Day 8 (1): Pathology of the Retina and Vitreous Flashcards

1
Q

What are the causes of retinal edema?

A

Due to breakdown of the integrity of the INNER blood-retina barrier (retinal vessel endothelium) secondary to:

  1. Increased intravascular pressure (hydrostatic pressure)
  2. Vessel ischemia
  3. Pericyte loss
  4. Inflammation
  5. Abnormal vascular formation
  6. Others:
    - Toxic retinopathy: secondary to a toxic agent
    - Solar/Photic retinopathy: secondary to prolonged or high intensity exposure to light
    - Preeclampsia/Eclampsia-associated retinopathy: retinal arteriolar narrowing due to systemic hypertension and ischemia
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

How does increased intravascular pressure cause retinal edema?

A

+ Due to a physical block in retinal VEINS
1. Branch Retinal Vein Occlusion:
- location: arterial-venous crossing due to a shared adventitia
- atherosclerotic artery compresses the vein
- vein lumen narrows, increasing the intraluminal pressure and disturbing the laminar flow of blood
- resulting sheer stress causes endothelial damage and thrombus formation ending in vein occlusion
2. Central Retinal Vein Occlusion
- location: small passages of the cribriform plate

Acute Phase: increased pressure in veins and capillaries
1. Brush-shaped hemorrhages in NFL
2. Cystoid macular edema
- leakage of blood or fluid bet. INL (inner) and OPL (outer) layers
- appearance: soggy, fuzzy macula with loss of normal contour
- OCT: formation of cystoid spaces between INL and OPL
3. Serous/Exudative retinal detachment
- fluid accumulation in the subretinal space
- detachment of the NSR from the RPE
4. Hard exudates
- due to stretching of vein walls and escape of high molecular weight proteins and lipoproteins
- yellow to yellow-white depending on lipid content
- older: white due to decreased lipid content
- maybe discrete or confluent
- resorbed or phagocytosed by macrophages

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How does retinal ischemia cause retinal edema?

A
  1. Increased VEGF production: EXTRAcellular fluid accumulation
    - ischemic retina stimulates RPE cells, macrophages, Muller cells and ganglion cells to secrete VEGF
    - larger ischemia = more VEGF
    - VEGF: increases vascular endothelial permeability
    + rearrangement of actin filaments in endothelial cell cytoplasm
    + increased phosphorylation and deactivation of tight junctions
    + end-point: defective INNER BRB with escape of fluid from intravascular to extravascular space
    - BRVO, CRVO, DM Retinopathy, AMD
  2. Hydropic degeneration: INTRAcellular fluid accumulation
    - loss of oxygen leads to a defective Na-K pump and breakdown of the integrity of the plasma membrane
    - sudden influx of ions and water into the cells causes cellular swelling and death
    - appearance: cotton-wool spots = retinal whitening or opacity
    - HPN Retinopathy, BRAO, CRAO, Ocular Ischemic Syndrome

Ocular Ischemic Syndrome
- severe carotid artery occlusive disease (stenosis or occlusion) from atherosclerosis leading to ocular hypoperfusion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

How does pericyte loss cause retinal edema?

A

Pericyte
- specialized contractile mesenchymal cell in CAPILLARIES
- analogue: smooth muscle cells in larger vessels
- function: regulates vascular tone and perfusion pressure
- NORMAL pericyte to endothelial cell ratio: 1:1

Diabetic Retinopathy
- hyperglycemia causes excessive formation of glycosylation products which can result in oxidative stress to the endothelium
- link between pericyte and endothelial cell disrupted causing pericyte hypoxia, apoptosis and loss
- retinal vascular walls become defective and leaky
- loss of vascular tone causes outpouchings in vessel walls
- pericyte to endothelial cell ratio: 1:4
- (+) central MICROaneurysms with surrounding circinate pattern of hard exudates: tiny outpouchings of the vessel walls becoming sites of fluid and lipoprotein leakage

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

How does inflammation cause retinal edema?

