Abstract  

 

Amblyopia is a common
cause of visual morbidity in children.

We Will Write a Custom Essay Specifically
For You For Only $13.90/page!


order now

Anisometropic amblyopia is the second most common cause,
it is caused by unequal focus between the two eyes, resulting chronic blur on
one retina. Unlike strabismic amblyopia, the eyes appear normal to the observer.
Anisometropic amblyopia can occur with small amounts of astigmatism or asymmetric
hyperopia. However, large amounts of anisomyopia are needed for amblyopia to
develop. This literature review
looks into whether or not refractive surgery is an effective way of treating anisometropic
amblyopia. 

 

Introduction

 

In the past hundred years Anisometropic
amblyopia management hasn’t changed greatly. Traditional therapy consists of
correcting the refractive error with contact lenses or spectacles, followed by occlusion
of the good eye if the amblyopia persists, this forces the brain to use the
amblyopic eye hence improving visual acuity. These therapies fail not
infrequently.

Recent
advances in refractive surgery suggest that surgical treatment may be a good alternative
to traditional therapy in selected situations. The science of correcting
refractive error has undergone an interesting evolution. Spectacle correction
has been around since the 13th century and contact lenses since the
1880s. Refractive surgical procedures began in the 1970s with radial keratotomy
followed by epikeratophakia and now excimer laser procedures. Most recently,
clear lens extraction and phakic intraocular lenses have been accepted as treatment
for selected refractive error problems in the adult population.

POTENTIAL
INDICATIONS FOR SURGICAL INTERVENTION

Why should we consider surgical
interventions for anisometropic amblyopia? There are several reasons:

(1) Conventional therapy sometimes
fails, leaving patients with no other alternatives
(2)Not getting the desired vision even after being successfully treated
 (3) Residual amblyopia is very common
and could possibly be prevented if the refractive error were normalized at an
earlier age
(4) With severe anisometropia, correcting the refractive error  for severe anisometropia often causes
aniseikonia, reduced stereopsis/ binocularity, and image distortion
(5) Lastly, it is incumbent upon all physicians to continue to responsibly
explore potential new treatment options that may offer better outcomes and/or
simplify treatment regimens.

We know that the success rate
of traditional therapy declines with increasing anisometropia, and the severity
of the amblyopia increases with increasing anisometropia so what then are the
potential indications for surgical intervention of anisometropic amblyopia? An
obvious potential indication would be failure with conventional therapy.
Another possible indication could be a certain level of severe anisometropia known
to be associated with a poor visual outcome. Amblyopiogenic levels of
anisometropia are well known. Two dioptres of anisomyopia, 1 D of
anisohyperopia, and 1.5 D of anisoastigmatism are known to lead to amblyopia if
left uncorrected. Is this entry level of anisometropia, however, enough to
offer refractive surgery? It probably is not, because the success rate for this
entry level of anisometropia is exceedingly high with conventional therapy. From
data, it is probably reasonable to con- sider refractive surgery for
anisometropic amblyopia when at least 3 to 4 D of anisomyopia or anisohyperopia
is present.

POTENTIAL
REFRACTIVE SURGICAL PROCEDURES FOR ANISOMETROPIA

The specific refractive procedures that
may be applicable for children are photo- refractive keratectomy (PRK), laser
in situ keratomileusis (LASIK), laser assisted subepithelial keratectomy
(LASEK), clear lens extraction, phakic intraocular lenses, and intrastromal
corneal rings (Intacs). The only refractive procedures that have undergone any
significant investigation in children are LASEK, LASIK AND PRK.

 

RISKS AND BENEFITS OF VARIOUS REFRACTIVE
SURGICAL PROCEDURES

As with any medical or surgical intervention,
there are pros and cons associated with each of these excimer laser procedures.
The advantages of PRK include achieving a stable refractive correction with a
less invasive procedure than LASIK as it is a surface ablation. The disadvantages
of PRK when compared to LASIK are the risk of postoperative corneal haze that
may require four to six months of topical corticosteroid use, longer recovery
time (approximately three days for the epithelium to heal), and more
discomfort. When compared to PRK, LASIK enjoys the same advantages of stable
correction, but it offers the benefits of faster recovery and limited pain. The
potential disadvantages/ complications
of LASIK, however, are significant, potentially vision threatening, and include
flap dislocation, tear (or hole) keratectasia, epithelial ingrowth, and possible
long-term corneal endothelial cell loss. LASEK essentially has the same risk
profile as PRK, though it may be associated with less discomfort.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

TABLE

SUMMARY OF STUDIES ON EXCIMER REFRACTIVE SURGERY FOR
ANISOMETROPIC AMBLYOPIA

 

 

 

Study

Procedure
 

Age (yrs)

No of patients

Pre mean SE (D)

Mean post SE (D)

Uncorrected VA improvement

BCVA improvement

Mean follow up month

Corneal haze

Complications

Paysse
 

PRK

2-11

8
3

-13.70
+4.75

-3.55
+1.41

5/7 children – 2 lines
 

4/7
children – 2 lines
 
1-
7 lines

31

Min
 

None
 

Dedhia

Lasik

3 under 18yrs

21

N/A

N/A

2 or more lines for
all patients
12yr old gained 4
lines

1 or more lines in 61.9% of
eyes
 

3

Min

none

4

Lasik

8-15

9

-7.66

-0.22

All eyes- at least 5
eyes

N/A

3

N/A

none

5- LIN

Lasik

5-14

24

+7.35
-8.01
 

+3.30
-1.32

Pre = 0.06
Post= 0.43
 
 

Pre-0.26
Post-0.67

33

3 cases mild

none

Zhang

Lasik

6-16

33

-10.00

-0.60

Pre to post 1.74 to
0.45 (UDVA)

Pre to post 0.98 to
0.41 (CDVA)

8

None

none

Ghanam

Lasik

 

18

-7.75

-0.50

N/A

Pre 0.72
Post 0.47

24

N/A

none

Yin

Lasik

6-14

42
32

N/A

N/A

N/A

Myopia Pre to post 0.40
to 0.59 (CDVA)
Hyperopia Pre to post
0.53 to 0.31 (CDVA)

36
36

N/A

none

Agarwal

Lasik

5-11

16

-14.88

-1.44

N/A

Pre 0.53
Post 0.54
12 eyes regained
their BCVA, 2 eyes lost 1 line BCVA, 2 eyes gained 1 line

12

3 eyes grade 2 haze

No eyes with induced
astigmatism of more than 0.5D, no complications

 

 

Conclusion

All
studies have shown consistent, predictable refractive correction, mild to
excellent visual acuity improvement, and minimal or no complications. In
studies that evaluated stereopsis, more than 50% of patients tested improved
regardless of age at time of refractive procedure. Sample size, however, has
been small in all studies to date and very few studies have included a control
group.
Randomized clinical trials are now needed to optimally evaluate these surgical
alternatives for anisometropic amblyopia. 

x

Hi!
I'm Joan!

Would you like to get a custom essay? How about receiving a customized one?

Check it out