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Flashcards in Aqueous Humor Dynamics Deck (37)
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1

What are the two ways in which aqueous humor leaves the eye

-unconventional pathways: through the ciliary muscle and other downstream tissues (minor 5-35%)
-conventional pathway: though the trabecular mesh work (TM) and Schlemm’s canal (SC) (major 65-95%)

2

Unconventional pathway for AH outflow

-uveoscleral outflow
-minor route (5-35%)
-AH enters the connective tissue between the ciliary muscle bundles, through the suprachoroidal space, and out through the sclera
-to fairly constant amount not affected by IOP
-the outflow rate through this route tends to decrease with age

3

Conventional outflow of AH

-corneoscleral pathway
-major route (65-95%)
-AH passes through the TM, across SC, into its lumen and into draining collector channels, aqueous veins and epislercal veins
-two models
-IOP dependent

4

Two models of conventional pathway

Bulk flow model
Pumping method

5

Bulk flow method

A simplest hydraulic model of conventional pathway
-classic Goldmann equation
-deltP=IOP-EVP
-Fout=Trab(IOP-EVP)+UVEO
-an acute rise in EVP results in a 1:1 ratio of increased IOP

6

Pumping model of conventional pathway of AH outflow

The aqueous outflow pump receives power from transient increases in IOP such as occurs in systole of the cardiac cycle during blinking and during eye movement

7

AH produced from

Pars plicata

8

Conventional pathway and IOP

IOP dependent
-increase of IOP caus drainage increase
-with constant very high IOP, Schlemm’s canal can collapse on itself and obstruct entry into the venous system

9

TM and AH outflow

-the TM is suspended between two fluid compartments (anterior chamber and Schlemm’s canal) at different pressures
-the TM can sense the pressure differential and strives to maintain these parameters within a homeostatic range

10

Occlusive angle in diabetes

Neovascularisation from proliferating diabetic retinopathy

11

Occlusive angle in uveitis

Inflammatory cells and peripheral anterior synechiae

12

Unconventional pathway of AH outflow and IOP

IOP independent

13

Hypema and occlusive angel

Blood accumulates in the anterior chamber

14

Occlusive angle and pseufoexfoliative glaucoma

Aging epithelial cells of the iris and lens capsule can release pigment and pseudoexfoliative material

15

Occlusive angle and pigment dispersion glaucoma

Pigment is released from the posterior layer of the iris due to posterior bowing of the iris against the lens zonules

16

In humans, 75% of the resistance to the AH outflow is localized to the _____ and 25% occurs beyond ______

TM
Schlemms canal

17

Fuchs heterochromic iritis

Results in chronic inflammation that can cause TM permanently damaged

18

Glaucomatocyclitic crisis

Acute inflammation of the TM

19

Long term influence of IOP

Genetics
Gender
Refractive error

20

Short term influence of IOP

Diurnal
Postural variation
Lid and eye movement
Systemic conditions
Environmental conditions
Food and drugs

21

Genetics and IOP

Hereditary influence

22

Gender and IOP

-equal between men and women 20-40
-in older ages, the apparent increase in mean IOP with age is more in women

23

Refractive error and IOP

-a positive correction between IOP and both axial length and incfressing degrees of myopia
-myopic people also habe a higher incidence of OAG

24

Diurnal variation in IOP

-fluctuates throughout the day
-ranges from 3-6mmHg
-highest in the morning

25

Peak IOP is in the ___ hours

Morning

26

Postural variation in IOP

-IOP increases when changing from sitting to the supine position, average pressure difference between 0.3-0.6mmHg
-patient with systemic HTN have greater IOP increase after 15 minutes in supine

27

Lid and eye movement and IOP

-blinking has been shown to rise the IOP 10mmHg, while hard lid squeezing may raise it as high as 90mmHg
-there is an increase in IOP on up-gaze in normal individuals

28

Systemic conditions and IOP

-thicker corneas cause artificially high readings while thinner corneas cause artificially low read gains
-reduced during pregnancy (progesterone)
-HIV have lower than normal mean IOPs

29

Environmental conditions and IOP

Cold reduces IOP
Reduced gravity increases IOP

30

Foods and drugs and IOP

-Alcohol, heroin, and marijuana lowers it
-caffeine and tobacco increases it
-corticosteroids increase it