A
  • Pathophysiology: inflammatory reaction causes increased production of VEGF, TNF-alpha, IL1 and other inflammatory mediators causing vascular dilation and leukocytosis
  • Also present in DM retinopathy, CRVO and BRVO
  • End-point: increased vascular permeability and leaky vessel walls
  • Diagnostics:
    1. Slit Lamp Biomicroscopy with contact fundus lens:
  • cystoid macular edema +/- hard exudates
    2. Fundus Fluorescein Angiography
  • petaloid pattern: cysts showing leakage of fluorescein in the Henle’s layer (OPL) are arranged around a central dark zone
  • treatment: Corticosteroids to subdue inflammatory reaction

Etiology:
- Location: Anterior Segment vs Posterior Segment
+ anterior: transvitreal transport of prostaglandins from the CB and iris to the retina
- Infection vs Primary Inflammatory Disease (Uveitis) vs Iatrogenic

Examples:
- TB uveitis
- HIV retinitis
- CMV retinitis: partial macular star-formation (hard exudates radiating from the fovea)
- Behcet’s Disease
- Foreign body reaction (parasites, intraocular FB)
- Post-cataract Surgery

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How does abnormal vascular formations cause retinal edema?

A

Newly-formed vessels usually have compromised wall integrity resulting in:
- MACROaneurysms: large outpouching of vessel walls
- Hemorrhages: due to rupture of macroaneurysms
- Macular/Retinal edema
- Hard exudates: implies leakage of intravascular fluid and edema
- Exudative retinal detachment
- Blurring of vision: due to scattering and distortion of light as it encounters the edematous retinal layers with cystoid spaces

Examples:
1. Vascular malformations
2. Coats Disease
- idiopathic, unilateral, progressive telangiectatic neovascularization in the retina
3. Eales Diseases
- idiopathic occlusive vasculitis of the mid-peripheral retina characterized by retinal venous inflammation (periphlebitis), occlusion, and neovascularization
- hallmark: recurrent vitreous hemorrhage
4. Von-Hippel-Lindau
- mutations in the tumor suppressor gene VHL manifest as retinal hemangioblastomas

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What are the causes of retinal hemorrhage?

A
  1. Increase intravascular hemorrhage
  2. Weakened vessel walls (aneurysms)
  3. Fragile neovascularization
  4. Trauma
  5. Iatrogenic
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How does retinal hemorrhage cause blurring of vision?

A
  1. Blocking pathway of light to the foveal photoreceptors and causing scattering of light
  2. Iron in the blood is toxic to the photoreceptors
  3. Iron catalyzes conversion of hydrogen peroxide to hydroxyl radicals causing oxidative damage to the retina
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the relationship between color of the hemorrhage and depth?

A

Color of hemorrhage differs according to location and chronicity.

Dark red
- outer layers nearer to sclera: RPE, PRL, ONL, OPL
- usually in the subretinal space between NSR and RPE
- pigmented RPE adds to the darker appearance of blood
- retinal vessels crossing over the hemorrhage

Bright red
- inner layers nearer to vitreous: NFL, GCL, IPL, INL
- retinal vessels DO NOT cross over the hemorrhage

Yellow or Gray
- old/chronic hemorrhage
- dehemoglobinized with time

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the relationship of hemorrhage shape and location?

A

Shape is influenced by the arrangement of cellular structures or the lack of it wherein they are located.

