Ophthalmic Epidemiology A brief introduction

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					Ophthalmic Epidemiology:
     A Clouded Vision
          April 10, 2000
 Michael B. Gorin, M.D. Ph.D.
      gorinmb@msx.upmc.edu
     Objectives of ophthalmic
          epidemiology
• Establish the incidence and prevalence of
  eye disorders that cause vision impairment
  and/or blindness
• Determine the societal impact (social and
  economic) of vision loss
• Assess the potential and real impact of
  preventive and treatment efforts for eye
  problems
         Causes of Worldwide Blindness
•   Cataract                                  17 million
•   Trachoma                                  6.0 million
•   Glaucoma                                  3.0 million
•   Xerophthalmia                             0.5 million
•   Onchocerciasis                            0.5 million
•   AMD                                       1.0 million
•   Diabetic retinopathy                      0.25 million
•   Leprosy                                   0.25 million
•   Others                                    2.5 million
     – 85% of blindness is in Africa and Asia
     – 85% of cases are potentially treatable or preventable
• Prevalence:
     – 0.125-0.25% in Western world
     – 0.2-1.5% (av 0.75%) in Asia
     – 0.3-3.1% (av 1.2%) in Africa
                  Allen Foster in Clinical Ophthalmology - Duane, ed. (1991)
              Aging and Blindness
• Prevalence (in Germany) :
   – 15 % lose sight < 20 years old
   – 51% lose sight >50 and <80
   – 15 % lose sight > 80 years old
• Incidence:
   – 50% of new cases are people over 80
• “Imbalance” due to differences in life expectancy and
  duration of blindness.
   – Blind < 10 years - 74%
   – Blind >10 years - 26%
   – Blind > 20 years - 10%
             What is vision?
• Central visual
  acuity
  – Uncorrected and
    corrected
  – Refractive error
    (definition of
    myopia)
  – The Snellen chart
    and the ETDRS
    chart
What is vision?
 • Contrast
   sensitivity
   – Pelli Robison
     chart
   – grating systems
              What is vision?
• Peripheral vision
   – Visual Fields
      • Kinetic and
        static




                          • Manual versus
                          automated
             What is vision?
• Color vision
  – Color plates,
    color chips,
    anomaloscopes



• Adaptation
  – Light recovery
    from bleach
  – Adaptometry
           What is vision?

• Other measures of visual function
  – Electrophysiology
  – Ocular movements
  – Visual function questionnaires - VF-14
     • Initially validated for cataracts
     • more extensive use in all eye studies
  What is the definition of blindness?
• 20/10 - 20/25: Normal
• 20/30 - 20/60: Near-normal
• 20/70 - 20/160 : Moderate vision impairment - eligible for
  education assistance in US
• 20/200 - 20/400: Severe vision impairment - legal
  blindness in US (visual field < 20 degrees)
• 20/500 - 20/1000: profound vision impairment - WHO and
  several European countries definition of blindness (visual
  field < 10 degrees), CF < 3m
• < 20/1000: Near-total visual impairment: used by some
  developing countries as definition of blindness (visual field
  < 5 degrees), HM, LP
• NLP: Total visual impairment
           Ocular pathology
• Clinical examination:
   – Slit lamp biomicroscopy
   – Ophthalmoscopy (fundus examination)
                    Ocular pathology
Grading systems:
   – Ocular dryness
      (use of vital dyes, rose bengal and lissamine green) -
      comparison with standard photos (CSP).
  – Conjunctival scarring -
    CSP

  – Cataracts - LOCS III
    (CSP)

  – Optic nerve- optic
    nerve cupping, CSP
  – Retina - disease-
    specific (ie ARM,
    diabetes)
    Documentation of ocular pathology
• Ratings by
  clinicians tend to be
  poorly standardized
  and inconsistent.

• Major emphasis in
  recent years has
  been on
  photodocumentatio
  n and the use of
  Reading Centers to      • The general level of photographic
  grade pathology           quality in the medical community is
                            low. For research studies, extensive
                            training and certification of
                            photographers is required.
    Documentation of ocular pathology
• Reading Centers have been very effective in studies of
  diabetic retinopathy. (subjects diagnosed prior to entry)
• Reliability of graders for large numbers of patients with
  mixed (and unspecified) disorders is unknown.
     Specific issues in eye research
•   Is one assessing the subject or the eye?
•   Relatedness between eyes of a single individual
•   Research design with bilateral and monocular cases
•   Use of the contralateral eye as a control
•   Masking of the subject and observer

• Is one comparing the same definition of the disease among
  studies? (ie AMD, myopia, glaucoma)
• Diagnostic reliability, sample bias
• 10% of cases have vision loss from 2 different conditions,
  though studies often only cite the cause of the second eye.
           Causes of vision loss
• Trauma
   – Recreational, work-related, military
• Systemic Disease
   – Diabetes, vascular disease, hypertension
• Aging/Eye Specific
   – Cataracts, age-related maculopathy, glaucoma
• Infectious
   – Trachoma, onchocerciasis, immunocompromised individuals
• Congenital/Hereditary -
   – Cataracts, malformations, glaucoma, retinal degenerations
• Nutritional and Toxic
   – Vitamin A deficiency, methanol
• Tumors
   – Metastatic, primary malignancies (children / adults)
 Infectious causes of vision loss
• Trachoma
  – Affects 500 million
  – Estimated 6 million are blind

