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This is a Glossary Page, a page specially filled with terms and phrases which are frequently used on singaporeeyecentre.org. By creating this page, it will hopefully avoid any kind of confusion regarding terms and phrases.
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- Anterior chamber
The anterior chamber is the fluid-filled space inside the eye between the iris and the cornea‘s innermost surface, the endothelium. Aqueous humor is the fluid that fills the anterior chamber. Hyphema and glaucoma are two main pathologies in this area. In hyphema, blood fills the anterior chamber. In glaucoma, blockage of the canal of Schlemm prevents the normal outflow of aqueous humor, resulting in accumulation of fluid, increased intraocular pressure, and eventually blindness.
cataract is a clouding of the lens inside the eye which leads to a decrease in vision. It is the most common cause of blindness and is conventionally treated with surgery. Visual loss occurs because opacification of the lens obstructs light from passing and being focused on to the retina at the back of the eye.
It is most commonly due to biological aging but there are a wide variety of other causes. Over time, yellow-brown pigment is deposited within the lens and this, together with disruption of the normal architecture of the lens fibers, leads to reduced transmission of light, which in turn leads to visual problems.
Those with cataract commonly experience difficulty appreciating colors and changes in contrast, driving, reading, recognizing faces, and experience problems coping with glare from bright lights.
Signs and symptoms vary depending on the type of cataract, though there is considerable overlap. People with nuclear sclerotic or brunescent cataract, often notice a reduction of vision. Those with posterior supcapsular cataract usually complain of glare as their major symptom.
The severity of cataract formation, assuming that no other eye disease is present, is judged primarily by visual acuity test. The appropriateness of surgery depends on a patient’s particular functional and visual needs and other risk factors, all of which may vary widely.
- Cataract Surgery
Cataract surgery is the removal of the natural lens of the eye (also called “crystalline lens“) that has developed an opacification, which is referred to as a cataract. Metabolic changes of the crystalline lens fibers over time lead to the development of the cataract and loss of transparency, causing impairment or loss of vision. Many patients’ first symptoms are strong glare from lights and small light sources at night, along with reduced acuity at low light levels. During cataract surgery, a patient’s cloudy natural lens is removed and replaced with a synthetic lens to restore the lens’s transparency.
Following surgical removal of the natural lens, an artificial intraocular lens implant is inserted (eye surgeons say that the lens is “implanted”). Cataract surgery is generally performed by an ophthalmologist (eye surgeon) in an ambulatory (rather than inpatient) setting, in a surgical center or hospital, using local anesthesia (either topical, peribulbar, or retrobulbar), usually causing little or no discomfort to the patient. Well over 90% of operations are successful in restoring useful vision, with a low complication rate. Day care, high volume, minimally invasive, small incision phacoemulsification with quick post-op recovery has become the standard of care in cataract surgery all over the world.
This description of cataract surgery was brought to you by wikipedia at this link: http://en.wikipedia.org/wiki/Cataract_surgery
The cornea is the transpartent, dome-shaped lens that covers the front of the eye that covers the iris, pupil, and anterior chamber. Although the cornea is clear and seems to lack substance, it is actually a highly organized group of cells and proteins. The cornea, with the anterior chamber and lens, refracts light, with the cornea accounting for approximately two-thirds of the eye’s total optical power.
The cornea receives its nourishment from the tears and aqueous humor (a fluid in the anterior portion of the eye) that fills the chamber behind it. The cornea must remain transparent to refract light properly, and the presence of even the tiniest blood vessels can interfere with this process. To see well, all layers of the cornea must be free of any cloudy or opaque areas.
While the cornea contributes most of the eye’s focusing power, its focus is fixed. The curvature of the lens, on the other hand, can be adjusted to “tune” the focus depending upon the object’s distance.
- Eye Examination
An eye examination is a series of tests performed by an ophthalmologist (medical doctor), optometrist, or orthoptist assessing vision and ability to focus on and discern objects, as well as other tests and examinations pertaining to the eyes. 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.
Eye examinations may detect potentially treatable blinding eye diseases, ocular manifestations of systemic disease, or signs of tumours or other anomalies of the brain.
Ideally, the eye examination consists of an external examination, followed by specific tests for visual acuity, pupil function, extraocular muscle motility, visual fields, intraocular pressure and ophthalmoscopy through a dilated pupil.