  1. Pre-Retinal
    - boat: settles on the most dependent area due to gravity
    - extra-retinal neovascularization
    - pre-retinal space: between NSR and vitreous
    + sub-hyaloid: between vitreous and ILM
    + sub-ILM: between ILM and NFL
  2. Intra-Retinal
    - flame, dot, blot: due to tight arrangement of cellular structures in the retinal layers
    - diseased retinal vessels
    - between NSR layers
  3. Sub-Retinal
    - amorphous, spreading, irregular, dome: follows circular contour of the RPE or choroid
    - choroidal neovascularization
    - sub-retinal space: between NSR and RPE
  4. Choroidal
    - almost similar in appearance to sub-retinal hemorrhage
    - dome: follows circular contour of the choroid and sclera
    - altered choroidal vessel hemodynamics or trauma
    - locations:
    + sub-pigment space: at Bruch’s membrane between RPE and choriocapillaris
    + supra-choroidal space: between choroid and sclera
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Discuss pre-retinal hemorrhage.

A

Location: Pre-Retinal Space
1. Sub-hyaloid: between vitreous and ILM
2. Sub-ILM: between ILM and NFL

Note:
1. If exact location could not be ascertained: OCT
2. No significant difference in clinical presentation of the two since both can cause BOV if it blocks path of light into the fovea
3. Important to differentiate exact location because using ND-YAG laser to treat blood in the Sub-ILM will just cause blood to escape into the Sub-hyaloid space

Phases:
1. Acute: large red blob like an egg yolk
2. Sub-Acute: liquefies and settles down after a few days in the most dependent area due to gravity –> boat-shaped

Causes:
1. Extra-retinal neovascularization
2. Valsalva retinopathy
3. Leukemic retinopathy
4. Diabetic retinopathy
5. Macroaneurysm
6. Trauma
7. Shaken Baby Syndrome

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Discuss intra-retinal hemorrhage.

A

Flame-Shaped
- tracks along the axons of the NFL
- comes from ruptured superficial BVs due to increased intraluminal pressure resulting from occlusion of the central retinal vein at the level of the cribriform plate
- periphery: less flame-shaped due to retinal thinning
- e.g. CRVO/BRVO, HPN retinopathy, NPDR, Vasculitis

Blot
- located in the INL or OPL (junction of inner and outer retina)
- round, uniformly shaped hemorrhage limited in size by the tight arrangement of retinal layers
- disruption of deeper capillary networks
- does not usually cause BOV unless located in the fovea
- e.g. CRVO/BRVO, HPN retinopathy, NPDR, Vasculitis

Dot
- also located in the INL or OPL
- disruption of deeper capillary networks
- does not usually cause BOV unless located in the fovea
- either due to:
1. True pinpoint hemorrhage
+ locked by tight arrangement of cells in the retina
+ FFA: HYPOfluorescent
2. Microaneurysms
+ small outpouchings of retinal capillaries or arterioles
+ FFA: HYPERfluorescent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Discuss sub-retinal hemorrhage.

A
  • sub-retinal space: between PRL and RPE
  • shape: amorphous, spreading, irregular, dome-shaped following the circular contour of the RPE or choroid
  • difficult to differentiate with choroidal hemorrhage based on appearance
  • cause: disruption of fragile choroidal neovascularizations growing into the RPE and PRL
  • vision is disrupted if macula is involved because:
    1. iron is toxic to photoreceptors
    2. iron catalyzes conversion of hydrogen peroxide to hydroxyl radicals causing oxidative damage
  • FFA: leakage of dye from retinal vessels surrounding the area of hemorrhage
  • e.g. AMD, Idiopathic Polypoidal Choroidal Vasculopathy, Coat’s Disease
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Discuss choroidal hemorrhage.

A

Locations:
1. Sub-Pigment Space
+ between RPE and choroid in the Bruch’s membrane
2. Supra-Choroidal Space
+ between choroid and sclera
+ rarer

  • dome-shaped: follows circular contour of the choroid or sclera
  • almost similar in appearance to sub-retinal hemorrhage
  • FFA: retinal vessels intact and crossing over the areas of hemorrhage
  • causes:
    1. disruption of RPE-choroidal attachment (trauma)
    2. disruption of fragile choroidal neovascularization (AMD, Coat’s Disease)
    3. sudden decompression in a hypertensive patient causing altered choroidal hemodynamics
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are the different retinal membranes?

