TERMINOLOGY Flashcards
(331 cards)
1
Q
Abbe Number
A
A measure of lens light dispersion
2
Q
Aberration
A
The failure of a refracting surface or lens to produce an exact point-to-point correspondence between an object or its image.
3
Q
Accommodation
A
Adjustment by the eye for focusing clearly on near targets, which is accomplished by changing the shape of the crystalline lens through action of the ciliary muscle.
4
Q
Add
A
the total dioptric power added to a distance prescription to supplement accommodation for reading
5
Q
Against-the-rule Astigmatism
A
When the steepest meridian of the lens/prescription lies near the 0”-180” line
6
Q
Age-Related Macular Degeneration (AMD/ARMD)
A
Age related deterioration of the macula
7
Q
Albinism
A
A hereditary absence of pigment in the skin, hair, iris and retina; usually associated with the loss of visual acuity, nystagmus and photophobia; often accompanied by refractive errors
8
Q
Amaurosis
A
Partial or total blindness
9
Q
Amblyopia
A
Decreased visual acuity in one or both eyes, usually due to lack of sensory input during childhood. Often occurs without any apparent disease of the eye
10
Q
Ametropia
A
An optical error of the eye in which the image of an object does not focus on the retina, when the visual system is at rest.
11
Q
Amsler Grid
A
A diagram with horizontal and vertical lines used to detect macular distortion.
12
Q
Anesthetic
A
A drug that induces an insensitivity to pain
13
Q
Aniseikonia
A
The images of an object, which appear on each retina, are unequal in size or shape and cannot be fused into an image
14
Q
Anisometropia
A
A difference in refractive error between the two eyes
15
Q
Anterior Chamber`
A
The aqueous-filled space in the forward portion of the eye, bounded in front by the cornea and behind by the iris
16
Q
Anterior Chamber Angle
A
The junction between the cornea and the iris where aqueous filters out of the eye
17
Q
Anterior Segment
A
Referring to the front part of the eye (the lens forward)
18
Q
Antihistamine
A
Drug used in the treatment of allergies
19
Q
Antireflective Coating (ARC)
A
Reduces light reflections and increases the transmission of light through the lens
20
Q
Aphakia
A
Absence of the crystalline lens of the eye
21
Q
Applanation Tonometry
A
A method for determining intraocular pressure (IOP) by measuring force required to flatten an area of the cornea
22
Q
Aqueous Humor (Aqueous)
A
Clear, watery fluid which fills the anterior chamber of the eye
23
Q
Aspheric Lens
A
A non-spherical lens, in which the radii of the curvature increase towards the periphery rather than remaining equal at all points. Aspheric lenses reduce optical aberration and improve resolution
24
Q
Asthenopia
A
Ocular fatigue caused by tiring of the muscle in and around the eye
25
Astigmatism
A refractive error in which light rays fail to come to a single focus on the retina because of differing amounts of refraction in the various meridians of the eye
26
Atroric Lens
Ophthalmic lens with aspheric curves on the back surface
27
Auto-refractor
A computerized machine that estimates the eye's objective refractive power
28
Axial Length
Length of the eyeball
29
Bandage Contact Lens
Soft contact lenses used to protect the cornea
30
Base Curve
the curvature of the central portion of the posterior surface of the lens
31
Bicentric Grind
The grinding of the lower part of the spectacle lens to help compensate for a lens-induced vertical prism power that occurs with unequal power lenses
32
Bifocal
A lens with two optical zones, one for near vision and one for distance vision
33
Bilateral
Both eyes
34
Binocular vision
The ability to use both eyes simultaneously to focus on the same object and to fuse the images from both eyes into a single image
35
Biomicroscope
A corneal microscope for examination of the front portions of the eye, which provides a narrow beam of strong light
36
Blepharitis
Inflammation of the lid margins; AKA dandruff of the eyelids
37
Blepharoplasty
Any plastic surgery performed on the eyelids
38
Blind Spot
The natural sightless area of the visual field generated by the lack of photoreceptors where the optic nerve enters the eye
39
Blue Light
High energy visible light suspected to cause eye damage
40
Bowman's Membrane
Layer of the cornea located between the epithelium and stroma
41
Braille
Tactile writing system used by individuals who are visually impaired
42
Bridge
the portion of the frame front that joins the two eye wires together. This part supports the frame on the patients nose
43
Canaliculi
Canal where tears pass from the puncta into the lacrimal sac
44
Canthus
The angle formed by the meeting of the upper and lower eyelids; specified as outer or temporal, and inner or nasal
45
Capsulotomy
A laser procedure used to remove capsular haze secondary to cataract surgery
