IOL Selection in a Patient with Cataract and Significant WTR Astigmatism Example
This real world example demonstrates the process of IOL selection, to correct spherical refractive error and astigmatism optimally, in a patient having cataract surgery. This case was selected because of the significant astigmatism in each eye. This requires accurate preoperative measurements and marking, as well as intraoperative IOL alignment, to obtain optimal refractive results.
80 year old female with a visually significant left cataract and ATR astigmatism. Preoperative best corrected distance visual acuity (BCDVA) was 6/12 (20/40) in each eye. The following explains the method that resulted in the tIOL choices for each eye, using the preoperative measurements of Autokeratometry, Biometry and Topography. Calculations are performed using the Goggin Adjustment Factor, the Corneal Astigmatism and Toric Power Relationship, the Barrett Toric Formula and the Kane Toric Formula.
Cataract Surgery OD (Right Eye) using : Acrysof + 19.50D SN6AT7 @ 3
Cataract Surgery OS (Left Eye) using : Acrysof +19.50D SN6AT6 @ 162
Vertometry
Right Eye -3.50 + 4.00 x 60
Left Eye -2.75 + 2.50 x 1700
Auto Keratometry : Zeiss® Visuref 100
Right Eye Dioptre (D) Meridian (0)
R1 8.02 mm 42.00 D 93
R2 7.50 mm 45.00 D 3
Avge 7.76 mm 43.50 D
Cylinder 3.00 D 3
Left Eye
R1 7.90 mm 42.75 D 75
R2 7.56 mm 44.75 D 165
Avge 7.73 mm 43.75 D
Cylinder 2.00 D 165
Autokeratometry indicates the anterior corneal astigmatism is in the :
Right Eye 3.00 D at 30
Left Eye is 2.00 D at 1650
This tells us that the anterior corneal is significantly greater than 0.75 D which is the minimum threshold of astigmatism to be corrected. So, a tIOL is going to be used.
Biometry : Zeiss®IOL Master 700
The Biometry IOL Master 700 (Barrett TK Formula) tells us that if an Alcon Toric SN6AT IOL is to be used the likely Spherical Equivalent (SE) IOL Power, Toric Power (T2-9) and meridian is:
Right Eye is either +19.5 D or + 20.00 D T6 @60 (Ref SE = + 0.18, – 0.17 D)
Left Eye +19.5 D @ 166 (Ref SE = – 0.06 D)
The resultant refractive errors (spherical error and residual cylinder) are likely to be:
Right Eye (OD) either -0.41 + 0.48 x 6 or -0.06 + 0.49 x 6
Left Eye (OS) – 0.23 + 0.35 x 166
Kane Formula Calculations for Each Eye
These Kane Formula calculations for an Alcon SN6AT IOL for this patient are:
Right Eye (OD) IOL : + 20.0 D T7 at 50.
Left Eye (OS) IOL : + 19.5 D T5 at 1680
The resultant refractive errors (spherical error and residual cylinder) are likely to be :
Right Eye (OD) – 0.09 + 0.19 x 95
Left Eye (OS) + 0.05 + 0.03 x 78
Topography : Sharaz Daya Overview Nidek ® OPD III
Right Eye
Right Eye (OD) anterior corneal astigmatism is:
3.25 at 1800, and the WF Cornea Grp Low Order (net) Astigmatism is 3.75 at 40.
Topography : Sharaz Daya Overview Nidek ® OPD III
Left Eye
Left Eye (OS) anterior corneal astigmatism is :
2.38D at 1650. The WF Cornea Group Low Order (net) Astigmatism is 2.75 D at 1620.
Postoperative Results
Surgical Technique s described below (see Dr Macken’s preferred technique for Marking and Alignment).
Left cataract surgery was performed first.
At three weeks postoperatively, the uncorrected distance visual acuity (UCDVA) for the Left Eye (OS) = 6/6.
Autorefraction of the Left Eye (OS) at same visit was = – 0.25 DS.
As a result of the modest myopic postoperative result in the Left eye, the selected IOL for the Right Eye was the first hypermetropic (+) spherical equivalent power closest to emmetropia.
At three weeks postoperatively, the UCDVA Right Eye (OD) = 6/6
Autorefraction of the Right Eye (OD) at the same visit was = -0.50+0.50 x 180