Abrasion: See: Corneal Abrasion.
Accomodation: Focusing within the eye to increase the optical power to maintain a clear image as an object is moved closer. This is accomplished by the natural lens of the eye changing its shape (both contracting to focus up close and then relaxing to focus on more distant objects). A combination of ciliary muscle contraction and the zonular relaxation facilitates this change in shape.
Accomodative Spasm: A muscle spasm of the natural lens of the eye in which the lens does not relax after accommodating. This results in vision that is sharp for near but blurry for distance. This condition can be helped with Dr. Mandel’s computer tips.
Amblyopia (AKA: “lazy eye”): Decreased vision in one or both eyes when the eye(s) are otherwise physically normal. This can be due to muscle alignment problems called strabismus or different prescriptions in the eyes, which is called anisometropia. This condition can usually be improved with patch therapy, but only if this is initiated prior to age 5. The earlier the intervention, the better the prognosis will be.
Amsler Grid: A test card of equally spaced horizontal and vertical lines forming a grid that can be used at home, daily, to detect early ARMD (Age related macular degeneration).
Angle: see: Anterior Chamber
Anterior Chamber: The space within the eye between the innermost layer of the cornea (endothelium) and the iris. This space is filled with a fluid known as aqueous humor. An open angle is necessary to drain the normal fluid within the eye. If the angle closes, it can lead to narrow angle glaucoma, which is an ophthalmic emergency when acute.
Aphakia: absence of the natural, crystalline lens of the eye.
Applanation Tonometry: The measurement of intraocular pressure , given in millimeters of mercury, in which the amount of force required to flatten an area of the cornea, by contact, is documented. This is a routine screening test for glaucoma.
Aqueous Humor: Clear, watery fluid that fills the anterior chamber and bathes the natural lens of the eye. This fluid brings nourishment to the cornea, iris and crystalline lens and maintains intraocular pressure.
ARMD (Age Related Macular Degeneration): A condition of the eye which involves deterioration of the macula resulting in loss of central vision. There are two types of ARMD, “dry” in which treatments are limited, and “wet” in which abnormal blood vessels grow under the retina and leak fluid and blood. The “wet” type of ARMD can usually be treated with laser photocoagulation which seals the leaky blood vessels. Although treatable in some cases, the prognosis is often worse with the wet type.
Astigmatism: A condition of the eye in which the curvature of the cornea focuses light rays at two different spots within the eye. This can create eyestrain and in some cases, blurry vision. This can be corrected with special toric contact lenses or spectacles, as well as with laser vision correction. Almost all people have some degree of astigmatism.
Bandange Contact Lens: A soft contact lens that is used to cover and protect the epithelium of the cornea so that it is able to regenerate following trauma (eg: a corneal abrasion) or PRK refractive surgery.
Bifocal Lens: A special type of eyeglass lens that incorporates two different optical powers in the same lens, typically to correct both distance and near visual acuity.
Binocular Vision: The blending of the separate images seen by each eye into one single image. Insufficient functioning of this process can lead to diplopia (double vision).
Blepharo- (prefix): Pertaining to the eyelid.
Blepharitis: Inflammation of the eyelids which can be accompanied by redness, swelling and itching of the eyes and/or lid margins. This condition can be caused by inflammation and/or infection and is often chronic. Treatment can include oralantibiotics as well as lid scrubs and hygiene and anti-inflammatory and antibiotic eye drops.
Blepharoplasty: A surgical procedure of the eyelids to remove redundant skin and fat. It is usually cosmetic, but in some cases it can affect vision.
Blepharospasm: Involuntary spasm of the muscle that controls the function of theeyelids which may lead to uncontrolled blinking and lid squeezing.
Canaliculus: Tiny channel in each eyelid that forms part of the tear drainage system. It connects the punctum (tiny opening seen on the inner eyelid) of each eye to the nasolacrimal duct. (Plural: canaliculi)
Cataract: An opacity or cloudiness of the crystalline lens of the eye. This can cause blurry vision as it can prevent a clear image from forming on the retina. Click here to watch a video about cataract surgery on our Mandel Vision YouTube channel.
Chalazion: An inflamed bump within the eyelid that is within a meibomian gland.
Ciliary Muscle: The smooth muscle portion of the ciliary body which is responsible for the contraction and relaxation of zonules which allow the lens of the eye to focus (accommodate) for near visual acuity.
Concave Eyeglass Lens: A lens that is thicker at the edges than in the center which causes light rays from an object to diverge. This causes light rays in a myopic eye to focus on the retina which brings a blurry image in focus. Nearsighted eyes focus their light rays in front of the retina.
