Posterior segment

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11 Posterior segment

Anatomy

Retina (Figure 11-3)

Neurosensory Retina (9 Layers)

Inner refers to proximal or vitreous side of retina

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Figure 11-3 Normal fundus as seen through indirect ophthalmoscope.

(From A Manual for the Beginning Ophthalmology Resident. 3rd edn, edited by James M. Richard. 1980, p. 122 Figure 60.)

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Figure 11-4 Neuronal connections in the retina and participating cells.

(From Schubert HD: Structure and function of the neural retina. In: Yanoff M, Duker JS (eds) Ophthalmology. London, Mosby, 1999.)

RPE

Monolayer of hexagonal cells with apical microvilli and basement membrane at base

RPE and outer segments of photoreceptors have apex-to-apex arrangement, resulting in a potential subretinal space

Merges anteriorly with pigmented epithelium of ciliary body

Functions

RPE cells may undergo hypertrophy, hyperplasia, migration, atrophy, and metaplasia

Choroid

Posterior part of uveal tract that extends from ora serrata (outer layers end before inner) to optic nerve. Attached to sclera by strands of connective tissue at optic nerve, scleral spur, vortex veins, and long and short posterior ciliary vessels; derived from mesoderm and neuroectoderm; 0.22 mm thick posteriorly and 0.1–0.15 mm thick anteriorly

Physiology

Visual pigments

4 types, each composed of 11-cis-retinal (vitamin A aldehyde) + a protein (opsin); 3 cone pigments and 1 rod pigment (Table 11-1)

Table 11-1 Visual pigments

Photoreceptor Pigment Peak sensitivity
Rod Rhodopsin 505 nm
Red cones Erythrolabe 575 nm
Green cones Chlorolabe 545 nm
Blue cones Cyanolabe 445 nm

Electrophysiology

Electroretinogram (ERG)

Measures mass retinal response; useful for processes affecting large areas of retina

Photoreceptors, bipolar and Müller’s cells contribute to flash ERG; ganglion cells do not

Light is delivered uniformly to entire retina, and electrical discharges are measured with a corneal contact lens electrode

Components (Figure 11-10)

Early receptor potential (ERP) (Figure 11-11): outer segments of photoreceptors; completed within 1.5 ms
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Figure 11-10 The photopic (cone-mediated) ERG is a light-adapted, bright flash-evoked response from the cones of the retina; the rods do not respond in the light-adapted state.

(From Slamovits TL: Basic and Clinical Science Course: Section 12: Orbit, Eyelids, and Lacrimal System. San Francisco, American Academy of Ophthalmology, 1993.)

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Figure 11-11 Normal human early receptor potential (ERP). This rapid response is complete within 1.5 ms and is believed to be generated by the outer segments. An intense, bright stimulus in the dark-adapted state is needed for an ERP to be obtained.

(Redrawn from Berson EL, Goldstein EG: Early receptor potential in dominantly inherited retinitis pigmentosa. Arch Ophthalmol 83:412–420, 1970. From Slamovits TL: Basic and Clinical Science Course: Section 12: Orbit, Eyelids, and Lacrimal System. San Francisco, American Academy of Ophthalmology, 1993.)

Disease states (Figure 11-14, Table 11-2)

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Figure 11-14 Electroretinogram patterns.

(From Slamovits TL: Basic and Clinical Science Course: Section 12: Orbit, Eyelids, and Lacrimal System. San Francisco, American Academy of Ophthalmology, 1993.)

Table 11-2 ERG patterns for various ocular diseases

Extinguished ERG abnormal photopic, normal ERG Normal a-wave, reduced b-wave Abnormal photopic, normal scotopic ERG
RP CSNB; Oguchi’s disease Achromotopsia
Ophthalmic artery occlusion X-linked juvenile retinoschisis Cone dystrophy
DUSN CVO  
Metallosis CRAO  
RD Myotonic dystrophy  
Drug toxicity (phenothiazine; chloroquine) Quinine toxicity  
Cancer-associated retinopathy    

Electro-oculogram (EOG)

Indirect measure of standing potential of eye (voltage difference between inner and outer retina) (Figure 11-16)

Depolarization of basal portion of RPE produces light peak; normal result requires that both RPE and sensory retina be normal

Retinal Imaging

Optical Coherence Tomography (OCT)

Creates cross-sectional image of tissue using light

Provides retinal thickness measurements and cross-sectional retinal imaging to ∼5–10 µm depending on light source; anterior segment spectral domain OCT is useful to image anterior segment, in particular the cornea and angle

