Download Tropical Ophthalmology. Part I.

Tropical Ophthalmology.
Part One of Three
Dr. Steve Waller
Uniformed Services
University
of Health Sciences
Bethesda, Maryland, USA
[email protected]
Author
• ophthalmologist and global health
faculty at Uniformed Services
University of the Health Sciences, a
US government school
• US Air Force officer for over 30 years
• taught and performed eye surgery in
16 countries
• dedicated to reducing preventable
blindness throughout the world
Overview of
three lectures
• Tropical Ophthalmology in
three parts: topically divided
• Epidemiology of blindness: cataract (toxoplasmosis)
• Synergy of diseases: vitamin A + measles, trachoma
+ bacterial keratitis, HIV + many diseases
• Disease Control: EKC, oncho
• Environmental: fungal keratitis, pterygium
• Exotics: atypical TB, leprosy, beach apple, loa loa,
tarantula
• Zoonotics: toxocara, myiasis
• Iatrogenic: rabies, acanthamoeba
• Working together for a better world
Epidemiology of Blindness
• Blindness is a tropical disease!
• Poor vision is #3 cause* of disability
worldwide
• Approximately 75% of global blindness
is curable or preventable (US National
Eye Institute, Nov 2006)
• Top worldwide cause is cataract
– India, China, Africa
– Solution is efficient, accessible surgery
* Uncorrected refractive error big issue
Global Distribution of
Blindness by Cause
Other
28 %
Macular degeneration
Diabetic retinopathy
Onchocerciasis
1%
Glaucoma
14%
Trachoma
15 %
Cataract
42 %
State of Global Blindness
80% of
Present estimate:
blindness
– 45 million people blind is preventable
or curable
+
– 135 million visually disabled
< 6/18 - 3/60
Low
Vision
Blind
< 3/60 (or 20/400)
International classification ignores the burden of uncorrected refractive error
Prevalence of Blindness
90%+ live in
lower income
countries
Relationship between blindness
and socio-economic status
Blindness
Poverty
However - the link between prosperity
and health is not automatic -
National cataract surgical rates
and corresponding GDP
30,000
25,000
20,000
15,000

10,000

Real GDP
per capita
($)
5,000
outliers
prove the
case!
0
0
1,000
2,000
3,000
4,000
5,000
6,000
Cataract operations per million population per year
Cataract – ‘the #1 cause’
efficient, accessible surgery =
a huge impact on blindness
Toxoplasmosis
•
•
•
•
Chrorioretinal scars hidden by cataract
Very common in developing world
Significant cause of strabismus (evil eye)
#1 cause (20%) of
reduced vision after
successful cataract
surgery in Central
American country in
our study, 2004
Toxoplasma gondii
• Intracellular protozoan
• Global distribution
• Transmission:
– Direct ingestion of oocyst
• Uncooked meat
• Mucosal inoculation
– Transplacental
• Cats are definitive host,
but infects all mammals
Ocular
Manifestations
• Prominent vitritis
“headlight in the fog”
• Necrotizing
retinochoroiditis
Toxoplasmosis
• Clinical diagnosis with help from ELISA,
Western blot, PCR
• Negative serology argues against
infection, but positive serology does not
prove disease
• Tx: sulfadiazine, pyrimethamine, Septra
(off label), cryotherapy
• Cover sandbox; don’t shake litter box
• Freezing temperatures are not adequate
– cysts survive in sand up to one year
Synergistic Diseases
• Sum is greater than
individual parts
• Etiology often cultural
and economic
• Three examples:
– Vitamin A + measles
– trachoma + bacteria
– HIV + many diseases
Vitamin A deficiency
• a leading cause of preventable
childhood blindness
• associated with other deficiencies
• first symptom - night blindness
• scaly skin, dry eye, prone to ulcer
• prompt response to 200,000 unit
pill x 3
WHO classification
•
•
•
•
•
•
•
•
XN – night blindness (easy to screen)
X1A – conjunctival xerosis
X1B – Bitot’s spot
X2 – corneal xerosis
X3A – keratomalacia and small ulcer
X3B – large ulcer
XS – corneal scar
XF – xerophthalmic fundus
Bitot spot:
early sign,
foamy
appearance
to conjunctiva
progression
of untreated
disease to
blindness
Vitamin A and measles
Vitamin A
deficiency
greatly
enhances
measles
virulence and
lethality
Trachoma
• Chlamydia trachomatis, eye
disease same strains as genital
disease
• Multiple infections, poor hygiene
• Direct contact, children worst
• Passed on hands and by flies
• Upper lid scarring, lashes in-turned
• Soap/water, TCN or erythro ung
• Zithromycin helpful, temporarily
Trachoma epidemiology
• 500 million people infected
• Most common preventable
blindness
• 2 million blind in endemic areas
–North and sub-Sahara Africa
–Middle East
–North India
–Southeast Asia
Infectious
(WHO ‘TF’ stage)
Clinical diagnosis of trachoma
at least two of the following:
–lymphoid follicles on upper tarsal
conjunctiva
–typical conjunctival scarring (Arlt’s
line)
–limbal follicles or
Herbert’s pits
–vascular pannus

Conjunctival
scarring
(Arlt’s line )

Chronic epithelial
defect from
misdirected
lashes
chronic irritation
setup for blinding
bacterial keratitis
Secondary bacterial infection
HIV eye disease
• Most blinding opportunistic
infections are chorio-retinal
– cytomegalovirus (beta Herpes 5) most common
– toxoplasmosis, others
• Kaposi’s sarcoma of conjunctiva
• Corneal microsporidiosis (no photo)
Cotton-wool spots
CMV retinitis
Kaposi’s sarcoma
inner canthus tumor
Kaposi’s
sarcoma
of nose
see lecture
parts two and
three for
more Tropical
Ophthalmology