PPO III: Intro to posterior Segment

Structures of the posterior segment

• Vitreous

• Optic nerve

• Macula

• Vasculature

• Periphery

En-face

• Refers to the view that fundus photos get of the retina

• Anatomically accurate as if the eye is pointed at you

Functions of the vitreous

• 80% of total globe volume

• Stabilizer

• Shock absorber

• Light transmitter

• Buffering zone for metabolic waste

Categories of vitreous

• Cortical vitreous

  • Peripheral shell of vitreous

  • Densely packed collagen fibrils

  • Thicker anterior > posterior

• Central vitreous

  • Loosely packed collagen fibrils

Strength of vitreous attachments within the globe

Vitreous Base (strongest) > Posterior lens > Optic Disc > Macula > Retinal Vessels (weakest)

Syneresis

• Liquefaction of the vitreous

• Begins centrally

• Increases with age & axial length

Posterior vitreous detachment

• Detachment of the vitreous from the retina

• Occurs in over 60% over 80 years old

• Flashes and floaters (Photopsia)

• Not painful

• PVD leads to complications in 27% of pts

Weiss ring

• Circular floater of condensed vitreous

  • Previously attached to the ONH

Retinal tear

• Can occur as the vitreous detaches from the retina

  • Strong adhesions rip the retina off the RPE

Macular hole

• During a PVD strong adhesions may remain on the fovea

• As the vitreous pulls away, this pulls the macula from the RPE

  • → Central scotoma

Epiretinal membrane

• As PVD progresses, cortical vitreous remnants secrete collagen

  • → Sheet of glial cells develops

    • → Epiretinal membrane

Epiretinal membrane

Vitreous hemorrhage

• PVD → Tears blood vessel → Vitreous hemorrhage

• Traumatic

• Associated with retinal tears

Vitritis

• Inflammatory cells within the vitreous

• Associated with systemic diseases that are

  • Infesctious

  • Inflammatory

  • Autoimmune

Diseases associated with vitritis

• Tuberculosis

• Sarcoidosis

• Multiple Sclerosis

Asteroid Hyalosis

• Calcium-lipid deposits within the vitreous collagen

• Benign finding

How many ganglion cell axons pass through the lamina cribrosa

• ~1.1 million

Cup / Disk ratio

• Compares size of central depression of the ONH (The cup) to the full diameter of the disc

ONH rim tissue is usually thickest…

Inferior > Superior > Nasal > Temporal

ISNT rule

Normal recording of the optic nerve

Healthy, pink rim tissue 360

Recording c/d ratio

0.50 V/0.45 H OD

⁃ 0.20 V/0.25 H OS

Glaucoma

• Death of ganglion cells in the inner retina and loss of their axons within the optic nerve

• Associated with increased intra-ocular pressure

Glaucoma statistics

• 1/40 adults over 40 have vision loss from glaucoma

• 8.4 million bilaterally blind

• Half of all cases are undiagnosed in developed countries

Open vs. Narrow-angle glaucoma

• Open-angle

  • Optic nerve damage while the anterior angle is open

• Narrow-angle

  • Optic nerve damage from an acute or chronic rise in IOP from narrowed trabeculae

Most common glaucoma

• Primary open-angle glaucoma (POAG)

Risk factors for POAG

• High IOP

• Age

• Race

• Genetics

• Myopia

• Smoking

• Thin cornea

Work-up requirements for POAG exam

• 24-2 SITA-Standard

• RNFL OCT

• Macular OCT with GC analysis

• Pachymetry

• Gonioscopy

Secondary open-angle glaucoma

• Associated with a specific cause for a rise in IOP

• Pre-trabecular → Neovascular glaucoma

• Trabecular → Pseudo exfoliation, pigmentary glaucoma

• Post trabecular → Carotid-cavernous fistula

Symptoms of acute angle closure

• Intense ocular or peri-ocular pain

• Blurry vision, haloes around lights

• Nausea, vomiting

Acute angle closure signs

• High IOP (50-100 mmHg)

• Corneal edema

• Mid-dilated pupil

• Conjunctival injection

Optic neuritis

• Inflammation of the optic nerve

• Typically unilateral

• Pain on eye movements

• Associated with autoimmune conditions

  • Multiple sclerosis

Papilledema

• Bilateral swelling due to increased intracranial pressure

• Risk: Obese, young females

• Headaches

• Untreated → Optic atrophy

Regions of the macula

Perifovea (Outer) → Parafovea → Fovea → Foveola

Oxidation of the macula

• Macula is one of the most metabolically active tissues

• Light exposure → Reactive oxygen species (ROS)

