Definitions PT3/4 Flashcards
Emmetropia
a normal eye with no refractive error
Ametropia
an eye abnormality (hyperopia, myopia and astigmatism) resulting from a faulty refractive ability of the eye
Presbyopia
farsightedness caused by loss of elasticity of the lens of the eye, occurring typically in middle and old age
Hyperopia
AKA farsightedness.
Distant light rays of light focus behind the retina when the eye is at rest.
Plus lens is used for correction.
Causes: short axial length, flatter than normal corneal curvature, smaller eye
Latent
hyperopic error that can be corrected by the eye’s accommodation
Manifest
hyperopic error that can be corrected by either plus lenses or by the patient’s own accommodation
Absolute hyperopia
hyperopic error that is not compensated for by accommodation (needs corrective lenses)
Myopia
AKA nearsightedness.
Parallel light rays of light focus in front of the retina when the eye is at rest.
Minus lens is used for correction.
Causes: steeper than normal cornea, a longer than normal eye
Axial myopia
eyeball is too long for the normal refractive power of the lens and cornea
Curvature myopia
eye is of normal size but the curvatures of the cornea and lens are steeper
Index myopia
change in the index of refraction of the lens (cataracts or diabetes can cause); requires minus lens to compensate
Astigmatism
condition where light rays are not refracted equally in all directions, so a focus point on the retina is not attained
Regular astigmatism
correctable by spherocylinder lenses and the principal meridians are at right angles to each other
Simple (astigmatism)
one of the focal lines always falls on the retina, the other falls in front (myopic) or behind (hyperopic) it
Compound (astigmatism)
both focal points lie either in front (myopic) of the retina or behind (hyperopic) it
Mixed astigmatism
one focal point lies behind the retina, whereas the other focal point lines in front of it
Irregular astigmatism
the surface of the cornea is not smooth (irregular) and therefore light rays do not refract in a predictable way to a single point.
Causes: trauma, inflammation and/or scar tissue
Outer coat
cornea, sclera and limbus
Middle coat
uvea, which consists of iris, ciliary body (ciliary muscles and ciliary processes) and choroid
Inner coat
retina, optic nerve and optic disc
Outer lipid layer
prevents evaporation of aqueous layer
Aqueous layer
provides nutrition and defense
Inner mucoid layer
keeps tear film on the epithelium
Focal power formula
F=1/f
Pupillary distance
distance between the centers of each pupil in each eye. Determines where to put the optical center in each lens
COBC Code of Ethics
General Duty to the public Duty to clients Duty to the profession Duty to colleagues
General
honest and knowledgeable, improve clients well being
Duty to the public
educating the public in promotion of ophthalmic health
Duty to clients
confidentiality, maintain records
Duty to the profession
don’t warrantee or guarantee success of care or treatment
Duty to colleagues
don’t compete for clients, compare professional competence
Three regulatory documents
HPA Opticians Regulation
Standard of Practice
Code of Ethics
Authorization document
Rx for glasses or an assessment record
Assessment record
record produced by an independent automated refraction
Prescription
authorization to dispense a vision appliance
Automated refraction
refraction for assessing visual acuity, using computerized components
Independent automated refraction
automated refraction conducted without the involvement of a prescriber
Eye examination
includes both eye health assessment and refractive error assessment, conducted by an optometrist or ophthalmologist
Refraction
when light travels from one medium into another the path of light ray will be diverted
Reflection
when light changes direction as result of “bouncing off” a surface like a mirror
Index of refraction (RI) formula
RI = Speed of light in air / speed of light in new substance
What are the units for focal length?
Unit is in Metres
What are the units for power?
Unit is in Diopters
Prism bends light towards ___
the base
Prism displaces image towards ___
the apex
Meibomian
eyelid glands that create the lipid layer of the tear film
Horizontal Visible Iris Diameter
Size of the average iris (~12mm)
Size of the average eye (~24mm)
Lid margin
flat part of the lid that meet when your eyes blink
Caruncle
sweat and oil glands for the tears
Plica semilunaris
fleshy tissue beneath the caruncle
Palpebral Fissure
distance between the upper and lower lids
5 steps that tear flow
- secretions from the lacrimal, meibomian and conjunctival goblet cells are distributed onto the cornea
- secretions separate to form the 3-tier film layer
- With each blink, tears are directed towards the nasal canthus and into the puncta
- Afterwards, tears flow through the canaliculi to the lacrimal sac
- tears drain through the nasolacrimal duct and into your nose
5 angle structures for proper aqueous humor outflow to prevent glaucoma
- root of the iris
- ciliary body
- scleral spur
- Schlemm’s Canal
- Trabecular Meshwork
3 tear film functions
- forms a smooth refractive optical surface
- maintains a moist environment of the epithelium
- carries oxygen to the eye
Hyperemia
Redness of the conjunctiva.
- caused by exposure to dust, wind or air pollutants
- fatigue
- excessive reading
- excessive dryness
Conjunctival Hemorrhage
Extreme redness beneath conjunctiva.
