Block 12 Flashcards
What is the simplified cause of glaucoma?
Aqueous flow in does not equal flow out
What is the unconventional pathway?
Aqueous moves through the ciliary muscle and other downstream tissues
It is minor (5-35%)
What is the conventional pathway?
Aqueous moves through the trabecular meshwork and Schlemms canal
It is major (65-95%)
Where all does aqueous flow in the unconventional pathway
AH enters the connective tissue between the ciliary muscle bundles, through the suprachoroidal space, and out through the sclera
Is the unconventional pathway affected by IOP
NO
How does unconventional pathway change with age
It decreases
In the conventional pathway where does aqueous flow?
Through the TM across Schelmms canal, into its lumen and into the draining collector channels, aqueous veins, and episcleral veins
What are the 2 models for conventional pathway
Bulk flow model
Pumping Model
Is the conventional pathway affected by IOP
YES
What is the Bulk Flow model of conventional aqueous flow
Change n pressure=IOP-EVP
An acute rise in EVP results in a 1:1 ratio of increase IOP
What is the pumping model of the conventional pathway
The aqueous outflow pump receives power from the transient increases in IOP such as occur in systole of the cardiac cycle during blinking and during eye movement
An increase in IOP causes what change in drainage?
Increase drainage
What happens with very constant high IOP
Schlemm’s canal can collapse on itself and obstruct entry into venous system
What is the role of the TM in aqueous flow
The TM is suspended between 2 compartments with different pressures
TM can sense the pressure differences and tries to maintain them within a homeostatic range
What are some things that can occlude the angle
Diabetes Uveitis Hyphema Pseudoexfoliative glaucoma Pigment dispersion glaucoma
How does diabetes occlude the angle
Neovascularization from the proliferative diabetic retinopathy
How does uveitis occlude the angle
Inflammatory cells and peripheral anterior synechiae
How does hyphema obstruct the angle
Blood accumulates in the anterior chamber
How does pseudoexfoliative glaucoma occlude the angle
Aging epithelial cells of the iris and lens capsule can release pigment and pseudoexfoliative material
How does pigment dispersion glaucoma occlude the angle
Pigment is released from the posterior layer of the iris due to posterior bowing o the iris against the lens zonules
In humans, ____% of the resistance to the aqueous humor outflow is localized to the TM
75%
The other 25% occurs beyond Schlemms canal
What is Fuch’s heterochromic iritis
Chronic inflammation that can cause permanent TM damage
What is glaucomatocyclitic crisis
Acute inflammation of the TM
What are some long term influences on IOP
Genetics
Gender
Refractive error
What are short term factors that influence IOP
Diurnal Postural variation Lid/eye movement Systemic conditions Environmental conditions Food and drugs
Does genetics affect IOP
YES
How does gender affect IOP
It is equal between men and women 20-40 yoa
In older ages, there is an increase in IOP with age more in women
How does refractive error affect IOP
Positive correlation between IOP and axial length/increased degrees of myopia
Myopic people have a higher incidence of open-angle glaucoma
T/F IOP fluctuates throughout the day
True
What is the range of IOP throughout the day
3-6 mmHg
When is IOP the highest
In the morning hours
How does posture affect IOP
Increase when changing from sitting to laying down
T/F patients with systemic hypertension have greater IOP increase after 15 minutes in supine
True
How do lids affect IOP
Blinking can raise IOP 10 mmHg
Hard squeezing can raise it as high as 90 mmHg
How do eye movements affect IOP
Increase in IOP in upgaze
Thicker corneas give…
Artificially high readings
Thinner corneas cause….
