Download Refractive - UMF IASI 2015

OCULAR
REFRACTION
1
Visual analyser
performances



Phisical status of
refractive
components (correct
focus on the retina);
Retinian neurons
quality;
Brain neurons
quality.
2

Ocuar refraction is defined
by the anatomical components
which contribute on light array
optical modulation
3
transparent mediums
lacrimal layer
 cornea
 aqueous humour
 lens
 vitrious

4
Ocular refraction
static refraction
 dinamic refraction

5
Subjects
1.
2.
3.
4.
5.
6.
7.
Ametropia
Hyperopia
Myopia
Astigmatism
Anizometropia
Accomodation
Presbyopia
6
EMETROPIA

emetropia is that optical condition in
which there is no refraction error so
that rays of parallel to the visual axis
appear entering the eye are brought
to a focus on the fovea centralis
when no accommodation is used
7
AMETROPIA classification

spherical or stigmic disorders in
which enter:
myopia
 hyperopia

8

asferical or astigmic disorders in
which we include astigmatisms:
regular
 iregular

9
HYPEROPIA

refractive condition of the eye in
which (with accommodation
suspended) parallel rays of light are
intercepted by the retina before
coming to focus
10
Clasification of hyperopia
Axial = when the globe is too short
to the amount of the refractive power
present;
 Refractive = when the power of the
cornea and lens is inadequate for the
length of the globe

11
Type of hyperopia



Total hyperopia = amount of the hyperopia
with all accommodation suspended (by
using the cycloplegic drugs);
Manifest hyperopia = is the maximum
hyperopia that can be corrected with a
convex lens when accommodation is active;
Latent hyperopia = is the difference
between total and manifest hyperopia.
12
Signs and symptoms




Visual acuity is reduced when accommodation
is not able to fully substitute the hyperopia;
Vision is blurred, especially after near work;
The increased of the accommodation may
stimulate an excessive degree of convergence,
manifested as a tendency of for the eyes to
deviate inward (esodeviation);
The cornea is smaller than normal, and even
the globe itself may be smaller;
13
Oftalmoscopy

optic disk congestive, with indistinct
margins and the absence of the
physiologic cup (pseudopapiledema)
14
Treatment


convex lenses (glases or contact lenses)
corneal refractive surgery:






Laser thermal keratoplasty
Lamellar keratoplasty
Photorefractive keratectomy
Laser in situ keratomileusis (LASIK)
phakic intraocular lenses using iris-claw IOL;
clear lens extraction with posterior chamber
lens implantation.
15
LASIK
16
MYOPIA

optical condition in which rays of light
entering the eye parallel to the visual axis
come to focus in front of the retina
17
Clasification of myopia


Axial = because the refractive power of
the cornea and lens is too great for the
length of the eye;
Refractive = because the eye is to long
for the refractive power present
18

physiologic myopia
refractive (lenticular myopia – is refractive
myopia related to the lens power)
 axial


pathologic or degenerative myopia – is
axial myopia
19
physiologic myopia




is the most common type
onset usually between 5 and 10 years of
age but may begin as late as 25 years age
gradually increase until the eye is fully
grown about 18 years of age
seldom exceeds 6 diopters.
20
pathologic or degenerative myopia
Symptoms
decreased vision
 axial length of the eye is excessive,
primarily because of overgrowth of
the posterior two thirds of the globe

21
oftalmoscopy
crescent of the optic disc that begins at the
temporal side and progresses to surround the disc.
 Staphyloma of the posterior pole .
 hyperpigmented spot in the macula (Fuchs spot).
 degeneration of the retinal pigment epithelium
 choroidal sclerosis.
 peripheral retinal thinning with lattice
degeneration and retinal breaks.
22

Treatment
is neutralized by concave lenses
 contact lenses (in high myopia,
anizometropia); highly fitted contact
lenses may temporarily reduce the corneal
curvature and thus may show an apparent
decrease in myopia

23
Refractive surgery
radial keratotomy acts through peripheral radial
incision that flatten the central cornea
 photorefractive keratectomy (PRK) ablates tissue
directly from central cornea.
 laser in situ keratomileusis (LASIK) excimer
application (PRK) after creation of a hinged flap
 posterior chamber phakic intraocular lens
(implantable ocular lens)
 intracorneal implants
24

25
For high myopia
laser photocoagulation for symptomatic retinal
breaks
 extrafoveal or juxtafoveal laser
photocoagulation therapy
 combination between LASIK and phakic
intraocular lens = “BIOPTIC”
 scleral enforcement to stop or to retard the
progression of disease (controversial and under
investigation