- Subconjunctival hemorrhage is caused by a ruptured conjunctival blood vessel
- coughing or high blood pressure
Conjunctivitis
Inflammation of the conjunctiva
- infection
- allergy
- toxicity
Allergic Conjunctivitis
Inflammation of the palepebral conjunctiva
- allergy response to allergen
Pinguecula
Wedge-shaped tissue mass not on cornea
- irritation of the conjunctiva associated with dry, hot climate
Pterygium
Wedge-shaped tissue mass on cornea
- irritation of the conjunctiva associated with dry, hot climate
Keratoconus
Degenerative condition of the cornea. Early resembles normal myopia. Later = thinning, steepening, irregular astigmatism, scarring
Keratitis (4)
Inflammation of the cornea
Bacterial - caused by bacteria such as psuedomonas and acanthameoba
Viral - caused by virus such as the herpes virus
Toxic - caused by harmful chemicals or solutions
Mechanial - caused by directly contact with the cornea
Entropion
in-turning eyelids
Ectropion
out-turning eyelids
Ptosis
drooping of the upper lid
Trichiasis
in-turning eyelashes
Blepharitis
inflammation of the lid margin
Hordeolum (acute)
localized infection or inflammation of the eyelid margin involving hair follicles of the eyelashes
external (stye) - zeis glands
internal - meiobomian gland
Chalazion (chronic)
cyst in the eyelid due to a blocked oil gland
Basal cell carcinoma
90% of malignant lid tumors
Dry eyes (Marginal or severe)
insufficient tears to lubricate and nourish the eye
Central Retinal Artery Occlusion
- retinal artery is blocked by an embolus.
- sudden and total loss of vision, retina is grey, blood vessels are unnaturally thin and segmented.
- (cherry red spot)
Central Venous Occlusion
- blockage of the central retinal vein.
- diabetes, any conditions that causes stasis of blood flow.
- blockage causes the walls of the vein to leak blood and excess fluid into the retina.
- (leaking blood vessels)
Diabetic retinopathy
caused by damage to the blood vessels of the light-sensitive tissue at the back of the eye (retina).
Retinal detachments
- usually tear induced
- retina peels away from its underlying layer of support tissue
Age-related macular degeneration (AMD)
- loss of central vision, degradation of macular tissue
Wet AMD
- exudative (oozing)
- more severe (acute)
- quick onset
Dry AMD
- atrophic (decreasing in size/drying)
- chronic (persisting or constantly reoccurring)
- slow forming
Hypertension (high blood pressure)
- flame-shaped hemmorrhages
- exudates
- “cotton-wool” spots
- narrowing of the retinal arterioles
- decreased visual acuity
Glaucoma
a condition of increased pressure within the eyeball, causing gradual loss of sight.
Types of glaucoma (4)
- primary open angle (chronic)
- angle closure (acute)
- secondary glaucoma
- congenital or infantile
Tonometry
-Measurement of intraocular pressure
14 - 20 mmHg is normal
“Puff of air” measures ocular resistance
Amblyopia
reduced vision in one eye caused by abnormal visual development early in life
Cataracts
- Result from the natural aging and degeneration of crystalline lens tissue causing cloudiness = reduced VA
- Removed when they are “ripe”
Types of cataracts (5)
Nuclear sclerosis cataract Cortical cataract Posterior subcapsular cataract Traumatic cataract Diabetic cataract
Cataract treatment
common = phacoemulsification aphakia = crystalline lens is removed pseudophakia = new intraocular lens (IOL) is inserted
Strabismus
abnormal alignment of the eyes; the condition of having a squint.
a muscle imbalance occurring in one or both eyes
CR-39
1.498 lighter than glass more impact resistant higher UV protection tintable
Water
1.33
Air
1
Segment types
Round seg flat top curved top panoptik B-seg (ribbon) R-seg (ribbon) executive (Franklin) blended
Neutralizing bifocals
checking front vertex
Image jump
unintended but predictable consequence in almost all segmented bifocal designs
Polycarbonate
1.49/1.50
safest material
low ABBE value
Crown glass
1.523 heavy not as impact resistant scratch resistant good optics stable material
Abbe value
x>35 = no chromatic aberration x<35 = chromatic aberration
Photochromic lenses
changes, gets darker to UV lights or cold conditions
Polarized lenses
eliminates horizontal glare from reflective surfaces
Higher refractive index
higher the chromatic aberration
lower ABBE value
thinner lens
Medial rectus
in towards the nose
Lateral rectus
out towards the temple
superior rectus
up
inferior rectus
down
superior oblique
intorsion
inferior oblique
extorsion
levator palpebrae superioris
elevates the upper eyelid
orbicularis oculi
closes the lids
Fusion
the ability of the rectus and oblique muscles to keep the position of the eyes aligned so that both fovea project to the same point in space
Heterophoria
when muscular imbalance occurs that means that there is one muscle working better than another and fusion cannot be maintained with both eyes
esophoria
inward drifting of the eye when it is covered
exophoria
outward drifting of the eye when it is covered
hyperphoria
upward drifting of the eye when it is covered