Artificially low readings
How does pregnancy affect IOP
It is reduced during pregnancy
Possibly progesterone
How does HIV affect IOP
They have lower than normal IOP
Exposure to cold air causes
Reduced IOP
How does gravity affect IOP
A sudden marked increase in IOP
How does alcohol affect IOP
Lowers it
How does caffeine affect IOP
Causes a transient rise in IOP
How does tobacco smoking affect IOP
It causes a transient increase
How does heroin and marijuana affect IOP
Lowers it
How does LSD affect IOP
Elevates it
What do steroids do to IOP
Increase IOP
What is the largest organ of the eye
Virtuous
What is the vitreous
A highly transparent gel
It is located between the crystalline lens and the retina
The vitreous transmits ___% of light
90
What are the 3 zones of the vitreous
Outermost: vitreous Cortex
Center: Cloquets canal
Intermediate: inner to cortex and surrounds canal
What is teh vitreoretinal interface
Where the vitreous is attached to the inner limiting membrane of the retina by anchoring fibrils and membrane limitans interna (MLI)
Where is the vitreous base ?
At the ora serrata
What is the vitreous base attached to
NPCE and the internal limiting membrane of peripheral retina
It the the strongest attachment
Is the vitreous base attachment affected by age?
No
What is Weigers Ligament
It is between the posterior surface of lens and the anterior face of vitreous
It is a firm attachment
Is weigers ligament affected by age?
Yes, it declines after age 35
What is peripapllary adhesion
It is around the edge of optic disc
It is a medium attachment
Declines with aging
Weiss’ ring
What is the macular/peripheral attachment
Weak
Controversial
May have an attachment 3-5mm posterior to vitreous base. Attach to retinal blood vessels
What is in high composition in the vitreous
H2O (99%) Collagen (T2) HA (GAG) Vitreal Cells (hyalocytes, fibroblasts) Vitamin C
What is the gel structure of vitreous due to
Arrangement of collagen fibrils suspended in network of HA
What do hyalocytes do
Synthesize glycoproteins for the collagen fibrils
Synthesize HA
What do fibroblasts do
Synthesize the collagen fibrils
What are the functions of the vitreous
Support retina
Diffusion barrier
Metabolic buffer
Transparency
What are the support functions of the vitreous
- Prevents retinal detachment
- reduce mechanical deformation
- supports lens during trauma
- decreases transmission of light at 300-350 nm
- mechanical support
What is posterior vitreous detachment (PVD)
10% of eyes have a strong vitreous retina attachment
Vitreous traction can cause retinal tears
Possibility of vitreous hemorrhage
High risk of rhegmatogenous retinal detachment
What is macular edema due to
Vitreous-retinal traction
Increase in passive permeability
Decrease in active transport across Blood retinal barrier
Increase osmotic pressure
What is the diffusion barrier of the vitreous
Slow diffusion across vitreous
Bulk flow is limited across vitreous
Prevents topically administered substance from reaching the retina
Prevents substances in blood stream from reaching vitreous center
No diffusion barrier for small molecules
What is the metabolic buffer of the vitreous
Reservoir for ciliary body and retinal metabolism
Movement of water soluble substances into vitreous and their dilution
Reservoir of glucose and glycogen for retinal metabolism
Reservoir of potassium for retinal metabolism
Reservoir for Vitamin c
What can full PVD or vitrectomy) cause
Nuclear sclerotic cataract (NSC)
Reduce neovasculariztion in retina
Neovascualr glaucoma
What causes the transparency of the vitreous
Low [macromolecules]
Low [protein]
Specific collagen/HA configuration
Blood vitreous barrier
What is synchisis scintillations
Rare
Not age related
2% to injury or inflammation
It is an accumulation of the cholesterol
What is asteroid hyalosis
In people aged 60-65
Common in white people
No decrease in VA
It is an accumulation of calcium
What is dry eye syndrome
A disorder of the tear film caused by tear deficiency or excessive tear evaporation that causes damage to the interpalpebral ocular surface and is associated with symptoms of ocular discomfort
What is the function of the tear film
Provides a smooth refractive surface for clear vision
Maintains the health of corneal and conjunctival epithelia
Acts as the first line of defense against microbial infections
What are the layers of the tear film
Lipid layer
Aqueous layer
Mucous layer
What is the mucus layer of the tear film composed of