A

PRE-Retinal Membranes: between ILM and vitreous
1. Epiretinal membranes: AVASCULAR
2. Proliferative vitreoretinopathy: AVASCULAR
3. Fibroproliferative membranes: VASCULAR

SUB-Retinal Membranes:
4. Chronic retinal detachment bands: AVASCULAR
- between PRL and RPE (subretinal space)
5. Choroidal neovascular membranes: VASCULAR
- between PRL and RPE (subretinal space) or between RPE and choroid in the Bruch’s membrane (subpigment space)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How does retinal membranes cause blurring of vision?

A
  1. Inducing retinal edema and thickening
  2. Retinal surface distortion causing metamorphopsia or image distortion
  3. Macular detachment
  4. Blockage of path of light into the photoreceptors
17
Q

What are Epiretinal Membranes and risk factors for its formation?

A
  • thin sheets of AVASCULAR fibrous tissue that develop on the surface of the macula above the ILM
  • white to transparent
  • causes BOV by:
    1. Retinal edema and thickening causing light scattering
    2. Retinal wrinkling causes metamorphopsia
  • risk factors:
    1. Myopia: long AL causes retinal detachment
    2. Aging: vitreous liquefaction and detachment
    3. Narrow retinal artery diameter
    4. Previous cataract surgery: iatrogenic fibrosis
    5. Diabetic retinopathy
    6. Hypercholesterolemia
    7. Idiopathic: vitreoretinal traction causing complete posterior vitreous detachment ~ 95% of cases
  • clues:
    1. Cellophane Maculopathy: (+) sheen similar to glass
    2. Macular Pucker/Surface Wrinkling Retinopathy: wrinkling and distortion of the perifoveal vessels
    3. Macular Fibrosis
  • treatment: Surgical removal of membranes to restore the foveal pit
18
Q

How does Epiretinal membranes form?

A

Cause: Physical disruption of the ILM
- Posterior Vitreous Detachment: traction of the vitreous causes microdehiscence in the ILM surface

Stage 1: Microglial cells spread over the ILM surface, proliferate and interact with hyalocytes and laminocytes in the vitreous cortex
- activated into fibroblasts which deposit fibrin over the retinal surface
- minor and MICROscopic changes
- INTACT foveal pit

Fibrin contraction causing traction and distortion of the retinal surface: MACROscopic changes
Stage 2:
- Loss of foveal pit (FIRST change)
- Stretching of the ONL (Henle’s Layer)
Stage 3:
- Retinal layers discernible due to edema and thickening (SECOND change)
Stage 4:
- Retinal wrinkling and disruption of layers (THIRD change)

Differential: Proliferative Vitreoretinopathy
- also AVASCULAR
- associated with a retinal TEAR and RRD
- due to RPE differentiation
- NON-contractile

19
Q

What is Proliferative Vitreoretinopathy?

A
  • Formation of proliferative, contractile AVASCULAR membranes in the vitreous and on both sides of the retina, resulting in tractional retinal detachment with fixed retinal folds.
  • MCC of retinal re-detachment post-retinal surgery
  • Appearance:
    + acute/fresh: smooth surface
    + chronic: wrinkled “star fold” appearance
  • BOV due to retinal detachment NOT the PVR
  • Seen in: Advanced/Proliferative DM Retinopathy
  • Treatment: surgical disruption of membranes
    + high rate of retinal reattachment
    + reattachment not an assurance to recovery of visual function likely due to the chronic macular detachment
20
Q

How does Proliferative Vitreoretinopathy form?

