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Glossary

ALT
Argon Laser Trabeculoplasty (see Trabeculoplasty) Anterior
Front

Anterior Chamber
Space filled with aqueous bounded anteriorly by the cornea and posteriorly by the iris.

Anti-reflective Coating
Proprietary Ocular Laserlight® coating on a lens to reduce the reflections caused by the laser and incandescent light source during examination and/or laser treatment. Coating also increases percentage of laser beam transmission through lens and increases image contrast.

Aphakia or aphakic
Absence of the natural crystalline lens.

Aqueous Humor
(or Body)
The watery fluid that fills the [anterior] chamber of the eye immediately behind the cornea and in front of the lens, maintaining the shape of the corneal surface. It is continually being formed - chiefly by capillaries of the ciliary processes - and it drains away into Schlemm's canal, at the junction of the cornea and sclera. (see Aqueous Humor Flow)

Aqueous Humor Flow
From the posterior chamber, the fluid passes between the iris and the lens and through the pupil, towards the anterior chamber. In the anterior chamber, aqueous flows toward the filtering elements of the trabecular meshwork, and into Schlemm canal. From this canal, fluid is conducted by way of small collector channels and larger aqueous veins into the venous system. The normal production and outflow of aqueous humor account for the maintenance of the shape of the anterior chamber and can be expressed by means of the intraocular pressure, whose usual values range from 10mm Hg to 20mm Hg. An impairment of the drainage system at the outflow channels leads to a rise in intraocular pressure, and is the most common cause of glaucoma.

Argon Laser Trabeculoplasty
Commonly known as ALT (see Trabeculoplasty)

Astigmatism
Refractive error which prevents the light rays from coming to a single focus on the retina because of different degrees of refraction in the various meridians of the cornea.

Branch Retinal Vein Occlusion
Blockage of the retinal vein produces hemorrhage and fluid leakage. The laser treatment reduces leakage and growth of abnormal new vessels and may prevent vitreous hemorrhage and improve vision.

Canal of Schlemm
A circular modified venous structure in the anterior chamber angle through which the aqueous from the anterior chamber drains.

Capsule
Thin, transparent membrane that encloses the crystalline lens of the eye.

Capsulotomy
Typically, a YAG laser is used to focus on the center of the remaining posterior capsule and non-invasively cut the capsule thus opening a "window" to allow the patient to regain their vision.

An Ocular Capsulotomy Lens is the preferred device to use in conjunction with the laser for several reasons:

  1. It decreases the laser spot size while increasing the power of the laser beam allowing a lower power setting.
  2. It stabilizes the eye and keeps the patient from moving his/her eye, thus preventing accidental laser irradiance of the wrong tissue.
  3. It increases the cone angle of the laser beam thus allowing the laser beam energy to disperse over a larger angle (greater area) thus minimizing the possibility of damage to the cornea and the retina.
  4. It magnifies the image thus allowing the smaller laser spot to be placed more precisely and reducing the likelihood of "nicking" the intraocular lens and it allows the target tissue to be seen more easily.

Cataract
A cataract occurs in the eye when the crystalline lens becomes cloudy causing a decline in one's vision. There are many theories as to the cause of lens opacification, but in addition to the certainty of death and taxes, everyone will develop cataracts, if they live long enough.

If you compare the cataract to a peach, the skin of the peach is analogous to the capsule (anterior capsule is the front half and posterior capsule the back half). The meat of the peach is analogous to the cortex of the lens and the pit is analogous to the nucleus of the lens.

In many patients, after a cataractous lens is successfully removed via extracapsular or phacoemulsification surgery where the anterior capsule (peach skin), cortex and nucleus (meat) are removed, the remaining posterior capsule of the lens becomes cloudy and impairs vision.

The preferred method of regaining the lost vision, when this happens, is to perform a Nd:YAG laser capsulotomy (see Capsulotomy).

