Transcript The Impact of Cataract Surgery on Patients with Low Vision

The Impact of Cataract Surgery
in Patients with Low Vision
Irene C. Kuo, MD
Clinical Research Methods
July 23, 2010
Background
• Cataract extraction with intraocular lens
implantation
– 1.7 million cases done in
Medicare beneficiaries
per annum
Background
• Definition of low vision
– ≤ 20/70 and not correctable
– 14 million Americans
– Age-related macular degeneration,
diabetic retinopathy, glaucoma,
cerebrovascular accident, albinism
Background
• Aging of population
– Increase of ≥ 5 million Americans ≥ 85 years
in next 25 years
– Age-related macular degeneration and
glaucoma
• Two leading causes of low vision/blindness
• Prevalence increases with age
Background
• Few publications on benefits of cataract extraction in
those with underlying low vision
– Patients may be dissuaded from surgery
• ocular comorbidity
• lengthier evaluation and counseling by surgeon
• Controversy over association between cataract
surgery and age-related macular degeneration
– Cataract extraction may accelerate macular degeneration
– Different study designs; may not be causal
Preliminary Data
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Uncontrolled study in Wilmer clinic of
prospectively collected data from one surgeon
30 eyes of 20 patients with low vision
Mean change in visual acuity was improvement
of 0.25 ± 0.26 (SD) logMAR* units (95% CI of
the mean change, 0.15 to 0.35 logMAR units; two-tailed
p=0.00001)
*LogMAR = log (Snellen visual acuity)
Hypothesis
• Patients with low vision experience a mean
improvement in visual acuity of 0.25
logMAR units or greater after cataract
surgery compared to patients who do not
have surgery.
Study population
• Consecutive patients in Low Vision Clinic
at Wilmer undergoing evaluation for
cataract surgery will be approached to
participate.
Methods
• Randomized controlled trial
– Patients will be randomized to have surgery at time 0
(surgical intervention) or 3 months later (delayed
surgery)
– 3-month delay in surgery is acceptable, feasible, ethical
– Only one eye per patient will be studied
• Baseline and 3-month visual acuity in logMAR units (log
Snellen visual acuity) will be measured by staff masked to
presence or absence of surgical intervention.
• Compare mean change in visual acuity between the
intervention groups
Sample size calculation
n = 2 [(zα - z β ) σ / μ1 – μ2]2
zα= 1.96
α = 0.05, β=0.2
zβ= -0.84
σ = 0.26 logMAR
-> n = 17 patients per group
Sample size calculation
• Stratify patients by 4 major etiologies of
low vision:
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age-related macular degeneration
glaucoma
diabetic retinopathy
cerebrovascular accident
 4 x 17 patients = 68 patients per group
136 patients total
Data analysis
• Stratification of patients by etiology of low vision
– Two-sample t-test to compare mean change in log
MAR between two intervention groups in each stratum
or general linear models to examine differences in mean
change for all patients but controlling for etiology
– Which patients benefit the most from surgery?
• Other outcome measures
• Activities of daily living (questionnaire)
• Contrast sensitivity
• Ability to use low vision aids
Discussion
• Natural progression of underlying disease
• Alternative study design
– Randomize each patient by eye (one eye has
surgery, the other does not)
– However, activities of daily living are measured
at patient (not eye) level.
Significance
• Cataract surgery is highest volume
Medicare procedure
• Aging population with increasing number of
persons with low vision and cataracts
• Benefit of cataract extraction in such
patients is unknown
Acknowledgements
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Shabina Ahmed, MD
Kathryn Carson, ScM
Charles Flexner, MD
Judit Gordon, MD
Aaron Horne, MD, MBA
Ikue Nakayama, MD
Mary Katherine Nutini, DO
Dan Ford, MD, MPH