Ophthalmic Epidemiology: a clouded Vision April 10, 2000


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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


What is vision?

  • Color vision

  • Adaptation

    • Light recovery from bleach
    • Adaptometry


What is vision?

  • Other measures of visual function

    • Electrophysiology
    • Ocular movements
    • Visual function questionnaires - VF-14


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

    • 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 photodocumentation and the use of Reading Centers to grade pathology



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

  • Aging/Eye Specific

    • Cataracts, age-related maculopathy, glaucoma
  • Infectious

  • Congenital/Hereditary -

    • Cataracts, malformations, glaucoma, retinal degenerations
  • Nutritional and Toxic

  • 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



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




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%















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