A

Cause: Chronic Rhegmatogenous Retinal Detachment
- comparable to an aberrant wound-healing process following tissue insult, specifically, retinal detachment
- nidus for epi/subretinal membrane formation through induction of ischemia and apoptosis arising from separation of the NSR from the choroidal blood flow
- apoptosis triggers a break down in the BRB facilitating the influx of inflammatory mediators and growth factors
- this induces RPE de-differentiation into fibroblast-like cells which migrate through the tear into the inner retinal surface and vitreous where they secrete ECM
- NO inherent contractile ability: contraction happens when fibroblast-like cells interact with the ECM
- contraction of membranes leads to retinal traction and recurrent retinal detachment
- INTRAretinal PVR: due to activated glial tissue that proliferates within the retina causing retinal shortening

Content: Fibroblast-like cells + extracellular matrix
- similar to glial cells on the ILM and RPE cells

Differentials:
1. Subretinal Fibrotic Bands
- etiology unknown
- thick ROPE-like fibrous tissue BUT found in the SUB-retinal space
- also associated with difficulty in reattachment of retina
2. Epiretinal Membranes
- also AVASCULAR
- NOT associated with a retinal tear and RRD
- ONLY the ILM is damaged
- due to microglial differentiation (RPE is intact)
- inherently CONTRACTILE

21
Q

What are Fibroproliferative Membranes?

A
  • formation of abnormal proliferating blood vessels WITH supporting fibrous membranes extending from the retina to the vitreous
  • appearance:
    1. white lace-like sheets of membrane +
    2. neovascularization: fine, incompletely-formed blood vessels that do not follow the normal dichotomous pattern located only in the membranes
    3. ischemic peripheral retina
  • BOV due to macular traction by the membrane resulting in surface distortion and detachment
  • DDX:
    1. DM Retinopathy
    2. Vaso-occlusive diseases (CRVO,BRVO, OIS)
    3. Eales Disease
    4. Occlusive Vasculitis
    5. Retinopathy of Prematurity
    6. Sarcoidosis
    7. Sickle Cell Disease
22
Q

How does Fibroproliferative Membranes form?

A

Cause: Retinal Ischemia
- signals the increased production of VEGF by RPE, Muller cells, Ganglion cells and macrophages
- VEGF binds to the endothelium of venules causing its activation and secretion of enzymes degrading the BM
- Compromised BV walls causes leakage of inflammatory mediators into the extravascular space with proliferation and migration of activated endothelial cells
- Grow into the vitreous which serve as the scaffolding in which ECM is deposited and remodelled to form fibrous membranes with new blood vessels

Phases:
1. Acute Phase
- (+) thickened white opaque membranes
- (+) abundant vessels in the membrane
2. Burnt-out Phase
- ischemic retina neutralized by supply from neovascularization
- VEGF levels decrease
- thinned out translucent membranes
- sparse or no vessels in the membrane

23
Q

What are Choroidal Neovascular Membranes?

A
  • Choroidal membrane formation WITH neovascularization located either in the:
    1. Subretinal Space: between PRL and RPE
    2. Subpigment Space: between RPE and choroid in the Bruch’s membrane
  • Induced by ischemia causing increased VEGF levels
  • Similar to FPM but:
    1. new vessels arise from choroid NOT retinal vessels
    2. yellowish color due to pigmentation in the RPE
    3. intact retinal vessels seen crossing over membranes
  • BOV due to:
    1. retinal surface and layer distortion causing metamorphopsia
    2. macular edema and thickening
    3. central serous retinopathy: NSR detachment at the macula due to subretinal fluid formation
    4. photoreceptor death due to detachment from RPE
  • signs of increased disease activity:
    1. OCT: macular thickening/edema
    2. SL + contact fundus lens: subretinal hard exudates and subretinal hemorrhages
  • treatment: intravitreal Bevacizumab (anti-VEGF)
24
Q

What are the different abnormal vascular changes to be noted in the retina?

A
  1. Vessel dilation
  2. Vessel atrophy
  3. Atherosclerotic changes
  4. Vessel remodelling
  5. Vasculitic changes
  6. Neovascularization
25
Q

How to differentiate retinal artery from veins?