Superluminescent diode fires beam of infrared light through fiberoptic Michelson interferometer at both the eye and a reference mirror; the reflected light from the retina is compared with the light from the reference mirror and analyzed so that the tissue reflectivity (similar to ultrasound) and density can be determined. With time-domain OCT (TDOCT), the reference mirror moves; with spectral-domain OCT (SDOCT) the mirror does not move and a Fourier transform is used to obtain imaging information (this makes SDOCT much faster than TDOCT)

Useful for optic nerve (glaucoma) and macular pathology (edema, hole, pucker); can compare thickness in cases of macular edema from one visit to next; can diagnose and differentiate vitreomacular pathology e.g. stage 1 macular hole vs full-thickness hole (≥stage 2) vs pseudohole or lamellar holes (Figures 11-17, 11-18)

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Figure 11-17 Optical coherence tomography principle.

(Adapted from Shuman JS, Hee MR, Puliafito CA et al: Quantification of nerve fiber layer thickness in normal and glaucomatous eyes using optical coherence tomography. Arch Ophthalmol 113:586-596, 1995. From: Yanoff M, Duker JS (eds) Ophthalmology. London, Mosby, 1999.)

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Figure 11-18 Stage 2 macular hole. A, fundus photograph, B, OCT.

(From: Yanoff M, Duker JS (eds) Ophthalmology. London, Mosby, 1999.)

Ultrasound

Acoustic imaging of globe and orbit

A-scan

1-dimensional display (amplitude of echoes plotted as vertical height against distance) (Figures 11-19 to 11-21)

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Figure 11-19 A-scan ultrasound demonstrating high internal reflectivity.

(From Friedman NJ, Kaiser PK, Pineda R II: The Massachusetts Eye and Ear Infirmary Illustrated Manual of Ophthalmology. 3rd ed. Philadelphia, Elsevier, 2009.)

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Figure 11-20 A-scan ultrasound demonstrating medium internal reflectivity.

(From Friedman NJ, Kaiser PK, Pineda R II: The Massachusetts Eye and Ear Infirmary Illustrated Manual of Ophthalmology. 3rd ed. Philadelphia, Elsevier, 2009.)

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Figure 11-21 A-scan ultrasound demonstrating low internal reflectivity.

(From Friedman NJ, Kaiser PK, Pineda R II: The Massachusetts Eye and Ear Infirmary Illustrated Manual of Ophthalmology. 3rd ed. Philadelphia, Elsevier, 2009.)

B-scan

2-dimensional display (amplitude of echoes represented by brightness on a grey scale image) (Figure 11-22)

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Figure 11-22 B-scan ultrasound demonstrating choroidal detachment.

(From Kaiser PK, Friedman NJ, Pineda R II: Massachusetts Eye and Ear Infirmary Illustrated Manual of Ophthalmology, 2nd edn. Philadelphia, Saunders, 2004.)

Specific lesions

(Tables 11-3 and 11-4) (Figures 11-22 to 11-27)

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Figure 11-23 B-scan ultrasound demonstrating serous retinal detachment with shifting fluid, shallow peripheral choroidal detachment, and diffuse scleral thickening.

(From Kaiser PK, Friedman NJ, Pineda R II: Massachusetts Eye and Ear Infirmary Illustrated Manual of Ophthalmology, 2nd edn. Philadelphia, Saunders, 2004.)

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Figure 11-24 B-scan ultrasound demonstrating scleral thickening and the characteristic peripapillary T sign.

(From Kaiser PK, Friedman NJ, Pineda R II: Massachusetts Eye and Ear Infirmary Illustrated Manual of Ophthalmology, 2nd edn. Philadelphia, Saunders, 2004.)

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Figure 11-25 B-scan ultrasound demonstrating elevated mass with underlying thickened choroid.

(From Kaiser PK, Friedman NJ, Pineda R II: Massachusetts Eye and Ear Infirmary Illustrated Manual of Ophthalmology, 2nd edn. Philadelphia, Saunders, 2004.)

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Figure 11-26 B-scan ultrasound demonstrating dome-shaped choroidal mass.

(From Kaiser PK, Friedman NJ, Pineda R II: Massachusetts Eye and Ear Infirmary Illustrated Manual of Ophthalmology, 2nd edn. Philadelphia, Saunders, 2004.)

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Figure 11-27 B-scan ultrasound of a patient with choroidal metastasis demonstrating elevated choroidal mass with irregular surface and overlying serous retinal detachment.

(From Kaiser PK, Friedman NJ, Pineda R II: Massachusetts Eye and Ear Infirmary Illustrated Manual of Ophthalmology, 2nd edn. Philadelphia, Saunders, 2004.)

Fluorescein Angiogram (FA)

Phases

choroidal filling, arterial, venous, recirculation

Disorders

Vitreous Abnormalities