This document discusses accurate biometry measurements and toric intraocular lens (IOL) calculations for cataract surgery patients. It emphasizes the importance of precise keratometry and axial length measurements, and describes techniques to obtain accurate readings. It also discusses toric IOL calculators, choosing the appropriate residual astigmatism, proper IOL alignment and centration, and managing unexpected refractive outcomes. The document provides information on various multifocal IOL models and pearls for maximizing outcomes with these lenses.

1. M.Khanalri.MD
IOL CALCULATION FOR UNUSUAL EXPECTATION

2.  In recent years beneficial advances in IOL technology now offer
patients, premium IOL
 Aspheric designs
 Astigmatism correction (Toric IOLs)
 Simultaneous far and near vision correction
○ Multifocal IOLs (Restore, Tecnis zmb ,Symphony , Acrilisa,Panoptix)
○ Acommodative IOLs (Crystalens)
 Protective UV blocking capabilities.
 These new IOL’s are designed to solve more vision problem and
need more accurate biometry

3. Pearls for accurate biometry
Keratometry
 Measure K readings on an untouched clear cornea (no drops,
applanations)
 Take note of any dry eye or other ocular pathology
 Ensure that contact lens use has been discontinued
 Take two readings one week apart showing stable measurements
 Make sure the device is calibrated on a regular basis
 Have the patient blink frequently between measurements
 Manual
 Take at least three readings per eye to ensure accuracy and consistency of
measurements
 Repeated measurements should be within 0.12 D in each meridian
 IOL Master
 Alignment is important; make sure all six measuring points must be in
focus ,visible and between the two auxiliary circles

4. Pearls for accurate biometry
Axial length measurment
 Make sure your machine is set properly
 Phakic, pseudophakic, etc.
 Gates and gain
 Immersion
 Ensure all five spikes are high and steeply rising
 SD should be within 0.09 mm
 IOL Master
 Maneuver the central focusing spot within the measurement reticule to
obtain the best signal curve display
 You can defocus (in or out) if needed to improve the display
 Good Signal-to-noise ratio (SNR) above 2

6. Toric IOLs
 There are some pitfalls along the way that need to be
addressed.
 Measuring corneal astigmatism
 Toric IOL calculators
 Toric optimizer
 Choosing the residual astigmatic target
 Proper IOL alignment and centration
 Managing unfortunate outcomes of residual astigmatism and
higher-order aberrations

7. Toric IOLs
Measuringcorneal astigmatism
 Manual or automated keratometer usually measure four points on a ring
○ In manual keratometer points are 3.2 mm apart;
○ In IOLMaster points are 2.5 mm apart
○ In Lenstar has two rings and points 2.2 and 1.7 mm apart.
 For symmetrical astigmatism the result should be the same.
 Unfortunately, this is rarely the case In general, the smaller the sample
zone, the smaller the magnitude of the measured astigmatism and axes
will change if shaped like a crab claw

8. Toric IOLs
Measuringcorneal astigmatism
 Topography and tomography do a much better job, when
irregularity is present (thousands of points are measured within a 3 mm to 4.5 mm zone)
 The Sim K values use the same ring as the manual keratometer
and yield essentially the same values.

9. Toric IOLs
Measuringcorneal astigmatism
 In normal corneas with only slight irregularities, both
tomography and topography determined over a 3 mm to 4.5 mm
zone are superior to keratometry.
 For irregular corneas, measurements with these devices are
imperative. In most of these instruments, these area values are
referred to as zonal power and zonal astigmatism

10. Toric IOLs
Toric calculators
 The commercial calculators have
implemented the effect of the incision on the
corneal astigmatism
 One source of error, however, is the value of
the surgically induced astigmatism (SIA).
 The average magnitude of the SIA is usually
between 0.2 D and 0.7 D for small incisions (2.2
mm to 3.0 mm),but the actual magnitude and axis
vary widely within this range
 The meridian of the incision is normally within 7°
of the target, but this imprecision also adds to the
variability.