A minimal eye examination consists of tests for visual acuity, pupil function, and extraocular muscle motility, as well as direct ophthalmoscopy through an undilated pupil.
- Eye Floaters
Eye Floaters are deposits of various size, shape, consistency, refractive index, and motility within the eye’s vitreous humour, which is normally transparent. At a young age, the vitreous is transparent, but as one ages, imperfections gradually develop. The common type of floater, which is present in most people’s eyes, is due to degenerative changes of the vitreous humour. The perception of floaters is known as myodesopsia, or less commonly as myodaeopsia, myiodeopsia, myiodesopsia. They are also called Muscae volitantes(Latin: “flying flies”), or mouches volantes (from the French). Floaters are visible because of the shadows they cast on the retina or refraction of the light that passes through them, and can appear alone or together with several others in one’s visual field. They may appear as spots, threads, or fragments of cobwebs, which float slowly before the observer’s eyes. Since these objects exist within the eye itself, they are not optical illusions but are entoptic phenomena.
- Eye Surgery
Eye surgery, also known as ocular surgery, is surgery performed on the eye or its adnexa, typically by an ophthalmologist.The eye is a fragile organ, and requires extreme care before, during, and after a surgical procedure. An expert eye surgeon is responsible for selecting the appropriate surgical procedure for the patient, and for taking the necessary safety precautions.
- Human Eye
The human eye is similar to that of your camera, it gathers light, focuses the light through a lens to create an image of the environment on to the back of the camera and eye. In a camera, image is inversely created on film, whereas for the eye, the image is created on the retina at the back of the eye. The lens of a camera is used to focus the image onto the film, but the eye lens bends, or refracts, light that enters the eye.
The cornea, which is a clear, transparent covering the front portion of the eye also contributes to focusing light on the retina. Nerve fibers extending back from the retina’s nerve cells come together behind the retina to form the optic nerve, a “cable” of nerve fibers connecting the eye with the brain.
The optic nerve transmits messages about what we see from the eye to the brain. Like a camera, the human eye controls the amount of light that enters the eye through the lens under various lighting conditions.
The Human Eye which is not sphere in shape as what we think, is joined by two pieces called the cornea and the sclera. The cornea and sclera are connected by a ring called the limbus. The eye is made up of three enclosing transparent structures. The outermost layer is composed of the cornea and sclera. The middle layer consists of the choroid,ciliary body, and iris. The innermost is the retina, which gets its circulation from the vessels of the choroid as well as the retinal vessels.
The iris – the colour of the eye – and its black centre, the pupil, are seen instead of the cornea due to the cornea’s transparency. To see inside the eye, an ophthalmoscope is needed, since light is not reflected out. The fundus (area opposite the pupil) shows the characteristic pale optic disk (papilla), where vessels entering the eye pass across and optic nerve fibers depart the globe.
The Human Eye makes vision similar to that of your camera. Light enters from the cornea to the iris to the retina and with rod cells and cone cells in the retina, it allows conscious light perception and vision including color differentiation and the perception of depth.
- posterior compartment
- ora serrata
- ciliary muscle
- ciliary zonules
- canal of Schlemm
- anterior chamber
- lens cortex
- lens nucleus
- ciliary process
- inferior oblique muscule
- inferior rectus muscule
- medial rectus muscle
- retinal arteries and veins
- optic disc
- dura mater
- central retinal artery
- central retinal vein
- optical nerve
- vorticose vein
- bulbar sheath
- superior rectus muscule
- Implantable Contact Lens
Implantable collamer lens also known as Implantable Contact Lens or ICL, is a soft, flexible gel-lens used in refractive surgeries for the permanent correction of myopia (nearsightedness), made of a collagen copolymer material, named by combining “collagen” and “polymer”. The ICL procedure is a popular alternative to LASIK and PRK since it requires no removal of the corneal tissue and reportedly produces better visual results
You can find more about implantable collamer lens or implantable contact lens at wikipedia at : http://en.wikipedia.org/wiki/Implantable_Contact_Lens
- Intraocular Lens
An intraocular lens (IOL) is a lens implanted in the eye used to treat cataracts or myopia. The most common type of IOL for cataract treatment are known as pseudophakic IOLs which work by replacing the crystalline lens which has been clouded over by cataracts. The second type of IOL, more commonly known as a phakic intraocular lens (PIOL), is a lens which is placed over the existing natural lens used in refractive surgery to change the eye’s optical power as a treatment for myopia or nearsightedness. IOLs usually consists of a small plastic lens with plastic side struts, called haptics, to hold the lens in place within the capsular bag inside the eye. IOLs were traditionally made of an inflexible material (PMMA), although this has largely been superseded by the use of flexible materials. Most IOLs fitted today are fixed monofocal lenses matched to distance vision. However, other types are available, such as multifocal IOLs which provide the patient with multiple-focused vision at far and reading distance, and adaptive IOLs which provide the patient with limited visual accommodation.