Choroid
Mainly vascular tissue continuous with the ciliary body and the iris anteriorly, providing most of the blood supply to the retina. The vascular middle coat between the retina and sclera.

Choroidal Neovascularization
New proliferative growth of weak blood vessels in the choroid which tend to leak and cause retinal tears, holes and detachments.

Ciliary Body
The portion of the uveal tract between the iris and the choroid. It consists of the ciliary processes and the ciliary muscle.

Ciliary Muscle
It consists of longitudinal, radial and circular portions and its function is to contract and relax the zonular fibers connected to the lens capsule.

Ciliary Processes
Composed of capillaries and veins that drain through vortex veins. They produce the aqueous humor.

Concave Lens
Lens having the power to diverge rays of light, also known as a negative, myopic, or minus lens and denoted by the minus sign (-).

Cones
Light sensing cells located mainly in the macula which provide central vision. The cones also provide color vision.

Conjunctiva
The delicate membrane that covers the cornea and lines the inside of the eyelid.

Convex Lens
Lens having power to converge rays of light and to bring them to focus, also known as converging, magnifying or plus lenses and denoted by the plus sign (+).

Cornea
Transparent portion of the outer coat of the eye forming the anterior wall of the aqueous chamber. The cornea is the first optical interface stricken by light rays as they reach the eye. The convex corneal surface possesses high refractive quality and hence high power of convergence, directing light rays to the pupil and lens. Corneal grafts have been used successfully to replace diseased areas of cornea; since the cornea has no blood supply, the graft cannot be rejected by blood-borne antibodies.

Corneal Graft
(see Keratoplasty)

Crystalline Lens
A semi-transparent biconvex structure suspended in the eyeball behind the pupil, between the aqueous and the vitreous, and enclosed in a thin transparent capsule. It helps refract incoming light and focus it onto the retina.

Diabetic Retinopathy
A complication of diabetes that affects the eyes. It is caused by the deterioration of the blood vessels nourishing the retina. These weakened blood vessels may leak fluid or blood into the vitreous, develop fragile brush-like branches and become enlarged in certain places.

Another type of diabetic retinopathy is Proliferative Diabetic Retinopathy where retinal blood vessels close off and large areas of the retina cease to function. Abnormal new blood vessels appear. This is called neovascularization. These blood vessels are of no value to the eye as they do not nourish the retina and bleed frequently. They also grow scar tissue on the retina which may detach the retina. Pan-retinal photocoagulation is used to stop the growth of new blood vessels. It does not improve vision, it just stabilizes the eye at the expense of peripheral and night vision in order to save the central vision.

Diopter
Unit of measurement of strength of refractive power of lenses or of prisms.

Endolaser
Use of laser within the eye by inserting a fiber optic laser probe through the pars plana.

Equator of the Eye

The point on the eye where it is the largest diameter.

Expulsive Hemorrhage
Sudden, large, uncontrolled bleeding from the fundus of the eye. May occur during corneal transplant procedure when the diseased cornea is removed.

Focal Laser Therapy
Specific bleeding vessels in the retina are found by fluorescein angiography and treated with laser to stop the leakage or bleeding.

Focus
The point to which rays are converged after passing through a lens; focal distance is the distance between the lens and the focal point.

Fovea
Depression in the macula adapted for most acute vision.

Fundus
Posterior portion of the eye including the optic disk, macula, retina, retinal vessels, choroid, and sclera.

Funduscopy
Examination of the fundus with a slit lamp and diagnostic or laser contact or indirect lens.

Glaucoma
Glaucoma is caused by the increased production of aqueous humor (clear fluid produced by the ciliary body which is located behind and to the side of the iris) and/or when the eye cannot adequately drain aqueous from the anterior chamber (chamber located in front of the iris and behind the cornea). As a result, a rise in intraocular pressure occurs. As the pressure rises, the optic nerve and the optic artery are compressed, damaged and even destroyed. Nourishment to the retina is gradually decreased and the transmission of visual messages to the brain is interrupted resulting in impaired vision and if untreated, blindness.