46
Cataract
A clouding of the crystalline lens of the eye or its capsule, or both, with consequent loss of visual acuity
47
Cellulose Acetate
The most commonly used plastic frame material
48
Center Thickness
Thickness of the lens (measured in mm)
49
Central Retinal Artery Occlusion (CRAO)
Disease of the eye where retinal arterial blood flow is blocked. Symptoms include sudden painless, profound vision loss in one eye
50
Chalazion
Inflammatory enlargement of a meibomian gland in the eyelid
51
Chief Complaint
The main reason the patient has booked an appt
52
Chorioretinitis
Inflammation of the choroid and retina
53
Choroid
The vascular, intermediate layer of the eye, lying between the retina and sclera, which furnishes nourishment to the other parts of the eyeball
54
Choroiditis
Inflammation of the choroid
55
Ciliary Body
A portion of the vascular layer between the iris and the choroid, which consists of ciliary processes and ciliary muscle
56
Color Deficiency
Diminished ability to perceive differences in color- usually for red or green, rarely blue or yellow
57
Computer Vision Syndrome
Eye and vision related problems resulting from prolonged focus on a computer screen or digital device
58
Concave lens
A lens in which both surfaces curve inward, so it produces focal power by diverging parallel rays of light. It is also called a minus lens and is denoted by a minus sign
59
Congenital
Present at birth
60
Conjunctiva
Mucous membrane which lines the eyelids and covers the front part of the eyeball
61
Conjunctivitis
Inflammation of the conjunctiva
62
Contact Lenses
Lenses that are placed on the corneal surface or sclera. They have either and optical, therapeutic or cosmetic purpose
63
Contrast Sensitivity
A measurement which determines the observer's ability to see a wide range of everyday objects under normal and reduced illumination conditions
64
Convergence
The process in which the visual axes of the two eye are directed toward the same near point, with the result that the eyes are turned inward
65
Convex lens
A lens in which both surfaces curve outward, so it produces focal power by converging parallel ray of light to a focal point. AKA plus lens and is denoted by +
66
Cornea
The transparent, dome-shaped tissue covering the iris and the pupil. The front "window" of the eye, diameter approx 12mm, responsible for approx 2/3 of refractive power of eye
67
Corneal Abrasion
An erosion of the superficial layer of the epithelium of the cornea (missing or injured cells) normally quite painful
68
Corneal Edema
Excessive accumulation of fluid in the cornea, due to disturbance in the mechanism of fluid exchange
69
Corneal Topography
A non-invasive imaging technique for mapping the corneal curvature in 3D
70
CR-39
A conventional plastic ophthalmic lens material
71
Crystalline Lens
The transparent lens which is suspended inside the eye immediately behind the iris. It is responsible for approx 1/3 of the refractive power of the eye
72
cup-to-disc ratio (C/D)
the relationship between the size of the optic cup and the optic disc of the optic nerve
73
Cycloplegic
A drug that temporarily paralyzes the ciliary muscle and dilates the pupil; often used to ascertain the refractive error
74
Cylindrical Lens
a toric lens, that is, one which has differing radii of curvature in different meridians, which causes the refractive power to vary in the different meridians; used to correct astigmatism
75
Dacryocystitis
Inflammation of the lacrimal sac
76
Daily Wear
Contact lenses worn during the waking hours
77
Dark Adaptaion
The ability of the eye to adjust to a dimly lit environment
78
Datum Line
The horizontal line that runs through the vertical center of a frame
79
Decentration
the displacement of the optical center of an eyeglass lens (not placing it in the geometric center of the frame) This is done purposefully to place the optical center in line with the visual axis of the eye or to induce prism
80
Depth Perception
The ability to perceive the relative position of objects in space
81
Dermatochalasis
Excess eyelid skin drooping over eye
82
Deutaronopia
A red-green colour deficiency resulting from an insensitivity to green light
83
Diastolic Pressure
The pressure in the arteries when the heart is at rest between beats. the bottom number in BP reading
84
Diopter
A unit of measurement of strength or refractive power of lenses; also can refer to the relative curvature of a lens surface
85
Diplopia
Double vision
86
Disposable Lens
Soft contact lens that is discarded after a specific time period
87
Distance Between Lenses (DBL)
The shortest distance between the nasal edges of 2 lenses
88
Distometer
instrument that measures vertex distance
89
Drusen
Yellowish deposits under the retina made up of lipids
90
Dyslexia