11. Toric IOLs
Toric calculators
 All of the toric calculators use an approximation method rather than
the exact solution.
 This involves using a constant for the ratio of the IOL toricity to
corneal astigmatism.
 The commercial ratios used are from 1.41 to 1.48 and are correct for a
22 D spheroequivalent power IOL and an average ELP of 5.50 mm
(equivalent A-constant of 118.9).
 The power of the IOL and depth within the eye (effective lens position,
ELP) are the two direct factors that influence this ratio
 The exact ratio is greater the lower the power of the IOL and the deeper
the IOL in the eye (ratio is 1.745 for a 10 D SEQ IOL at 6.5 mm ELP

13. Toric IOLs ( Acrysof Toric)
www.acrysoftoriccalculator.com

14. Toric IOLs (Acrysof Toric)
www.acrysoftoriccalculator.com

15. Toric IOLs ( Staartoric)
www.staartoric.com

16. Toric IOLs ( StaarToric)
www.staartoric.com

17. Toric IOLs (Acrilisa Toric)
www.meditec.zeiss.com/iolmaster-online

18. Toric IOLs (Acrilisa Toric)
www.meditec.zeiss.com/iolmaster-online

19. Toric IOLs (Acrilisa Toric)
www.meditec.zeiss.com/iolmaster-online

20. Toric IOLs (Hoya)
http://us.hoyatoric.com/

21. Toric IOLs (Hoya)
https://www.amoeasy.com/toric2

22. Toric IOLs
Toric incision location optimizer
 With the patient’s original keratometry readings and knowledge
of the magnitude of the SIA by location, it is possible to
determine the precise location of the incision to eliminate or
minimize the residual astigmatism.
 Notice there are four locations (50°, 130°, 230° and 310°) for
which the residual astigmatism is zero
 In any case, the computer can always find the best result with
the constraints present to give the surgeon the optimal locations
for the incision.

23. Toric IOLs
Choosingthe optimal residual astigmatism
 At the beginning of your experience with a toric IOL, you may be uncomfortable
placing the incision at any meridian ,so it will not be possible to completely eliminate
the final residual ocular astigmatism.
 For examplefor a patient with 1.5 D with-the-rule astigmatism you have two choices
○ 1.50 D toricity yielding 0.50 D × 90° of residual astigmatism (flipping the axis)
○ 2.25 D toricity yielding 0.12 D ×180 of residual astigmatism(mininmizing residual
astigmatism)
 Flipping the axis is only of concern in glasses, in which meridional aniseikonia and
spatial distortion from spectacles occur due to the base curves, power, astigmatism and
vertex distance.
 In toric IOLs the only difference is the size of the blur circle in the conoid of Sturm, so
the choiceshouldalwaysbe to minimizing the residual astigmatism.
 Onlyif the choiceis exactlyequal wouldyou choosethe IOL withlower toricity.
 If postoperatively the axis is flipped and the patient needs a spectacle, consider leaving
out the cylinder and giving the spheroequivalent prescription.

24. Toric IOls
Proper IOL alignment, centration
 Angle alpha is the angle betweenthe geometric centersof the cornea and crystalline
lens(or IOL) forming the optical axis andvisual axis of the which induces small
amounts of astigmatism and coma.
 For spherical surfaces this astigmatism and coma are on the order of 0.25 D to 0.50
D and have little effect on the final refraction.
 For toric surfaces (cornea and IOL), the tilt and decentration result in secondary
astigmatism, coma and other higher-order aberrations.
 For corneal astigmatism greater than 3 D, the induced aberrations are often the
limiting factor in the visual quality.
 The optimal location of the IOL on the 3 mm to 4 mm pupil should be decentered
slightly nasal in the bag to achieve pupillary centration.
 For toric IOLs, dueto this decentrationrelative to the cornea, it is usually impossible
to alignthe IOL toric markswith the markson the limbus; at best they can be
parallel to this axis