Conjunctivitis (AKA: “pink eye”): Inflammation of the conjunctiva. This condition is usually characterized by discharge, grittiness, redness and swelling. It can be allergic, viral or bacterial and is typically treated with eyedrops.
Convergence Insufficiency: A weakening of the eye muscles responsible for pulling the eyes toward each other to maintain single vision during near vision fixation. This can cause eye fatigue as well as diplopia (double vision).
Convex Eyeglass Lens: A lens that is thicker in the center than at the edges, which causes light rays from an object to converge. This causes light rays in a hyperopic (farsighted) eye to focus on the retina which brings a blurry image in focus. Farsighted eyes usually focus their light rays behind the retina.
Cornea: The transparent window of the eye that covers the iris, pupil and anterior chamber and provides most of the eye’s optical power. The cornea consists of 6 layers: epithelium, Bowman’s membrane, stroma, Dua’s Layer, Descemet’s membrane and endothelium.
Corneal Abrasion: An injury of the cornea in which the epithelium is scraped off.
Corneal Dystrophy: An acquired or developed abnormality of the cornea. This can lead to cloudiness of the cornea, discomfort, as well as reduced vision.
Corneal Edema: Swelling of the cornea.
Corneal Pannus: Infiltration of the cornea by abnormal blood vessels in an otherwise avascular tissue. This is typically the body’s defensive response to a lack of oxygen to the cornea which can be caused by an improper fitting contact lens and/or sleeping in contact lenses.
Corneal Ulcer: A discontinuity or break in the epithelial tissue of the cornea associated with inflammation in the cornea, that could be sterile or may be caused by bacterial, fungal or viral infection. This is commonly seen in patients who over wear and/or sleep in their contact lenses and requires immediate treatment because it can be vision threatening, especially if it is located in the area of central vision.
Cylindrical Eyeglass Lens: A lens that produces a different refractive power in each meridian which is used for correcting astigmatism.
Detachment: Separation of tissues from their normal anatomical attachments.
Diabetes Mellitus: A condition in which the pancreas no longer produces enough insulin or cells stop responding to the insulin that is produced, so that glucose in the blood cannot be absorbed normally into the cells of the body. This is usually a chronic disease that can cause serious health complications including renal (kidney) failure, heart disease, stroke, and blindness.
Dilation (Pupillary): The widening of the pupil induced by eye drops to facilitate an examination of the fundus, the posterior portion of the eye, which includes: the retina, optic nerve and disc, macula and blood vessels.
Diopter: The unit of measure used in ophthalmology to designate the refractive power of a lens.
Diplopia (AKA: double vision): The perception of two images from one object. These 2 images can be vertical, horizontal or diagonal from each other. It occurs only with two eyes together and disappears when one eye is covered.
Dominant Eye: The preferred eye for visual tasks. This is also the eye that leads and controls the other eye during binocular eye movements.
Dry Eyes: See: Keratitis Sicca
Dua’s Layer: One of the 6 layers of the cornea. Previously undetected, the discovery of this layer was published by scientists at The University of Nottingham in 2013 after several years of research. This layer is situated between the stroma and Descemet’s membrane. Although this layer is thin, (only one hundredth the thickness of the entire cornea) it is a very strong layer.
Dystrophy: See: Corneal Dystrophy
Ectasia: In ophthalmology this term can mean a weakening of the cornea.
Endothelium: The innermost surface of the cornea, situated between Descemet’s membrane and the anterior chamber. It acts as a pump to keep excess water out of the stroma. The cornea needs to be more dehydrated than the rest of the body in order for it to be a clear window in the front of the eye.
Epithelium: The outermost layer of the cornea, situated between Bowman’s membrane and the tear film. This is the part of corneal tissue that is removed with the excimer laser during laser vision correction.
Exophthalmos: See: Proptosis
Eye (Eyeball, Globe): A sensory organ for sight which is composed of three major structural layers (corneo-sclera, uvea and retina). The eye receives light imagery from objects and transmits this visual information to the brain.
Eyeglasses: See: Spectacles
Farsightedness: See: Hyperopia
Flashes: Sensation of light often a result of the tugging of the vitreous away from the retina. It can also be caused by a newly formed retinal tear, retinal detachment or a form of migraine. This symptom should be evaluated by an ophthalmologist as quickly as possible to rule out a retinal hole or retinal tear which may be repaired by laser or surgically.
