|Year : 2014 | Volume
| Issue : 2 | Page : 57-61
Determination of post-operative toric IOL alignment - Analyzed by two different methods: Slit-lamp versus Adobe Photoshop
Javed Hussain Farooqui, Archana Koul, Ranjan Dutta, Noshir Minoo Shroff
Department of Cataract and IOL Services, Shroff Eye Center, New Delhi, India
|Date of Web Publication||6-Feb-2015|
Javed Hussain Farooqui
C-44, Panchsheel Enclave, New Delhi - 110 017
Source of Support: None, Conflict of Interest: None
Purpose: To compare two different methods of determining the post-operative position of the toric IOL and to calculate the alignment error with each method. Setting/Venue: Cataract and Intraocular Lens Implantation Service, Shroff Eye Center, New Delhi, India. Design: Case series Materials and Methods: Eighty-nine eyes of 61 patients with cataract and co-existing corneal astigmatism ranging from 1 to 4 diopters planned for toric IOL implantation were included. All eyes underwent pre-operative automated keratometry and biometry. Toric IOL cylindrical power, axis of implantation, and anticipated residual astigmatism were calculated using the web-based Acrysof Toric calculator. All eyes underwent pre-operative reference marking to denote the 0° and the 180° positions (using bubble marker) followed by digital slit-lamp photography. All eyes were operated by the same surgeon, at the same incision location. At 3 months, the achieved IOL alignment was analyzed by aligning the slit-beam of the slit-lamp with the pair of marks denoting the axis of the IOL after pupillary dilation. Additionally, the IOL position was determined after capturing a digital retro-illuminated slit-lamp photograph, which was superimposed on the pre-operative photograph using single prominent major episcleral vessel around the limbus as landmark. The axis of orientation of the toric IOL was determined using tools in Adobe Photoshop (version 7.0) by aligning a line through the marks denoting the IOL axis. The amount of alignment error (in degrees) by both methods induced with respect to the desired axis of alignment was calculated and statistically analyzed. Results: The mean pre-operative keratometry was 44.19 ± 1.51 D, and the mean corneal cylinder was 2.54 ± 0.90 D. The mean post-operative absolute cylinder was 0.57 ± 0.28 D. Toric IOL models used were T3(1.03 D): 28 eyes (31.5%), T4(1.55 D): 21 eyes (23.6%), T5(2.06 D): 18 eyes (20.2%), T6(2.57 D): 11 eyes (12.4%), T7(3.08 D): 4 eyes (4.5%), T8(3.60 D): 4 eyes (4.5%), and T9(4.11 D): 3 eyes (3.4%). Mean post-operative alignment error was 3.44 ± 2.60 D by the slit-lamp method and 3.89 ± 2.86 D by the Photoshop method with no significant difference seen between the two methods (P = 0.384). Fifty-six eyes (62.9%) by the slit-lamp method and 52 eyes (58.4%) by the Photoshop method had rotation error ≤ 5 degrees (P = 0.526), and 78 eyes (87.6%) by the slit-lamp method and 75 eyes (84.3%) by the Photoshop method had rotation error ≤ 10 degrees (P = 0.422). Conclusions: Both Adobe Photoshop method and slit-lamp observation were reliable and predictable methods of assessing IOL alignment. Although the sensitivity is more with the Photoshop method, the slit-lamp method is more accessible in an outpatient setup. The clinical outcome following toric IOL implantation can be refined by reducing the alignment error, which is dependent on an accurate keratometry and biometry, surgeon-specific SIA, reference and intra-operative marking, and finally, placement of IOL in the bag.