26
ASTIGMATISM


optical condition in which the refractive
power of the eye is not the same in all
meridians.
variation in the curvature of the cornea or
lens at different meridians induces light
rays focusing to more than one point.
27
Classifications


irregular = when the meridian are not at right
angle to each other
regular = when the meridian of minimal and
maximal refraction are at right angle to each
other. Regular astigmatism can be:



with the rule – when the vertical meridian is steepest and a
correcting plus cylinder should be placed at axis 90°
against the rule – when the horizontal meridian is steepest
and a correcting plus cylinder should be placed at axis 180°
oblique astigmatism – the principal meridian do not lie at
or close to 90° and 180°
28
Classifications II


simple: when one meridian is emetropic and
other is ametropic (myopic and hypermetropic)
composed: when both meridian are ametropic



myopic = both meridian are in front of the retina
hypermetropic = both meridian are intercepted by
retina before coming to a focus
mixed astigmatism: one meridian is myopic and
other is hypermetropic
29
Classifications III


congenital astigmatism
acquired astigmatism:



surgical incision o the cornea
trauma and scarring of the cornea
tumors of the eyelid pressing upon the globe
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Pathogenic aspects

parallel rays of light do not focus at a point. Each
meridian has a focal line; the distance between
these focal lines is the “interval of Sturm”.
Between the focal lines, in the circle of least
diffusion (conffusion), the diverging and
converging tendency of the light rays is the same.
In this area the image is clear enough to satisfy the
patient
31
Symptoms and signs
the image is not clear
 the accommodation is interfered
 severe astigmatism may cause the optic
disc to appear oval rather then near
circular

32
Treatment
Minor degree of astigmatism with good VA
and without symptoms – correction is not
indicated
 Simple astigmatism – cylindrical lens
placed in the meridian 90 degrees away
from the axis of the ametropic meridian
 Composed and mixed astigmatism –
sphero-cylindric lenses (combination of a
sphere and a cylinder -plus or minus- )

33
Hard contact lenses may be used to correct
regular astigmatism and especially the
irregular astigmatism
 Surgery

incisional surgery (relaxing incisions, block
resection, compressive suture) is indicated in
congenital regular astigmatism
 excisional surgery (excimer laser – PRK and
LASIK) is recommended both in regular and
irregular astigmatism

34
ACCOMMODATION

process by which the refractive
power of the anterior lens
segment increases so that a near
object may be distinctly imaged
upon the retina
35
complex reflex





the stimulus is a blurred retinal image
this is coming to brain
different area of the brain send order to the
periphery
stimulation of the short ciliary branch of the
oculomotor nerve constricts or relaxes the
circular ciliary muscle
the eye almost instantly adjust to provide clear
vision.
36
For near vision





contraction of the ciliary muscle causes
the zonulae fibers to relax
then lens become more convex
the power is increased
the focal line is projected onto retina.
37
For long distance
ciliary muscle relaxes
 the zonulae fibers are pull and
tensioned
 the convexity of the lens surface
becomes minimal

38
amplitude of accommodation
is distance between far point of the
eye and nearest point at which the
eye can maintain focus
 amplitude of accommodation is
properly a monocular expression and
is measured for each eye
independently

39
accommodation associated
reactions
convergence of the eyes
 pupilary constriction (miosis)

40
presbyopia

with ageing
lens capsule becomes less elastic
 nucleus becomes harder and less compressible


this causes a gradual loss of accommodation
41
Symptomes



inability to see near work distinctly
patient places reding mater farther away
from the eyes than previously
ocular discomfort
42
Evolution of accomodation

10 years age - 14Dpt.

45 years age - 1Dpt.,
50 years age - 2Dpt. ,
55 years age - 2.5Dpt. ,
60 years age - 3Dpt. ,
70 years age - 3.5Dpt




43
Special situations


Myopic patients may compensate for
presbyopia by removing the lens that
corrects the distance vision.
Presbyopia is aggravated in a
hypermetropic patients if the lens that
corrects the hypermetropia is removed
44
Treatment


convex lenses added to the distance correction;
Rules:


the weakest possible convex to permit the
individual to carry an vocational and avocational
tasks;
if a subject requires lenses for distance, bifocal,
trifocal or multifocal lenses should be worn as
soon as are indicated
45
Convergence insufficiency (CI)


the inability to maintain fusion at near as a
result of a reduced amplitude of fusional
convergence power.
Symptomes:




eye discomfort
headache
blurred vision from reading or doing near work
Signs:


reduced amplitude of accommodation
exoforia
46
Accomodative insufficiency (AI)



symptoms develops after 20-40 min of reading
(same as CI) but:
these patients have normal fusion capacities
when a 4 diopters base in prism is placed in
front of the eye while reding
patients with AI benefit from reading glases
47
Accomodative spasm (AS)



inability to relax ciliary muscle (involuntary)
is associated with stressful situations or
functional nevroses
Symptoms:




bilateral blurred distance vision
headache,
fluctuating vision
Sings:



cycloplegic refraction reveals hyperopia
abnormally close near point of focus
miosis
48
ANISOMETROPIA



condition in which the refractive error of each
eye is different
the different is more than 2 diopter there is a
different in image size of the two eyes named
anizeiconia
total amount of aniseiconia suported by patient
must be less then 8%
49
several problems



the difference of the power of the two lenses
(bifocal lenses) induce a vertical prism, so that
the image from each eye is on a different level
(anisophoria);
severe anisometropia may cause ambliopia
because of the developing infant`s failure to use
the eye with greater refractive error;
failure of central vision leads to strabismus, to
absence of binocular vision or to deficiency of
binocular vision
50
Treatment
must be done in the first year of life
 must to equalize the size of the retinal image.
When:
 the refractive difference between two eyes is
smaller then 4D = full corection with glases
 this difference is greater we can use:



contact lens corection
specific surgical procedure for each type of
refractive error
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