Innovations in cataract and refractive surgery

Modern ophthalmic cataract surgery now employs sophisticated techniques to improve outcomes and patient satisfaction. This includes surgical systems providing better control, lasers to perform manual techniques, and intraoperative evaluation to evaluate surgical endpoints before the patient leaves the operating room (OR).

Advances in phacoemulsification

Cataract surgery involves a corneal incision as well as a paracentsis, removal of the cataract and implantation of the intraocular lens (IOL), while maintaining the pressure in the eye.  Incisions are often fewer than 3 mm because implants are engineered to be placed in smaller incisions.

Modern lens removal occurs using phacoemulsification (phaco), which incorporates ultrasound to emulsify and vacuum to extract a cataractous lens. The ultrasound hand piece is connected to a phaco system, which drives the procedure using settings as dictated by the surgeon. The phaco tip, or fragmentation needle, vibrates at an ultrasonic frequency and emulsifies a cataract when connected to the ultrasonic hand piece. The tip has a hole, which allows the fragmented lens as well as irrigation solution (BSS) to be aspirated.

More from Dr. Swartz: Effectively comanaging femtosecond laser-assisted cataract surgery

Fluidics is the dynamic between the fluid entering the eye and the intraocular pressure (IOP) during cataract surgery. If pressure is maintained at a constant level, the anterior chamber is more stable. Variable control is important for successful outcomes, particularly for surgeons who desire greater control for femtosecond laser-assisted procedures (which require less power), and dense cataracts (requiring more power).¹

A high and uninterrupted flow rate is ideal to draw segments out of the capsular bag while maintaining the tip in the iris plane. Venturi pumps create optimal fluidic conditions for segment removal in a stable anterior chamber. They generate much higher flow rates than peristaltic pumps and require lower vacuum levels than peristaltic systems.

Systems that incorporate both pumping types are typically preferred. New systems include Centurion Vision System (Alcon), WhiteStar Signature System (Abbot Medical Optics), Stellaris Vision Enhancement System (Bausch + Lomb,), and Ocusystem ART Phacoemulsifier (Surgical Design)

Next: Femtosecond laser-assisted phacoemulsification

Femtosecond laser-assisted phacoemulsification  

Four platforms are now fully approved in the U.S. for corneal and lens incisions. These include Catalys (Optimedica), LenSx (Alcon Laboratories), LensAR (Lensar) and Victus (Technolas). Most systems create the capsulorhexis, fragment the lens to facilitate removal, and create corneal incisions (see Figure 1). Zeimer FEMTO LVD Z8 (Zeimer Group) received CE approval in Europe in May 2014 for clear corneal incisions, arcuate incisions, capsulotomy, and lens fragmentation, but applications are currently limited to corneal and presbyopia in the U.S.

Debate continues regarding whether femtosecond laser-assisted cataract surgery results in superior refractive outcomes, reduced phaco time,² improvement in the capsulotomy and corneal incisions,^3,4 and corneal endothelial cell loss.⁵ Total treatment times are longer than manual procedures.⁶

Related: Comparing laser-assisted vs. conventional refractive cataract surgery

Complications are rare but may occur. Suction loss is typically noncomplicating but may be serious.⁷ Patient movement during surgery has resulted in grid patterns imprinted on corneas.⁸ Corneal incisions are typically superior to manual incisions but are then manipulated during surgery during implantation, causing edema similar to that caused by manual incisions.

Complications such as perforations have occurred.⁹ Use of femtosecond laser technology is reported to address quality of vision via “less posterior chamber lens (PCL) tilt, more centralized position of the PCL, possibly less endothelial damage, less macular edema, and less posterior capsule opacification (PCO) formation.”¹⁰ This may be due to the quality of the capsulotomy and reduced amount of internal aberrations following femtosecond-assisted procedures.¹¹

Next: Intraoperative aberrometry

Intraoperative aberrometry

Optiwave Refractive Analysis (ORA) system (WaveTec Vision) measures wavefront aberrometry intraoperatively. The system attaches to the surgical microscope for intraoperative measurements of sphere, cylinder, and axis to aid in IOL power choice in real time (see Figure 2). This is extremely helpful in those patients with a history of keratorefractive surgery, toric IOLs, and presbyopia-correcting IOLs.  