Fovea: The central point of the macula that produces the sharpest vision.
Geometric optics: The area of optics that deals with the transmission of light rays and is concerned with the effect of lenses on light and the production of images.
Globe: See Eye (Eyeball).
Hard Contact Lens: Lens made of a rigid plastic material that floats on the corneal tear film.
Herpes Zoster Virus (AKA: Shingles): Caused by a resurgence of the chickenpox virus that resides in the nerve roots. In ophthalmology this condition may cause painful, blister-like skin lesions on the eyelids and face and can cause inflammation of the cornea, sclera, ciliary body and optic nerve.
Hyperopia: A refractive error of the eye created by an underpowered eye that is too short for its optical power. Light rays from an object enter the eye and come to a focus beyond the retina, creating a blurry image. This condition can be corrected with plus powered convex lenses in spectacles and contact lenses or with laser vision correction. Younger patients may be able to compensate for this naturally.
Indirect Ophthalmoscope: Instrument consisting of a bright light source and a handheld magnifying lens used to visualize the posterior portion of the eye (the fundus). It creates an inverted image of the fundus projected in the front of the eye. This instrument has a wider field of view than the direct ophthalmoscope and the binocular model allows stereoscopic depth perception of the retina.
Intraocular Lens (IOL): A plastic lens that is surgically implanted to replace the natural lens of the eye. The lenses are available in various optical powers that can correct myopia and hyperopia. This is done routinely during cataract surgery and is also implanted during clear lens extraction, a form of intraocular refractive surgery.
Iris: The pigmented tissue behind the cornea which gives color to the eye and controls the amount of light entering the eye by changing the size of the pupillary opening. This function of the iris is similar to the aperture of a camera lens.
Iritis: Inflammation of the iris that can cause pain, tearing, blurred vision, small pupil and redness, but can also be painless.
-itis (suffix): Pertaining to inflammation.
Irregular Astigmatism: A type of astigmatism producing distorted imagery in which the light rays are not oriented 90 degrees apart. It may be due to contact lens wear, trauma, inflammation as well as developmental abnormalities.
Kerato- (prefix): Pertaining to the cornea.
Keratoconus: A degenerative corneal disease which may affect vision and is characterized by thinning and cone-shaped protrusion of the central cornea. This disease typically affects both eyes, although not symmetrically, and usually becomes apparent in the 2nd decade of life.
Keratoplasty (Penetrating Keratoplasty): A corneal transplant.
Keratitis Sicca: (AKA: Dry Eyes): A condition of the eye which involves both corneal and conjunctival dryness due to deficient tear production. Symptoms include foreign body sensation, redness and burning.
Lacrimal Gland: Structure under the upper eyelid that produces tears.
Lacrimal Sac: See: Tear Sac
LASIK (Laser In-Situ Keratomileusis): LASIK is a laser vision correction procedure that combines a flap created by a microkeratome or an intralase laser, along with an excimer laser to correct visual refractive abnormalities. It combined two previously used surgical procedures (listed below) and has been performed millions of times worldwide:
1. The creation of a corneal flap by a procedure known as keratomileusis.
2. The use of an excimer laser to precisely reshape the corneal tissue beneath the flap. This enables light rays to be more accurately focused on the retina at the back of the eye, thereby improving vision. The flap is then returned to its original position.
Lazy Eye: See: Amblyopia
Legally Blind: Best corrected visual acuity of 20/200 or less, in the better-seeing eye.
Low Vision Aids: High powered plus lenses which help patients who have poor vision.
Macula: The central area of the retina surrounding the fovea which is responsible for acute vision (for reading and discriminating fine detail and color).
Macular Degeneration: See: ARMD
Maculopathy: Non-specific abnormality of the macula.
Mast Cells: Cells that release histamine during an allergic reaction.
Meibomian Gland: Oil gland within the eyelid tissue whose duct opens onto the eyelid margin. Secretions from these glands supply the outer portion of the tear film which prevents rapid tear evaporation and tear overflow.
Meibomianitis: Inflammation of the meibomian glands.
Monovision: An alternate method of correcting presbyopia. One eye (the dominant eye) is corrected for distance vision and the other eye (non-dominant eye) is corrected for near. This can be accomplished with contact lenses or refractive surgery, but usually does not work with eyeglasses. Read more in our Monovision blog.
Myopia: (AKA: Nearsightedness): A refractive error of the eye created by an overpowered eye which has too much optical power for its length. Light rays coming from a distant object are brought to a focus before they reach the retina, creating a blurry image. Nearsighted people can read clearly without glasses but distance vision is blurry. This condition can be corrected with minus powered, concave lenses in spectacles and contact lenses or with laser vision correction.
