Astigmatism, Amblyopia, Retinitis Pigmentosa

Question 1

Vision Review (Refractive Error (cont’d))

Answer 1

f)  Astigmatism
1)  It may be accompanied by nearsightedness or farsightedness
2)  corneal astigmatism
i.  Usually it is caused by an irregularly shaped cornea.
3)  Lenticular astigmatism
i.  the result of an irregularly shaped lens,
4)  Either kind of astigmatism can usually be corrected with
eyeglasses, contact lenses or refractive surgery.
5)  Astigmatism Symptoms and Signs
6)  Pt with a small amount of astigmatism
i.  may not notice it
ii.  May have slightly blurred vision
7)  uncorrected astigmatism can
i.  cause headaches or eyestrain
ii.  Pt uses accomodation to focus at distance
iii.  strain the accomodation structures results in
headaches or eyestrain
iv.  distort or blur your vision at all distances
8)  in a recent study of 2,523 children that more than 28 percent
of them had astigmatism
9)  Children may be even more unaware of the condition than
adults, and they are unlikely to complain of the blurred or
distorted vision.
10)  can affect their ability to see well in school and during sports,
so it’s important to have their eyes examined at regular
intervals in order to detect any astigmatism early on.

Question 2

Astigmatism

Answer 2

Imagine the visual field 
divided into radial portions, 
like pieces of a pie. Here, 
two portions that are 
opposite to each other are 
blurred because of the 
oblong shape of the 
cornea.

Question 3

Refractive Error

Answer 3

f.  Astigmatism
10)  Distorted vision caused by a variation in refractive power
along different meridians of the eye
11)  Regular Astigmatism
i.  Varying refractive powers in different meridians can be
reduced to 2 principle meridians at 90o to each other
ii.  In Astigmatism “with the rule” the vertical meridian has
the greater curvature, most common in young Pts since
most cases are caused by the shape of the cornea
iii.  In Astigmatism “against the rule” the horizontal meridian
has the greater curvature, more common in older pt as
the cornea starts to flatten and astigmatism with the rule
disappears
12)  Irregular Astigmatism
i.  Due to uneven buldges of keratoconus, corneal scarring,
lens irregularities, and pressure on the cornea from small
tumors of the eyelids
13) Identified as to the type of cylindric lens needed to correct it
i.  A concave cylinder used for myopic astigmatism
ii.  A convex cylindric lens for hyperopic astigmatism
14) Classified as
i.  Simple (no myopia or hyperopia)
ii.  Compound hyperopic astigmatism
iii.  Compound myopic astigmatism
iv.  Mixed (myopic combined with hyperopic astigmatism or
hyperopic combined with myopic astigmatism)

Question 4

Eye Disorders Usually Not

Associated with Systemic Disease

Answer 4

Congenital Disorders

Question 5

Congenital Disorders

Answer 5

A.  Ambylopia and Strabismus

Question 6

A.  Ambylopia and Strabismus

Answer 6

1.  Normal development of visual pathways depends on
simultaneous and appropriate retinal stimulation in
early childhood.
2.  Ambylopia, def. incomplete visual development
a.  Categorized as
1)  Strabismic
2)  Anisometropic
3)  Deprivational
b.  Minimized/prevented by early Dx and Rx
3.  Strabismus, def: misalignment of the eyes
a.  Results in two separate images appearing on the two
retinas
b.  Diplopia is avoided by involuntary suppression of one
image
1)  Alternating images may be suppressed, in which
case excellent vision may develop in each eye,
however, binocular vision will not develop
2)  More commonly, the image from one eye is
constantly suppressed, preventing normal visual
development in that eye (Cortical Blindness)

Question 7

Genetic Disorders:

A.  Ambylopia and Strabismus

Answer 7

1.  Esotropia, is the most common strabismus of
childhood
a.  Congenital esotropia may not manifest until 3-4 mos of
age, often called infatile esotropia
1)  Usually a large angle deviation or cross fixation, in
which each inturned eye views the contralateral
visual field
2)  Abduction should be demonstrated to differentiate
congenital bilateral VI nn palsies
3)  Occurs frequently in cerebral palsy,
prematurity,hydrocephalus, and Trisomy 21
4)  Sx often needed to straighten eyes
5)  Binocular vision can rarely be produced

2.  Anisometropia - condition where refractive states
of the two eyes differs
1.  One eye may focus a clear image on the retina without
accomodation while the contralateral image is blurred
leading to a unilateral amblyopia
2.  Children may squint the affected eye
3.  Glasses or contact correction, and occlusion of the
favored eye may reverse visual loss if done before age
9.

3.  Deprivation amblyopia may be caused by any
opacity along the visual axis
1.  Congenital blepharoptosis
2.  Eyelid hemangiaomas produce ptosis and induce
astigmatism

Question 8

A.  Autosomal Recessive Transmission

Answer 8

1.  Retinits pigmentosa (RP) is a group of
photoreceptor dystrophies in which rods and
cones degenerate
a.  Nyctalopia (night blindness) and gradual
progressive loss of peripheral vision are typical
features
b.  Advanced stages can see attenuated retinal
vessels, optic disk pallor, and “bone spicule”
pigmentation of the peripheral fundus in most
cases.
c.  Prevalence in US 1 in 3000
d.  Electroretinogram (ERG) is required for a definitive
Dx
e.  ERG demonstrates the progressive loss of
function of rods early in the disease
f.  Therapy is 15,000 IU’s/day of oral Vit A
g.  Central visual acuity may remain well preserved
despite the severe constriction of the visual field