A

Artery/Arterioles
- bright red
- thinner
- wide central light reflex: thicker walls

Vein/Venules
- dark red
- wider
- narrow central light reflex: thinner walls

26
Q

Examples of disease entities that cause vascular

A

CRVO/BRVO
- venous dilation due to obstruction of outflow at the:
+ Central: small passages of the cribriform plate
+ Branch: arterial-venous crossing due to atherosclerotic artery
- resultant increased intravascular pressure dilates the veins and compromises the integrity of the capillary walls causing extravasation of fluid (macular edema) and blood (hemorrhages)

Retinopathy of Prematurity
- retinal ischemia resulting from the incomplete formation of retinal vessels induces VEGF production
- VEGF activates endothelial cells which remodel the capillary walls and cause decreased capillary resistance
- blood flow in the vessels increase resulting in changes in vessel shape:
+ artery: tortuous (not distensible)
+ vein: dilate
- associated changes:
1. Fibroproliferative membranes with neovascularization
2. AV shunts: border of the vascular and ischemic retina

27
Q

What are the causes of vascular atrophy?

A
  • commonly due to fibrosis and sclerosis of vessels due to chronic inflammation
  • appearance:
    1. White linear vessels: NOT all are white
    2. Decreased vessel caliber
    3. NO associated hemorrhages
  • causes:
    1. Chronic CRVO/BRVO
    2. Pathologic myopia: elongated AL with retinal thinning
    + higher oxygen tension and blood flow in the choroid makes the inner retina less reliant on the retinal vessels leading to decreased vessel caliber and blood flow
    3. Chronic vasculitis or inflammation
    4. Laser photocoagulation:
    + retinal destruction decreases demand for blood flow and oxygen leading to vessel atrophy
28
Q

What happens in retinal vessel atherosclerosis?

A
  • Usually associated with chronic hypertension and hyperlipidemia
  • Lipid deposition in the vessel walls causes wall thickening and narrowing of the lumen

Normal retinal arterioles:
- thin arteriolar walls with INTACT blood column
- thin light reflex: good blood flow
- more RED than white

Abnormal retinal arterioles: older, hypertensive
- atherosclerosis causes thickened arteriolar walls and narrowed lumen with OBSCURE blood column
- diffuse light reflex: increased optical density of walls
- more WHITE than red
- graded based on size of light reflex and loss of blood column:
+ Grade I - III: yellowed or copper-wire appearance with increasing size of light reflex; subjective
+ Grade IV: white or silver-wire appearance due to complete sclerosis; NO blood column
- BRVO: complication of severe atherosclerosis with complete occlusion of the vein
+ increased intraluminal pressure –> capillary rupture
–> hemorrhage –> ischemia in terminal arterioles –> cotton-wool spots and macular edema

Clues:
- in the A-V crossing, both vessels share a common adventitial sheath which keeps them adjacent
- as the arteriole hardens, it will impinge on the venule:
1. Salus’ Sign: deflection of vein
2. Gunn’s Sign: tapering of vein

29
Q

What happens in hypertensive retinopathy?

A
  • Due to chronic uncontrolled hypertension
  • Cause: vascular autoregulation causing vasoconstriction
    1. ischemia causes gradual fibrinoid necrosis of smooth muscle in the media layer of blood vessels
    2. weakening and compromised integrity of vessel walls resulting in:
  • exudation of fluid (EDEMA/THICKENING) and
  • lipoproteins (HARD EXUDATES) into the retina
  • small outpouchings in the walls (MICROANEURYSMS or DOT HEMORRHAGES)
    3. complete break in vessel wall resulting in:
  • hemorrhages (FLAME/BLOT)
  • opacification of the NFL caused by ischemia in the areas supplied by terminal arterioles (COTTON-WOOL SPOTS)
    + ischemia –> decreased oxygen perfusion –> malfunction of Na-K pump –> intracellular edema
    + disruption of the normal retrograde axoplasmic flow
    –> deposition of cellular by-products forming cytoid bodies –> coalesce into opaque cotton-wool spots
30
Q

What are examples of vessel remodeling?