dysfunction in which the ability to read is diminished due to neurological or other non-optical problems
91
Ectropion
Turning out of eyelid
92
Effective Diameter (ED)
2x the distance from the geometric center of a lens to the furthest edge of a lens
93
Emmetropia
The focal condition of the normal eye in which there is no refractive error
94
Endophthalmitis
Inflammation of most of the internal tissues of the eyeball
95
Endothelium
innermost corneal layer which is a single layer of cells
96
Endpiece
The outer part of the frame front where the temples are attached
97
Entropion
Turning in of eyelid
98
Enucleation
complete surgical removal of the eyeball
99
Epiretinal Membrane
thin fibrous tissue that forms on the retina
100
Epithelium
outermost layer of the cornea
101
Esophoria
tendency of the eyes to turn too far inward under certain conditions
102
Esotropia
condition in which one or both eyes turn too far inward at all times AKA convergent strabismus CROSSED EYES
103
Exophoria
tendency of the eye to turn too far outward under certain conditions
104
Exophthalmos
abnormal protrusion of the eyeball
105
Exotropia
condition in which one or both eyes turn too far outward at all times AKA divergent strabismus
106
Extraocular/Extrinsic Muscles
6 muscles that are responsible for moving the eye; 4 recti and 2 oblique
107
Exudate
yellowish lesions (lipid proteins) found within the retina from leaking blood vessels caused by systemic diseases
108
Extended Wear
Contact lenses that can be worn during sleep
109
Eye Dominance
the tendency of one eye to assume the major function of seeing, being assisted by the less dominant eye
110
Eyewire
the portion of the frame that surrounds the lens
111
Face Form
the curve on the front of a frame AKA wrap
112
False Negative
failing to see a stimulus that was previously seen (ie px becomes tired during VF)
113
False Positive
Seeing a stimulus when one is not present (trigger happy during VF)
114
far-sightedness
hyperopia
115
Field of Vision (Visual Field)
the entire area which can be seen without shifting gaze
116
Fitting Cross
the location of a lens sitting right in front of a px pupil
117
Fitting Triangle
when a frame touches the head only on the nose and against the sides of the head round the ears
118
Fixate
the ability of an eye to move so an image is focused on the fovea
119
Floaters
Small particles consisting of cells or fibrin which move in the vitreous
120
Fluorescein Angiography
technique for examining the circulation of the retina and choroid using a fluorescein dye that is injected into the veins and viewed using a specialized camera
121
focus
point at which rays are converged after passing through a lens
122
fornix
pocket formed where the bulbar conjunctiva meets the palpebral conjunctiva
123
fovea
small depression in the central retina at the back of the eye; the part of the macula adapted for most acute vision
124
Frame PD
horizontal distance between the geometric centers of 2 lenses
125
Fresnel prism
a series of small prisms in a plastic sheet, which attach to eyeglass lenses to temporarily correct for eye misalignments
126
fundus
the back of the eye including the retina, optic nerve, macula and fovea
127
Fusion
the power of coordinating the images received by the 2 eyes into a single image
128
Gas Permeable Lenses
Contact lenses that allow oxygen and carbon dioxide to pass through them. this usually refers to a rigid lens, although soft lenses are also gas permeable
129
Geocenter
the intersection of the datum line and horizontal centers of each lens shape
130
Giant papillary conjunctivitis (GPC)
is a long-term hypersensitivity or allergic reaction resulting in bumps called papillae developing on the underside of the upper eyelid, usually accompanied by mucus discharge and itching
131
Glare
caused by a brightness greater than the eye can adjust to
132
Glaucoma
disease in which vision is lost due to damage of the optic nerve, it is often associated with increased pressure inside the eye
133
Gonioscope
a magnifying device which is placed on the cornea and in conjunction with strong illumination, is used to examine the angle of the interior chamber
134
Grave's Disease
autoimmune thyroid disease that causes protrusion of the eyes
135
half-eye
frame designed to sit lower on the nose, to allow a patient to read and to look over the top to see distance
136
hemianopsia
blindness of one half the field of vision of one or both eyes
137
hepatitis B
infectious disease caused by a virus that affects the liver
138
heterochromia
different coloured irises
139
Human Immunodeficiency Virus (HIV)
disease caused by a virus that weakens the immune system and can lead to AIDS
140
Hybrid Lens
a contact lens that has both soft and permeable materials
141
Hyperopia