Narrow Angles: A shallower than normal anterior chamber which is the space between the iris and cornea. This can restrict the drainage of the aqueous fluid through the trabecular meshwork which can cause an increase in intraocular pressure.
Narrow Angle Glaucoma: A form of glaucoma which is categorized by a rise in intraocular pressure in patients with narrow anterior chamber angles. This condition can be acute with accompanying pain and loss of vision if not treated promptly.
Nasolacrimal Duct: Tear drainage channel that connects the lacrimal sac to an opening in the mucous membrane in the nose.
Nearsightedness: See: Myopia
Occluder: An ophthalmic instrument used for covering one eye at a time during vision testing or treatment.
Ocular Hypertension: Elevated intraocular pressure without any optic disc changes or visual field loss. Patients with ocular hypertension are glaucoma suspects and need to be monitored more closely for signs of glaucoma for their whole life.
Ocular Migraines (AKA: Ophthalmic Migraines): A disorder in which spasm and then dilation of blood vessels, or unusual electrical brain activity, causes a temporary change of vision the eye. Symptoms can include lightening flashes, expanding circles of light and temporary vision loss.
Ocular Motility: The movement of the eyes which involves the extraocular muscles and their effect on eye movement.
Open Angle Glaucoma: The most common type of glaucoma in which the anterior chamber is open. It is characterized by an increase in intraocular pressure which causes damage to the optic nerve as well as visual field (peripheral vision) loss. There are types of open angle glaucoma called low tension, or low pressure, glaucoma that do not have an increased level of pressure but do damage to the eye. Open angle glaucoma is painless and that is why regular eye exams are so important. Vision may not be affected until it is too late to treat. Click here to watch a video about open angle glaucoma on our Mandel Vision YouTube channel.
Ophthalmic: Pertaining to ophthalmology.
Ophthalmic Migraines: See: Ocular Migraines
Ophthalmic Technician: An allied health professional (both certified and non-certified) who performs preliminary diagnostic testing for an ophthalmologist.
Ophthalmologist: A surgeon (M.D.) who specializes in diagnosis and treatment ofrefractive, medical and surgical problems related to eye diseases and disorders, as well as vision conditions with spectacles and contact lenses.
Ophthalmoscope: An illuminated instrument for visualizing the interior of the eye, particularly the fundus at the back of the eye. There are two types of ophthalmoscopes, the direct ophthalmoscope and the indirect ophthalmoscope.
Optic Cup: A depression in the center of the optic disc located in the posterior part of the eye. The optic cup usually occupies one-third or less of the total disc diameter. It is evaluated as part of a glaucoma exam.
Optic Nerve: The second cranial nerve and the largest sensory nerve of the eye. The optic nerve carries impulses for sight from the retina to the brain’s visual cortex.
Optics: The branch of physics that deals with the properties of light and vision, for instance its refraction and reflection by lenses, prisms, mirrors and the eye. Two principal areas of optics that apply to ophthalmology are physical optics and geometric optics.
Optometrist: Doctor of Optometry. (O.D.) specializing in vision problems, treating vision conditions with spectacles, contact lenses and vision therapy and may also prescribe medications for certain eye diseases.
Orbit: Pyramid-shaped cavity in the skull, lined by seven orbital bones, which contains the eyeball, its extraocular muscles, blood supply, nerve supply and fat.
Orbital: Pertaining to the orbit.
Orthokeratology (AKA: Ortho-K): A system of treating myopia and astigmatism with a sequential series of flatter-than-normal contact lenses that gradually flatten the cornea. In orthokeratology, patients wear the contact lenses while sleeping.
Orthophoria: Eyes that are aligned normally; the absence of an eye deviation (or eye turn).
Pachymetry: A diagnostic tool used for measuring corneal thickness using ultrasound (sound waves). This is a very important tool for laser vision correction candidates. Pachymetry can also be measured using a pentacam diagnostic tool.
Pannus: See: Corneal Pannus
Patch Therapy: Treatment of amblyopia which involves occluding an ambyopic patient’s better seeing eye to improve vision in the amblyopic eye. This form of therapy is most effective when it is begun before age 8.
Perimetry: A method of charting the extent of a stationary eye’s visual field (peripheral vision) with test objects of various sizes and light intensities.
Phakic: Refers to an eye that possesses its own natural crystalline lens.
