3. Average Range
Axial Eye Length 23.5mm 22.00-24.5
AC Depth 3.24mm Varies with AL
Lens Thickness 4.25mm Up to 6.9
Keratometry 43.0-44.0 D Usually within 1D of
each other
6. Calibrate & check the accuracy of the
keratometer
Explain the procedure to the patient
Should be done before AL measurement
If high or low results encountered, advisable to
have a 2nd person check the measurements
Repeat if the difference in total keratometric
power between the eyes exceeds 1.50 D
7. Poor patient fixation
Dry eye
Drooping eye lids
Irregular cornea
1 D error in measurement will cause a 0.9 D
of refractive error
10. a: Initial spike
(probe tip and
cornea)
b: Anterior lens
capsule
c: Posterior lens
capsule
d: Retina
e: Sclera
f: Orbital fat
11. a: Probe tip. Echo from tip of probe,
now moved away from the cornea and
has become visible
b: Cornea. Double-peaked echo will
show both the anterior and posterior
surfaces
c: Anterior lens capsule
d: Posterior lens capsule
e: Retina. This echo needs to have
sharp 90 degree take-off from the
baseline
f: Sclera
g: Orbital fat
12. It measures the distance from the
corneal vertex to the retinal
pigment epithelium by partial
coherence interferometry.
Provides following measurements:
.AL . Keratometry
. ACD . Lens thickness
.White to white distance
14. Immersion ultrasound IOL master
Posterior staphyloma Difficult Yes
Silicone oil Difficult Yes
Pseudophakia Variable Yes
4++brunescent lens Yes No
Central PSC plaque Yes No
Vitreous hemorrhage Yes No
Central corneal scar Yes No
15. Ensure the machine is calibrated and set for the
correct velocity setting
Echoes from cornea, anterior lens, posterior lens,
and retina should be present and of good amplitude
Gain set at a low level at which a good reading is
obtained
Don't push too hard – corneal compression commonly
causes errors
Must take reading of both eye
21. • SRK/T -Very long eyes >26mm
( High myopes)
• Holladay 1
-long eyes 24-26 mm
• Hoffer Q
-Short eyes<22mm
(Hypermetropes)
AL 22-24.5 mm- Either of the 3 formulas
22. Haigis formula
-Appropriate for all ranges of axial lengths
Holladay 2 - Currently most sophisticated formula
- Most accurate
- All ranges of axial lengths
- Requires 7 different variables
1.White to white
2. Lens Thickness
3. Corneal diameter
4. ACD
5. AL
6. Preoperative Rx
7. Patient’s Age
23. Sulcus Decrease by 1.0 D
ACIOL Decrease by 2.0 D
Scleral fixation IOL Increase by 2.0 D
24. Axial Length (mm) IOL Power (D)
17 28
18 27
IOL Power
Undercorrection
Age (years)
20% 2-4
10% 4-8
No Need >8
26. o Anterior surface is flattened with no change in the
posterior radius
o Important to store pre refractive surgery keratometry and
refractive power
o Formula
- Haigis L
- Masket Method
- Clinical History Method
- Contact Lens Method
- Shammas Method
- Double K SRK/T
- Online Calculators (doctor-hill.com, ASCRS)
27. o Low sound velocity results in sound
attenuation & difficulty in identifying retinal
spikes
o Proper sound velocity must be selected or
else long AL measurement is obtained
o Sound velocity in silicone oil
1040 m/s 5000 cs
980 m/s 1000 cs
28. Barrett Universal Formula- Can be used for
all eye types & all lens types
Verion Image guided system
Intraoperative Wavefront Aberrometry
Notas do Editor
Today's cataract surgeons have the most advanced phaco machines and premium intraocular lenses available to them, and patient expectations regarding surgical outcomes are at an all-time high. –
Twenty-five years ago, if you removed the cataract and implanted a lens, you were successful. Today, of course, that's not enough. Now, not only are we going to remove the cataract and implant a lens, but we are going to get patients seeing better without glasses than before they had their cataract. In fact, what we'd really like to do is give them clear uncorrected near and distance vision.
Accurate preoperative measurements play an important role in surgical outcomes. -
Accurate prediction of estimated lens position
(half a mm shift in lens position can have a dramatic effect on final vision)
Desired post op refraction
