BIOMETRY COURSE Module 1 Anatomy & Vision Welcome to Anatomy - - PowerPoint PPT Presentation

BIOMETRY COURSE

Module 1 Anatomy & Vision

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Welcome to Anatomy

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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 of structures important for IOL Calculation

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What is a Cataract

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How we see

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Average Measurements

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How to read Spectacle Prescriptions

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What is Spherical Equivalent

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Different types of Test Chart

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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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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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Crystalline Lens

๏ About 10mm wide by 4mm thick ๏ Gets thicker with age ๏ Cataract develops as cells within lens get opaque ๏ Measurements used to calculate replacement lens

• Axial Length (length of eye)
• K Readings (curve of cornea)
• ACD (Depth of the anterior chamber)

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Retina

๏ Macula is the centre of vision ๏ Retina made up of layers ๏ Pathology - Age Related Macular Degeneration,

Diabetes, Tears, Holes

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Question Time

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Cataract

๏ Cataract is an opacification of the Crystalline lens ๏ Classification takes into account how the cataract was formed

– Age – Trauma – Drug Induced – Congenital – And also position

๏ Denser cataracts are more difficult to measure

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How we see

๏ Emmetropia - Perfect Vision ๏ Light entering the eye is “bent” to come to a focus on

the retina

Length of eye Retina Cornea Light Rays

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Myopia

๏ Eye is “too strong” Also known as short sight ๏ Light entering the eye is focussed short of the retina ๏ Vision is corrected by minus lenses

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Hyperopia

๏ Eye is “not strong enough” ๏ Light enters the eye and focusses behind the retina ๏ Vision is corrected using plus lenses

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Astigmatism

๏ Eye is “different powers in different directions” ๏ Corrected by lenses of different powers (900) apart

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Astigmatic Lenses

๏ Cylinders make things rotate

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Presbyopia

๏ In the ageing eye it is more difficult to focus for

near

๏ Plus lenses designed focus at 1/3m are used

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Average Dimensions

Measurement Average Normal Range K Reading 43 Ds 40-47 Ds Axial Length 23.5mm 22-26mm Pupil Size 5.5mm 3-9mm White to White 11.5mm 10-13mm CCT 555µm 500-600µm ACD 3.25mm 3.00-3.75mm

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Average Dimensions

Measurement Average Normal Range IOP 15-16 mmhg 10-20 mmhg Lens Thickness 4mm Thickens with age Retinal Thickness 300 microns Anterior Chamber Angle Varies 20-350

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Question Time

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Spectacle Prescription

Add is the amount added to the Distance Prescription to get the Reading Prescription Rx

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Spherical Equivalent

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SE = Sph + 1/2 Cyl

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This is used when an “average prescription” is needed

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KMean is similar and is the average between K1 and K2 (more later)

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Calculate the SE for the Left eye Distance Rx

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Types of Chart

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Snellen Test Chart used normally 6m

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Top Letter Distance tested

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Bottom Letter Line seen

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Eg 6/6 6/36

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LogMAR

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ETDRS

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5 letters on each line

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Line = 0.1 Letter =0.02

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LogMAR VA = Best line read +0.02 x (number of seen letters on last incomplete line)

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Near Vision Chart

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Terms for Vision

Term Explanation Amblyopia 1 eye can't see so well no matter how many lenses you put in front of it Aphakic The eye has no lens - patient has to wear very thick specs

• r Cls)

BCVA Best Corrected Visual Acuity Binocular Both eyes together CF Count Fingers - Patient can count fingers DCVA Distance Corrected Visual Acuity Dilation Drops to make the pupil larger. Will effect visual acuity Dioptre Unit of measure for power - K readings, Spectacle prescription etc HM Hand Movements - Patient can detect hands moved infront

• f face

Keratoconus A condition where the corneal curvature changes over time. Leads to very irregular K readings and very difficult to calculate IOL Monocular One eye eg: record monocular vision Monovision Correcting 1 eye to see for distance and 1 eye for reading. Can be done with contact lenses and IOLs Objective refraction The eye test is taken from a machine (auto refractor) or by shining a bright light on the eye and observing how it moves ( Ret- Retinoscope) PH Pinhole - Vision recorded with patient looking through a black lens with a small hole in it Phakic The eye has its natural crystalline lens Phakic IOL an IOL is fitted in the sulcus or anterior chamber in addition to the patients natural lens. To correct a refractive error Pseudophakic The eye has an IOL fitted to replace the lens subjective refraction The eye test is refined by asking the patient UCVA Uncorrected Visual Acuity Vision Recorded without correction Visual Acuiity recorded with correction

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Question Time

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Today we have learnt

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Anatomy of structures important for IOL Calculation

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What is a Cataract

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How we see

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Average Measurements

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How to read Spectacle Prescriptions

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What is Spherical Equivalent

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Different types of Test Chart

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Thank-you

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We hope this session was useful

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Please send us your questions

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See you on the next module

• Biometry