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Mar 29, 2023 938 likes •1.23k views

1. Anatomy and Topography Devices www.medsalesacademy.co.uk www.medsalesacademy.co.uk Welcome to Anatomy & Topography Devices Emma Deighan Trainer in Ophthalmology for 20 Years Please ask questions! Email

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1. Anatomy and Topography

Devices

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Welcome to Anatomy & Topography Devices

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Emma Deighan

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Trainer in Ophthalmology for 20 Years

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Please ask questions!

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Email emma@medsalesacademy.co.uk

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Today we will learn

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Anatomy - Anterior Segment

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Pathology - Keratoconus, scars, PMD, Dry Eye

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History of Topography

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Placido

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Statistics and Indices scales

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Scanning Slit, Scheimpflug

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Anatomy

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Cornea

๏ Epithelium

Protects eye from outside
Regenerates every 7 days

๏ Bowman’s Membrane

Strong boundary layer
Prevents objects penetrating stroma

๏ Stroma

Main body of cornea
Gives transparent properties to cornea

๏ Decemet’s Membrane

Basement membrane for endothelium

๏ Endothelium

Controls water flow in and out of cornea

Epithelial cells Bowman’s Membrane Stroma Decemet’s Membrane Endothelium

½ mm

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Dua’s Layer

๏ Posterior-most 10 - 20 μm of the stroma ๏ provides a plane of cleavage in DALK.1, 2

1. Dua HS, Faraj LA, Said DG, Gray T, Lowe J. Human corneal anatomy redefined: a novel pre Descemet's layer (Dua's layer). Ophthalmology 2013; 120: 1778–1785. [PubMed] [Google Scholar] 2. Dua HS, Mastropasqua L, Faraj L, Nubile M, Elalfy MS, Lanzini M et al. Big bubble deep anterior lamellar keratoplasty: the collagen layer in the wall of the big bubble is. unique. Acta Ophthalmol 2015; 93: 427–430. [PubMed] [Google Scholar]

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Cornea Dimensions

๏ Dimensions

Width ( White to White) 11.5-12.5mm
Depth (Central Corneal Thickness) 550 microns
Curvature (K readings) 43-46 D

๏ Associated Structures

Limbus
Connection between the Sclera (White of the Eye) and

the Cornea

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Anterior Chamber

๏ Made up of

Aqueous, Iris, Pupil

๏ About 2.75mm deep (3.25 if measured including the

cornea)

๏ Aqueous flows to maintain eye pressure (IOP)

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Anterior Chamber Dimensions

๏ ACDepi - from Anterior Surface of Cornea

to lens Ave 3.25

๏ ACDendo - From Posterior Surface

cornea to Lens Ave 2.75

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Pathology

๏ Keratoconus ๏ Scarring ๏ Graft ๏ Fuchs Dystrophy ๏ Dry eye

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Corneal Curvature

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K readings

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K1 & K2

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Only measured at specific point

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Today we will look at corneal curvature over the whole surface

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Front and Back!!

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Topography

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First described by Christopher Schiener in 1619

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Discovered reflecting images in a marble gave an idea of their shape

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Theodore Scheimpflug expanded on an idea from an Englishman to develop the Scheimpflug principle to photograph mountains

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Topographer vs Topographer

๏ Topography - Reflected Image eg Placido ๏ Tomography - Slice images built into 3 D image eg

Schiempflug

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Placido

๏ Measures anterior surface only ๏ Reflected Image in tear film ๏ Assumes centre of pupil in the

same place as fixation

๏ Assumes curvature there is

zero

๏ Watch out for big noses

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Placido

๏ However

Good for astigmatism and axis
Measuring curvature in different

points

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Placido

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Indices

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Pentacam Indices

IHD Index of Height Decentration Value of decantation of anterior surface height data in vertical meridian KI/ CKI Keratoconus Index ISV Index of surface variance Variance in curvature from mean anterior corneal curvature IVA Index of Vertical Asymmetry Anterior Corneal vertical curvature compared to upper and lower areas IHA Index of Height Asymmetry Anterior Surface height compared upper and lower area

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Scheimpflug vs Placido

Pentacam Topographer

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What is Scheimpflug

๏ Camera used to image the anterior

segment

It is based on the Scheimpflug

principle

Allows a cross sectional view of

the structures

Various reports and analysis are

linked to the sw

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Scheimpflug

Scheimpflug allows greater depth of focus
Uses camera in different plane to object

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Why is it good for the eye?

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Cross Section of Anterior Chamber and Lens

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Edge Detection

Anterior surface of Cornea to posterior

surface of Lens

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3-D

๏ 3D model computed using

ray tracing

๏ Eyetracker corrects small

saccadic movements

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4 Maps Refractive

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Today we have learnt

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Anatomy - Anterior Segment

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Pathology - Keratoconus, scars, PMD, Dry Eye

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History of Topography

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Placido

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Statistics and Indices scales

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Scanning Slit, Scheimpflug

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Thank you!

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We will email you some questions.

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Please send your questions and comments to emma@medsalesacademy.co.uk

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We look forward to seeing you on the next course Interpreting Basic Reports