J R Soc Med 2003;96:277-279
doi:10.1258/jrsm.96.6.277
© 2003 Royal Society of Medicine
Laser management of diabetic retinopathy
Jonathan G F Dowler MD FRCOphth
Medical Retinal Service, Moorfields Eye Hospital, City Road, London EC1V
2PD, UK
E-mail:
j.dowler{at}btclick.com
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INTRODUCTION
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The UK National Service Framework for Diabetes recommends nationwide
screening
of people with diabetes for development of sight-threatening
retinopathy.
1 All
health workers who provide diabetes care require an understanding
of the
common ophthalmic treatments that can be offered for
such disease. The
principal conditions to consider are
diabetic maculopathy and
proliferative retinopathy.
In diabetic maculopathy, central vision may be compromised by macular
(central retinal) oedema with varying degrees of ischaemia. The oedema may
respond to laser therapy, ischaemia does not. Therapy takes the form of
‘focal’ (Figure 1)
or ‘grid’ (Figure
2) macular laser, consisting of up to 200 small (e.g. 100 µm)
gently applied burns to areas of central retinal thickening. This tends to
encourage resolution of thickening.
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Figure 1. Focal macular laser therapy for focal macular oedema. Fluorescein
angiography reveals focal leakage from diabetic microvascular abnormalities
(white arrow). Laser burns (white spots) are placed on the area of thickened
retina. Colour version available on
[www.jrsm.org]
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Figure 2. Grid macular laser therapy for diffuse macular oedema. Fluorescein
angiography reveals diffuse leakage from diabetic microvascular abnormalities
(white arrows). Laser burns (spots) are placed on the area of thickened
retina. Colour version available on
[www.jrsm.org]
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In proliferative retinopathy, central and peripheral vision may be
compromised by bleeding from new vessels arising on the optic disc (NVD) or
elsewhere in the retina (NVE). These vessels typically bleed because of the
tendency of the overlying vitreous gel, to which the new vessels are attached,
to retract, stretching vessels between vitreous and retina. Therapy takes the
form of panretinal photocoagulation, in which perhaps 2000 large (e.g. 500
µm) burns, of greater intensity than employed in macular laser, are applied
to retina outside the central thirty-degree zones (Figure
3a3b).
This tends to encourage a reduction in the calibre of new vessels.
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Figure 3a. Panretinal photocoagulation for proliferative retinopathy. Laser
burns (spots) are placed outside central retina (a) as can be seen in
the fluorescein angiogram
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Figure 3b. Panretinal photocoagulation for proliferative retinopathy. Laser
burns (spots) are placed outside central retina (b). Colour version
available on
[www.jrsm.org]
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MACULAR LASER THERAPY
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Technique
Treatment is an outpatient procedure; admission to hospital
is not
required. The patient sits at a slit lamp similar to
that used in routine
ophthalmic examination but modified to
accept a laser fibreoptic cable
(
Figure 4). Proxymetacaine or
benoxinate
drops are used to anaesthetize the cornea and a therapeutic
contact
lens is applied. As treatment is started, the patient
experiences bright
flashes of light but no pain. The eye must
be kept as still as possible during
treatment to ensure accurate
application of the laser and to avoid damage to
the fovea; a
typical treatment takes about ten minutes. Therefore the patient
needs
some means of communicating with the ophthalmologist so that
the
treatment can be safely interrupted. The usual signal is
a raised hand or a
noise in the throat; if the patient speaks,
jaw movement may displace the
laser beam. Commonly the patient
is very dazzled after the treatment, and
sometimes the laser
spots are visible to the patient. Typically though not
invariably,
this effect fades over the next few days. No special precautions
need
to be taken after the laser, and no additional eye drops or
oral therapy
are needed.
Side-effects
Some reduction in colour vision or small dark spots near the central vision
are quite commonly perceived by the patient after treatment. If the patient
looks directly at the laser beam during treatment, the fovea can be damaged,
with potential for severe visual loss, especially if laser power is at any but
a very low setting. This is a rare occurrence. Another rare but serious
complication results from application of high power levels over a small area
(high fluence), which can rupture Bruch's membrane, which separates choroid
from retina. Acutely, this can cause haemorrhage; later, vascular ingrowth can
result in macular scarring similar to that in age-related macular
degeneration, with loss of central vision.
Effects of treatment
In the Early Treatment Diabetic Retinopathy
Study,2 macular
laser therapy for clinically significant macular oedema approximately halved
the rate of moderate visual loss, defined as doubling of the visual angle, and
equating to a change from 6/6 to 6/12 or from 6/12 to 6/24. A modest
improvement (one line on the Snellen visual acuity chart) was seen in 40% of
treated and 20% of untreated eyes. The number needed to treat to prevent one
case of moderate visual loss over 3 years is 8.
