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Quick Recap from Biometry

๏ Spherical Equivalent ๏ SPH EQ = SPH + (1/2 CYL)

๏ Eg +2.00/-4.00 x180๏ Eg -1.00/-2.00 x180๏ Eg +2.00/+2.00 x 180

Biometry Course3. Diagnostic Devices

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Equipment for Biometry Clinic

๏ Vision Testing๏ Biometer, Optical or Ultrasound๏ Measure K- Reading - Biometry, Auto K, Manual๏ Way of Calculating , Paper, on board calculator,

Internet

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Complex Patients and Complex Lenses

๏ Newer Generation Biometers, eg IOL Master 700๏ Immersion Ultrasound, B Scan Biometry๏ Topography, understanding front and back

surface of cornea๏ Useful for Premium IOL and Complex cases๏ Aberrometers, measure visual quality

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Busy NHS Clinic

๏ Standard Patient๏ Expect range of ALM to be normal range 22-27๏ Astigmatism under 2?๏ Standard biometer will be quick and accurate for

normal cases

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K Readings

๏ Based on formula ๏ KD = n-1/rmm

๏ Can vary instrument to instrument - Centration Pupil or Visual Axis - Area measured Zone or Ring

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Curvature

๏ The cornea is not a uniform shape๏ It varies depending on where we measure the K

reading- Auto Keratometer 3-3.3 mm- IOL Master 2.4mm- Pentacam 3mm

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K Readings Vary

๏ Where they are taken๏ Are they taken as an average over an area or at

a point๏ Changes in Refractive Index

X

X

X X

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Visual Axis vs Pupil Centre

๏ Pupil centre is not coincident with the

visual axis.๏ If the difference between them is too

great they may experience problems

with multifocal IOL

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Axial Length

๏ Optical ๏ Uses light to bounce off the retina๏ Problems with fixation๏ Have you measured RPE or ILM๏ Modern Biometers use composite

measure

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Signal to Noise Ratio

๏ Measure of clarity of the medium measurement

is taken through๏ The higher the noise the more difficult it is to

take and accuracy of measure decreases๏ However Good SNR does not always equal

accurate measurement.๏ Check other eye

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Question Time

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Case Study

• A colleague calls in a panic. He has implanted

the patient and ended up refractive surprise• PreOp • ALM R23.5 K1 43.15x178 K2 45.76 x 88• ALM L 20.81 K1 47x180 k2 47x90• Implant L 28 SuperLens A const 118 SRK/T• What caused the refractive surprise?• What steps would you take in your

investigation?

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Ultrasound

๏ Only used if - Cataract Dense (A scan)- Macular issue or further investigation needed

(B-Scan)- Some biometrists feel immersion biometry is

the most accurate

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White to White

๏ Can measure with a ruler, calliper, biometer,

topographer๏ Check for error messages, normally need to be

able to see at least 70% limbus for auto

measurement๏ Why are you measuring WtoW?๏ What type of lens implanting? AC Lens, PIOL?๏ Should you be measuring at sulcus or angle?

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White to White

๏ White to White ๏ Angle to Angle๏ Sulcus to Sulcus

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Anterior Chamber Depth

๏ What are you

measuring?๏ Anatomical -

Ultrasound๏ External ACD -

Optical

•

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Average MeasurementsMeasurement 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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Question Time

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Complex Cases

๏ Corneal surface is not regular๏ Need to understand how K readings are

measured

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K Readings

๏ Estimation of the curvature of Surface๏ Used to calculate power of IOL๏ Can get different measures taking measure in

different place

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Power Distribution

๏ 1 normal 1 ab showing variation

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Complex Cases

๏ Use topography/ tomography๏ Image front and back or cornea helpful to avoid

surprise in Toric patients๏ Aberrometry may help understand visual quality,

useful for Multifocal or Toric IOL

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Wavefront Basics

๏ Zernike is a way of describing a wavefront as it exits the eye๏ Different instruments measure different things

– Whole Aberrations (Eg OPD III)– Anterior Surface only (Eg Zeiss Atlas)– Anterior and Posterior Cornea (Eg Pentacam)

๏ In cataract we are interested in Anterior and Posterior Cornea

mainly as the rest will be removed with the cataract

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Aberrometers

๏ Becoming more common๏ Useful to determine vision๏ Eg Point Spread Function

HD AnalyzerHARRINGTON, YVETTEPreop1

Visiometrics3/16/2018 18:38

OD ManifestRefraction

Sph: Cyl: Axis:

UCVA:BCVA:

0.000 0.00 0

Simulation of the image on the patient's retina

SnellenDecimal

Double-pass Image

Retinal Image

Objective refraction images:

-1.750-1.500-1.250-1.000-0.500-0.2500.0000.250 -0.750

MTF cutoff (c/deg): 14.4450.110Strehl ratio:

Potential VA 100%:Potential VA 20%:Potential VA 9%:

0.50.40.2

20/4020/5020/100

MTF

2.6

Artificial pupil diameter: 4.0

No correction.

Notes:Best focus position:Selected focus position:

-0.750-0.750

Measured pupil diameter: 4.8

An OQAS product by Visiometrics

OSI:0 1 2 3 4 5 6

HD AnalyzerCARTER, JANEpreop

Visiometrics3/16/2018 18:03

OS ManifestRefraction

Sph: Cyl: Axis:

UCVA:BCVA:

1.500 -0.75 100

Simulation of the image on the patient's retina

SnellenDecimal

Double-pass Image

Retinal Image

Objective refraction images:

1.2501.5001.7502.0002.2502.7503.0003.250 2.500

MTF cutoff (c/deg): 47.4460.199Strehl ratio:

Potential VA 100%:Potential VA 20%:Potential VA 9%:

1.61.00.5

20/1320/2020/40

MTF

0.5

Artificial pupil diameter: 4.0

Astig. correction.One cylinder trial lens.

Notes:Best focus position:Selected focus position:

2.5002.500

Measured pupil diameter: 3.8

An OQAS product by Visiometrics

OSI:0 1 2 3 4 5 6

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Measuring the Wavefront

• How do we measure the wiggly line?

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Zernike Polynomials

• Shapes we fit together to describe the wavefront

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Question Time

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Thank you!

๏ We will email you some questions.๏ Please send your questions and comments to

emma@medsalesacademy.com๏ We look forward to seeing you on the next

course Topography & Interpreting Basic Reports