• Defense: RPE transports ROS from subretinal space → Choroid

Age-related macular degeneration

Acquired degeneration of the retina that causes central vision impairment

• Non-exudative = Dry AMD

• Exudative/CNVM = Wet AMD

  • Choroidal Neovascular Membrane

Statistics about AMD

• Leading cause of blindness in the US for pts >60 yrs

• 8 million pts have early AMD

Risk factors for AMD

• Age

• Race

• Genetics

• Smoking

• Diet

• UV exposure

Drusen definition

Hard Vs. Soft drusen

• Build up of waste products from visual cycle metabolism

  • Partially digested photoreceptors

• Hard drusen → Small, yellow, discreet margins _(Image)

• Soft drusen → Large, yellow, nodules with indistinct borders

Geographic atrophy

• Late-stage AMD

• Loss of photoreceptors and RPE

• On the fovea → Permanent, central scotoma

Choroidal neovascular membrane

• New vessel growth from choroid → Leaks fluid into the subretinal space

• Finding that makes exudative-AMD “wet”

• Left untreated → Forms disciform scar

Bullseye Maculopathy

• Changes in RPE due to Hydroxychloroquine (Plaquenil)

• Irreversible

Risk factors for Plaquenil toxicity

• High daily dose

• Medication use > 5 years

• Concomitant renal or liver disease

• Age > 60 years

Screening requirements when bullseye maculopathy is presented

• HVF 10-2

• Macular OCT

Retinal capillaries supply….

Choricocapillaries supply…

• Retinal capillaries supply the inner 2/3rd of the retina

  • CRA/CRV

• Choricocapillaries supply the outer 1/3rd of the retina

  • Long and short ciliary arteries

  • Vortex

Retinal vein occlusion associated systemic disorders

• Hypertension 66%

• Hyperlipidemia 33%

• Diabetes 15%

Central retinal vein occlusion

• Thrombus formation at the ONH

• “Blood and thunder”

• Ischemic & non-ischemic form

What type of CRVO causes (+) RAPD

• Ischemic

Main mechanism of a BRVO

• Thickening/hardening of arterial wall

• Compression of vein at crossing point

CRAO is most likely caused by…

• Typically from cholesterol embolus

  • → Ischemia → Thickening + whitening of the retina → Necrosis

Signs of CRAO

• Cherry red spot

• 90 minutes to unlock → Permanent, irreversible VA loss

Changes in the retina from CRAO

• Acute thickening of the inner retina

• Thinning of inner retina upon resolution

Microangiopathy

• Damage to very small blood vessels

• Seen in diabetic retinopathy

  • Hyperglycemia degrades vessel walls

  • Inflammation + pericyte damage

Ischemia of the retina from diabetic retinopathy results in upregulation of…

• VEGF

  • Formation of new leaky blood vessels

Non-proliferative diabetic retinopathy (NPDR) signs

• Micro-aneurysm

• Dot and blot hemorrhage

• Cotton wool spot

• Venous beading

• Intraretinal microvascular abnormality (IRMA)

Signs of proliferative diabetic retinopathy (PDR)

• PDR → VEGF upregulation → Neovascularization

  • Neovascularization of the disc (NVD)

  • Neovascularization elsewhere (NVE)

• Neovessles = Fragile, leaky

  • Increased risk of DME

Main cause of decreased VA from diabetic retinopathy

Macular edema

• Occurs at any stage of DMR

• Exudates

  • Circular ring

  • Signal presence of DME

Clinically significant diabetic macular edema (CSME)

• DME defined by ETDRS VA score

Hypertensive retinopathy signs

• Arterial attenuation

• Copper wiring

• AV nicking (Picture)

• Venous tortuosity

• Optic disc edema

Retinal landmarks anterior to the equator

• Ora serrata

• Vortex veins

• Long + Short posterior ciliary nerves

Floaters

• Subjective perception of an opacity

• Dark/Translucent

• 1-2 is normal, many new floaters is concerning

Flashes

AKA photopsia

• Subjective perception of a burst of illumaince

• Occurs due to traction on the retina

• Concerning symptom

Lattice degeneration

• Focal patch of inner retinal thinning

  • Vitreous attached at the periphery

  • Vitreous liquified over the lesion

• Present in 8% of patients

Most common lesion associated with retinal detachment

Lattice Degeneration

• 40% of retinal detachments

• Associated with retinal holes

Retinal holes

• Atrophic (thinning)

• Operculated (Tractional)

• May have a cuff of edema

• Less likely to lead to attachment (Compared to retinal tears)

Horseshoe tear

AKA flap tear

• Apex attached to the vitreous

• Base attached to the retina

• Most common lesion leading to Rhegomatogenous retinal deatchment

Definition of retinal detachment (RD)

2 types

Detachment of the sensory retina from the RPE

• Mac-on → Fovea still attached

  • Treat immediately

• Mac-off → Fovea detached from RPE

  • Treated urgently (Within the week)

  • Damage already done

Retinochiasis

• Splitting the retina at the outer plexiform layer

• Causes an absolute visual field defect

• Most common inferior + temporal