The principal effect of macular laser therapy is to reduce the rate of
visual loss. Patients should be encouraged to hope for stabilization of vision
and not to expect visual improvement. Once visual loss occurs, it is unlikely
to be reversed. Furthermore, laser treatment does not invariably prevent
visual loss. In some patients, oedema persists despite adequate initial
treatment to the oedematous area; in others, oedema arises in new areas. In
these patients, further laser therapy may be required. Eyes with significant
macular ischaemia in association with macular oedema may continue to show
visual deterioration despite resolution of oedema. Treatment can take several
months to work, and vision may vary during this period. Commonly, as oedema
resolves, lipoprotein exudate is deposited in the retina, to be removed
ultimately by macrophages.
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PANRETINAL LASER THERAPY
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Technique
This treatment is likewise usually undertaken in outpatients,
although
admission to hospital may be required in the few patients
unable to cooperate
with slit-lamp-delivered laser. In the latter
group laser is applied under
subtenons local anaesthesia or
general anaesthesia, through a binocular
indirect ophthalmoscope,
with the ophthalmologist standing and the patient
supine. The
arrangement for outpatient treatment is similar to that for
macular
laser therapy, although a wide angle contact lens may be required
to
reach peripheral retina. Treatment consists of a greater
number of larger,
more intense burns, more rapidly applied than
in macular laser therapy. This
may cause sharp but transient
pain, especially if laser is applied over a
nerve or over an
old laser burn. For this reason it is particularly important
that
the patient has some means of communicating with the ophthalmologist,
so
that treatment can be safely interrupted until the pain fades.
The eye must be
kept as still as possible during treatment to
ensure accurate application of
the laser. A typical treatment
takes about thirty minutes. Commonly the
patient is so dazzled
immediately after treatment that he or she cannot see at
all
from the treated eye. This tends to fade over the next few days
to weeks.
No special precautions need be taken after laser treatment,
but oral
nonsteroidal anti-inflammatory agents such as ibuprofen
or flurbiprofen are
valuable in lessening the dull ache that
can follow treatment.
Side-effects
Macular oedema is a material side-effect of treatment, and may be
sufficiently severe to reduce visual acuity. It is particularly troublesome in
eyes with proliferative retinopathy and pre-existing macular oedema;
panretinal photocoagulation may then need to be fractionated over several
visits to minimize worsening of macular oedema. The application of laser to
peripheral retina also tends to impair peripheral retinal function, and
patients may suffer glare and light sensitivity. In addition, visual field may
be compromised, in some patients to the extent that they are rendered
ineligible to drive. Patient movement or misplaced burns may damage retinal
blood vessels.
Effects of treatment
In the Diabetic Retinopathy
Study,3 panretinal
photo-coagulation for high-risk proliferative retinopathy approximately halved
the risk of severe visual loss, defined as the inability to see the top letter
on a Snellen chart from 1.56 m. Depending on the pattern of proliferative
retinopathy, the number needed to treat to prevent one case of severe visual
loss over 2 years is between 3 and 7.
As with macular laser therapy, the principal effect of panretinal
photocoagulation is to reduce the rate of visual loss. Again, patients should
not expect visual improvement but hope for stabilization of vision. They
should be advised that, once visual loss occurs, it is unlikely to be
reversed. Growth of new vessels, visual loss and haemorrhage into the vitreous
cavity may occur despite well applied treatment. In these patients, further
laser therapy may be required, although this may be hampered or prevented by
vitreous haemorrhage. Even if the calibre of new vessels is considerably
reduced, contraction of the vitreous gel may result in recurrent haemorrhage.
If haemorrhage is persistent, preventing laser therapy, or if contraction of
the vitreous gel, acting through new vessel stalks, has detached the retina,
vitrectomy surgery, involving removal of the vitreous gel, may be required to
clear haemorrhage, apply panretinal photocoagulation, or reattach retina.
Panretinal photocoagulation typically takes several months to achieve full
effect, although some response can often be seen much sooner. The number of
burns required to achieve regression of new vessels varies considerably. In
patients with type 1 diabetes and very aggressive disease, many thousands of
burns and several sessions of treatment may be required. In patients with type
2 diabetes and less aggressive disease, a thousand burns may suffice.
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CONCLUSION
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Common laser treatments applied to patients with sight-threatening
forms of
diabetic retinopathy are effective in preventing but
not reversing visual
loss. It is therefore imperative that patients
with sight-threatening disease
are referred before visual loss
occurs. This requires an effective retinopathy
risk reduction
programme and referral chain.
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REFERENCES
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- Department of Health. National Service Framework for Diabetes.
[http://www.doh.gov.uk/nsf/diabetes/].
Accessed 26 March 2003
- Early Treatment Diabetic Retinopathy Study Research Group.
Photocoagulation for diabetic macular edema. Early Treatment Diabetic
Retinopathy Study report number 1. Arch Ophthalmol1985; 103:1796
-806[Abstract/Free Full Text]
- Diabetic Retinopathy Study Research Group. Photocoagulation
treatment of proliferative diabetic retinopathy. Clinical application of
Diabetic Retinopathy Study (DRS) findings, DRS Report Number 8.
Ophthalmology1981; 88:583
-600[Medline]
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INTRODUCTION
MACULAR LASER THERAPY