25. Toric IOls
Managingunfortunateoutcomes
 When the final refractive outcome has greater than expected residual astigmatism,
 The first step check for tilted or decenteration
 The second step is to measure the postoperative corneal astigmatism and make sure that the
alignment marks on the toric IOL are parallel with the steepest meridian of the cornea. If it is
not aligned with the postoperative steep meridian, then the treatment is to rotate the toric
IOL to this meridian.
 Back toric calculators also will be available that will take the postoperative refraction
and keratometry to calculate the axis of the toric IOL to confirm that it is the same
as the axis measured at the slit lamp. If the axis at the slit lamp and the axis
determined by the back calculator do not agree, then something else is wrong, such
as decentration, tilt or mislabeled toric IOL.
 A wavefront may be obtained, and if the coma, secondary astigmatism and other
higher-order aberrations are significant and they are not on the topographic
wavefront, then the IOL is decentered or tilted. In most of these cases, if the
wavefront is stable and repeatable, a wavefront-guided ablation may be performed
to achieve the best vision. Moving the IOL would be unpredictable for correcting the
higher-order aberrations.

26. Toric IOls
Managing unfortunate outcomes
Berdahl & Hardten Toric IOL Calculator

27. Measuring corneal astigmatismand calculating toric IOLs
Devices
 Various measuring methods are available, including
 manual keratometry,
 automated keratometry,
 corneal topography,
 slit-scanning technology,
 optical coherence tomography, and
 Scheimpflug imaging.
 The first three methods measure the anterior corneal surface only.
 Using a standardized corneal refractive index, most commonly 1.3375, they assume a
fixed posterior:anterior corneal curvature ratio to calculate total corneal power and
astigmatism.
 The second three methods measure the anterior and posterior corneal
surface.
 Therefore, they provide total corneal power and astigmatism based on the measured
anterior and posterior corneal data.

28. Measuringcorneal astigmatismand calculating toric IOLs
The role of the posterior cornea
 Recent studies) have shown the importance of considering the posterior
corneal surface when determining total corneal astigmatism and
planning astigmatism correction. The posterior cornea acts as a minus
lens.
 It generally has a steeper vertical meridian, and remains steeper vertically
with increasing age.
 The anterior corneal steeper meridian is also commonly oriented
vertically in younger individuals, but shifts towards the horizontal
meridian as patients get older.
 Thus, in general, posterior corneal astigmatismpartially
compensates for anterior corneal astigmatismin young adults
and increases total corneal astigmatismin older individuals.

29.  The mean magnitude of posterior corneal astigmatism is - 0.30 D.
 Koch et al. have shown that one cannot accurately predict the
posterior corneal astigmatism based only on anterior corneal
measurements.
 They found
 maximal values of posterior corneal astigmatism of over 0.8 D in corneas that had WTR
astigmatism on the anterior corneal surface and
 of over 0.5 D in corneas that had ATR corneal astigmatism on the anterior
corneal surface.
 The correlation between anterior and posterior corneal astigmatism
was
 moderate when the steep anterior meridian was aligned vertically,
 weak when it was oriented obliquely, and

30.  They found an overestimation of WTR astigmatism of
 1) 0.5 to 0.6 D in eyes that had WTR astigmatism on the anterior
corneal surface and
 2) 0.2 to 0.3 D in eyes that had ATR corneal astigmatism on the
anterior corneal surface.
 Posterior corneal astigmatism can be measured directly using
devices such as the dual Scheimpflug analyzer, although the
accuracy on an individual basis is still uncertain.
 Alternatively, one can account for posterior corneal astigmatism using
nomograms such as the Baylor Toric IOL Nomogram

31. Baylor Toric IOL Nomogram

33. Maximizing outcomes
 Accurate selection of patients
 Biometry : Calculation of lens power
 Choice of lens model
 Construction of astigmatically neutral incision
 No perfect device available for correction of presbyopia
 Patients should have reasonable expectations
 Operate on healthy eyes
 Best candidates presbyopic hyperopes
 Patients who must drive at night not generally good
candidates for multifocal IOLs

34. Choice of lens model
 Refractive Multifocal IOLs
 ReZoom:
 M-flex:
 Sulcoflex:
 AF-1 iSii:
 Diffractive Multifocal IOLs
 ReSTOR: spectacle independence of 88% reported
 TECNIS: 93% spectacle independence reported
 TECNISSYMPHONY
 Acri.LISA:, toric version corrects £12 D
 PANOPTIX

