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Peter G. Swann BSc (Hons), MAppSc, FCOptom, FAAO and Katrina L. Schmid BAppSc (Optom) (Hons), GradCertEd (Higher Ed), PhD
Fundus changes in myopia
An overview
Myopia is the most common of the
refractive errors. Due to this, and the
fact that many patients have a
relatively low degree of myopia, with
no deleterious ocular changes, there
is perhaps a tendency to regard
myopia as a simple refractive
condition without considering the
serious visual problems which can
arise. This article describes the
changes which can occur in the
ocular fundus due to axial myopia. A
treatment to slow or arrest the axial
elongation of the eye and, thus, these
complications is required. Band-aid
approaches such as spectacles or
refractive surgery, which do not
prevent the elongation of the eye, will
have no beneficial effect in terms of
preventing such consequences.
Figure 1
Optic disc crescents are common in
myopes. They can vary in size and location
but are typically situated at the temporal
disc margin as in this three dioptre myope.
Figure 2
A much larger crescent in a nine dioptre
myope
The extent to which members of a
population are myopic varies between races. In
the United States and other Western countries,
about a quarter of the population are myopic
by their late teens 1 with this figure rising to
approximately one third by 40 years of age.
Many people experience a slight decrease in
their level of myopia after about 45 years of
age, most likely due to decreased power of the
crystalline lens 2 .
The prevalence of myopia is dramatically
higher in many Asian races, Jewish and Arabic
people, and also tends to be more severe. The
reasons for this are not known, with both
genetic and environmental factors being
suggested 3,4 . While approximately one quarter
to one third of the myopic population has a
degree of myopia greater than six dioptres, the
prevalence of severe myopia is likely to be
higher in these countries 4 . It is probable that
the prevalence and severity of myopia is
increasing worldwide as, therefore, will its
public health impact 5 .
Pathological myopia has a prevalence of
about 2% in the USA and is the seventh
leading cause of blindness in that country 6 .
Figures from Canada, albeit somewhat dated,
indicated that 9% of blindness was due to
pathological myopia 7 .
Pathological myopia usually refers to a
condition where there is greater than six
dioptres of myopia or an axial length greater
than 26-27mm 8 . It is a progressive, probably
autosomal recessive disorder where serious
ocular complications can develop such as
chorioretinal degeneration, posterior
staphyloma, retinal detachment, primary open
angle glaucoma and posterior subcapsular and
nuclear cataract. Highly myopic eyes also have
greater responsiveness to topical
corticosteroids and, therefore, there is a
higher risk of raised intraocular pressure (IOP)
with their prolonged use 9 .
Furthermore, other ocular and general
conditions or diseases can be associated with
pathological myopia. Some examples include
retinitis pigmentosa, ocular albinism, infantile
glaucoma, retinopathy of prematurity, Down’s
syndrome, Marfan’s syndrome, Ehlers-Danlos
syndrome and Sticklers syndrome 6,10 .
FUNDUS CHANGES IN MYOPIA
In this review, we have divided ocular fundus
changes in terms of their location, that is, the
posterior pole or the fundus periphery. A brief
summary is given in Table 1 (page 35).
Blacharski 7 divides chorioretinal changes in
myopia into biomechanical, neovascular and
degenerative types. Biomechanical changes
include the so-called “lacquer cracks”, where
fractures or tears occur in Bruch’s membrane,
and posterior staphylomas. Choroidal
neovascularisation can arise, usually in older
myopes, and resolution may be seen in the
form of a Fuchs’ spot. Various degenerative
changes are common such as chorioretinal
atrophy, lattice degeneration and pavingstone
degeneration.
POSTERIOR POLE
Optic disc crescent
This is an early change in the myopic fundus
and is due to a pulling away of the choroid and
pigment epithelium, usually from the temporal
edge of the nerve to expose the sclera
(Figure 1). Curtin and Karlin 11 found optic disc
crescents in all eyes which had an axial length
of 28.5mm or more. Temporal and annular
crescents predominated. Other studies have
found that the width of the crescent was
strongly associated with the degree of myopia
(Figure 2).