Keywords: Adobe Photoshop method, post-operative toric IOL alignment, slit-lamp method
|How to cite this article:|
Farooqui JH, Koul A, Dutta R, Shroff NM. Determination of post-operative toric IOL alignment - Analyzed by two different methods: Slit-lamp versus Adobe Photoshop. Sudanese J Ophthalmol 2014;6:57-61
|How to cite this URL:|
Farooqui JH, Koul A, Dutta R, Shroff NM. Determination of post-operative toric IOL alignment - Analyzed by two different methods: Slit-lamp versus Adobe Photoshop. Sudanese J Ophthalmol [serial online] 2014 [cited 2022 May 20];6:57-61. Available from: https://www.sjopthal.net/text.asp?2014/6/2/57/150996
| Introduction|| |
It has been estimated that 15% to 29% of patients with cataract have more than 1.5 diopters (D) of pre-existing astigmatism. , Apart from correcting corneal astigmatism with spectacles and contact lenses, treatment options include excimer laser refractive procedures such as photorefractive keratectomy, laser in situ keratomileusis, and laser-assisted sub-epithelial keratomileusis, astigmatic keratotomy using limbal or corneal relaxing incisions, opposite clear corneal incisions (OCCI), and toric phakic or pseudophakic intraocular lens (IOL).  Toric IOLs were developed to neutralize pre-existing corneal astigmatism in cataract patients.  They provide the opportunity to correct pre-existing astigmatism, offering patients optimum distance vision without the use of spectacles or contact lenses. 
There are various methods to align the toric IOL at the intended axis.  However, most methods follow a 3-step procedure. First, the horizontal axis (0 to 180 degrees) of the eye is marked preoperatively with patient sitting upright to correct for cyclotorsion. This is usually done using a reference marker or a slit-lamp along with a rotating slit. Next, intraoperatively, the desired alignment axis for the toric IOL is marked with an angular graduation instrument. Finally, the toric IOL is implanted and rotated until the IOL markings agree with the alignment marks. 
In our series, we have studied the achieved IOL alignment 3 months after surgery. Two different methods were compared to determine the post-operative position of the toric IOL using slit-lamp method and Adobe Photoshop (version 7). The purpose of this study was to compare the alignment error by the two methods as a means of establishing the post-operative position of the toric IOL. This was done to achieve an outcome as close as possible to emetropia.
| Materials and Methods|| |
Study design and patient population
This prospective study comprised recruitment of 89 eyes of 61 patients with corneal astigmatism ranging from 1 to 4 diopters presenting to the outpatient department of Shroff Eye Center, New Delhi from August 2012 to August 2013. All these cases underwent a conventional phacoemulsification under peribulbar anesthesia with implantation of Alcon AcrySof toric intra ocular lens by a single surgeon.
| Pre-operative assessment|| |
A detailed history was taken to exclude any ocular pathology. All patients underwent pre-operative ocular examination including slit-lamp examination, slit-lamp photograph (in the dilated condition was taken as baseline for assessing IOL alignment post-operatively), intraocular pressure measurement (by Nidek, NT4000 Auto Non Contact Tonometer), keratometry (using IOLMaster keratometer, Topcon KR-8100 Auto Keratorefractometer), axial length measurement (using IOLMaster keratometer), IOL power (calculation using 3 rd or 4 th generation formula (wherever applicable)), Schirmer's test (using Schirmer strips No. 41 Whatmann filter paper), Specular Microscopy (using SP 3000P specular microscope), fundus examination (by Indirect Ophthalmoscopy), IOL cylinder power, alignment axis, and anticipated residual astigmatism were calculated using web-based toric IOL calculator program available at http://www.acrysoftoriccalculator.com. Patient was counseled regarding explanation of the procedure along with a formal written consent, possible need for spectacles after the procedure; that the results may not be 100% and small degree of residual cylinder may occur.