Mucin* Immunoglobulin Urea Salts Glucose Leukocytes Cellular debris Enzymes
What is mucin
A high molecular weight glycoproteins that is heavily glycosylated
What are the 2 types of mucins
Membrane associated
Secretory
What is membrane associated mucins
A dense Barrie to pathogen penetrate, at the epithelia cell tear film interface
What are secretary mucins
Act as cleaning crew, moving through the tear film and collecting debris that can be removed via the nasolacrimal duct during blinking
What is the function of the mucus layer
Maintain water on the surface of the eye
Mucins also interact with tear lipids to lower surface tension thereby stabilizing the tear film
Provides lubrication for eyelid movement
Traps exploited surface cell, foreign particles and bacteria
What are the sources of the mucus layer
Goblet cells (cornea and conj) Squamous cells (cornea and conj)
What is the neural control of the mucus layer
Sensory nerves Parasympathetic nerves (increases)
Sympathetic
What is the aqueous layer composed of
Water Electrolytes Proteins Peptide Growth factors Vitamins Hormones
What are the electrolytes in the aqueous layer
Na* Cl* K* Ca* Mg HCO3 Phosphate
What is the importance of Na and Cl in the aqueous layer
They are the main controllers to osmolarity of tear film
Osmolarity increases with dry eye
What is the importance of K and Ca in the aqueous layer
Important for maintaining corneal epithelial health
What are some proteins in the aqueous layer
Albmin Immunoglobulins (IgA) Histamine Lactoferin Lysozyme Interleukins Antimicrobials
What are the functions of the aqueous layer
Electrolytes act as a buffer to maintain constant pH and contribute to maintaining epithelial integrity of the ocular surface
Offers a strong defense system to protect against invading microorganisms through contained proteins
Peptide growth factor A acts via autocrine and paracrine mechanisms to regulate epithelial proliferation, motility and differentiation
The buffering system of the eye allows the eye to tolerate ophthalmic solutions of what pH
3.5-10.5
What happens to eye pH while we are sleeping
It decreases (due to aerobic respiration)
What happens to pH in dry eye
It increases (due to osmolarity increases)
What are the resources of the aqueous layer
Lacrimal glands* (reflex and emotional tearing)
Accessory lacrimal glands (maintenance tearing)
What is the neural control of the aqueous layer
Main lacrimal glands: parasympathetic, sympathetic, sensory nerves
Accessory glands: parasympathetic
What is the lipid layer of the tear film composed of
Meibomian oil
What are the 2 phases of the lipid layer
Polar surfactant phase
Nonpolar phase
What is the polar surfactant phase
It is primarily composed of phospholipids and glycolipids
Acts as a surfactant between the hydrophilic aqueous mucin layers and thick, nonpolar lipid layer
What is the nonpolar phase
It is primarily composed of wac, cholesterol esters, and triglycerides
Provides the air-tear film interface and is responsible for retarding evaporation
What is the function of the lipid layer
Major barrier to evaporation from ocular surface
Provides stability to tar film through interaction with aqueous-mucin phase
Provides a smooth optical surface for the cornea
Acts as a barrier against foreign particles
What are the resources of the lipid layer
Meibomian glands
Assistance from Zeis and Moll glands
What is the neural control of the lipid layer
Parasympathetic innervation
How can you access the tear film
Tear secretion Tear film stability Tear film osmolarity Lipid layer evaluation Ocular surface evaluation
What is tear deficient dry eye
There is a disorder in the lacrimal gland function, resulting in either reduced aqueous tear production and tear flow, or a failure to transfer lacrimal fluid into the conjunctival sac
What is the largest dry eye category
Tear deficient
What is evaporative dry eye
Lacrimal gland function is normal and the volume is sufficient to cover the surface, but another tear film abnormality exists that leads to increased tear evaporation
What can lead to evaporative dry eye
Hyperosmolarity
Meibomian gland disease
What tests access tear secretion
Schirmer 1 and 2
Phenol red thread test
Meinscometry
What tests look at tear film stability
TBUT
Ocular protection index
Videokeratography
Tear turnover
What tests tear film osmolarity
Tear film osmolarity
Tear ferning
Tear evaporation
What tests lipid evaluation
Interferometry
Meibometry
What tests ocular surface evaluation
Fluorescein
Rosa bengal
Lissamine green
