Foundations Anterior Seg Flashcards
What is the carbonic anhydase reaction equation?
- Catalyzes hydration of carbon dioxide to carbonic acid leading to liberation of hydrogen & bicarbonate atoms
- Enzyme immunohistochemically localized to ciliary epithelia in major processes of pars plicata region only

How does carbonic anhydrase inhibitors work and what are they used for?

- NHE-1 (NHE = sodium hydrogen exchanger) and AE2 (AE = anion exchanger) antiports on the stromal side of the PCE cell membrane
- Underlie uptake of Na+ and Cl- form the ciliary body stroma, in exchange for H+ and HCO3- respectively
- Cytoplasmic carbonic anhydrase II enhances the delivery rate of H+ and HCO3- and thus facilitates Na+ and Cl- uptake for use in making aqueous.
- The Na+ and Cl- ions taken up by the PCE are passed into the NPCE via gap junction where the Na-K-ATPase pumps them into the cleft between NPCE cells
- Carbonic anhydrase inhibitors used in the treatment of glc likely reduce inflow and IOP by inhibiting the NHE-1 and AE2 antiports in the PCE

Describe how beta-1 & 2 and alpha-2 receptors work?
- Phosphorylated by GTP (not ATP)
- Receptor binding by agonist = molecule binds to the receptors which lead to activation of G protein
- G protein phosphorylated by GTP - leads up up regulation of adenocyclase, ATP, kinase A
- And cascade leads to various effects - ultimately to which Na-ATPase will turn and will pump out sodium and produce aqueous humor
- B-agonist attaches to receptors = more aqueous made, IOP will increase
- B-blocker attaches to receptor = G protein cant be activated
- A2 receptor attaches to g protein (inhibitory g protein) = everything will spin down (not up) = aqueous humor production stops

Aqueous humor outflow is ___ flow, along a __ __ __, from the anterior chamber to the ___ ___
Passive flow, downhill pressure gradient, episcleral veins

IOP must over come ___ in order for aqueous humor to leave the eye
- Episceral venous pressure
EVP averages approximately __ mmHg if the patient is seated and DOES NOT change with age
9 mmHg
If you see a dilated episcleral vessel and elevated IOP what can this suggest? What should you ask the patients about? What can you give to reduce elevated episcleral venous pressure?
- Ask about recent trauma, specifically craniofacial or any head injury, that can suggest a carotid cavernous sinus fistula.
- A complete past medical history should be obtained to rule out etiologies that may cause venous obstruction, including but not limited to hyperthyroidism, amyloidosis, congestive heart failure, hypercoagulable states, vasculitis, superior vena cava syndrome and sturge-weber syndrome.
- Use of the alpha-agonist apraclonidine, the calcium channel blocker, verapamil and the new rho-kinase inhibitors reduce EVP

Describe elevated EVP in Sturge-Weber
- Sturge-weber syndrome aka encephalotrigeminal angiomatosis is a rare congenital neurological and skin disorder.
- It is one of the phakomatoses and is often associated with port-wine stains of the face (A congenital hemangioma composed of excess capillaries around branches of one or more of the three division of CNV), glaucoma, seizures, intellectual disability, and ipsilateral leptomeningeal angioma (cerebral malformations and tumors)
- Elevated EVP is likely the cause of glaucoma associatd with the vascular phakomatosis sturge-weber syndrome
- Elevated EVP has not yet clearly and consistently been shown to play a contributing role in POAG

Describe the case for pulsatile aqueous outflow
- non-NIH reviewed and funded research suggest that there is an ocular pulse-related pumping of aqueous out of the eye and the outflow system is NOT the passive downhill flow just described
- When doing tono you will see a pulse - easy to believe that pulse squeezes the aqueous out of the eye
- Trabecular outflow REMAINS THE SAME - the only difference is the episcleral pressure goes from in-vivo 9 mmHg to 0 mmHg and everything else scales down proportionally but maintains the same ouflow resistance and IOP
- The presence or absence of a vascular pulse makes no difference

Study the Image

Study the image
Name the angle



Study the image
What is the most direct way out and sees the most flow? What happens in this area as we age?
- posterior meshwork (PM) has schlemm’s canal behind it
- With that flow, over many years, comes “wear and tear” pigment, which is phagocytized more by the TM cells in the PM than the AM
- Note abrupt reduction in pigment portion of the TM anterior to the end of schlemm’s canal. This is a normal older angle - NOT PDS


- Uveal meshwork (below red line) - extends from the uveal tissue to schwalbe’s line
- Corneoscleral meshwork (between red and blue line) extends from scleral spur to the deep stroma of the cornea
- Juxtacanalicular connective tissue (JCT region - between blue line and schlemm’s canal - SC).

What are the dimensions of the uvealmeshwork, corneoscleral meshwork, and the JCT region?
- As one progresses deeper into proximal portions of the conventional outflow pathway, the sizes of the open spaces are reduced
- Uveal meshwork = 25-75um
- Corneoscleral meshwork = 2-15um
- JCT region = 1-2um
- Given the sizes of the openings in the uveal and corneoscleral meshwork, neither region is considered to contribute any measurable resistance to aqueous flow
Where does the longitudinal bundle insert (ciliary muscle)?
- Longitudinal bundle
- Inserts onto posterior surface of scleral spur but its tendons also extend into the meshwork and even to the inner wall of schlemm’s canal

What is the cribriform plexus?
- Tendons from the tips of muscle cells in the longitudinal bundle do not all attach to the undersurface of the scleral spur (SP). Many extend into the TM and even make direct, elastin-containing connections directly to the inner wall of schlemm’s canal

Cribriform plexus - do miotics really decrease IOP by pulling on the scleral spur and “opening up” the meshwork?
- Some of the longitudinal bundle attaches to the scleral spur, but most enter the TM and even connect to the inner wall of SC
- As IOP increases, SC wants to collapse. Miotics seem to work mainly by holding up schlemm’s canal, by analogy with the cordae tendinae attached to the mitral and bicuspid valves of the heart. They brace the inner wall to prevent collapse

Most of the trabecular meshwork is composed of __ __ __ composed of a __ and __ __, wrapped by a single layer of __ __ __. As with the corneal endothelium there is an age-related __ in these cells.
- avascular trabecular beams
- collagen & elastin core
- trabecular endothelial cells
- decrease

Describe the JCT region?
- No beam structure
- Open connective tissue matrix of collagens (C) and elastin
- Resident cells are fibroblast and not epithelial
- These cells send long extended processes that attach to the inner wall of schlemm’s canal (E) with mushroom shaped pads (small arrows). This allows JCT to spread away from the inner wall without losing contact

Describe giant vacuoles
- The pressure difference across the inner wall of SC drives formation of focal detachments of endothelial cells that form “giant” vacuoles
- As pressure increases, the size and andnumber of vacuoles increase in normal eyes (less so in eyes with POAG)
- They open, release aqueous into SC and collapse

What are the 2 types of pores?
- I-pores (Intracellular-left)
- B-pores (border right)
- These are found as tiny openings through I or between B inner wall cells. It is through pores that aqueous enters SC
- Pores of obth types decrease significantly in glc but without a change in pore diameter
- The pores in the inner wall tend to be widely spaced, approx 20-30um apart


The distal outflow pathway from SC to the EPV