Research on Chinese subjects in Hong Kong
has provided further insights 12,13 . Whereas the
incidence of crescent formation was
significantly associated with increasing axial
length and myopic refraction, when acquired
rather than physiological crescents were
considered, the size of the crescent was not
related to increased axial length or myopic
refraction. Also, optic discs were more
vertically oval in highly myopic eyes – a factor
which must be considered when examining the
optic disc of a myope who is also a glaucoma
suspect, glaucoma being certainly more
common in myopic eyes, especially the high
myopes 14 . Appropriate assessment of the optic
disc cup can be a challenge in the myope,
particularly when the optic disc is tilted and a
crescent or zone of peripapillary atrophy is
present. In the moderate myope, the cup to
disc ratio may be greater than average,
whereas the higher myopes may appear to have
little cup because of posterior staphyloma
formation. A stereoscopic evaluation through
dilated pupils is, therefore, mandatory.
Posterior staphyloma
A posterior staphyloma is a backward ectasia
of the fundus, the hallmark being tessellation
and pallor of the area involved (Figure 3). The
edges of the staphyloma may be anything but
discrete. Curtin 15 divides staphylomas into five
types, with the first, where the area of
tessellation and pallor includes the region of
the optic disc and macula, being the most
common. Type two tends to encompass the
region of the macula, type three is
peripapillary and type four extends nasally
from the optic disc. The fifth type is the most
rare and involves the fundus inferior to the
optic disc. Posterior staphylomas are often
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ot
Figure 3
The most common type 1 posterior
staphyloma. The edge of the
staphylomatous region is arrowed
progressive and result in vision loss 16 .
Steidl and Pruett 17 found that eyes with the
shallowest staphylomas showed the largest
drop in visual acuity as well as the greatest
frequency of choroidal neovascular membranes
and haemorrhage. They suggested that with
less advanced staphylomas, the choriocapillaris
was better preserved, thus increasing the
likelihood of the development of neovascular
membranes.
Lacquer cracks
Lacquer cracks, thought to be healed linear
ruptures in the retinal pigment epithelium-
Bruch’s membrane-choriocapillaris complex 18 ,
are present in about 4% of highly myopic eyes 19
(Figure 4). They are frequently seen in
conjunction with posterior staphylomas and up
to a third can have associated neovascular
membranes. The resolution of any resultant
haemorrhage may lead to the formation of a
pigmented Fuchs’ spot (Figure 5). Lacquer
cracks often progress to form more advanced
fundus changes 19 . Patients with lacquer cracks
and/or Fuchs’ spot should receive a guarded
prognosis for vision.
Chorioretinal atrophy
More commonly seen in the younger myope,
these areas appear as small, punched-out
yellow/white lesions in the presence of
posterior staphylomas, and potentially close to
lacquer cracks and the macula (Figure 6). With
time, smaller lesions frequently coalesce to
form larger areas 20 (Figure 7). Chorioretinal
atrophy may be the result of stretching and
thinning of the retinal pigment epithelium and
choroid as the eye enlarges, thus exposing the
sclera 21 .
FUNDUS PERIPHERY
The major threat to vision in the myopic eye is
retinal detachment, especially as posterior
vitreous detachment (PVD) and predisposing
retinal degenerations, such as lattice
degeneration, are more common in these eyes.
Figure 4
Lacquer cracks near the macula
Akiba 22 suggested that in high myopia, PVD
develops increasingly with age and the degree
of myopia, and that it may be seen as much as
10 years earlier in highly myopic eyes
compared to emmetropic eyes. In a study of
218 patients with myopia of six dioptres or
more in both eyes, Celorio and Pruett 23 found
that one third had lattice degeneration, with
the greatest prevalence being in eyes having
six to nine dioptres of myopia. Lattice
degeneration represents vulnerable areas of
retinal thinning. It is non-age specific and is
seen in about 40% of eyes with retinal
detachment 9 .