35. Multifocal IOLs
Restore ,Rezoom and …
 Accurate preoperative biometry is essential to attaining optimal results with the Multifocal IOLs.
Preoperative biometry measurements include axial length and corneal curvature.
 Axial Length
 Use of a IOLMaster (optical biometry ) or standard immersion A-scan is recommended
 Keratometry
 manually or by an automated method.
 Personalisation
 It is important to target emmetropia and to personalise the A constants for all IOLs.
 Formula
 Calculations on patients with axial lengths of between 22 and 25 mm with corneal powers of between
42.00 and 46.00 D will do well with current third-generation formulas (the Holladay 1,SRK/T,and
Hoffer Q). For cases outside this range, the Holladay 2 or optimized haigis should be used to ensure
accurac
 Astigmatism
 Post-operative astigmatism needs to be reduced to one diopter or less. For patients with astigmatism
greater than this, limbal relaxing incisions, LASIK, or other corneal refractive procedures may be
needed

36.  Although IOL design is the primary factor in the constant , variation in surgical technique such as
 The placement of the Iol
 The location of the incision
 design of the axiometers and keratometers also affects the personalized lens constant
 Most surgeon must perform 20 to 40 cases in order to personalize their lens constant
A constant
nominal
A constant
SRKII
A constant
SRKT
Haigis
A0
Haigis
A1
Haigis
A2
P ACD SF
Restor
SA60D3
118.1 118.7 118.5 -0.123 0.099 0.189 5.23 1.46
Restor
SA60D1
118.9 119.3 119.1 0.385 0.197 0.204 5.61 1.83
Acrilisa
tri839MP
118.3 119.0 118.9 -1.477 0.058 0.262 5.48 1.72
AMO Tecnis
ZMB00
118.8 119.7 119.7 1.73 0.40 0.10 5.96 2.15
Alcon Panoptix
TFNT00
119.1 119.3 119.1 1.39 0.40 0.10 5.63 1.83
AMO Tecnis 1
ZCB00
118.8 119.6 119.3 -1.302 0.210 0.251 5.80 2.02
Multifocal IOLs
Personalization…

37. Multifocal toric IOLs and online calculation

38. Multifocal toric IOLs and online calculation

39. Multifocal IOLs
CHOOSINGTHEPOSTOPERATIVEREFRACTIVETARGET
 Determining the desired postoperative refractive target for multifocal IOLs is slightly
different than for monofocal IOLs, where a slight amount of myopia may be beneficial.
 With the refractive ReZoom and AcrySof Restor ,Panoptix, Acrilisa or Tecnis multifocal
the target should be
 exactly zero (plano) or the nearest hyperopic choice to zero. Patients' near vision with each of these
lenses is excellent, but slight myopia moves the near point too close for comfortable reading.
 With the Symphony aim for plano in 1 eye and -0.75 in the second eye to get excellent
reading and distance vision
 With the Crystalens accommodating IOL the refractive target may be
 slightly myopic (-0.50 D) for the patient's "reading eye" to achieve slightly better near vision.
 This choice must be discussed with patients, however, especially if they may compare their
two eyes for distance.
 They should understand the possibility of a slight sacrifice in depth perception to have near
vision in one eye.

41. Accommodative IOLs
Crystalens
 Care should be taken to achieve excellent biometry by optical
methods to measure the axial length, such as partial coherence
interferometry
 In order to maximize the patient's visual results, we need to
address the corneal astigmatism to ensure that it is
approximately 0.50D or less for most cases.

43.  The SRK-T formula will be used for eyes with axial lengths measuring 22.01 mm or longer
 Recommended starting A constant for the
 Crystalens AO™ is 119.1,
 Crystalens HD™ is 118.8, and
 Crystalens Five- O™ is 119.0
 The Holladay II formula will be used for eyes with axial lengths measuring 22.0 mm or shorter
 The Holladay II is suggested for eyes with Ks flatter than 42.00 D or steeper than 47.00 D independent
of axial length
 Manufacturer’s recommended starting ACD for
 Crystalens AO is 5.61,
 Crystalens HD is 5.43, and
 Crystalens Five-O is 5.55
 The typical accommodative amplitude with Crystalens implantation is about 1.50D to 1.75D.
 With this in mind,
 the dominant eye should be targeted as close to plano as possible and
 the non-dominant eye targeted for a slight amount of residual myopia, approximately -0.50D, in order to further
enhance the near vision..
Accommodative IOLs (Crystalens )
IOL Calculations and TargetRefractions