Intraoperative aberrometry was studied intraoperatively for stability and reproducibility, and researchers found that measurements could be obtained 57 percent of the time.¹² Measurements were most easily obtained in aphakia with viscoelastic, but the size of the range led investigators to suggest that the technology required refinement prior to being used for real-time decision making intraoperatively.

Systems currently in use in the U.S. are used in patient S/P refractive surgery in which IOL calculation is problematic. ORA reportedly improves outcomes significantly in these patients,¹³ although variability remains a concern in this population.¹⁴

Holos IntraOp from Clarity Medical Systems is another microscope-mounted aberrometer for real-time intraoperative determination of astigmatism, but it is not currently approved for use in the U.S.

Next: Three-dimensional surgical viewing

Three-dimensional surgical viewing

Three-dimensional surgery can be performed using a system called TrueVision Computer-Guided System (TrueVision 3D Surgical) and since January 2015, the Cirle Surgical Navigation System (Cirle and distributed by Bausch + Lomb). The TruVision system utilizes a stereoscopic high-definition visualization system which displays the surgical field of view in real-time on a 3D flat-panel display in the operating room.

The system is currently being incorporated into surgical microscopes (Leica microsystems), Cassini topographer (i-Optics) and femtosecond laser systems (LENSAR). TrueVision enables the surgeon to sit straight up rather than hunched over the microscope while looking at a 3D monitor while wearing 3D lenses to perform stereoscopic surgery.

Supporters suggest this is advantageous ergonomically and reduces back problems for surgeons later in life. The video can be replayed and watched in 3D for teaching facilities.

Related: Why wait to recommend cataract surgery?

In addition to real-time images and improved ergonomics, the systems can perform real-time displays to guide the surgeon in the OR in real time (see Figure 3). Using an image of the preoperative, undilated pupil, the TruVision system eliminates the need for manually marking the eye prior to surgery. The eye tracker and automated cyclotorsion registration aid in toric lens implantation. In addition, digital overlays can be displayed to facilitate capsulorhexis’s size and location, manual LRI arcs, optical zone size, axis, and length.¹⁵ An undilated image overlay also helps to locate the pupillary center to maximize the IOL’s centration, which is important with multifocal lenses.

Next: Advancements in toric correction

Advancements in toric correction

Corneal astigmatism evaluation, toric IOL alignment, and surgical planning are quickly evolving areas using advanced technology. Topographers rather than simple keratometers are now typically used to evaluate corneal astigmatism. Many systems display the angle kappa and angle alpha, which are now used in surgical planning.

Angle alpha is the angle between the visual axis and the center of the limbus. The center of the limbus is believed to approximate the center of the capsular bag where the IOL will also center. If the angle alpha is significant, the IOL may decenter, and a presbyopia-correcting lens may not have the desired effect.

Angle kappa is the angle between the visual axis and center of the pupil. Those patients with a large angle kappa will not look through the IOL center and experience negative effects with presbyopia-correcting IOLs (see Figure 4).           

Various toric calculators are utilized to determine the optimum IOL power, typically from the IOL manufacturer. Efforts to improve outcomes may also be addressed using computer programs developed for this purpose, including the AASORT program and the iTrace Zaldivar Toric Caliper. The AASORT program, developed by Noel Alpins, integrates the refractive astigmatism and corneal astigmatism in the calculation of toric power.

Double-angle vector diagrams are used to determine the refractive cylinder effect compared to the corneal astigmatism and simulate the postoperative manifest refractive cylinder based upon IOL chioce.¹⁶ iTrace Zaldivar Toric Caliper (Tracey Technologies) overlays a guide for IOL axis placement based upon a slit lamp image to aid in toric IOL placement (see Figure 5).

iTrace features an integrated IOL calculator that works with most toric IOLs. It also incorporates the induced astigmatism from the corneal incision (typically 0.50 D) and the corneal incision location to aid in toric IOL selection. The Zaldivar Toric Caliper tool can then be used in the OR after marking the eye and capturing an image.

