Errors Of Refraction Flashcards
Refraction is the ___________ that light rays undergo as they pass through _____ of varying _______.
change in direction
media
densities
Refraction in the eye takes place mainly at the ________ and the _______.
cornea
Lens
The aim of refraction in the eye is to ____________________ so that a clear image ,of the object of regard ,can be formed on the ________.
focus light rays entering the eye
retina
A eye with normal refraction is said to be _______________.
emmetropic
Eyes with refractive errors are said to be ____________.
ammetropic
_________ is a leading cause of low vision and a cause of blindness.
Refractive error
Dimensions of an adult eyeball
Anteroposterior diameter ________ mm Horizontal diameter ________ mm
Vertical diameter ________ mm
Circumference ________ mm
Volume ________ ml
Weight ________ gm
Anteroposterior diameter 23- 25 mm Horizontal diameter 23.5 mm
Vertical diameter 23 mm
Circumference 73.5 mm
Volume 6.5 ml
Weight 7 gm
Refractive index (R.I) of the lens: _____
Refractive index (R.I) of the cornea : ______
1.42
1.36
The total dioptric power of the human eye is __________.
The cornea and lens are the major refracting surfaces in the eye.
Cornea contributes ________ of these(_____D)
60D
two thirds
40
The Cornea ,with refractive index of ~ ______, has the dual purpose of ________ the eye and ____________ as it enters the eye.
After light passes through the cornea, a portion of it passes through the _______ and from there enters the ___________.
1.38
protecting
refracting light ; pupil; crystalline lens
The crystalline lens, which has a refractive index of ~_______ , is able to change its ______ and thus serves to ________ the vision process.
The lens is attached to the _________ which relax and contract in order to change the shape of the lens.
By carefully adjusting the lens shape, the ciliary muscles assist the eye in producing an image on the retina.
1.40; shape
fine-tune
ciliary muscles
The retina contains the ________ that serve the task of detecting the _______ and the ___________ of the incoming light.
These send nerve impulses to the ___________ , the ________ cranial nerve, which convey the message to the brain for interpretation.
photoreceptors; intensity
frequency; optic nerve
second
There are three main types of ametropia;
_________,__________,__________
Myopia. Hypermetropia. Astigmatism.
MYOPIA
Common error of refraction, also known as __________ or ___________ in which parallel rays of light coming from infinity are focused _____________ when accommodation is at rest. ______ objects are seen clearly, but objects _________ are blurry.
short sightedness or near sightedness
in front of the retina
Near
farther away
Most common refractive error is???
Myopia
Myopia: epidemiology
About 70-90% in some ______ countries and about 10-20% in _______ countries.
Asian
African
Aetiology and Risk factors for MYOPIA
Risk factors include a positive family history , frequent _____ work.
_____eased axial length (_____ eyeball). Increased ____________
near
Incr; Long
corneal curvature
Aetiology and Risk factors for MYOPIA
Risk factors include a positive family history , frequent _____ work.
_____eased axial length (_____ eyeball). Increased ____________
near
Incr; Long
corneal curvature
Classification of MYOPIA
Based on Aetiology:
Axial- due to _____ease in ___________ of the eye in relation to its refractive components e.g physiological _____ eyeball, ____________ , ________________ surgery
incr; antero-posterior diameter
large; buphthalmos
post-scleral buckle
Classification of MYOPIA
Based on Aetiology
Curvature- due to an ______ease in the curvature of the ______ or one or both surfaces of the ______ e. g _________,_________, or _____________
Index- due to an ____ease in the ________ of the lens e.g ___________ or ___________
incr; cornea
lens
keratoconus, anterior lenticonus, or posterior lenticonus
incr; refractivity
nuclear sclerosis or poorly controlled DM
Classification of MYOPIA
Based on clinical appearance:
Simple – normal overshooting of eye development, usually below ____D, onset usually after ________, normal visual acuity after __________ and __________________ changes
Pathological ( progressive, degenerative)- definite pathological entity, usually above -6D, onset usually before 4years, visual acuity not normal after correction and fundal degenerative changes present
-6; 4years
correction; no degenerative fundal
Classification of MYOPIA
Based on degree:
Low : ______________
Moderate : ______________
High : ______________
Based on age at onset:______,________,______
Low : less than -3.00D
Moderate :-3.00D to -6.00D
High : >-6.00D
Infantile, Youth,Adult
Signs and symptoms of MYOPIA
_______ distance vision
_________
__________ retina
Sub-retinal ___________
_______ spot
Choroidal _____________
Blurry; Floaters
Thin pale
haemorrhages; Fuchs
neovascularization
COMPLICATIONS of MYOPIA
Posterior _______________
________ _____________
Primary _______________
Staphyloma
__________
Vitreous detachment
Retinal detachment
open angle glaucoma
Visual loss
Hypermetropia (hyperopia) or ________ -sightedness is the refractive state of the eye wherein parallel rays of light coming from infinity are focused ______________ with accommodation being at rest.
