Abstract
Background
The purpose of this prospective observational study is to analyse posture-induced cyclotorsion in eyes undergoing conventional phacoemulsification with toric intraocular lens (IOL) implantation and femtolaser-assisted cataract surgery (FLACS) using the Verion image-guided system.
Methods
Cyclotorsion was assessed in patients who underwent conventional phacoemulsification with toric IOL implantation and FLACS between June 2017 and November 2017 with registration of iris architecture, limbal and bulbar conjunctival blood vessels acquired preoperatively using the Verion Reference Unit (the patient in sitting position) and intraoperatively under the microscope using the digital marker of the Verion image-guided system with the patient in supine position.
Results
Forty-four eyes of 30 patients (21 men and 9 women) were included with the mean age of 56.5 ± 17.1 (range, 19–89; median, 62) years. The mean cyclotorsion induced by change in posture from sitting to supine position was 5.84 ± 3.25° (range, 1–17; median, 5). Overall, clockwise (CW) rotation (59.1%) was noted to be more common than counter clockwise (CCW) rotation (40.9%). Furthermore, CW rotation was more common in men than in women, and CCW rotation was significantly more common in women. Patients who underwent bilateral sequential cataract surgery show similar cyclorotation (CW or CCW) in both eyes more often than mixed rotation (85.7% vs 14.3%).
Conclusion
Significant cyclotorsion can occur in supine position during cataract surgery. Accurate assessment of the amount and direction of cyclotorsion aids in appropriate alignment of the toric IOL for optimal visual outcomes.
Keywords: Astigmatism, Cyclotorsion, Postural ocular rotation, Toric intraocular lens, Verion image-guided system
Introduction
Cyclotorsion induced by change in posture is an important factor to be considered for correction of astigmatism in cataract and refractive surgery. With the introduction of toric intraocular lenses (IOLs) to correct astigmatism at the time of cataract surgery, accurate positioning of the IOL is very important for good visual outcomes. In a previous study, a residual cylinder of one third corneal astigmatism was noted when a toric IOL was misaligned by 10° in the presence of equal cylinder values for the cornea and IOL.1 There was 100% loss of astigmatic correction when the toric IOL was 30 degrees off the target axis.2
Previous studies using keratometry/double Maddox rod tests concluded that body position did not significantly influence ocular torsion, but under monocular viewing conditions, significant cyclotorsion occurred.3,4 Subsequently, various studies carried out on patients with laser in situ keratomileusis (LASIK) showed significant cyclotorsion from sitting to supine position.6,11,15
The Verion image-guided system (Alcon, Fort Worth, TX, USA), consisting of a reference unit and a digital marker, is an image-guided system which is being used by the cataract surgeons in patients undergoing toric IOL implantation for accurate placement of incisions and the toric IOL. The reference unit has a keratometer to calculate the IOL power and an imaging device which gives a still image of the eye and records the limbus, pupillary diameter, position of pupil and corneal reflex. During surgery, the digital marker provides image registration of the perilimbal conjunctival vasculature, limbus and iris structures which is then aligned with previously measured parameters taken by the reference unit. Therefore, posture-induced cyclotorsion is corrected, and accurate placement of incisions and good alignment of the toric IOL is achieved. To our knowledge, this will be the first study to measure cyclotorsion from sitting to supine position using the Verion Reference Unit (Alcon Laboratories, Inc.) image-guided system. This could have important implication in the correction of astigmatism in refractive cataract surgeries.
Material and methods
Consecutive patients with cataract from the outpatient department scheduled for femtolaser-assisted cataract surgery (FLACS) with IOL and conventional phacoemulsification with toric IOL implantation from 1st March 2017 to 31st May 2017 have been included in the study. Corneal ectasias such as keratoconus, previous refractive surgery and corneal transplantation were excluded. The study was approved by the Institute's Ethics Committee and adhered to the tenets of the Declaration of Helsinki. Using Verion image-guided system (Alcon, Fort Worth, TX, USA), a preoperative scan of both eyes was performed in the sitting position. Subsequently, during cataract surgery, cyclotorsion was measured in supine position before giving incisions in conventional phacoemulsification and before opening femtolaser incisions in FLACS. Cyclotorsion was also measured before IOL implantation and after wound hydration. Preoperative measurements taken with the patient seated were used as the reference point for the amount of cyclorotation in supine position which was reported on the screen as either clockwise (CW) or counter clockwise (CCW) rotation. Statistical analysis was performed using Stata SE, version 12.1.
Results
The study enrolled 44 eyes of 30 patients, 23 of them were right eyes. The mean age of the patients was 56.5 ± 17.1 years (range, 19–89; median, 62), and 9 patients were women. FLACS with IOL implantation was performed in 7 eyes, and conventional phacoemulsification with toric IOL implantation was performed in 37 eyes.
