IOL Master

This ppt is about IOL master machine

1. IOL Master Presented By Shagufta Kadri B.Sc ( Optom ) 3rd year Aditya Jyot Institute of Optometry

2. Optical Biometry The IOL master is a combined Biometry device for measurements of Human eye required for the pre- operative computation of IOL power. It uses Optical Low Coherence Reflectometry a similar technology that is used in OCT devices.

3. History Albert Michelson (1852 – 1931) the first American scientist to win the Noble Prize, invented the Optical interferometer. The Michleson Interferometry has been widely used for over a century to make precise measurements of wavelength and distance

4. Principle Based on Partial coherence intereferometry (PCI): Diode laser (780nm) measures echo delay and intensity of infrared light reflected back from tissue interfaces – cornea and RPE. The Interference produces dark and light band pattern which is detected by a photo detector. The signals are amplified, filtered and recorded as a function of the position of the interferometer mirror

5. Principle An optical encoder is used to convert the measurements into axial length measurements.

6. Optical Biometry Joystick Display Canthus alignment Instrument lock knob Connector panel Mouse connector Keyboard connector Keyboard optional: printer

7. Intended use of the device Axial length measurement Corneal curvature Anterior Chamber depth White to white dot Calculation of the required IOL

8. Optical Biometry ALM: It is based on patented interference optical method known as partial coherence interferometry . Corneal curvature: It is determined by measuring the distance between reflected light images projected onto the cornea. ACD: It is determined as the distance between the optic sections of the crystalline lens and the cornea produced by lateral slit illumination. White to white dot: It is determined from the image of the iris

9. Axial Length Measurement ALM: The IOL master requires 5 measurements to be taken. The meassage measure again will appear. With stronger lens opacities,it may be advisable to defocus the device. Defocusing and shifting the reflection within the circle will have no effect on the result, because interferometric axial length is completely independent of the distance. AL <22mm (indicates short ocular axis) AL >25mm (indicates long ocular axis)

10. Axial Length measurement When both eyes have been measured, the difference in AL between right and left is also checked.If the latter exceeds 0.3mm a message appears to check the reading agai n ALM modes: Phakic Psuedophakic Aphakic Silicone filled eyed

11. Keratometry Reading Corneal curvature: The IOL master requires 3 K’metry reading . The IOL master reflex 6 points of light, arranged in 2.3 mm diameter hexagonal pattern (measured by digital callipers ) from the air/tear film interface. The seperation of opposite pairs of lights is measured objectively by the instruments internal software and the toroidal surface curvatures calculated

12. K’metry reading In some cases Eg : ( Keratoconus,Keratoglobus , corneal lesions etc) it may not be possible to reach the green traffic light for optimum measurement. The following possibilities may come out: R >8.4mm Very flat corneal curvature R <7.2mm Very steep corneal curvature (R1 - R2) – 0.5mm High Astigmatism If the difference in the Keratometry readings between two eyes exceeds 0.2mm or 1D, you have to check the readings.

13. K’metry reading If the last 3 readings differ by more than 0.5D or if the tolerance of the mean radius of the last three readings of 0.08 to 0.01mm is exceeded the evaluation has to be checked.

14. ACD measurement The lateral slit lamp is automatically turned on.This illumination subjectively appears to be very bright to the patients. The ACD may only be measured on phakic eyes! ACD measurements on pseudophakic eyes resulting in measuring errors and/or incorrect readings. The readings for pseudophakic eyes do not reflect the anterior chamber depth. Five ACD readings will be taken,togther with the calculated mean.

15. White to White dot measurement Ask the patient to look at the fixation point. Focus on the iris not on the spot light The validity of the WTW determination depends on this check of correct recognition of the iris edge. The WTW is the horizontal diameter of the iris.In addition of the wtw value,the deviation of the visual axis from the centre of the iris (X,Y) will also be displayed.

16. IOL calculation Once all the measurements have been taken (depending on the IOL calculation formula)options can be generate for IOL to be implanted. Click on the appropriate tab to select the desired formula. The IOL Haigis , HofferQ , Holladay, SRK 2 and SRKT formulas are implanted as standard. After Refractive corneal surgery the Haigis -L formulae may be selected.

17. Optical Biometry SNR (Signal to Noise) ratio RED indicates incorrect value Yellow indicates Uncertain value/Borderline Green indicates good value

18. Screen Layouts

19. Screen layouts ALM

20. Screen layouts Keratometry reading

21. Screen Layouts (white to white dot)

22. Advantages Learned very quickly Extensive integrated safety features Non contact measurements It gives the true refractive length than anatomical axial length. Accuracy of IOL master is 0.02um wich is operator dependent.

23. Advantages It is upright non contact, ultra high resolution biometry. Highly ametropic patient can wear glasses while sitting on the IOL master which aids in fixation. It has the advantage of measuring fovea in case of posterior staphyloma .

24. Limitations Cannot measure AL in media opacities like corneal opacities, dense cataract, NS IV grade, posterior polar cataract. Cannot measure axial length in case of vitreous haemorrhage . Difficulty in measuring axial length in Infants, small children and mentally handicapped patients. Patients with poor fixation.