Transcript Visual acuity

Lecture 1
EYE ANATOMY
VISUAL FUNCTIONS
REFRACTION
ACCOMMODATION
SRABISMUS
Lecture is delivered by Ph. D., associate professor
Tabalyuk Tetyana Anatolyivna
Visual organ consists from:
1) peripheral part – eyeball with ocular adnexa;
2) guiding pathway – optic nerve, chiasm, optic tract;
3) undercortex centers – lateral geniculare nucleus and
optic radiation;
4) higher visual centers in the occipital cortex.
Structure of Visual Analisator
1
2
3
4
5
6
7
-
retina,
optic nerve (non-crossed fibers),
optic nerve (crossed fibers),
optic tract,
lateral geniculare nucleus,
radiatio optici,
lobus opticus
EYEBALL
I. External (structural) layer – cornea & sclera;
II. Middle (vascular) layer – iris, ciliary body & choroid;
III. Internal layer – retina.
Internal nucleus of the eye includes: lens, vitreous & aqueous
humor, which fill in eye chambers.
The eyes lie within two bony cavities, or orbits.
OCULAR ADNEXA :
•
Lacrimal gland & excretory system
•
Oculomotor apparatus
•
Eyelids
•
Conjunctiva
OPTICAL SYSTEM of the EYE:
•
Cornea
•
Aqueous humor
•
Lens
•
Vitreous
VISUAL FUNCTIONS:
Peripheral vision (rods are response) includes:
Light sensitivity
Field of vision
Central vision (cones are response) includes:
Visual acuity
Colour vision
Light sensitivity
Eye adaptation to light lasts till 1 minute.
Eye adaptation to dark lasts till 1 hour.
Adaptometr is a special equipment
with the help of which we can measure
dark adaptation of the human eye.
The investigation durates 1 hour.
Hemeralopia is a light sensitivity disorder.
Functional hemeralopia is usually
caused by hypovitamonosis A.
Symptomatic hemeralopia is an index
of rods condition and may be a
symptom of retinitis pigmentosa,
optic neuritis or glaucoma.
Field of vision is a space which is seen by
non-moving eye (one eye, not both).
Perimetry – projection of visual field on spherical concave space,
which is concetric to retina.
Left picture – ancient perimetr of Ferster
Right picture – modern automatic computerized spheroperimetr
Campimetry is a projection of visual field on a plane
This method is useful to reveal and measure phisiological scotoma – blind
spot – projection in a space optic disc.
Usually blind spot is found in temporal part of visual field 12-18 degrees
of point of fixation (controposite nasal location of optic disc). Its vertical
size - 8-9 degrees (10-11 sm), its horizontal size – 5-7 degrees
(8-9 sm).
Normal bounders of visual field for objects
of different colour
Visual field defects
1.Narroving of visual field bounders:
 concetric (retinitis pigmentosa, optic atrophy, final

2.



glaucoma)
local (usual hemianopsia : homonim - dextra or sinistra &
heteronim - binasal or bitemporal)
Patch loosing of visual field - scotoma:
positive (with complaints) & negative (without complaints)
absolute & relative
physiological & pathological
I.e. blind spot is physiological, absolute & negative scotoma
Visual acuity
Visual acuity is measured in relative units.
visus=d/D,
where d-distance of investigation; D-distance, from each normal eye can
definite signs of this line (is written in the left of each line of Sivtcev
table).
For example, the person reads first line of Sivtcev table from 5 m. Normal
eye definites the signs of this line from 50 m. So, visus=5 m/50 m=0,1.
If the person does not see optotypes of first line of Sivtcev table from 5 m,
we ask him to come more near to the table.
For example, the person reads first line of Sivtcev table from 3 m. Normal
eye definites the signs of this line from 50 m. So, visus=3 m/50 m=0,06.
If the person does not see optotypes of first line of Sivtcev table even from
0,5 m, we project the light to his or her eye from different direcrion. If
the person gives correct answers, then his visus=1/∞ pr.l.certa. If the
person see light, but gives not correct answers even in one direction,
then his visus=1/∞ pr.l.incerta.
If the person does not see light, then his visus=0. In such cases usually
direct light reaction of pupil is absent & during objective measuring of
visual acuity with the help of nystagmoaparat optokinetic nystagmus is
absent.
VISUAL ACUITY TEST (UKRAINIAN & FOREIGN ONE)
Left picture – Snellen chart
Right picture – Sivtcev table
Visual acuity transcription
20 feet equivalent 6 meter equivalent 5 meter equivalent
(USA)
(Great Britain)
(Ukraine)
20/20
20/25
6/6
6/7.5
1,0
0,8
20/40
20/60
20/200
6/12
6/18
6/60
0,5
0,3
0,1
Normal data of visual acuity in children
Newborns – 0,005;
4 months – 0,01
1 year – 0,1-0,3;
2 years – 0,2-0,5;
3 years – 0,3-0,6;
4 years – 0,4-0,7;
5 years – 0,5-0,9;
6 years –0,7-1,0;
7-15 years – 1,0
Colour vision
Polichromatic Rabkins tables are used for investigation
Normal colour vision according to this method is called
normal trichromasia
Colour vision disorders:
Congenital usually bilateral
Aquired usually monolateral
Defect of one of three main colours is called dichromasia
White & black perceprion is called monochromasia
Anomal perception of red – protanomaly
Anomal perception of green – deyteranomaly
Anomal perception of blue - tritanomaly
PHYSICAL REFRACTION of the EYE:
average refractive power of the eye is approximetly 60 D
individual indices fluctuate from 52 till 71 D
Average refractive power of optical mediums of the eye:
 Cornea – 40 D
 Lens - 19-20 D
 Aqueous humor & vitreous – less then 1 D
In sum – 60 D
CLINICAL REFRACTION of the EYE:
correlation between refractive power of the eye & its length
EMMETROPIA & AMMETROPIA:
MYOPIA
HYPERMETROPIA
ASTIGMATISM
Emmetropia (E or Em) – refractive power of the eye
corresponds with its length, thus main focus is located on
retina
Ammetropia – refractive errow, abnormal correlation between
refractive power & length of the eye:

Myopia (M or My) – main focus is before retina due to
incresed refractive power or length of the eye

Hypermetropia (H or Hy) - main focus is behind retina
due to decresed refractive power or length of the eye

Astigmatism – different refractive power in two
perpendicular planes. Combination of different clinical
refraction or different degrees of one type of clinical
refraction in one eye is usually named astigmatism.
Myopia is subdivided into:
Light degree – till minus 2,75 D;
Middle degree – from minus 3,0 till 5,75 D;
High degree – minus 6,0 D and more
Hypermetropia is subdivided into:
Light degree – till plus 1,75 D;
Middle degree – from plus 2,0 till 4,75 D;
High degree – plus 5,0 D and more
Anisometropia
is different refraction of both eyes more then 1,0 dptr
I.
TYPES of ASTIGMATISM:
1. Simple – combination of emmetropia in one meridian & ammetropia in
perpendicular one.
A. Simple myopic - combination of emmetropia & myopia in two
perpendicular planes;
B. Simple hypermetropic - combination of emmetropia & hypermetropia in
two perpendicular planes.
2. Complex – combination of different degrees of one type of ammetropia in two
meridians.
A. Complex myopic - combination of different degrees of myopia in two
perpendicular planes;
B. Comlex hypermetropic - combination of different degrees of
hypermetropia in two perpendicular planes.
3. Mixt – combination of myopia & hypermetropia in perpendicular planes of one
eye.
II. 1. Direct – refractive power of vertical meridian is stronger then horizontal one
2. Indirect - refractive power of horizontal meridian is stronger then vertical one
III. 1. Regular - refractive power of hole meridian is the same
2. Irregular - refractive power in one meridian is different due to corneal
diseases, i.e. keratoconus, scars etc.
METHODS of MEASURING the REFRACTION
I. Objective methods:
• sciascopy or retinoscopy
• refractometry
• autorefractometry
• ophtalmometry
II. Subjective method
according to improving the visual acuity with trial glasses
Retinoscopy, refractometry, autorefractometry
Ophthalmometry, corneal topography
NORMAL DEVELOPMENT of REFRACTION in CHILDREN
Newborns – Hm 3,0-5,0 dptr;
1 year – Hm 3,5 dptr;
2 years – Hm 3,0 dptr;
3 years – Hm 2,5 dptr;
4 years – Hm 2,0 dptr;
5 years – Hm 1,5 dptr;
6 years – Hm 1,0 dptr;
7-8 years – Hm 0,75 dptr;
9-15 years – Hm 0,5 dptr;
EXAMPLES:
1. The results of refractometry of both eyes:
90 degrees –My (-) 5,0 dptr;
180 degrees – My (-) 5,0 dptr
It's middle degree myopia OU.
2. The results of refractometry of both eyes:
90 degrees – Hm (+) 2,0 dptr;
180 degrees – Hm (+) 2,0 dptr
It's middle degree hypermetropia OU.
Pay attention for patients' age! It may be physiological
refraction!
3. The results of refractometry of right eye:
90 degrees –My (-) 5,0 dptr;
180 degrees – Em
It's simple myopic direct astigmatism OD.
EXAMPLES:
4. The results of refractometry of left eye:
90 degrees – Hm (+) 5,0 dptr;
180 degrees – Hm (+) 10, 0 dptr
It's complex hypermetropic indirect astigmatism OS.
5. The results of refractometry of both eyes:
90 degrees – My (-) 2,0 dptr;
180 degrees – Hm (+) 3,0 dptr
It's mixt direct astigmatism OU.
6. The results of refractometry of right eye:
90 degrees –My (-) 2,0 dptr;
180 degrees – My (-) 2,0 dptr
The results of refractometry of left eye:
90 degrees – Hm (+) 5,0 dptr;
180 degrees – Hm (+) 5, 0 dptr
It's anisometropia. Light degree myopia OD. High degree
hyperopia OS.