Prior to surgery, the eye was anesthetized with 0.5% proparacaine drops. The patient was seated in the upright position and made to fixate at a distance target. A special Bubble marker (ASICO AE-2791TBL) [Figure 1] was used for marking the reference marks for identifying the 3-, 6-, and 9-o'clock positions on the limbus. The patient was made to sit while applying the reference marks [Figure 2] to compensate for the possible cyclotorsion, which may occur on lying supine. When the bubble was in between the two vertical lines, it indicated that the 3- and 9- wedges of the marker were truly horizontal. A special Gentian Violet pen was used to ink the wedges. The marker was gradually advanced towards the eye while the examiner ensured the bubble was in the central position when the wedges make contact with the limbus [Figure 3].
|Figure 1: Bubble marker (ASICO AE-2791TBL) used for pre-operative reference marking|
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|Figure 2: Bubble marker being used with the patient in upright seated position|
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| Surgical technique:|| |
INTRAOPERATIVELY, a three-plane near clear temporal corneal incision (2.75 mm) was made. A 5.5 mm capsulorhexis was performed followed by cortical cleavage hydrodissection and nuclear rotation. Nucleotomy was performed using a "Stop and Chop" phacoemulsification technique followed by cortical clean up. The Alcon AcrySof Toric IOL was implanted with an injector system and rotated appropriately to align the reference marks on the IOL surface with the corneal marks. The incision was adequately hydrated to ensure closure.
POSTOPERATIVELY, the patients followed up in the outpatient department at Shroff Eye Center on post-operative days 1, 7, 30, and 3 months
- Uncorrected visual acuity (UCVA) at day 1, 7, 30 and best corrected visual acuity (BCVA) at day 30 and 3 months.
- Slit-lamp examination on all post-operative visits to check AC reaction by Hogan's criteria.
- The achieved IOL alignment at 3 months was analyzed by aligning the slit-beam of the slit-lamp with the marks denoting the axis of the IOL after pupillary dilation [Figure 4]. In addition, the position of the IOL was determined after capturing a digital retro-illuminated slit-lamp photograph by a single masked observer. The post-operative photograph was imported in Adobe Photoshop (version 7.0) and by image analysis, the axis of orientation of the toric IOL was determined [Figure 5]. The amount of alignment error (in degrees) induced was noted both by slit-lamp method and by Photoshop method [Figure 6].
|Figure 4: Achieved IOL alignment at 3 months being analyzed by aligning the slit-lamp beam with the IOL marks after pupillary dilation|
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|Figure 5: Straight edge of a transparent rectangle aligned with the marks denoting the IOL plus axis|
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|Figure 6: After aligning the straight edge with the IOL marks, the degrees of rotation required for achieving the alignment is noted|
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| Statistical analysis|| |
Data analysis was done using descriptive analysis and frequency distribution to analyze age, sex, eye distribution, type of cataract preoperatively, most common model of toric intraocular lens implanted, anterior chamber reaction postoperatively, and contrast sensitivity.
Paired t test and Pearson correlation was used to correlate between corneal cylinder before and after toric intraocular lens implantation.
Statistical analysis was performed using SPSS for Windows software (version 15.0, SPSS, Inc.). The level of statistical significance was a P value less than .05.
| Results|| |
The mean age in our study was 64.09 years (SD = 11.688), with maximum number of patients being in age group of 55 years or younger (28.1%). In our study, we had 57% males (n = 37) and 39% females (n = 24). The mean axial length in our study was 23.97 mm (SD = 0.91) [Table 1]. The maximum number of toric IOLs were of T3 model, which was implanted in 28 eyes (31.5%) followed by T4 model in 21 eyes (23.6%) [Table 2]. The mean pre-operative cylinder was found to be 2.5403 D (SD = 0.9046), whereas mean post-operative absolute final cylinder was reported as 0.5703 D (SD = 0.28). This change was found to be statistically significant using Paired t test (P = 0.00) [Table 3]. The mean post-operative alignment error was found to be 3.43 degrees (SD = 2.6) on slit-lamp examination while it was calculated to be 3.89 degrees (SD = 2.8) on Adobe Photoshop in our study group [Figure 7]. In our study, according to the slit-lamp method, 56 (62.9%) patients and according to the Photoshop method, 52 (58.4%) patients showed misalignment of 5 degrees or less. Also, according to the slit-lamp method, 78 (87.8%) patients and according to the Photoshop method, 75 (84.3%) patients showed misalignment of 10 degrees or less [Figure 8].