Pigmentary degeneration, consisting of
extensive pigment deposition in the extreme
retinal periphery, and the non-predisposing
paving stone degeneration (yellow-white areas
of chorioretinal thinning) are also more
common in myopic eyes. The pigment
proliferation and RPE migration of pigmentary
degeneration may be due to retinal traction,
while the chorioretinal thinning in paving
stone degeneration may be due to localised
occlusion of the choroidal circulation 16 . White
without pressure (translucent whitish
Figure 6
Chorioretinal atrophy: small, punched out
lesions near the macula (the white streak at
the bottom of the photograph is artefact)
Figure 5
A developing Fuchs’ spot together with
haemorrhage and a serous detachment of
the macula. Vision was markedly reduced
circumferential patches), from a prominent
vitreous base and mild vitreous traction, is
more frequently seen in myopic eyes and
occasionally retinal breaks can occur in the
presence of such lesions 9,16 .
It has been estimated that potentially up to
80% of eyes suffering retinal detachment have
some degree of myopia. Also, a person with
five dioptres of myopia is at a 15 times greater
risk of developing retinal detachment than an
emmetrope. With 20 dioptres of myopia, the
risk increases to 110 times 7 . There are also
reports of retinal detachments in myopes
following clear lens extraction procedures used
to refractively correct the myopia 24 .
MANAGEMENT
Myopic patients, especially those with
pathological myopia, must be reviewed
regularly, preferably on an annual basis, and
always through dilated pupils. They should
receive appropriate warnings of signs
and symptoms that may indicate a
sight-threatening situation is developing,
and be advised to utilise protective eyewear in
Figure 7
Chorioretinal atrophy: larger geographic
areas involving the posterior pole
34
March 22, 2002 OT
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potentially hazardous circumstances. Patients
at risk for subretinal neovascular membrane
formation should be given a take-home Amsler
grid for daily testing. The increased incidence
of associated conditions, such as glaucoma,
must be remembered.
About the authors
Peter Swann is Associate Professor and
Katrina Schmid Senior Lecturer in the School
of Optometry, Queensland University of
Technology, Brisbane, Australia. Professor
Swann has a particular interest in eye disease,
and Dr Schmid in the aetiology of myopia.
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Table 1 Summary of potential ocular fundus changes in high myopia
FUNDUS CHANGE LOCATION AETIOLOGY PREVALENCE
EFFECT ON VISION
MAY LEAD TO
Optic disc
crescent
Posterior pole
Biomechanical
Observed in most myopes,
100% of eyes with axial length
≥28.5mm 11
None, unless other pathology
also present
----
Posterior
staphyloma
Posterior pole
Biomechanical
Observed in 76% of myopes,
-3 to -38D 16
Can be progressive and result
in vision loss
Choroidal neovascular
membranes
Lacquer cracks
Posterior pole
Biomechanical
Observed in 4% of high
myopes >6D 19
Guarded prognosis for vision
Choroidal neovascular
membranes
Chorioretinal
atrophy
Posterior pole
Degenerative
Observed more commonly in
younger high myopes, 23% of
myopic eyes with axial length
>24.5mm 11
Guarded prognosis for vision
if at the macula
Associated with posterior
staphylomas, lacquer cracks
Fuchs’ spot
Macula
Neovascular
Observed in 5-10% of eyes
with axial length ≥26.5mm 11
Guarded prognosis for vision
Associated with posterior
staphylomas, lacquer cracks
Lattice
degeneration
Periphery
Degenerative
Observed in 13-30% of
myopes 23,25
None, unless secondary
pathology occurs
Retinal detachment
Pigmentary
degeneration
Periphery
Degenerative
Observed in 17% of myopes 25
None
----
Paving stone
degeneration
Periphery
Degenerative
Observed in 27% of myopes 25
None
----
White without
pressure
Periphery
Biomechanical
Observed in 23% of myopes 25
None, unless secondary
pathology occurs
Occasionally retinal tears
Prevalence values should only be used as an indication of how common these changes are in the myopic eye.
Reported prevalence values vary greatly between studies, due to differences in the age of subjects and severity of the myopia.
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