Landmarks are used to direct IOL axis placement. While femtosecond lasers can currently perform limbal relaxing incisions, they do not recognize anatomical landmarks to account for the cyclotorsion that occurs when a patient lies down. Using pre-op images of the patient’s eye in an upright position and marking the desired landmarks position relative to the axis of the lens can aid positioning of the toric IOL.             

Planning tools are also available to aid surgeons in the event of toric IOL rotation. The AASORT and iTrace programs both indicate if rotation of the IOL would be beneficial. John Berdahl, MD, and David Hardten, MD, also developed a computer program which uses the manifest refraction and magnitude and axis of the current IOL to determine if lens rotation is warranted.¹⁷

Conclusion

The advancements in techniques, guidance systems, and intraoperative measurements within the ophthalmology suite during cataract surgery are impressive, and hopefully, we will see an improvement in patient outcomes and increase in safety with these advancements. 

References:

1. Murphy E. Developments such as high-tech fluidics improve outcomes and safety for microincision cataract surgery. Ophthalmology Management. 2014 Feb;18.

2. Conrad-Hengerer I, Schultz T, Jones JJ, et al. Cortex Removal After Laser Cataract Surgery and Standard Phacoemulsification: A Critical Analysis of 800 Consecutive Cases. J Refract Surg. 2014 Aug;30(8):516-20.

3. Schultz T, Joachim SC, Tischoff I, et al. Histologic evaluation of in vivo femtosecond laser-generated capsulotomies reveals a potential cause for radial capsular tears. Eur J Ophthalmol. 2015 Feb 12;25(2):112-8.

4. Menapace RM, Dick HB. Femtosecond laser in cataract surgery. A critical appraisal.  Ophthalmologe. 2014 Jul;111(7):624-37.

5. Abell RG, Kerr NM, Howie AR, et al. Effect of femtosecond laser-assisted cataract surgery on the corneal endothelium. J Cataract Refract Surg. 2014 Nov;40(11):1777-83.

6. Donaldson KE, Braga-Mele, R, Cabot F, et al. Femtosecond laser–assisted cataract surgery. J Cataract Refract Surg. 2013 Nov;39(11):1753–63.

7. Schultz T, Dick HB. Suction loss during femtosecond laser-assisted cataract surgery. J Cataract Refract Surg. 2014 Mar;40(3):493-5.

8. Lubahn JG, Kankariya VP, Yoo SH. Grid pattern delivered to the cornea during femtosecond laser-assisted cataract surgery. J Cataract Refract Surg. 2014 Mar;40(3):496-7.

9. Cherfan DG, Melki SA. Corneal perforation by an astigmatic keratotomy performed with an optical coherence tomography-guided femtosecond laser. J Cataract Refract Surg. 2014 Jul;40(7):1224-7.

10. Nagy ZZ. New technology update: femtosecond laser in cataract surgery. Clin Ophthalmol. 2014 Jun 18;8:1157-67.

11. Alió JL, Abdou AA, Puente AA, et al. Femtosecond laser cataract surgery: updates on technologies and outcomes. J Refract Surg. 2014 Jun;30(6):420-7.

12. Huelle JO, Katz T, Druchkiv V, et al. First clinical results on the feasibility, quality and reproducibility of aberrometry-based intraoperative refraction during cataract surgery. Br J Ophthalmol. 2014 Nov;98(11)1484-91.

13. Ianchulev T, Hoffer KJ, Yoo SH, et al. Intraoperative refractive biometry for predicting intraocular lens power calculation after prior myopic refractive surgery. Ophthalmology.  2014 Jan;121(1):56-60.

14. Canto AP, Chhadva P, Cabot F, et al. Comparison of IOL power calculation methods and intraoperative wavefront aberrometer in eyes after refractive surgery. J Refract Surg. 2013 Jul;29(7):484-9.

15. Weinstock RJ. The Latest and Greatest in Intraoperative Guidance Tools. Cataract and Refractive Surgery Today. 2014 June;14(6):74-7.

16. Alpins N, Ong JK, Stamatelatos G. Refractive surprise after toric intraocular lens implantation: graph analysis. J Cataract Refract Surg. 2014 Feb;40(2):283-94.

17. Toric Results Analyzer. Available at: http://astigmatismfix.com/. Accessed 9/20/2014.