The mean cyclotorsion from sitting to supine position was noted to be 5.84 ± 3.25° (range, 1–17; median, 5). Cyclotorsion of equal to or more than 5° was noted in 61.4% of eyes. Overall, CW rotation (26 eyes, 59.1%) was more common than CCW rotation (18 eyes, 40.9%). The mean CW cyclotorsion was 5.69 ± 3.40° (range, 1–17; median, 5), and the mean CCW cyclotorsion was 6.06 ± 3.09° (range, 1–17; median, 5).The mean cyclotorsion in right and left eyes was found to be 6.30 ± 3.0 and 5.33 ± 3.49, respectively (Table 1). It was noted that the magnitude of cyclotorsion tended to change minimally at various steps of cataract surgery (Table 2).
Table 1.
Measurements of cyclotorsion.
| Parameters | Total eyes (n = 44) | Right eyes (n = 23) | Left eyes (n = 21) | Females (n = 13) | Males (n = 31) | Age≤50 years (n = 12) | Age > 50 years (n = 32) |
|---|---|---|---|---|---|---|---|
| Mean cyclotorsion (degrees) | 5.84 ± 3.25 | 6.30 ± 3.01 | 5.33 ± 3.49 | 6.46 ± 3.26 | 5.58 ± 3.26 | 6.75 ± 4.59 | 5.5 ± 2.59 |
| Mean clockwise rotation (degrees) | 5.69 ± 3.40 | 5.57 ± 2.76 | 5.83 ± 4.15 | 7.5 ± 2.12 | 5.54 ± 3.48 | 6.2 ± 6.3 | 5.57 ± 2.54 |
| Mean counter clockwise rotation (degrees) | 6.06 ± 3.09 | 7.44 ± 3.17 | 4.67 ± 2.45 | 6.27 ± 3.47 | 5.71 ± 2.63 | 7.14 ± 3.43 | 5.36 ± 2.80 |
| Mean incyclorotation (degrees) | 5.21 ± 2.62 | 5.57 ± 2.77 | 4.67 ± 2.45 | 5.5 ± 2.78 | 5.06 ± 2.63 | 4.2 ± 1.3 | 5.5 ± 2.85 |
| Mean excyclorotation (degrees) | 6.52 ± 3.76 | 7.44 ± 3.17 | 5.83 ± 4.15 | 8 ± 3.67 | 6.06 ± 3.79 | 8.57 ± 5.31 | 5.5 ± 2.31 |
Table 2.
Mean cyclotorsion at various steps of cataract surgery.
| Various steps of surgery | Mean cyclotorsion (degrees) |
|---|---|
| Before incisions were given | 5.84 ± 3.25 |
| Before IOL implantation | 5.67 ± 3.43 |
| After hydration of ports | 6.52 ± 3.79 |
IOL, intraocular lens.
In men (31 eyes), CW cyclotorsion (24 eyes, 77.4%) was significantly more common than CCW cyclotorsion (7 eyes, 22.6%). In women (13 eyes), CCW cyclotorsion (11 eyes, 84.6%) was significantly more common than CW cyclotorsion (2 eyes, 15.4%). The mean cyclotorsion in individuals aged younger than or equal to 50 years and in individuals aged older than 50 years was found to be 6.75 ± 4.59 and 5.5 ± 2.59, respectively.
Overall, incyclotorsion was seen in 23 eyes (52.3%, 14 right eyes and 9 left eyes), and excyclotorsion was seen in 21 eyes (47.7%, 9 right eyes and 12 left eyes) (Table 3). In patients undergoing bilateral sequential cataract surgery (14 patients, 28 eyes), similar cyclorotation (12 patients; 24 eyes, 85.7%) was more common than mixed rotation; CW rotation was seen in both eyes in 7 patients (50%), CCW rotation in both eyes in 5 patients (35.7%) and in 2 patients (4 eyes, 14.3%), one eye showed CW and the other eye showed CCW rotation (Table 4).
Table 3.
Direction of rotation in right and left eyes.
| Right eye/left eye | Clockwise rotation | Counter clockwise rotation | Incyclotorsion | Excyclotorsion |
|---|---|---|---|---|
| Right eye (n = 23) | 14 (60.9%) | 9 (39.1%) | 14 (60.9%) | 9 (39.1%) |
| Left eye (n = 21) | 12 (57.1%) | 9 (42.9%) | 9 (42.9%) | 12 (57.1%) |
| Total | 26 (59.1%) | 18 (40.9%) | 23 (52.3%) | 21 (47.7%) |
Table 4.