44.  For the Crystalens HD, the optimal refractive target for each eye is plano. In those cases where the lens
calculation does not result in a lens that targets plano, the following is suggested:
 Distance eye: select the lens that predicts the first plus outcome above plano
 Near eye: select the lens that predicts the first minus below plano
 For the Crystalens AO and Crystalens Five-O:
 Distance eye: select a lens that predicts between plano and -0.25
 Near eye: select a lens that targets between -0.25 and -0.50
 Note: the lens power selection may have to be adjusted based on the refractive outcome of the first eye.
 In choosing which eye to operate on first, select the eye with the worse cataract. If cataracts are equal, select the
eye most likely to impress the patient.
Accommodative IOLs (Crystalens )
IOL Calculations and Target Refractions

47. Post-Op Evaluations
 Because Crystalens patients can accommodate,you should refract them as you would a young
myope which is very different from your normal post-op routine
 Before the examination most patients are sitting in the waiting room reading which means they are
probably accommodating
 Evaluate all distance measurements before doing intermediate and near measurements
 Ensure that the UCDVA and the target outcome correlate - Auto-refractors tend to over-minus—
DONOT use this sphere as your starting point – Tell the patient the letters might appear blurred
and see how far down the chart they can read Isolate the line that is two lines above the lowest line
that the patient can read. Slowly add plus sphere power until the line is fully blurred. It may take
1.50 D to 2.00 D of additional plus sphere to accomplish this.

48. Post-Op Evaluations
 Isolate the 20/25 line.Tell the patient it will be blurred.Slowly add minus until the patient can read
it.Next,isolate the 20/20 line and add minus sphere in small steps. Only give minus if the patient can read
more letters. Do not use the “which is better?” technique.By relying on letters read,you are making this a more
objective test.
 Refine the cylinder axis and power with the Jackson Cross Cylinder
 Maintain spherical equivalent by adjusting 0.25 D of sphere for every 0.50 D of cylinder change
 Have the patient read the smallest line possible At this point,the patient has to“earn”any more minus.
 If they can read more letters,or if it is“definitely clearer,” they get it. If they cannot see more letters, or if it is
“darker and smaller,”they DONOT get additional minus.
 Generally,you have reached your end point if adding a little plus makes the image blurred, and if you add
minus, it stays the same or darker.No matter how much they might like more minus, you have to stop unless it
truly helps them see better. Do not hesitate to repeat fogging if you think it is necessary. It is faster and easier
to do it now, rather than coming back after the next set of steps.(You can add +1.00 D sphere, change the
smallest line, and slowly reduce and slowly reduce power by 0.25 D steps to see if you have the same endpoint.

49. Post-Op Evaluations
 Measure uncorrected intermediate visual acuity (UCIVA) at28”to 32”and the uncorrected near visual acuity
(UCNVA) at16”, again giving the patient time to blink and focus
 Measure all ranges of vision (distance,intermediate,and near) as above, but through the distance correction
with the near card at16”,slowly add plus over the distance correction in 0.25D steps until the patient can
readJ1.If the add is more than +1.50 D, you may have over-minused the sphere.
 Do the uncorrected visions (all ranges) correlate with the refraction? • If you think the patient may be over-
minused and you cannot “undo”it,recheck the UCDVA.If the vision has decreased since the start of the
examination,ask the patient to relax and refocus at a distance target.
 Cycloplegic Refraction : If your patient is not reading J3 or better through the distance correction, you must do
a cycloplegic refraction to rule out subtle hyperopia/over-minus/accommodative spasm
 This is a very important step in assessing the true maximum plus refraction in an accommodating Crystalens
patient After following the steps above, give the patient Cyclopentolate® 1%, 1 drop q5 min x2.Wait at least 30
minutes before refracting(the patient may dilate before they are actually cyclopleged).
 Refine the refraction.Measure distanceVAonly.