1. Glaucoma Conference Intraocular pressure and tonometry
R3 정병주/Pf. 박찬기

2. Intraocular pressure

3. Distribution in general populations
Gaussian curve with a skew toward the higher pressures

4. Factors affecting IOP Genetics Environment Physiology Ethnicity
Sex
Age
Ethnicity
Refractive error
Diurnal and postural variation
Exertional influences
Eyelid and eye movement
Intraocular conditions
Systemic conditions

5. Factors affecting IOP Genetics Heredity contributes to IOP
10q22, 5q22, 14q22
Chromosomes 2, 5, 6, 7, 12, 15, and 19
But, no definite “ IOP genes”

6. Factors affecting IOP Environment
Cold air : reduce IOP(decreased episcleral venous pressure)
Reduced gravity : increase IOP(cephalad shifts)
Tobacco smoking : transient increased IOP
: vasoconstriction & increased episcleral venous pressure
: COAG – no evidence
General anesthesia : usually reduce IOP
Cf) Ketamine : not reduce IOP -> EUA 시 주의를 요함
Cf) succinylcholine & suxamethonium : increase IOP -> ruptured globe & intraocular surgery 시 주의를 요함

7. Factors affecting IOP Environment
Systemic medication : potentially affect IOP
: Corticosteroid : potential risk of IOP elevation & steroid-induced glaucoma
: Anticholinergic agent : AACG
Acute dose of alcohol : lower IOP
: combination of suppressed circulating ADH -> direct inhibition of aqueous secretion
: clinically effective? -> no evidance
Caffeine : slight, transient elevation
: no significant , sustained pressure elevation

8. Factors affecting IOP Physiology Sex No major effect on IOP
After menopause, apparent rise in mean IOP among women
Age
In children, Increase with age
In Adult, Gaussian between 20 and 40 yrs, increase with advancing age
Aqueous humor dynamics
: Reduced facility of aqueous outflow and uveoscleral outflow
: Decrease in aqueous production
: Episcleral venous pressure : not change

9. Factors affecting IOP Ethnicity Refractive error
Increased risk for COAG among blacks
Increased risk for AACG among some Asians
Refractive error
In children, no correlation between higher IOP and myopia
In adults, myopia is still a risk factor
: but some studies show no association

10. Factors affecting IOP Diurnal and postural variation
Cyclic fluctuation through the day
: During the day time?
: In the morning?
: Before noon?
Postural variation
: Elevation in the night due to supine position
: head-down tilt position = increased IOP due to elavated episcleral venous pressure
: optic nerve damage 여부가 증명된 것은 아니지만 Yoga, Inversion 과 같은 운동은 glaucoma 환자에서 주의를 요함

11. Factors affecting IOP Diurnal and postural variation
Adrenocortical steroid & catecholamines
Circadian rhythm of aqueous humor dynamics : not related melatonin level
Exertional influences
Straining, electroshock, high-resistance musical instrument
: Elevated episcleral venous pressure
Aerobic exercise : IOP lowering effect
: Maybe related to metabolic acidosis, hypocapnia, lactate

12. Factors affecting IOP Eyelid and eye movement : Elevate IOP
Blinking : 10mmHg
Hard eyelid squeezing : up to 90mmHg
Voluntary eyelid fissure widening : 2mmHg
Contraction of EOM

13. Factors affecting IOP Intraocular conditions
Anterior uveitis without angle abnormality : IOP reduction
: Decreased aqueous humor production
Rhegmatogenous retinal detachment : IOP reduction
: reduced aqueous flow
: shunting of aqueous from the posterior chamber into the subretinal space

14. Factors affecting IOP Systemic conditions Hypertension
: in some epidemiologic studies, positive correlation
: combination of ocular pulse pressure and ocular perfusion pressure
: retinal microvascular abnormality : not associated DM
: unclear
Translaminar pressure gradient across the lamina cribrosa
: relatively lower CSF pressure in COAG patients
Obesity & BMI : not clear

15. Tonometers and Tonometry

16. Classification of tonometers
Contact tonometer
: Deformation of the globe
Indentation tonometers
Applanation tonometers
Variable force
Variable area
Noncontact tonometer

17. Classification of tonometers
Indentation tonometers
Truncated cone
Shape : variable & unpredictable
Conversion table 이 필요함(empirical)
Schiöz tonometer
Applanation tonometers
simple flattening
constant shape
Mathematical calculation
Goldmann tonometer
Maklakoff tonometer

18. Classification of tonometers
Applanation tonometers
: differentiated on the basis of the variable
Variable force
Measures the force to be required to applanate(flatten)
Goldman applanation tonometer
Variable area
Measure the area of the cornea
to be flatten by a known force
Maklakoff tonometer

19. Classification of tonometers
Noncontact tonometer
Use a puff of air to deform the cornea
Measure the time or force to create “a standard amount of corneal deformation”
Grolman

20. Goldmann applanation tonometry
Imbert-Fick law
W=Pt X A
W = external force
Pt= pressure in the sphere
A= area flattened
Perfectly spherical
Dry
Perfectly flexible
Infinitely thin

21. Goldmann applanation tonometry
Modified Imbert-Fick law
W+S=Pt X A1 +B
S = surface tension
(d/t moisiture)
A1 = inner area
( d/t central corneal thickness)
B = a force to bend the cornea
(d/t a lack of flexibility)
- S=B 일 때의 원의 직경 3.06mm
- 이 때 이동되는 안구 용적은
0.50 mm3 의 적은양으로 ocular
ritidity는 큰 영향이 없다.

22. Goldmann applanation tonometry
3.06 mm

23. Goldmann applanation tonometry
Sources of error with Goldmann tonometry
amount of fluorescein
: wider meniscus : falsely higher pressure
Thicker cornea : falsely higher pressure
Thinner cornea : falsely lower pressure
: A lack of agreement on the correction factor
4D astigmatism = 1mmHg of error
: 45 degrees to the major axis
: An average of horizontal and vertical readings