Phoropter: Refraction device which incorporates a series of spherical and cylindrical lenses and also includes prisms, occluders and pinholes. This device is used to determine an eye’s refractive error as well as a prescription for spectacles and contact lenses.
Photocoagulation: A surgical procedure in which a laser beam is applied to burn or destroy selected intraocular structures.
Photophobia: Abnormal sensitivity to and discomfort from lights which may be accompanied by epiphora.
Physical Optics: The area of optics that describes the nature of light in terms of its wave properties.
Pinguecula: Yellowish brown elevation on the conjunctiva.
Pinhole device: An opaque disc with one or more holes which blocks all but the centermost light rays from an object. It is used as a quick screening device to determine whether reduced vision is caused by refractive error. (Vision through the pinhole will improve if the decreased vision is caused by refractive error.)
Pink Eye: See: Conjunctivitis
Presbyopia: Diminished power of accommodation due to loss of elasticity of the crystalline lens of the eye which changes shape to change focus between distant and near objects. Patients with presbyopia are unable to see up close and need a bifocal, trifocal or progressive lens for near vision tasks. This condition can also be corrected with monovision laser vision correction.
PRK (Photorefractive keratectomy): Refractive surgery performed with an excimer laser on the corneal surface after the epithelium is removed with the use of a gentle epithelial brush. The difference between this procedure and LASIK is that there is no flap created in PRK.
Progressive Eyeglass Lens (Invisible bifocals): An eyeglass lens that incorporates corrections for distance, middle and near vision without any visible bifocal line.
Ptosis: Drooping of the upper eyelid.
Punctal Occlusion: Blocking the punctum in the eyelids to prevent quick drainage of liquid from the eye to the nasolacrimal duct. When using eye drops, punctual occlusion is sometimes recommended so that eye drops stay on the eye longer. This is accomplished by closing the eye and pressing on the inner corner of the eye for 2 minutes after instilling drops. This can also be accomplished with the use of punctual plugs for the treatment of dry eye symptoms.
Punctal Plugs: Small silicone (permanent) or collagen (absorbable) inserts that are placed inside the punctum of the eyelids to prevent normal tear drainage. These plugs are used to treat dry eyes to keep natural tears on the eye longer to help the cornea and conjunctiva stay moist.
Pupil: Black circular opening in the center of the iris that changes size to regulate the amount of light entering the eye.
Pupillary: Pertaining to the pupil of the eye.
Pupillary Distance (P.D.): The distance between the pupillary centers of opposing eyes. This measurement is critical to making eyeglasses as the optical center of each lens needs to be centered over the pupil of each eye.
Pupillometer: An ophthalmic instrument used to measure the size (diameter) of the pupil.
Refract: To bend. In ophthalmology, light rays are refracted when they pass through different types of lenses.
Refraction: A subjective determination of an eye’s refractive error as well as the best prescription for eyeglasses and contact lenses to correct it. This test involves a series of lenses in graded powers which are presented to the patient to determine which lens, or combination of lenses, provides the sharpest visual acuity.
Refractive Error: Optical defect in which parallel light rays are not brought to a sharp focus precisely on the retina producing a blurred retinal image. Types of refractive errors include myopia, hyperopia, astigmatism and presbyopia which can be corrected with spectacles, contact lenses and refractive surgery.
Retina: Light sensitive nerve tissue in the eye, composed of rods and cones, that converts images from the eye’s optical system into electrical impulses that are sent along the optic nerve to the brain to be interpreted as vision.
Retinopathy: Any non-inflammatory degenerative disease of the retina.
Retinoscope: A hand held instrument which is used to determine an eye’s refractive error objectively (with no response required from the patient). Light from the retinoscope is projected into the eye and the movements of the light reflection are neutralized (eliminated) with corrective lenses.
Retinoscopy: An objective measurement of an eye’s refractive error by using a retinoscope.
Rod: A light-sensitive, retinal receptor that works at low light levels which enables the eye to adapt to night vision conditions.
Sclera: Opaque, fibrous, protective outer layer of the eye. The sclera is seen as the ‘white’ part of the eye surrounding the ‘colored’ part of the eye and is covered by the conjunctiva. The sclera is continuous with the cornea in front and the sheath covering the optic nerve in the back of the eye.
Single Vision Eyeglass Lens: An eyeglass lens that corrects only one type of refractive error.
Slit-Lamp Biomicroscope: A table-top microscope that is used to examine the anterior portion (front portion) of the eye. This instrument cross-sections the eye so that the structures of the eye can be viewed in layer-by-layer detail. With the aid of a special handheld lens, it can also be used to examine the posterior portion (back portion or fundus) of the eye.