This description on Intracaular Lens can be found on Wikipedia at : http://en.wikipedia.org/wiki/Intraocular_lens
Keratoconus is a degenerative disorder of the eye in which structural changes within the cornea cause it to thin and change to a more conical shape than its normal gradual curve.
Keratoconus can cause substantial distortion of vision, with multiple images, streaking and sensitivity to light all often reported by the patient. It is typically diagnosed in the patient’s adolescent years. If afflicting both eyes, the deterioration in vision can affect the patient’s ability to drive a car or read normal print.
- Lasik Surgery
Lasik Surgery commonly referred to as laser eye surgery, is a type of refractive surgery for the correction of myopia, hypermetropia, and astigmatism. The LASIK surgery is performed by an ophthalmologist who uses a laser ormicrokeratome to reshape the eye’s cornea in order to improve visual acuity. For most patients, LASIK provides a permanent alternative to eyeglasses or contact lenses. Major side effects include halos, starbursts, night-driving problems and eye dryness.
LASIK is most similar to another surgical corrective procedure, photorefractive keratectomy (PRK), and both represent advances overradial keratotomy in the surgical treatment of refractive errors of vision. For patients with moderate to high myopia or thin corneas which cannot be treated with LASIK and PRK, the phakic intraocular lens is an alternative.
The crystalline lens is a transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. The lens, by changing shape, functions to change the focal distance of the eye so that it can focus on objects at various distances, thus allowing a sharp real image of the object of interest to be formed on the retina. This adjustment of the lens is known asaccommodation (see also below). Accommodation is similar to the focusing of a photographic camera via movement of its lenses. The lens is more flat on its anterior side than on its posterior side.
This summary and description of the human lens is brought to you by wikipedia at: http://en.wikipedia.org/wiki/Lens_(anatomy)
Myopia, commonly known as being nearsighted and shortsighted, is a condition of the eye where the light that comes in does not directly focus on the retina but in front of it. This causes the image that one sees when looking at a distant object to be out of focus, but in focus when looking at a close object.
How to solve Myopia? Refractive Surgery can help you.
Ophthalmology is the branch of medicine that deals with the anatomy, physiology and diseases of the eye. An ophthalmologist is a specialist in medical and surgical eye problems. Since ophthalmologists perform operations on eyes, they are both surgical and medical specialists.
For a comprehensive list of surgeries performed by ophthalmologists, see eye surgery.
- Refractive Surgery
Refractive eye surgery is any eye surgery used to improve the refractive state of the eye and decrease or eliminate dependency onglasses or contact lenses. This can include various methods of surgical remodeling of the cornea or cataract surgery. The most common methods today use excimer lasers to reshape the curvature of the cornea. Successful refractive eye surgery can reduce or cure common vision disorders such as myopia, hyperopia and astigmatism, as well as degenerative disorders like keratoconus.
Retina is a light-sensitive layer of tissue, lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical events that ultimately trigger nerve impulses. These are sent to various visual centres of the brain through the fibres of the optic nerve.
In vertebrate embryonic development, the retina and the optic nerve originate as outgrowths of the developing brain, so the retina is considered part of the central nervous system (CNS) and is actually brain tissue. It is the only part of the CNS that can be visualized non-invasively.
The retina is a layered structure with several layers of neurons interconnected by synapses. The only neurons that are directly sensitive to light are the photoreceptor cells. These are mainly of two types: the rods and cones. Rods function mainly in dim light and provide black-and-white vision, while cones support daytime vision and the perception of colour. A third, much rarer type of photoreceptor, the photosensitive ganglion cell, is important for reflexive responses to bright daylight.