Farsightedness, hypermetropia. a refractive condition resulting from the tendency of rays of light to be out of focus on the retina when accommodation is relaxed. If the light rays could do so, they would reach their focal point behind the retina. mild=blurred vision near, higher=blurred vision at all distances
142
Hyperphoria
tendency of one eye to deviate upward under certain conditions
143
hypertension
high BP
144
hypertropia
condition in which one eye deviates upward at all times
145
hyphema
blood in the anterior chamber of eye
146
hypophoria
tendency of one eye to deviate downward under certain conditions
147
hypotropia
condition in which one eye deviates downward at all times
148
injection
congestion of ciliary or conjunctival blood vessels; redness of the eye
149
Inner Canthus
inner corner of the eye where the upper and lower lids meet
150
Instrument Myopia
occurs when looking into an optical instrument and the person focuses on their eyes closer then needed to see the image
151
Interpupillary Distance (PD)
pupillary distance, is the distance between the centers of the pupils of each eye (mm)
152
Intraocular Lens (IOL)
artificial lens that is implanted in the eye during cataract surgery to replace the anatomical lens
153
intraocular pressure (IOP)
fluid pressure or tension within the eye measured in millimeters of mercury (mmHg)
154
Iris
coloured, circular muscle tissue behind the cornea and immediately in front of the crystalline lens. regulates the amount of light entering the eye by changing the size of the pupil
155
Iritis
inflammation of the iris; pain, inflammation and discomfort from light, contraction of pupil, discolouration of iris
156
Jaeger Test
test for near vision; lines of reading matter printed in a series of various sizes and typeface
157
K-readings
corneal curvature measurements taken with a keratometer
158
keratitis
inflammation of the cornea
159
keratoconjunctivitis sicca
dry eye
160
keratoconus
progressive disease where the central corneal tissue protrudes forward dramatically making the cornea somewhat cone-shaped
161
keratometry
measurement of the anterior curvatures of the cornea with a keratometer
162
keratoplasty
the graft of a donor cornea to replace a damaged or diseased cornea
163
Lacrimal Gland
gland with secretes tears
164
lacrimation
production of tears
165
Lacrimal sac
upper part of the nasal lacrimal duct; receives tears from the canaliculi
166
LASIK
Laser-assisted in situ keratomileuses; laser eye surgery. corneal refractive surgery for the correction for myopia, hyperopia and astigmatism
167
lateral
toward the ear, away from midline of the body
168
Lateral Geniculate Body (LGB)
relay center that receives information from the retina and transmits it to the occipital lobe in the brain
169
Lazy eye/amblyopia
decreased visual acuity in one or both eyes with no detectable cause
170
Legal Blindness
visual acuity of 20/200 or less in the better eye after correction; or visual acuity of better than 20/200 but having a VF of no greater than 20'' in better eye
171
lens
refractive medium having one or both surfaces curved
172
lens blank
a lens before it has been edged to fit into a frame
173
lens calipers
instrument used to measure the center thickness of a lens
174
lens clock
instrument for measuring the base curve of a lens
175
Lens height (B)
vertical distance between the furthest top and bottom edges of a lens
176
Lens Size (A)
horizontal distance between the furthest temporal and nasal edges of a lens
177
Lensometer
manual or automated device used to determine the prescription of an ophthalmic lens
178
leukocoria
white pupil
179
light adaptation
the ability of the eye to adjust to an increased amount of light in the environment
180
limbus
boundary between cornea and sclera
181
low vision
binocular vision less than 20/60
182
low vision aids
optical devices of various types useful to persons with vision impairment
183
macula
the small area of the central retina that surrounds the fovea; this region provides the most distinct vision in the retina
184
Major Reference Point (MPR)
the point on the lens where the prism is equal to that called for by the prescription. if an rx has no prism, the optical center and the MRP are located at the same place; in an Rx with prism, the OC and MRP are at different places
185
Meibomian gland
gland located within the eyelids which secretes an oily layer of tear fluid
186
medial
toward the nose or toward the midline of the body
187
Minimal Blank Size (MBS)
the smallest lens blank that can be used to edge a given prescription
188
Miotic
a drug that causes the pupil to contract
189
monocular
refers to one eye only
190
monovision
a type of contact lens fitting in which one eye is corrected for distance vison and the other is corrected for near vison
191
mydriasis
pupil dilation.
