic image to leave an image in its wake, creating hundreds of persistent images (entomopia).
Microperimetry, sometimes called fundus-controlled perimetry, is a type of visual field test which uses one of several technologies to create a "retinal sensitivity map" of the quantity of light perceived in specific parts of the retina in people who have lost the ability to fixate on an object or light source. The main difference with traditional perimetry instruments is that, microperimetry includes a system to image the retina and an eye tracker to compensate eye movements during visual field testing.
Humphrey field analyser (HFA) is a tool for measuring the human visual field that is commonly used by optometrists, orthoptists and ophthalmologists, particularly for detecting monocular visual field.
Phacolytic glaucoma (PG) is a form of glaucoma which is caused due to a leaking mature or immature cataract. Inflammatory glaucoma which occurs in phacolysis is a condition which is a result of the leakage of protein within the lens into the capsule of a mature or hyper mature cataract and involves a simple procedure to be cured that is referred to as cataract extraction.
Uveitic glaucoma is most commonly a progression stage of noninfectious anterior uveitis or iritis.
