Cataract:
Demands and fresh insights
As the leading global cause of avoidable visual impairment
loss of sight from cataract remains a major and unresolved
world health problem 1. In this
issue of CE Optometry a number of key issues in relation to
cataract are discussed. The scale of the problem is vast.
Developed nations vary in their ability to cope with the demand
for surgical services and developing nations grapple with
huge backlogs of cataract blindness. Many individuals in under
privileged societies spend the final years of their lives
blind for want of a surgical procedure which takes less than
half an hour to deliver. Current projections based on expected
demographic shifts towards increased longevity suggest that
the problem of unmet need for cataract services will steadily
increase. By the year 2020, the number of blind people is
likely to have increased from the present 50M to 75M, with
35M or 45% of these blind from bilateral unoperated cataract.
In addition there are expected to be at least 3 times this
number of people with severe visual impairment due to cataract
(Johnson, this issue).
There are many challenges in relation to cataract. These
vary with time and place, and historical perspectives help
to shed light on successes and failures (Munton, this issue).
Broadly, the issues fall into two areas: service provision
for established disease; and research to aid understanding
of the causes of cataract with a view to development of non-surgical
interventions and /or risk modification strategies. Defining
the size of the surgical problem is a complex task (Minassian
& Reidy, this issue). Ideally this should be based on
assessments which include a self reported perception of a
visual problem, impaired quality of life related to vision,
willingness to undergo surgery, impaired visual function,
as judged by reduced corrected visual acuity and possibly
contrast sensitivity, cataract morphology (Pesudovs &
Elliott, this issue), and consideration of ocular and systemic
co-morbidity2. Cross sectional
prevalence surveys can be used to provide ‘snap-shot’ estimates
of current unmet need, although attempts at defining population
needs for surgery by means of age structured models of survey
data are fraught with inaccuracies. Cohort studies of incident
disease through time are costly and difficult to perform,
but would provide more secure information upon which to base
plans for service delivery. In resource restricted health
care environments, overt discussion of rationing would be
helpful if based on principles of equity, backed by randomised
trials of surgical intervention at various thresholds of pre-operative
morbidity. Such decision making algorithms would need to include
subgroups with ocular co-morbidity as the prevalence of conditions
such as age related maculopathy and glaucoma in cataract populations
is high. Over simplification, such as denial of second eye
surgery following successful first eye surgery fails to address
some of the main issues3 and
the current UK policy guidance offered in the ‘Action on Cataract’
statement4 acknowledges the
need for routine second eye cataract surgery where clinically
indicated. High volume surgery for routine operations is becoming
established with many surgeons now performing >8 operations
during an operating session. The development of multi-professional
integrated care pathways standardise and streamline processes
and facilitate audit and quality control at each stage of
the care delivery system. Thus, routine pre-operative and
post-operative assessments may be performed by non-medically
qualified team members such as nurses and optometrists (Green,
this issue) with no loss of quality of care. Technological
advances have resulted in the widespread uptake of phako-emulsification
surgery (Lavin, this issue) and improvements in IOL materials
and design offer opportunities for decreasing the rate of
posterior capsular opacification and the consequent need for
laser capsulotomy (Percival, this issue). In the developing
nations the challenges faced are far more extreme, with real
issues of long term blindness and high rates of unsuccessful
surgery. Barriers to access are both cultural and resource
based, and include fear of surgery, low expectations, inability
to travel, lack of surgical infrastructure, and a lack of
adequate numbers of trained health care providers, including
surgeons. Manufacture of cheap but safe IOLs should offer
some hope for improved surgery in impoverished societies.
Efforts to identify modifiable causes of cataract have had
limited success. Aetiological epidemiology has probed risk
factors in many populations and a number of risks have emerged
as relevant to cataract development5.
Demographic risk factors are dominated by the effect of increased
age, with females carrying a slightly higher risk than males.
As with many other medical conditions, smoking, excessive
intake of alcohol and lower socio-economic status are associated
with increased risk. Environmental exposure to UV-B appears
to carry a higher risk for cortical cataract, which is also
commoner among people of African origin. Cataract is associated
with various general health problems, including diabetes,
systemic hypertension, and the use of certain drugs, for example
steroids. Nutrition has been implicated and anti-oxidant vitamins
may be protective. To date no intervention studies have demonstrated
a clear benefit from the use of anti-cataract medications,
although the temptation to pursue this approach is strong,
because an intervention with even a moderate delaying effect
on cataract progression could significantly decrease the need
for cataract surgery in older populations. Recent results
from twin studies indicate that there is a strong genetic
component for the development of both nuclear and cortical
cataract 6,7. Approaches directed
towards risk modification by manipulation of environmental
and lifestyle exposures may now need to be modified and possibly
restricted to individuals with a family history of cataract.
The dream of genetic manipulation of the lens and its environment,
if ever realised, remains far in the future.
With many health care systems struggling to provide adequately for the needs of those afflicted by cataract, pragmatism demands that current efforts focus upon issues of surgical provision. Individual patients, will in the future, judge health care provision on the quality of their sight following the onset of cataract. Those who suffer the personal tragedy of severe loss of sight from untreated cataract will continue to bear testament to failure.
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1. Thylefors B, Negrel A-D, Pararajasegaram R, Dadzie KY. Available data on Blindness. WHO programme for the prevention of blindness. Geneva: World Health Organization; 1995.
2. Frost NA, Hopper CD, Frankel SJ, Peters TJ, Durant JS, Sparrow JM. The population requirement for cataract extraction: a cross sectional study. In Press: Eye.
3. Laidlaw DAH, Harrad RA, Hopper CD, Whitaker A, Donovan JL, Brookes ST, Marsh GW, Peters TJ, Sparrow JM, Frankel SJ. Randomised trial of the effectiveness of second eye cataract surgery. Lancet 1998; 352:925-929.
4. NHS Executive. Action on Cataract, good practice guidance. Department of Health, Feb 2000.
5. West SK, Valmadrid CT. Epidemiology of rsk factors for age related cataract. Surv Ophthalmol 1995; 39,323-334.
6. Hammond CJ, Snieder H, Spector TD, Gilbert CE. Genetic and environmental factors in age-related nuclear cataracts in monozygotic and dizygotic twins. N Engl J Med. 2000;342:1786-1790.
7. Hammond CJ, Duncan DD, Snieder H, de Lange ME, West SK, Spector TD, Gilbert CE. The heritability of age-related cortical cataract: the twin eye study. Invest Ophthalmol Vis Sci. 2001;42:601-605.
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