192
mydriatic
drug that dilates the pupil
193
myodisc
ophthalmic lens used to correct very high myopic prescriptions
194
multifocal lens
eyeglass lens that incorporates several different optical powers and allows the wearer to see clearly at multiple distances
195
Multiple Sclerosis (MS)
Autoimmune central nervous system disease causing demyelination of nerves
196
Myopia
nearsightedness; refractive error in which the eyeball is too long in relation to its focusing power, the focal point for rays of light from distant objects is in front of the retina. once the light rays reach the retina, they are out of focus
197
nasal
towards the nose or toward the midline of the body
198
Near Point of Accommodation
the nearest point at which the eye can perceive an object distinctly. it varies according to the power of accommodation
199
Near Point of Convergence
the nearest single point at which the two eyes can direct their visual lines, normally about 3inches from the eyes
200
nearsightedness
myopia
201
neovascularization
formation of new blood vessels in a part of the eye, can occur in the cornea when it does not receive enough oxygen
202
nevus
birthmark, freckle, mole
203
night blindness
a condition in which vision diminishes greatly in faint light
204
nystagmus
an involuntary, rapid movement of the eyeball; it may be lateral, vertical or rotary
205
oblique astigmatism
when the strongest (steepest) and weakest (flattest) meridians of a lens are not at 90' and 180' but rather 45' and 135'
206
occluder
an opaque or translucent device that is placed before and eye to block vision
207
Oculus Dexter (OD)
right eye
208
Oculus Sinister (OS)
left eye
209
Oculi Uniter (OU)
both eyes
210
ophthalmologist
medical doctor who specializes in diagnosis and treatments of defects and diseases of the eye, performing surgery whine necessary or prescribing other types of treatment; formerly called oculist
211
ophthalmoscope
instrument used to examine the interior of the eye
212
optic atrophy
degeneration of the nerve tissue, which carries messages from the retina to the brain
213
optical center
the location in a lens where light will pass through without being bent
214
optical cross (power cross)
represents an imaginary lens in which the power is labeled for both principal meridians, which are always 90' apart
215
optic chiasm
location where optic nerve fibres cross over in the brain
216
optic disk
head of the optic nerve in the eyeball where the retinal nerve fibers leave the eye; responsible for the physiological blind spot
217
optician
one who dispenses frames and lenses, based on a rx written by an Optometrist or Ophthalmologist; grinds lenses, fits them into frames, and adjusts the frame to the wearer
218
optic nerve
nerve which carries visual messages from the retina to the brain
219
optic neuritis
inflammation of the optic nerve
220
optic tract
extension of the optic nerve within the brain located beyond the optic chiasm
221
Optometrist
primary health care provider specializing in diagnosing and treating diseases and optical disorder of the eye, prescribing lenses, vision training, medicines and other treatments
222
Optyl
plastic frame material that has a 'memory', it can be bent into any shape when heated and cooled. when heated again it will return to original shape
223
orbital cellulitis
infection of the soft tissue of the orbit posterior to the orbital septum
224
orthokeratology
practice of purposely flattening the cornea with a specially designed contact lens, used to reduce or eliminate myopia
225
orthoptic training
series of scientifically planned exercises for developing or restoring the normal teamwork of the eyes
226
outer canthus
outer corner of the eye where the upper and lower eyelids meet
227
tachymetry
measuring the thickness of the cornea
228
palpebral
pertaining to the eyelid
229
palpebral fissure
space between the upper and lower eyelids
230
retinal laser photocoagulation
heat from a laser used to destroy leaking blood vessels in the retina
231
pantoscopic tilt
the angle of an eyeglass lens in relation to the vertical plane
232
perimeter
instrument for measuring the field of vision
233
Peripheral vision
ability to perceive the presence, motion or colour of objects outside the direct like of vision
234
phacoemulsification
ultrasound technique used during cataract surgery to remove the natural lens in the eye
235
phakic
refers to an eye that still possesses its natural lens
236
phoria
latent deviation in which the eyes tend to turn from the normal position for binocular vision
237
phoropter
instrument used for determining the refractive and binocular state of the eye
238
photochromic
lens tints that lighten and darken according to the amount of UV the lens is exposed to
239
Photophobia/photosensitivity
abnormal sensitivity to and discomfort from light