________ Objects appear blurry and those ________ clear.
long
behind the retina
Near
at a distance
HYPEROPIA: Epidemiology
Family history.
Most ____________ are mildly hyperopic but it gets better with increasing age.
Infants with moderate to high hyperopia develop __________ if not corrected by age ____.
full term neonates
strabismus; 4
HYPEROPIA: Aetiology
_______eased axial length is the most common cause.
_____eased corneal curvature
Decreased
Decreased
Classification of hyperopia
Based on Aetiology:
Axial: due to __________ in AP diameter
Curvatural: _______eased curvature of the cornea reducing its power
Index: _________ in RI of the lens
shortening
decr
reduction
Classification of Hyperopia
Based on degree:
________
_______
__________
Low
Moderate
High
Classification of HYPEROPIA
Based on clinical appearance:
Simple or developmental hypermetropia : the commonest form that results from _______________________
____________ hypermetropia
Functional : due to __________________ functions.
normal biological variations.
Pathological
loss of accomodative
Clinical features of HYPEROPIA
_______ near vision
___________
_____________
Blurry near vision
Asthenopia
Headaches
Complications of HYPEROPIA
__________
____________
Amblyopia
Strabismus
Astigmatism
Astigmatism is an imperfection in the ___________________ leading to blurred vision because light rays are not _______________ or have _____________ on the retina.
It often co exists with the other types of refractive errors.
curvature of the cornea
properly focused
multiple focal points
Risk factors for astigmatism
Positive __________
____________
Positive family history
keratoconus
Aetiology of Astigmatism
Idiopathic
__________________ cornea (idiopathic)
______
Corneal ________- and _______________
Irregularly shaped
Trauma
surgeries
anterior segment surgeries
Classification of ASTIGMATISM
Based on axis of the principal meridians
Regular :principal meridians are _________
Irregular : principal meridians are _________
Based on focus of the principal meridians
_________,___________,__________
perpendicular; not
Simple Compound mixed
Clinical features of ASTIGMATISM
Small amounts of astigmatism may ______________
Significant astigmatism would produce _________________
____________
______________
not have any symptoms.
blurred vision at any distance.
Headaches
Asthenopia
Presbyopia
This is an ______-related inability to focus at ______ distances
It is a (physiological or pathological?) change occurring in adult eye causing ______ vision impairment with advancing age
age; near
physiological; near
Presbyopia is strictly considered to be a refractive error
T/F
F
It’s not
Management of Refractive Error
History: to include bio-data, presenting complaints, _________.
Examination:________ using Snellen’s chart, ____________ for IOP, _______ examination for structures of the anterior segment and ___________ to examine the retina
Investigations: Refraction (________ and ____________ ) , keratometry , corneal ________
spectacle use
Visual acuity; Tonometry
Slit-lamp; Fundoscopy
objective and subjective
topography
General Treatment for Refractive Error
Good ___________
Good ___________ for close work
Career choice/ modification
Adequate follow -up
Nutrition
Illumination
Treatment
Several options are available ,however, the doctor and patient would determine that which is best suited for each patient.
They include;
Corrective lenses : _______ lens , _______ lens , _________ lens
concave
Convex
cylindrical
Treatment
_______ lens
Refractive surgeries: these are aimed at ______________ are also available
Contact
reshaping the cornea