Direction of rotation in bilateral eyes (14 pairs, 28 eyes).
| Rotation type | No of pairs of eyes | Incidence |
|---|---|---|
| Bilateral clockwise rotation | 7 | 50% |
| Bilateral counter clockwise rotation | 5 | 35.7% |
| Mixed rotation | 2 | 14.3% |
Visual and refractive outcomes
Preoperatively, the mean best-corrected visual acuity (BCVA) was 0.73 ± 0.25 (range, 0.5–1.8), and the mean astigmatism was 1.8 ± 0.83 (range, 0.17–4.82). The mean uncorrected visual acuity and BCVA postoperatively was 0.22 ± 0.07 (range, 0–0.3) and 0.03 ± 0.07 (range, 0–0.2), respectively, with mean postoperative astigmatism of 0.38 ± 0.22 (range, 0–0.75).
Discussion
Toric IOL implantation, cornea-based astigmatic corrections, such as opposite clear corneal and limbal relaxing incisions, and various refractive procedures, such as wavefront-based treatments, are based on the preoperative examination performed with the patient in seated position, while the procedures are then performed in the supine position.
Earlier studies using double Maddox rod3/hand held keratometer4/video oculography5 showed that change in body position did not significantly influence ocular torsion. Subsequently, with a manual marking technique, Swami et al.6 concluded a mean torsional misalignment of 4.1° in patients undergoing refractive surgery. Various studies have also shown static individual changes in ocular rotation from seated to supine position ranging from −10.3° to +24.0°.7, 8, 9, 10, 11, 12, 13 To measure this posture induced cyclorotation, iris registration systems have been developed and eye rotation was accordingly adjusted in the wavefront-based customised excimer laser treatments.14, 15, 16, 17 A recent systematic review of literature concluded that image-guided systems used for cataract surgery are superior to the conventional manual marking techniques for alignment of toric IOLs in terms of precision, reliability and reproducibility.18
Kim et al.17 using a Visx WaveScan wavefront aberrometer have shown a mean cyclotorsion in the supine position of 2.59 ± 1.91° (range 0.10–9.50°). In our study, using the Verion image-guided system (Alcon, Fort Worth, TX, USA), we found significant cyclotorsion in eyes from sitting to supine position (5.84 ± 3.24°) with 61.4% of eyes showing torsion of more than or equal to 5°. Theoretically, it has been shown that with the increase in the axis error, there is a concomitant under correction of astigmatism or induced astigmatism.19 The residual astigmatism can be calculated using the formula 2 F × sinα, where F is the original astigmatic power in dioptres and α is the amount of axis misalignment.20 For example, in eyes with cyclotorsion of 5° or more, the astigmatism would be undercorrected by at least 17.5%.
To remove the complexity involved in knowing the directions of incyclotorsion and excyclotorsion in right and left eyes, we have shown our results in CW and CCW direction in either eye. In our study, we note that CW rotation (59.1%) was more common than CCW rotation (40.9%). However, in terms of incyclotorsion and excyclotorsion, there was no significant difference (52.3% vs 47.7%).
An earlier study carried out on patients undergoing FLACS showed a significant difference in the magnitude and direction of cyclotorsion (observations were made on docking) between right and left eyes.21 We noted that the mean cyclotorsion in right eyes was slightly more than that in left eyes (6.30 ± 3.01 and 5.33 ± 3.49). Although we had 7 patients who underwent FLACS, we deliberately did not take cyclotorsion that occurred after docking as we believed there could be some amount of cyclotorsion which could be caused by the docking of patient interface and the suction applied.
Furthermore, it was seen that the amount of cyclotorsion which occurred was dynamic in nature which tended to change at various steps of surgery performed under topical anaesthesia when it was measured before giving incisions, before IOL insertion and after hydration of ports. This was in sync with the observations noted in eyes undergoing LASIK wherein cyclotorsion occurred continually throughout the LASIK procedure warranting consistent monitoring and compensation using a dynamic rotational eye tracker.22
We tried to analyse the effect of gender and age on cyclotorsion. Although no explanation can be offered, we have noted that CW rotation was significantly more common in men and CCW rotation in women. In individuals aged 50 years and younger, we found that the mean cyclotorsion was slightly more (6.75 ± 4.59) than that of individuals aged 50 years and older (5.5 ± 2.59). We infer that age probably may not have an influence on postural cyclotorsion of the eye ball.
Previous studies carried out on patients with LASIK have reported binocular excyclorotation as the dominant trend.22 An earlier study carried out on patients with FLACS showed bilateral incyclorotation (one eye CW and other eye CCW rotation) as the most common occurrence.21 However, in our study, both eyes showing either CW or CCW rotation was more common than mixed rotation in both eyes. This could be attributable to the docking system that was used21 or the head misalignment22 and is likely user dependent.
Conclusion
We conclude that significant cyclotorsion occurs in the lying posture while performing cataract surgery. Proper understanding and accurate calculation by use of an appropriate device are very essential to achieve accurate alignment of the toric IOL for good visual outcomes.
Disclosure of competing interest
All authors have none to declare.
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