|Figure 7: Mean post-operative alignment error slit-lamp versus adobe Photoshop|
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|Figure 8: Alignment error of ≤5° and ≤10° measured using slit-lamp and Photoshop|
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|Table 3: Mean pre-operative cylinder and absolute post operative cylinder |
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| Discussion|| |
Accurate positioning of a toric IOL is the most important factor determining the efficacy of the astigmatism correction.  Although precise axis alignment is critical to good outcomes of toric IOL implantation, misalignment of toric IOLs remains a major barrier to optimization of post-operative results.  In our study, we have compared two different methods of determining the post-operative position of the toric IOL and to calculate the alignment error with each method- slit-lamp versus Adobe Photoshop. The mean residual refractive astigmatism was 0.57 D (SD = 0.29 D) at the final follow up, which was at 3 months. This was similar to the study done by Bauer et al. where the residual refractive astigmatism was less than 0.75 D in 74% of eyes and less than 1.00 D in 91%.  Also, the mean post-operative cylinder was 0.92 D with STAAR AA4203 toric IOL and 0.53 D with AcrySof SN60T toric IOL in a comparative study done by Chang in the USA.  A study from Ruhswurm et al. showed the mean astigmatism was reduced to 0.84 D.  The residual refractive cylinder was less than 0.75 D in 62% of the eyes and less than 1.00 D in 81% of eyes.  Other studies have also shown similar results. A study done in Australia had a mean post-operative cylinder of 0.81 (SD = 0.59).  In our study, we found a mean alignment error of 3.44 degrees (SD = 2.60) by slit-lamp method and 3.88 degrees (SD = 2.86) by Photoshop method. Also, we found that 46 (71.9%) eyes showed misalignment of 5 degrees or less, 60 (93.8%) eyes showed misalignment of 10 degrees or less. Sixty-four (100%) eyes showed misalignment of 15 degrees or less. Initially, the U.S. Food And Drug Administration (FDA) trial results showed a mean misalignment of less than 4 degrees.  These results were correlating to other studies done around the world. In one study, done in Spain, mean toric IOL axis rotation was 3.63 degrees (SD 3.11).  Another study done in Australia showed mean IOL misalignment by slit-lamp to be 2.55 degrees (SD = 2.76) by slit-lamp method and 2.65 degrees (SD = 1.98) by internal map method.  A likely reason for the improved rotational stability of the AcrySof toric IOL is the stronger tendency for its hydrophobic acrylic material to adhere to the capsule. This 'tackiness' is in contrast to the slippery surface of a plate-haptic silicone IOL, which has shown to be far less adherent to the posterior capsule in animal studies.  Additional clinical advantages of the AcrySof toric IOL are its more popular single-piece acrylic design and the presence of a truncated posterior edge. 
We found that Adobe Photoshop method and slit-lamp observation were reliable and predictable methods of assessing IOL alignment. Although the sensitivity is more with the Photoshop method, the slit-lamp method is more accessible in an outpatient setup. The clinical outcome following toric IOL implantation can be refined by reducing the alignment error, which is dependent on an accurate keratometry and biometry, surgeon specific SIA, reference and intra-operative marking, and finally, placement of IOL in the bag.
| What was known|| |
- 15% to 29% of patients with cataract have more than 1.5 diopters (D) of pre-existing astigmatism.
- It is seen that with 10 degrees of axis deviation, 1/3 rd of the desired effect is lost. With 20 degrees of axis deviation, 2/3 rd of the effect is lost.
- Lens misalignment greater than 30 degrees will actually increase the net astigmatic error.
| What the paper adds|| |
- Both Adobe Photoshop method and slit-lamp observation were reliable and predictable methods of assessing IOL alignment.
- Although the sensitivity is more with the Photoshop method, the slit-lamp method is more accessible in an outpatient setup.
- Careful attention to correct axis positioning of the IOL at the time of surgery will help reduce rate of rotation.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]
[Table 1], [Table 2], [Table 3]