BIOMETRY COURSE Module 1 Anatomy & Vision
Welcome to Anatomy Emma Deighan ๏ Trainer in Ophthalmology for 20 Years ๏ Please ask questions! ๏ Email emma@medsalesacademy.co.uk ๏ www.medsalesacademy.co.uk
Today we will learn Anatomy of structures important for IOL Calculation ๏ What is a Cataract ๏ How we see ๏ Average Measurements ๏ How to read Spectacle Prescriptions ๏ What is Spherical Equivalent ๏ Di ff erent types of Test Chart ๏ www.medsalesacademy.co.uk
Anatomy www.medsalesacademy.co.uk
Cornea ๏ Epithelium - Protects eye from outside Epithelial cells - Regenerates every 7 days Bowman’s Membrane ๏ Bowman’s Membrane - Strong boundary layer - Prevents objects penetrating stroma ½ mm Stroma ๏ Stroma - Main body of cornea - Gives transparent properties to cornea ๏ Decemet’s Membrane Decemet’s Membrane - Basement membrane for endothelium Endothelium ๏ Endothelium - Controls water flow in and out of cornea www.medsalesacademy.co.uk
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 www.medsalesacademy.co.uk
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) www.medsalesacademy.co.uk
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) www.medsalesacademy.co.uk
Retina ๏ Macula is the centre of vision ๏ Retina made up of layers ๏ Pathology - Age Related Macular Degeneration, Diabetes, Tears, Holes www.medsalesacademy.co.uk
Question Time www.medsalesacademy.co.uk
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 di ffi cult to measure www.medsalesacademy.co.uk
How we see ๏ Emmetropia - Perfect Vision ๏ Light entering the eye is “bent” to come to a focus on the retina Cornea Retina Light Rays Length of eye www.medsalesacademy.co.uk
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 www.medsalesacademy.co.uk
Hyperopia ๏ Eye is “not strong enough” ๏ Light enters the eye and focusses behind the retina ๏ Vision is corrected using plus lenses www.medsalesacademy.co.uk
Astigmatism ๏ Eye is “di ff erent powers in di ff erent directions” ๏ Corrected by lenses of di ff erent powers (90 0 ) apart www.medsalesacademy.co.uk
Astigmatic Lenses ๏ Cylinders make things rotate www.medsalesacademy.co.uk
Presbyopia ๏ In the ageing eye it is more difficult to focus for near ๏ Plus lenses designed focus at 1/3m are used www.medsalesacademy.co.uk
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 www.medsalesacademy.co.uk
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 Varies 20-35 0 Angle www.medsalesacademy.co.uk
Question Time www.medsalesacademy.co.uk
Spectacle Prescription Add is the amount added to the Distance Prescription to get the Reading Prescription Rx www.medsalesacademy.co.uk
Spherical Equivalent SE = Sph + 1/2 Cyl ๏ This is used when an “average prescription” is needed ๏ K Mean is similar and is the average between K 1 and K 2 ๏ (more later) Calculate the SE for the Left eye Distance Rx ๏ www.medsalesacademy.co.uk
Types of Chart Snellen Test Chart used normally 6m ๏ Top Letter Distance tested ๏ Bottom Letter Line seen ๏ Eg 6/6 6/36 ๏ www.medsalesacademy.co.uk
LogMAR ETDRS ๏ 5 letters on each line ๏ Line = 0.1 Letter =0.02 ๏ LogMAR VA = Best line read +0.02 x ๏ (number of seen letters on last incomplete line) www.medsalesacademy.co.uk
Near Vision Chart www.medsalesacademy.co.uk
Terms for Vision Term Explanation 1 eye can't see so well no matter how many lenses you put Amblyopia in front of it The eye has no lens - patient has to wear very thick specs Aphakic or 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 Unit of measure for power - K readings, Spectacle Dioptre prescription etc Hand Movements - Patient can detect hands moved infront HM of face A condition where the corneal curvature changes over time. Keratoconus Leads to very irregular K readings and very difficult to calculate IOL Monocular One eye eg: record monocular vision Correcting 1 eye to see for distance and 1 eye for reading. Monovision Can be done with contact lenses and IOLs The eye test is taken from a machine (auto refractor) or by Objective shining a bright light on the eye and observing how it moves refraction ( Ret- Retinoscope) Pinhole - Vision recorded with patient looking through a PH black lens with a small hole in it Phakic The eye has its natural crystalline lens an IOL is fitted in the sulcus or anterior chamber in addition Phakic IOL to the patients natural lens. To correct a refractive error Pseudophakic The eye has an IOL fitted to replace the lens subjective The eye test is refined by asking the patient refraction UCVA Uncorrected Visual Acuity Vision Recorded without correction Visual Acuiity recorded with correction www.medsalesacademy.co.uk
Question Time www.medsalesacademy.co.uk
Today we have learnt Anatomy of structures important for IOL Calculation ๏ What is a Cataract ๏ How we see ๏ Average Measurements ๏ How to read Spectacle Prescriptions ๏ What is Spherical Equivalent ๏ Di ff erent types of Test Chart ๏ www.medsalesacademy.co.uk
Thank-you We hope this session was useful ๏ Please send us your questions ๏ See you on the next module ๏ Biometry - www.medsalesacademy.co.uk
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