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Factors that influence the natural history of diabetic retinopathy
can be subdivided into:
External
factors
Alcohol consumption
The effect of alcohol consumption on the development of diabetic
retinopathy is still controversial. Some studies have found
a deleterious effect of drinking on diabetic retinopathy,
[Young
et al, 1984] whereas others have found that there may
be a protective effect of drinking, particularly in younger
patients. [Moss
et al, 1992]. These contradictory findings may be explained
by the different drinking habits and types of alcohol consumed
by the patients studied.
Cigarette smoking
Since cigarette smoking increases the risk of albuminuria,
[Chase
et al, 1992] it is therefore likely to cause microvascular
changes in the retina. However, the United Kingdom Prospective
Diabetes Study (UKPDS) found that current smokers actually
had a reduced incidence of retinopathy, as well as a reduced
risk of progression of retinopathy, compared with subjects
who had never smoked. [Stratton
et al, 2001]
Contraceptive pill
A greater advancement of diabetic retinopathy has been
observed in women taking the high-dose progesterone pill.
[Hamilton
et al, 1996]. It has also been reported that stopping
the pill results in the progression of retinopathy being halted.
[Hamilton
et al, 1996]
Aspirin
The Early Treatment Diabetic Retinopathy Study (ETDRS)
investigated the effect of aspirin on the development of or
advancement of existing diabetic retinopathy, and concluded
that aspirin does not confer any benefit. [ETDRS
Research Group, 1991]
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Internal
factors
Glycemic control
As mentioned above, the most important factor associated
with the development of diabetic retinopathy is control of
blood glucose. Recent studies such as the Diabetes Control
and Complications Trial (DCCT) in people with Type 1 diabetes,
[The DCCT Research Group, 1993]
and the UKPDS in people with Type 2 diabetes [UKPDS
Group, 1998] showed that tighter control of blood glucose
significantly reduced the risk of developing diabetic retinopathy.
Progression of existing retinopathy can also be reduced with
better control of blood glucose levels, and the effects of
good control are long-lasting. [The
Diabetes Control and Complications Trial/Epidemiology of Diabetes
Interventions and Complications Research Group, 2000]
Hypertension
Hypertension is commonly associated with Type 2 diabetes
and is another important risk factor for the development of
diabetic retinopathy. [UKPDS Group, 1998] The severity of retinopathy
is associated with both higher systolic and diastolic blood
pressure. Tight blood pressure control can reduce the risk
of its progression. [UKPDS
Group, 1998]
Lipids
Elevated total serum cholesterol, LDL-cholesterol and
triglycerides are also associated with an increased risk of
fat and protein deposits (hard exudates) in the retina, which
is associated with a decrease in visual acuity. [Chew
et al, 1996]
Diabetic Nephropathy
Proteinuria due to renal disease aggravates diabetic retinopathy
and macular edema. [Klein
et al, 1987] This association is independent of the duration
of diabetes or hypertension.
Pregnancy
Diabetic retinopathy is more likely to progress in pregnant
women, especially those with arterial hypertension. [Klein
et al, 1990]
Pituitary abnormalities
Evidence for endocrinologic effects on the formation
of diabetic retinopathy arises from the observation that diabetic
individuals with pituitary abnormalities rarely have the condition.
[Hamilton
et al, 1996] Prior to the advent of laser photocoagulation,
high-risk proliferative diabetic retinopathy could only be
controlled by pituitary ablation.
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Ocular
factors
High myopia with choroidal degeneration,
advanced glaucoma, choroidal atrophy
These condtions all protect against diabetic retinopathy,
probably in the same way as panretinal photocoagulation, by
reducing the metabolic needs of the retina. [Jain
et al, 1965]
Posterior vitreous detachment
Posterior vitreous detachment resulting from vitrectomy
may prevent the progression of proliferative diabetic retinopathy.
However, new vessels may spread to the posterior face of the
detached vitreous and haemorrhage in the gap between the retina
and the hyaloid. [Akiba
et al, 1990]
Cataract surgery
Removal of cataracts may aggravate existing proliferative
diabetic retinopathy and macular edema. In severe cases, therefore,
the retinopathy should be treated before the removal of the
cataract. [Schatz
et al, 1994]
Iris neovascularisation
Iris neovascularisation is a sign of rapid progression
of proliferative diabetic retinopathy. Patients with this
complication are at risk of losing the eye from secondary
glaucoma. [Hamilton
et al, 1996]
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