Early loss of vision occurs in the far peripheral retina and in many cases is undetected. This is why it is important to have an annual eye exam and have the pressure of the eye checked especially when there is a family history of glaucoma.

Medication is usually the first course of treatment and in the majority of cases is all that is required. If pharmaceuticals are ineffective, surgery is the next course of treatment.

The two most common forms of glaucoma are chronic and acute.

Types of Glaucoma Surgery: Trabeculectomy, Iridectomy and Trabeculoplasty. If these three types of surgery are ineffective, cyclocryotherapy or transscleral cyclophotocoagulation are performed. This involves destroying portions of the ciliary body which produces aqueous by freezing it or laser. A last resort sometimes involves the implantation of a valve which allows aqueous to drain from the eye.

Diagnostic Test for Glaucoma: Gonioscopy, IOP measurement.

Glaucoma, Acute
Not common. Marked by a sudden, severe pain in and around the eye, sharply decreased vision and often nausea and vomiting. Emergency surgery is often indicated.

Glaucoma, Chronic
Most common type. In chronic glaucoma vision is slowly destroyed. Since it is a gradual, painless process, many people are unaware of it happening.

Gonioscopy
A technique of examining the anterior chamber angle, utilizing a corneal contact lens, magnifying device and light source (slit lamp).

Gonioscopy is a glaucoma test involving a mirrored contact lens which allows a surgeon to examine the angle and trabecular meshwork to detect changes or a narrow angle which may indicate glaucoma. It also allows assessment of synechiae, pigmentation and special features such as vessels, deposits and infiltrates, all indicative of the extent of the disease.

Gonioscopy, Static
Gonioscopy performed with no pressure exerted on the eye.

Gonioscopy, Dynamic
Gonioscopy performed with pressure applied in an anterior-posterior axis, widening the anterior chamber angle. The pressure is applied and withdrawn while the angle is observed for the presence of peripheral anterior synechiae in order to judge the type of medical or surgical therapy to incorporate.

Goniotomy
Infantile glaucoma can be treated by surgical goniotomy using a contact lens for visualizing the angle. A special knife is introduced opposite the area to be incised. The opposite trabecular area is incised with a sweep of 50 degrees in each direction.

Hg
Symbol for Mercury

Iridectomy
Surgically removing a small section of the iris allowing aqueous to flow more freely from the posterior to the anterior chamber, thus relieving the pressure.

Laser iridectomy (properly called iridotomy) is performed to allow an increased flow of aqueous from the posterior chamber (formed by the anterior portion of the crystalline lens and the posterior portion of the iris) to the anterior chamber (formed by the posterior corneal endothelium and the front of the iris.

When the laser iridectomy is completed a hole in the iris results. The pressure in the two chambers equalizes allowing the iris to pull away from the angle thus allowing aqueous to drain more freely through the trabecular meshwork.

Iridotomy
Creating an opening in the iris using a laser, either Argon or Nd:YAG, allowing aqueous to flow more freely from the posterior to the anterior chamber, thus relieving the pressure and equalizing pressure between the anterior and posterior chamber allowing the iris to move posterior and open the angle.

Iris
Colored, circular membrane, suspended behind the cornea and immediately in front of the lens.

IOP
Intraocular Pressure

Keratoplasty (Corneal Graft)
An eye operation in which any diseased parts of the cornea are replaced by clear corneal tissue from a donor. All layers of the cornea may need to be replaced (penetrating keratoplasty) or only the superficial layers, the deeper layer remaining (lamellar keratoplasty). In the latter case the thickness of the replacement cornea is correspondingly reduced. Lamellar keratoplasty has the advantage over penetrating keratoplasty of not requiring the eye to be opened, and therefore the risk of infection is greatly reduced.