Snellen Chart: A test chart for assessing visual acuity. The chart contains rows of letters, numbers or symbols in standardized sizes with a designated distance at which each row should be legible to the normal eye. The standard testing distance is typically 20 feet.
Spectacles (Eyeglasses): Optical aid which incorporates a combination of the appropriate lenses (concave, convex and toric) to correct various refractive errors. There are many types of spectacles which include: Bifocal, trifocal, single vision, progressive, and transition lenses.
Specular Endothelial Microscopy: A diagnostic test which allows the examiner to visualize both the pattern and density of endothelial cells through magnification via a technique that uses a slit lamp microscope in combination with light reflection from the endothelium.
Spherical Aberration: Type of visual aberration caused by light rays from an object hitting the periphery of the eye (cornea and crystalline lens) instead of the center of vision. This can cause the light rays to be over-refracted (bent too much) which causes blurred vision (positive spherical aberration). Click here to learn more about spherical aberration, as well as Dr. Mandel’s personalized approach to laser vision correction in our blog: The Customization of Laser Vision Correction.
Stereopsis: See: Binocular Vision
Strabismus (Deviation): Eye misalignment or eyes that do not move normally, caused by extraocular muscle imbalance. This imbalance causes the foveas of opposite eyes to be focused on different objects. This can cause eyestrain as well as diplopia.
Stroma: The middle layer tissue that forms 90% of the cornea. It is situated beneath Bowman’s membrane and above Descemet’s membrane and is composed of layered collagen fibers and cells. It is this layer of the cornea that is mainly reshaped during laser vision correction.
Stye: An acute infection of the oil glands of Zeis, located in an eyelash follicle at the eyelid margin. The symptoms include tenderness to touch and presents as an inflamed red bump.
Subconjunctival Hemorrhage: Bleeding from a small blood vessel under the conjunctiva. It presents as bright red blood over the sclera and can be spontaneous of unknown cause or be caused by coughing or straining, for instance when lifting heavy weight. It usually resolves on its own in a week or two, without treatment.
Tear Break-Up Time (BUT): A test for tear film function, this is the interval between a blink and the development of a dry spot in the pre-corneal tear film. This test is performed using flourescein eye drops in combination with the ultraviolet filter in a slit-lamp biomicroscope. A lower BUT may indicate dryness.
Tear Drainage System: Orbital structures for tear production as well as drainage which include the lacrimal gland, puncta, canaliculi, tear sac and nasolacrimal duct.Click here to watch a video animation of the tear drainage system on our Mandel Vision YouTube channel.
Tear Film: Liquid that bathes the cornea and conjunctiva which consists of 3 layers, the outer oily layer secreted by the meibomian glands, the middle aqueous layer secreted by the lacrimal glands and the inner mucin layer produced by the conjunctival goblet cells.
Tonometry: See Applanation Tonometry
Topography: A measurement of the curvature of the cornea. A color map is created from a picture of the cornea that details the variations in the front surface curvature of the cornea.
Transition Eyeglass Lens: Spectacles with sun-activated tints. Lenses are clear indoors and darken outdoors for greater comfort in the sun.
Trifocal Eyeglass Lens: A spectacle lens that incorporates three distances (near vision, middle vision and distance vision) into one lens with visible lines of demarcation in the lens.
Ulcer: See: Corneal Ulcer
Ultrasound: A method of diagnostic testing in which high frequency sound waves are transmitted into the eye from a hand-held probe. The sound waves are reflected by the ocular tissues. This method is used in pachymetry to measure the thickness of the cornea, in Ascan biometry to measure the length of the eye and in Bscan biometry to aid in the diagnosis of eye and orbital problems.
Uveitis: Inflammation of any of the structures of the uvea.
Vascular: Referring to, affecting, or comprising a blood vessel or lymph vessel.
Visual Acuity: Assessment of the eye’s ability to distinguish object details and shape, using the smallest object that can be seen at a specified distance, typically at 20 feet. Click here to watch a video about the visual system on our Mandel Vision YouTube channel.
Visual Field: The full area of both central and peripheral vision that is visible to an eye that is fixating straight ahead. Also the name of a diagnostic instrument used to measure peripheral vision.
Vitreous Detachment: Separation of the vitreous gel from the retina. It can be innocuous, but can also cause retinal tears which may lead to retinal detachment. Signs include floaters and flashes and should be evaluated by an ophthalmologist.