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Rotational stability
Preventing toric IOL rotation
Rotational stability remains key to optimal results with toric IOLs. Dermot McGrath reports
Improvements in toric intraocular lens (IOL) material and design, as well as refinements in surgical technique, have greatly enhanced postoperative rotational stability of these lenses in recent years, according to Boris Malyugin MD.
“Toric IOLs deliver excellent visual acuity and high patient satisfaction by a reduction or elimination of the astigmatic error. However, residual error may happen and can impact on the clinical results we obtain, so the stability of the lens in the capsular bag is absolutely vital with these IOLs,” Dr Malyugin said at the World Ophthalmology Congress 2020 Virtual.
Underscoring the importance of stability in toric lenses, Dr Malyugin, Professor of Ophthalmology at the S. Fyodorov Eye Microsurgery Complex Federal State Institution, Moscow, Russia, noted that a postoperative rotation of 30-degrees equates to 100% loss of cylinder power.
“In other words, the entire effect of the toric lens is lost. Even just a 1-degree rotation translates to 3% loss of cylinder power and a 90% rotation actually doubles the astigmatism – this is why it is so important for the IOL to remain stable in the capsular bag,” he said.
Precise axis alignment is a critical step in obtaining optimal refractive outcomes with toric IOLs, and there are a wide range of low- and high-tech approaches available to achieve this, said Dr Malyugin. As well as traditional methods to mark the eye manually using handheld instruments, many manufacturers now offer specialised devices for intraoperative corneal marking, digital alignment and centration of the IOL.
“Although manual marking remains very popular, it is prone to error. There is a growing body of evidence in the scientific literature showing that digital marking or image guided systems are superior to manual marking methods, and we need to keep that in mind,” he said.
Another interesting high-tech approach, described by H Burkhard Dick and Tim Schultz, is to use spectral domain OCT combined with a femtosecond laser to create two perpendicular intrastromal marks on the anterior capsule for precise axis marking.
Dr Malyugin noted that certain ocular co-morbidities can also have a direct impact on postoperative toric IOL stability.
“High myopia, for instance, is usually associated with a large diameter of the capsular bag. Likewise, ocular trauma, pseudoexfoliation and uveitis are all conditions that may lead to the weakening of the lens zonular apparatus and create instability of the lens,” he said.
In terms of lens material, Dr Malyugin noted that several studies have shown greater propensity to rotation with lenses made of silicone compared to acrylic IOLs. Furthermore, a study by Draschl et al (JCRS, 43(2):234-238) comparing two identical non-toric IOL designs found that hydrophobic material offered greater rotational stability than the lens made of hydrophilic material.
The development of strong adhesions between the IOL and lens capsule in the early postoperative period seems to be a key factor in the superior performance of hydrophobic acrylic IOLs, added Dr Malyugin.
Early postoperative rotation is also influenced by axial length. A study by Shah et al (JCRS, 38(1):54-59) of the AcrySof (Alcon) toric IOL in 168 patients found a strong correlation between axial length and IOL rotation, with longer axial length associated with greater rotation of the lens.
SURGICAL TECHNIQUE Rigorous surgical technique can play a role in safeguarding toric IOL stability, said Dr Malyugin.
“It is very important at the end of the implantation step to ensure that all the ophthalmic viscosurgical device (OVD) is aspirated from the capsular bag. Otherwise it can remain underneath the IOL optic and allow the lens to rotate,” he said.
Certain situations may also call for the use of a capsular tension ring (CTR) to avoid rotation of the lens.
“The CTR has been shown to be effective with a silicone plate-haptic toric IOL and may also help to stabilise loophaptic hydrophobic acrylic IOLs. There are some publications showing double use of standard CTRs in the capsular bag to obtain rotational stability in patient with long axial length,” he said.
Suturing the CTR to the toric lens has also proved effective for long axial length eyes in a method described by Claudio Orlich (https://www.eurotimes.org/howto-deal-with-iols-in-large-eyes/).
Dr Malyugin noted that the vast majority of the postoperative rotation is believed to take place within the first hour after surgery.
“This was shown in an interesting study by Inoue et al (Ophthalmology. 2017 Sep;124(9):1424-1425). With that in mind, it is better that patients avoid physical activity or movement in the first hour after surgery in order to allow the lens to settle in the capsular bag,” added Dr Malyugin.
Summing up, Dr Malyugin said that careful biometry, precise axis alignment and rigorous surgical technique could help to ameliorate many of the problems related to postoperative toric IOL rotation and deliver consistently good outcomes for astigmatic patients.