Keratoprosthesis
Artificial cornea.

Laserlight® Anti-reflective Coating

Proprietary Ocular coating on a lens to reduce the reflections caused by the laser and incandescent light source during examination and/or laser treatment. Coating also increases percentage of laser beam transmission through lens and increases image contrast.

LASIK
(Laser-Assisted In-Situ Keratomileusis) A type of refractive eye surgery, in LASIK, a surgeon creates a flap in your eye, then uses a laser on the area underneath to correct your vision.

Lens
Focuses light rays onto the retina by changing its shape, becoming more convex or less convex, so as to increase or decrease convergence. This deformation of the lens is generated by the ciliary muscle, located in the ciliary body, which accomplishes its function by way of the onular fibers.

Limbus
Junction of the cornea and sclera.

LTK
(Laser Thermal Keratoplasty)

Macular Degeneration
Tissue breakdown with fluid collecting under the retina causing layers of the retina to separate and swell. When the layers become detached, vision is distorted in the central field. If the disease progresses, rods and cones may degenerate and die resulting in blind spots.

Macular Edema
Swelling of the macula which occurs during macular degeneration.

Macula Lutea
The small avascular area of the retina surrounding the fovea (commonly called the macula).

Major Vessel Arcade
Area in the posterior pole of the retina where the major blood vessel branches into smaller vessels.

Optic Disc
Ophthalmoscopically visible portion of the optic nerve.

Optic Nerve
The nerve which carries visual impulses from the retina to the brain.

Ora Serrata
The partly serrated anterior end of the retina.

Palpebral
Pertaining to the eyelids.

Pars Plana
A thin layer of ciliary muscle and vessels coated with ciliary epithelium located approximately three millimeters posterior of the limbus. It is the usual area for incision when performing a vitrectomy.

Perimeter
An instrument for measuring the field of vision or visual field.

Peripheral Vision
Ability to perceive the presence, motion or color of objects outside the direct line of vision.

Phakic
An eye with the natural crystalline lens.

Photocoagulation
A method of causing artificial inflammation of the retina and choroid for treatment of certain types of retinal disorders, particularly retinal detachment.

Pan-retinal Photocoagulation
During this procedure, the entire peripheral retina may be given a "scatter treatment" with the laser to curtail new blood vessels and cause many existing abnormal blood vessels to regress. Commonly called "PRP." May result in loss of peripheral vision and night vision, but preserving central and color vision.

Posterior
Back

Posterior Chamber
Space filled with aqueous anterior to the lens and posterior to the iris.

PRK
(Photorefractive Keratectomy) PRK is another laser refractive eye surgery. In PRK, a surgeon uses a laser on your eye's surface to correct your vision.

Proliferative Diabetic Retinopathy
A type of diabetic retinopathy where retinal blood vessels close off and large areas of the retina cease to function. Abnormal new blood vessels appear. This is called neovascularization. These blood vessels are of no value to the eye as they do not nourish the retina and bleed frequently. They also grow scar tissue on the retina which may detach the retina. Pan-retinal photocoagulation is used to stop the growth of new blood vessels. It does not improve vision, it just stabilizes the eye at the expense of peripheral and night vision in order to save the central vision.

Pseudophakic
An eye which has no natural crystalline lens and which has an intraocular lens implant.

Pupil
The round hole in the center of the iris which corresponds to the lens aperture in a camera. Pupil is a round orifice found in the Iris , which acts just like a camera diaphragm: it regulates the amount of light entering the posterior segment of the eye and increases the depth of focus by contracting itself.

Refraction
Deviation in the course of rays of light in passing from one transparent medium into another of different density. Also, determination of refractive errors of the eye and correction by glasses.

Refractive Error
A defect which prevents light rays from being brought to a single point of focus on the retina.