• Onchocerciasis
  – Endemic across equatorial Africa (99%), some areas of South and
    Central America
  – 80 million exposed, 18 million infected, 2 million blind
  – Transmitted by blackfly - filial nematode
  – Treatment - vector control, ivermectin (annual dose for a minimum
    of 10 years)

• Other ID: leprosy, syphillis
  – Estimated 10-12 million cases of leprosy
  – WHO estimated that 250,000 blind from disease
Leading causes of blindness
   in Western societies

Age-related macular
 degeneration
• (aka: AMD, ARM, SMD)
• Dry versus Wet
• Atrophic versus Exudative
  (CNVM)
• Most common cause of
  blindness
• Majority of cases are “dry”
  form (>80%), however 88%
  of those registered as legally
  blind (in Germany) from
  AMD had exudative disease.
Age-related macular degeneration (AMD)
   – AMD defined as macular changes and <20/30
   – ARM - no vision impairment
   Prevalence (%)
  Age range   AMD#     ARM# Blindness due to AMD*
  60 - 64      2.3     12.3              0.007
  65 - 69      5.9     18.0              0.012
  70 - 74     12.1     17.0              0.057
  75 - 80     27.3     17.8              0.115

                       # Vinding (1989) - Denmark
                       * Krumpasky et al (1996) - Germany
Age-related macular degeneration (AMD)
• Risk factors:
  – Smoking 2.5 fold increased risk
  – positive family history
  – Others - sex, diet, eye color, hypertension,
    cardiovascular disease are controversial
• Unilateral CNVM - risk to other eye:
  – Incidence of 12-15% per year for 60-69 year
    olds
Age-related macular degeneration (AMD)
 • Success of laser treatment
   – Vision 2 years after randomization to treatment
     or observation (subfoveal lesions)

      Deterioration in vision   Treated          Observed
      < 2 lines                 33%              18%
      2-3 lines                 23%              17%
      4-5 lines                 24%              28%
      > 6 lines                 20%              37%
                                          MPS 1991
Age-related macular degeneration (AMD)
• Success of laser treatment
   – Vision 2 years after randomization to treatment
     or observation (extrafoveal lesions)

      Deterioration in vision   Treated          Observed
      Unchanged, improved       57%              28%
      Decreased 2-5 lines       28%              27%
      Decreased 6-9 lines        6%              27%
      Decreased > 10 lines       6%              18%

                                          MPS 1982
Leading causes of blindness in Western societies

• Glaucoma
  – Loss of vision due to progressive optic nerve
    damage often (but not always) associated with
    increased intraocular pressure
  – Varying definitions - IOP, Visual fields, cupping
  – Different types of glaucoma
     •   Congenital
     •   Open- angle
     •   Narrow-angle
     •   Syndromic
• Glaucoma
  – Glaucoma affects 1.5-2.0% of population over the age
    of 40. Rises with age up to 8% for those over 80
  – Current prevalence is 15% of all cases of blindness
    (developed nations)
  – Age of onset of blindness from glaucoma
     • >60 years : 79%
  – Those under 65 years old
     • Glaucoma-related blindness associated with other
       conditions - 36%
  – Those greater than 65 years old
     • Glaucoma-related blindness associated with other
       conditions - 46%
 Leading causes of blindness in Western societies

• Diabetic retinopathy
  – Women greater than men:
     • 56% of the younger blind diabetic individuals
     • 87% of the older blind diabetic individuals
  – In those under the age of 65, diabetes is the
    most common cause of blindness
  – However, 2/3 of diabetics do not become blind
    until after the age of 60
  – Blindness from DR is a poor prognosis for
    survival
• Diabetes mellitus
  – IDDM: 0.5-1.0%
  – NIDDM: large variations among countries and
    ethnic groups 0.7-3.0%
  – Prevalence (%) of vision impairment among
    diabetics - (Klein et al 1984)
     Vision         Young Onset         Older Onset
     20/40 - 20/63        3.3                  7.3
     20/80 - 20/160       1.4                  3.0
     below 20/200         3.6                  1.6
  – Diabetic retinopathy:
     • Nonproliferative           Proliferative
     • Macular edema              Ischemic maculopathy
       Nonproliferative Diabetic Retinopathy




Proliferative Diabetic
Retinopathy
• Diabetes mellitus
  – Visual impairment in IDDM and NIDM
     Age range (yrs)       % of patients
                       Unilateral     Bilateral    Blindness
                          visual impairment
     IDDM
            <50            5.4           0.9         3.6
            >50           18.2           8.7        12.2
     NIDM
            <70            7.7           2.8         2.1
            >70           20.8          17.1         7.3

                                    Nielson 1982 (Denmark)
• Diabetes mellitus
  – Cumulative events of vision loss in DRS study
    after laser treatment
     Follow-up   Cumulative rate of events (%)
     (months)     Control group        Treated group
       12               3.4                   1.8
       24              13.6                   6.6
       48              27.4                  12.6
       60              32.1                  15.2
       72              34.2                  17.5
                               DRS 1981
 Leading causes of blindness in Western societies

• Cataract
     • Congenital - major cause of infantile blindness
     • Secondary to or associated with other disorders
     • Age-related
  – Age at onset of blindness from cataract
     • Age 70 and greater : 70-85% of cases
  – Risk factors
     • Age, poor education, myopia, hypertension,
       diabetes, glaucoma, smoking, beer drinking, certain
       drugs, low vital capacity, severe diarrhea, kidney
       failure

				
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