METHODS of AMMETROPIA CORRECTION:
1.
2.
3.
4.
GLASSES
CONTACT LENSES
SURGICAL, i.e. EXIMER LASER
ORTHOKERATOLOGY in light & middle myopia
Glasses is the most simple, most ancient
method of correction, but not always the
most effective
Sph concave for myopia
Sph convex for hyperopia
Cyl for simple astigmatism
Sph-cyl for complex &
mixt astigmatism
SOFT & HARD CONTACT LENS
Contact lenses give the better & more natural
vision, but the patient have to be under a special
doctors control
Medical indications for contact correction:
High myopia
High astigmatism
Aphakia
Irregular cornea, i.e. in keratoconus
Anisometropia
Lasik surgery – changing of cornea shape
Implantation of phakic intraocular lenses in
high myopia & astigmatism
ORTHOKERATOLOGY – changing of corneal shape in
light & middle myopia with the help of special
contact lenses to stop myopia progression in
children & in cases when laser surgery is
contrindicated (i.e. thin cornea)
Accommodation - adjustment of the eye
for vision in different distances
•.
In short distances - ciliary muscle
contracts – zonula ciliaris relax –
lens becomes more convex –
refractive power of lens increases
In long distances - ciliary muscle
relaxes – tensio of zonula ciliaris
increases – lens becomes more
concave – refractive power of lens
decreases
PRESBYOPIA – age loosing of accommodation
To correct it special multifocal glasses
(progressive) or glasses for near distance
are prescribed. Approximetly:
40 years – sph convex (+) 1,0 dptr
45 years – sph convex (+) 1,5 dptr
50 years – sph convex (+) 2,0 dptr
55 years – sph convex (+) 2,5 dptr
60 years – sph convex (+) 3,0 dptr
over 60 years – sph convex (+) 3,5 dptr
STRABISMUS
HIRSHBERG TEST
is used to determine angle of strabismus
Investigation of binocular vision – Worth
four-dot test
Differentiation of neurologycal & ophthalmological
srabismus
Paralytic
(nonconcominant)
strabismus
Concominant
(nonparalytic)
strabismus
Decreasing or absence of
eye movements in any
direction
Primary & secondary angle
of strabismus are different
Full amount of eye
movements
Diplopia
Primary & secondary angle
of strabismus
are equal
Diplopia is absebt
Types of concominant srabismus
Accommodative
strabismus
Nonaccommodative
strabismus
Angle of srabismus is visible only
for near distance (if it is esotropia)
or only for far distance (if it is
exotropia)
Angle of srabismus is present
constantly (for far & near
distances)
Using of cycloplegic agents (S.
Using of cycloplegic agents (S.
atropini, Mydriacili or Tropicamide) atropini, Mydriacili or Tropicamide)
corect angle of srabismus (if it is
does not influence on angle of
esotropia) or increases it (if it is
srabismus
exotropia)
Glasses corect angle of srabismus:
sph convex if it is esotropia
sph concave if it is exotropia
Glasses does not influence on
angle of srabismus
TREATMENT of NONACCOMMODATIVE
STRABISMUS only SURGICAL
Recession
(weakening of eye muscle)
&
Resection
(strengthening of eye muscle)
Amblyopia is decreasing of visual acuity
without any organic causes usually as a
complication of strabismus or anisometropia
light degree – visual acuity is decreased to
0,8-0,4
middle degree - visual acuity is decreased to
0,3-0,2
severe amblyopia - visual acuity is less then
0,2
Pleoptics is a method of amblyopia
treatment, which includes
Occlusio
Penalisation
Light or laser stimulation of macula
Ortoptics is a method of
development of binocular vision
Exercises on synoptofor