A

Causes:
1. Altered blood flow
2. Altered blood viscosity
3. Altered wall tonicity and integrity

Examples:
1. Telangiectasia
- capillary distention
2. Venous beading
- segmental changes in venous wall tone
- rosary appearance
3. Microaneurysms
- small outpouchings in the weakened arteriolar walls
- dot hemorrhages
4. Venous loop
- formation of multiple smaller collateral veins due to due to gradual occlusion of larger veins and ischemia
- DDX: Neovascularization
+ also a sign of retinal ischemia
+ BUT NOT leaky with intact wall integrity
+ (-) hard exudates, (-) retinal edema

31
Q

What vessel changes are seen in vasculitis?

A

Vasculitis
- inflammation of blood vessels
- causes: infectious or non-infectious
- appearance depends on chronicity and severity

(+) Vascular Sheathing
- white lines surrounding retinal vessels
- due to deposition of inflammatory cells or leukocytes in and along the vessel wall
- sign of non-infectious inflammation usually due to an autoimmune condition
- mistaken for atherosclerosis BUT involves almost all vessels
- may appear as the presenting or sole sign of acute leukemia

32
Q

What are neovascularizations?

A
  • fine, thin, wavy interconnecting vessels formed in response to retinal ischemia
  • angel hair pasta appearance
  • ischemic retina secretes VEGF which acts upon the endothelial cells of veins, causing remodelling and formation of new but fragile blood vessels
  • may be retinal or choroidal vessel in origin
  • do not follow the dichotomous branching pattern of normal vessels
  • commonly associated with hard exudates and retinal edema
  • if seen in DM retinopathy: Proliferative DM Retinopathy

Differential: Vessel Loops
+ also a sign of retinal ischemia
+ BUT NOT leaky with intact wall integrity
+ (-) hard exudates, (-) retinal edema

Associated with the following conditions:
1. DM Retinopathy
2. Vaso-occlusive diseases (CRVO,BRVO, OIS)
3. Eales Disease
4. Occlusive Vasculitis
5. Retinopathy of Prematurity
6. Sarcoidosis
7. Sickle Cell Disease

Treatment: Laser Photocoagulation

Complication: Fibroproliferative Membranes
- vessels extend beyond the ILM into the vitreous and interact with the cells in the vitreous cortex inducing the formation of fibrous membranes

33
Q

What are the different causes of vitreous opacities?

A
  1. Vitreous hemorrhage
    - blood prevents passage of light into the PRL causing BOV
    - form of preretinal hemorrhage = boat-shaped
    - if chronic: dehemoglobinized –> gray or ochre sheets of vitreous membranes
    - tx: vitrectomy
    + opacification will not spontaneously resolve; vitreous removed to determine underlying cause of hemorrhage
  2. Vitritis: inflammation of the vitreous
    - causes:
    + Anterior Uveitis: inflammation of the ciliary body
    + Endophthalmitis: inflammation of the inner eye
    - deposition of inflammatory cells in the vitreous gel causing opacification and blurring of vision
    + Homogenous: uniform distribution throughout the entire vitreous
    + Clumping: discrete collections of deposits
  3. Deposition of metabolic products (e.g. Asteroid Hyalosis)
    - exact pathogenesis unknown
    - Asteroid bodies: yellow to white brilliant hyperreflective deposits in the vitreous composed of Ca-associated phospholipids.
    - stars-in-the-night-sky appearance
    - does not usually cause BOV unless very dense and covers the macula
    - tx: vitrectomy
  4. Veils, Membranes and Bands
    - Persistent Fetal Vasculature (PHPV): failure of the regression of a component of fetal vessels within the eye
    - Ocular toxocariasis: migration of toxocara larvae into the eye
    + presenting as a yellow to white retinal granuloma located anywhere in the retina
    + may form fibrous bands extending from the peripheral retina to the optic disc causing retinal folds
  5. Malignancies
    - may initially present as floaters
    - Retinoblastoma: most common malignant ocular tumor
    + pearly white tumor presenting with leukocoria
    + vitreous seeding: tumor cells liberated from the mass floating in the vitreous
    + hard to treat with IV medications due to BRB
    - Choroidal melanoma: pigmented tumor
34
Q

What is syneresis?