240
photopsia
flashes of light
241
photoreceptors
rods and cones
242
pingeculae
yellow-white deposit on the conjunctiva
243
plano
a lens with no rx
244
plano-cylinder lens
lens where one principle meridian has no power. they are used for the correction of simple hyperopic astigmatism and simple myopic astigmatism
245
polarization
type of ophthalmic lens coating that screens out horizontal reflections and reduces glare
246
polycarbonate
high index plastic ophthalmic lens material that is impact resistant
247
Posterior Capsular Opacification (PCO)
haziness of the lens capsule secondary to cataract surgery
248
posterior chamber
narrow space between the back of the iris and the front surface of the crystalline lens, bounded by the ciliary body and filled with aqueous
249
PRK
Photo refractive Keratectomy. type of laser eye surgery where the outer layer of the cornea is removed
250
Prentice's Rule
formula for calculating the prismatic effect induced at any point in a lens; prism diopters = decentration (cm) x lens power in diopters
251
Presbyopia
condition common after age 40 in which gradual lessoning of the eye's power of accommodation causes difficulty in seeing near objects
252
Primary visual cortex
area within the brain responsible for processing visual information
253
prism
triangular wedge shaped lens that bends but does not focus light rays toward the position of its base
254
prism ballast
when a contact lens is thicker and heaver at the bottom so that it will remain oriented in a specific position
255
progressive addition lens
PAL, a lens that gradually increases in + towards the bottom of the lens
256
prosthesis
artificial substitute for a missing eye
257
protanopia
re-green colour deficiency resulting from an insensitivity to red light
258
pseudoisochromatic charts
charts with colour dots of various hues and shades indicating numbers, letters or patterns used for testing colour discrimination
259
pseudophakia
eye whose natural lens has been replaced with an artificial one
260
pseudotumor cerebri
neurological disorder characterized by increased pressure within the skull in the absence of a tumor or disease
261
pterygium
triangular fold of growing membrane which invades the cornea; usually on medial side
262
ptosis
paralytic drooping of the upper eyelid
263
punctal plugs
tiny plugs that are inserted into the lacrimal puncta to block the drainage of tears, dry eye treatment
264
puncta
small drainage holes located along the upper and lower lid margins
265
pupil
circular opening in the centre of the iris which regulates the amount of light that enters eye
266
pupillometer
device that measures the interpupillary distance (PD)
267
Radial Keratotomy
refractive surgical procedure that was used to correct myopia in the past by making incisions into the cornea
268
refraction
the bending of light rays as they travel from one medium to another
269
refractive error
defect in visual system that prevents light rays from being brought to a single focus on the retina
270
retina
thin membrane lining the back of the eye where optical images are received. converts images into electronic impulses and transmits them to the brain along the optic nerve
271
retinal detachment
separation of the retina from the choroid
272
retinitis
inflammation of the retina
273
retinitis pigmentosa
a hereditary degeneration and atrophy of the retina, usually accompanied by misplaced pigment in the retina
274
retinoblastoma
most common form of eye cancer affecting children
275
retinopathy
disease of the retina, due to various causes
276
retinopathy of prematurity
disease affecting pre-maturely born infants resulting in abnormal retinal blood vessels
277
retinoscope
instrument for determining the refractive state of the eye by observing the movements of lights and shadows across the pupil by the light thrown onto the retina from a moving mirror
278
retroscopic tilt
when bottom eye wires of a frame are further form the face than the top eye wires
279
rods and cones
types of nerve cells that form layer of the retina and act as light receiving media CONES visual acuity and colour discrimination RODS motion and vision at night
280
safety glasses
impact-resistant spectacles with or without correction for protection of eyes
281
Schlemm's canal
area where aqueous humour passes from anterior chamber into episcleral vessels
282
sclera
white part of the eye- tough covering with the cornea forms the external protective coat of eye
283
scleral contact lens
rigid contact lenses that vault over the cornea and are supported by the sclera
284
scleritis
inflammation of teh sclera
285
scotoma
blind or partially blind area in the visual field
286
segment
seg, an area of a lens with power differing from that of the main portion
287
segment height