Retina
Innermost coat of the eye, formed of light-sensitive nerve elements. It is about 1 mm thick and has the consistency of wet tissue paper. Retina is usually compared to a camera film. It contains photoreceptors that respond to different wavelengths - cones and rods - and convert light energy into electrical energy by means of chemical reactions. An intricate maze of neurons lead to the ganglion neurons and account for a pre-processing of the visual stimulus in the retina. The axons of the ganglion cells build up the optic nerve - the ultimate conductor of the eye's output to the occipital cortex of the brain.

Retinal Detachment
A separation of the retina from the choroid. When this occurs, fluid from the vitreous cavity seeps under the retina and separates it from the pigment layer causing vision to become darkened and distorted. If not treated, blind spots will result.

There are three types of retinal detachments: Rhegmatogenous which is created by a hole or tear in the retina. Intraocular fluid passes through the hole and the retina detaches. Usually more than one hole or tear occurs. Exudative or non-rhegmatogenous in which choroidal or retinal blood vessels accumulate below the retina. As the patient is sitting, gravity forces the fluid to the bottom of the eye. As the patient sleeps, the fluid moves to a posterior position and detaches the macula. Traction detachments are caused by vitreous pulling on the retina. Diabetic retinopathy leads to this type of detachment.

Argon laser photocoagulation and cryotherapy are used to surround the break and to stop further detachment and bond the retina to the choroid. Photocoagulation is also used seal leaking blood vessels which are common in diabetic retinopathy and which can lead to detachments. It also seals the leaking blood vessels of the macula or reduces their leakage and allows the macula to dry and the swelling to be reduced.

Two other types of laser treatment are focal and grid laser therapy. With focal laser therapy, specific leaking spots in the retina are found via fluorescein angiography treated with laser burns. In cases where blood vessels are leaking everywhere in the macula, a scatter of laser burns in a grid pattern is placed.

Rods
Light sensing cell in the retina located in the peripheral retina and the source of our peripheral or side vision. Rods are also the source for night vision.

Sclera
The white part of the eye. A tough covering which forms the external protective coat of the eye along with the cornea. Sclera, made up of collagen and elastic fibers, acts as a protective shell that envelopes the contents of the eye.

Serous Choroidal Hemorrhage
Hemorrhage in the fundus occurring suddenly.

Schlemm('s) Canal
(see Canal of Schlemm)

Slit lamp
A combination light and microscope for the examination of the eye, primarily the anterior segment.

Synechia
Adhesion of the iris to cornea (anterior synechia) or lens (posterior synechia).

Tonometer
An instrument for measuring intraocular pressure.

Transscleral Cyclophotocoagulation
Treating the ciliary body via a contact lens through the sclera to reduce the production of aqueous.

Trabeculectomy
Surgical removal of part of the blocked trabecular meshwork (mesh-like tissue which filters the aqueous as it drains from the eye) located in the "angle" (the angle formed by the back of the cornea and the front of the iris), thus allowing fluid to drain from the eye at an increased rate. The procedure is ab externo or outside of the eye.

Trabeculoplasty
A non-invasive method used to selectively destroy parts of the blocked trabecular meshwork via a laser beam (usually Argon or Diode) and hence reduce intraocular pressure in the treatment of glaucoma. Commonly called "ALT." Nd:YAG laser is sometimes used as one theory states that the holes created via a YAG laser are less likely to close. (Performed with any Ocular Laser Gonio Lens)

Uveal tract
Choroid, ciliary body and iris constitute the uveal tract.

Vitrectomy
Surgically removing the vitreous from the eye.

Vitreous
Transparent, colorless mass of soft, gelatinous material filling the eye behind the lens. Vitreous Body is a homogeneous gel made up of water, hyaluronic acid and collagen, which fills most of the eye. Its volume comprises approximately 2/3 of that of an adult eye. Light traverses this clear tissue in order to reach the retina.

Zonule
The numerous fine tissue strands which stretch from the ciliary processes to the lens equator (360 degrees) and hold the lens in place

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