Dr. Samreen Khanam, K18650,
Dr. Prolima Thacker, Dr. Yashpal Goel, Dr.
Kamlesh, Dr.Anju Rastogi
NTRODUCTION
Modern cataract surgery has moved ahead from mere implantation of transparent synthetically made Intra Ocular Lenses (IOLs) to techniques that provide greater degree of spectacle independence post surgery. Toric IOLs offer us the opportunity to correct astigmatism and make the patient spectacle independent for distance vision.
The first toric IOL was designed in 1992 by Shimizu et al.1 However, the earlier models showed an unacceptably high level of postoperative rotations. Toric IOLs require precise positioning in a predetermined axis and a small degree of rotation during or after surgery can affect the refractive results significantly. It has been estimated that for every one degree of error in a toric IOLs rotational alignment, there is a 3.3% decrease in correction of astigmatism.2 So, if a toric IOL is misaligned by 10 degrees, it is a 33% loss of toric correction. And if it is misaligned by 30 degrees, it is as though you put in a spherical IOL; the IOL is not correcting astigmatism at all. A number of improvements in material, designs and techniques have been made and the current error in toric IOL alignment has been estimated to be varying from about 5 degrees in some studies to as high as 13.59 ± 11.29 degrees 3 months post operatively.3,4 Individual patients have had much higher degrees of misalignment.
Apart from precise calculations and appropriate intra operative alignment, rotational stability of a toric IOL also depends on its positioning in the capsular bag. Asymmetric contraction of the capsular bag is known to cause lens decentration and has the potential to cause rotation of IOL. Capsular Tension Rings (CTRs) have been shown to enforce symmetry of the capsular bag and
control capsular contraction. In view of the need for validating the role of CTR in conferring rotational stability to a toric IOL, we conducted our study as mentioned here forth.
METHODS
Study Design
The study was conducted at a tertiary care centre. It was a randomized controlled trial approved by the institute’s ethics committee and written informed consent was obtained from all patients.
Study group, treatment and data collection
Adult Patients with visually significant cataract and regular corneal astigmatism ≥1.25 D were included in the study. Patients with corneal pathology, subluxated lenses, posterior segment diseases such as macular degeneration, prior history of corneal surgery and specular microscopy endothelial count ≤2000 cells/ mm2 were excluded from the study.
A total of 30 eyes were randomly assorted into 2 groups, A and B (using single blinding method). Patients in group A were implanted with CTR after standard phacoemulsification and a toric IOL was put. In the group B, only toric IOL was implanted after routine phacoemulsification, and no CTR was put. All the patients were operated by a single surgeon and a loop haptic acrylic toric IOL was used.
Preoperative assessment included a detailed history taking followed by ophthalmic examination including uncorrected distance visual acuity, manifest refraction, dilated fundus examination ( if possible), keratometry for amount and axis of astigmatism using autokeratometer (Potec Autoref keratometer PRK-5000), OrbscanTM IIz (Bausch & Lomb) and LensStar -LS 900 (wherever possible), axial length with A scan (PAC SCAN 300P) and Lens Star- LS 900 (wherever possible). Preoperative marking of the axis was done using a slit lamp. Patients were followed up post operatively and serial slit lamp images in retroillumination were taken on Day1, 1 week, 1 month and 3 months. These images were then analysed and the axis of the IOL was determined at each visit.
Statistical analyses
All Statistical analyses were performed using SPSS 20.0 software. To analyze the difference between the two study groups, two sample t-test was performed. P<0.05 was considered statistically significant.
Results:
The mean angular rotation in the group implanted with toric IOL with CTR (Grp A) was found to be 1.3±0.72 degrees. On the other hand, the mean angular rotation in the group with toric IOL without CTR (Group B) was 3.79±1.39. Statistical analysis demonstrated it to be significant (p < 0.05) There was no major intra operative or post operative complication in any of the patients, making CTR implantation a very safe surgical technique.
Discussion
The primary aim of the study was to compare the effect of co-implantation of CTR on the rotational stability of toric IOLs. The mean post-operative rotation of other 1-piece acrylic toric IOLs with loop haptics has been reported to be 3.0 degrees to 4.0 degrees. 5,6 These values are comparable to the amount of rotation seen in our study in the group with toric IOL without CTR.(3.79±1.39 degrees).
Though capsular shrinkage and asymmetry has been postulated to affect the rotation of toric IOLs, to the best of our knowledge, no randomized data on the rotational stability of toric IOLs with CTR has been published. The significantly lower degrees of rotation of toric IOL, as seen in the group with CTR (1.3±0.72 degrees), validates the hypothesis.
Intraocular lens haptic design is another major factor in rotational stability. Published data comparing rotational stability of IOLs with open-loop haptics and IOLs with plate haptics vary. Results in studies show that for acrylic IOLs, loop haptics and plate haptics provide comparable rotational stability.7
IOL material is another factor that has been said to contribute to better rotational stability.8 Acrylic IOLs with a hydrophobic surface have been shown to have the strongest IOL-capsule adhesion. Higher amounts of fibronectin on acrylic IOLs may be one reason for this.
IOL diameter is also said to be influencing intracapsular stability. Our IOL had an overall diameter of 13.0 mm, which is comparable to the studies mentioned above. To conclude, this study shows that toric IOLs when implanted along with a CTR are rotationally more stable than when done without it, and does not compromise with safety.
References
1.Shimizu K, Misawa A, Suzuki Y. Toric intraocular lenses: correcting astigmatism while controlling axis shift. J Cataract Refract Surg. 1994; 20:523-6.
2.Novis C. Astigmatism and toric intraocular lenses. Curr Opin Ophthalmol. 2000; 11:47–50.
3.Visser N, Berendschot TTJM, Bauer N J C, Jurich J, Kersting O, Nuijts RMMA. Accuracy of toric intraocular lens implantation in cataract and refractive surgery. J Cataract Refract Surg. 2011; 37:1394-402.
4.Maedel S, Hirnschall N, Chen Y, Findl O. Rotational performance and corneal astigmatism correction during cataract surgery: aspheric toric intraocular lens versus aspheric nontoric intraocular lens with opposite clear corneal incision. J Cataract Refract Surg. 2014; 40:1355-62.
5.Koshy JJ, Nishi Y, Hirnschall N, Crnej A, Gangwani V, Maurino V, Findl O. Rotational stability of a single-piece toric acrylic intraocular lens. J Cataract Refract Surg 2010; 36:1665–1670.
6.Kwartz J, Edwards K. Evaluation of the long-term rotational stability of single-piece, acrylic intraocular lenses. Br J Ophthalmol 2010; 94:1003–1006.
7.Patel CK, Ormonde S, Rosen PH, Bron AJ. Postoperative intraocular lens rotation: a randomized comparison of plate and loop haptic implants. Ophthalmology 1999; 106:2190–2195; discussion by DJ Apple, 2196
8.Linnola RJ, Werner L, Pandey SK, Escobar-Gomez M, Znoiko SL, Apple DJ. Adhesion of fibronectin, vitronectin, laminin, and collagen type IV to intraocular lens materials in pseudophakic human autopsy eyes. Part 1: histological sections. J Cataract Refract Surg 2000; 26:1792–1806.