height at which a bifocal/multifocal is placed in a lens based on the relationship of the patients facial structure to the shaper of a frame
288
silicone hydrogel
soft contace lens material
289
single vision lens
a lens having one focal length and spherical base curve
290
sjogrens syndrome
inflammatory disease characterized by dry eyes and mouth
291
slab-off
bicentric grind
292
slit lamp
biomicroscope
293
snellen chart
used for testing distance visual acuity, lines of letters, numbers or symbols in graded sizes drawn to Snellen measurements. Each size is labeled with the distance at which it can be read by the normal eye, most often used for testing vision at 20 feet
294
soft lens
contact lens made of soft plastic that contains water and allows for oxygen transmission. soft lenses are characterized by comfort and ease of adaptation
295
specific gravity
indicates the weight of a lens in grams per cm. the higher the number the heavier the lens material
296
spherical equivalent
calculated using the sphere power plus half the cylindrical power
297
spherical lens
a lens which refracts rays of light equally in all meridians
298
spherocylinder lens
the two principal meridians are different in power, and neither one is plano. they are used to the correction of compound hyperopic astigmatism, compound myopic astigmatism and mixed astigmatism
299
sphygmomanometer
instrument used to measure blood pressure
300
stereoscopic vision/depth perception
ability to use both eyes together to perceive the retative position of objects in space
301
strabismus/tropia/squint
a failure of the two eyse simultaneously to direct their gaze at the same object because of muscle imbalance
302
string-mounted frame
frame that holds a lens in place with only a small reinforcing arm and a very fine nylon cord. also referred to as a nylon cord frame
303
stroma
thickest corneal layer located between Bowman's membrane and the Descemet's membrane
304
stye/hordeolum
acute inflammation of a sebaceous gland in the margin of the eyelid, due to and infection and usually resulting in the formation of pus
305
surfactant
cleaning agents that are used to remove contact lens deposits
306
systolic pressure
amount of pressure that blood exerts on a vessel while the heart is beating. top number in a blood pressure reading
307
telescopic glasses
magnifying spectacles founded on the principles of a telescope; occasionally prescribed for improving very poor vision which connot be improved by ordinary glasses
308
temple
attaches to the frame front and wraps around the patients ears
309
temporal
toward the ear, away from midline of the body
310
tonometer
instrument for measuring pressure inside the eye
311
toric
lens with two different power curves at defined optical axes, used to correct astigmatism
312
trabecular meshwork
area within the eye responsible for draining aqueous humor
313
trabeculectomy
surgical removal of part of the trabecular meshwork used in the treatment of glaucoma to lower the IOP
314
trabeculoplasty
laser treatment on the trabecular meshwork used in the treatment of glaucoma to assist the flow of aqueous humor
315
transpose
convert a prescription of a sphero-cylindrical lens into the oppositely powered cylinder form (+ to - or vice versa)
316
trichiasis
eyelashes grow inward
317
trichromatic colour vision
normal colour vision derived from having three types of functioning cones
318
trifocal
lenses that have 3 areas of viewing, each with its own power
319
tritanopia
a rare from of colour blindness resulting from an insensitivity to blue light
320
trivex
impact resistant ophthalmic lens material
321
truncation
flattening of the lower edge of a contact lens, so that it will remain oriented in a specific position
322
tunnel vision
contraction of the visual field to such an extent that only a small area of central visual acuity remains, thus giving the affected individual the impression of looking through a tunnel
323
uveal tract
entire vascular layer of the eyeball including iris, ciliary body and choroid
324
vasoconstriction
narrowing of blood vessels
325
vertex distance
distance from the front surface of the eye to the back surface of the spectacle lens
326
vision
the faculty of seeing, sight
327
visual acuity
resolving power of the eye or the ability to see two separate objects as separate. ability of the eye to perceive the shape of objects in the direct line of vision, usually measure in terms of a Snellen fraction (20/20)
328
vitrectomy
surgical removal of the vitreous
329
vitreous humor (vitreous)
gelatinous transparent, colourless substance filling the space in the eyeball between the crystalline lens and the retina
330
with-the-rule astigmatism
when the steepest meridian of a prescription/lens lies near 90 degrees
331
zonules
radially arranged fibers that suspend the lens from the ciliary body and hold it in position