A
  • liquefaction of the vitreous gel due to:
    1. changes in the structural conformation of hyaluronic acid
    2. alterations in hyaluronic acid and collagen interactions
    3. aggregation and cross-linking of collagen
  • starts as pockets of liquefied vacuoles in the center which coalesce and progresses to the periphery
  • liquefied vitreous becomes mobile and slowly detaches from the retina with the help of gravity
  • susceptible populations:
    1. elderly
    2. myopics
35
Q

What is posterior vitreous detachment?

A
  • detachment of the vitreous from it’s connections to the retina due to syneresis and resultant mobility
  • attachments:
    1. Vitreous Base/Pars Plana: strongest attachment; last to detach
    2. Optic disc: second strongest
    3. Fovea
    4. Retinal vessels
    5. Posterior lens capsule: via the Hyaloideocapsular Ligament of Wieger
  • risk factors:
    1. aging: 7th decade (11%) vs 9th decade (46%)
    2. increased axial length: high myopics with AL > 30.0 mm ~ 60% with earlier onset

Note: High myopic diabetics
- because of the early onset vitreous detachment, even if at advanced stages of DM retinopathy, attachment of fibroproliferative membranes is prevented
- lower risk of traction retinal detachment

Symptoms of Acute PVD:
1. Photopsias
- sensation of flashes of light due to stimulation of the vitreo-retinal interface attachments as the vitreous peels off
- governed by the Law of Specific Nerve Energies
2. Floaters: could be due to either of the ff.
- pathologic crosslinked collagen molecules that becomes visible
- vitreous hemorrhage: tearing of the vessels due to detachment of the vitreous from retinal vessels
- Weiss ring: circular peripapillary attachment that is visible within the vitreous after detachment from the optic disc/nerve head

36
Q

What is the Law of Specific Nerve Energies?

A
  • Nature of PERCEPTION is defined by the PATHWAY over which sensory information is carried
  • ORIGIN of the sensation is NOT important
  • Thus, differences in perception of seeing, hearing and touch are not caused by different stimuli BUT by the different nervous structures that these stimuli excite
  • E.g. pressing on the eye causes light flashes because stimulation of neurons in the retina send signals to the occipital lobe; sensory input is MECHANICAL but the experience is VISUAL
37
Q

How is posterior vitreous detachment related to retinal tears and retinal detachment?

A
  • in symptomatic PVDs with:
    + floaters/flashes: 8.5% with retinal tears
    + vitreous hemorrhage: 71% with retinal tears

Progression: Rhegmatogenous Retinal Detachment
1. Progressive detachment of the vitreous from the retina
2. Continued traction of the vitreous can cause peripheral retinal tears and detachment of the NSR from the RPE exposing the subretinal space
3. Liquefied vitreous in the cavity can now enter through the retinal tear insinuating itself into the subretinal space, further detaching the NSR from the RPE

2 phases:
1. ACUTE phase:
- days to weeks
- retina appears opaque due to edematous layers: dehydration of the NSR is a function of the RPE
- PRL (outer segment) and ONL degenerate due to ischemia
- vision loss still REVERSIBLE if retina is reattached promptly with resolution of edema and regeneration of PRL outer segments
2. CHRONIC phase:
- months
- retina thins out and becomes transparent again
- (+) pigmented demarcation between the attached and detached retina
- (+) thick white AVASCULAR subretinal membrane
- vision loss is IRREVERSIBLE because of necrosis of all photoreceptors in the detached retina