Why do I use iris stretching in cataract surgery?

This is my second blog on my series – ‘difficult cataracts’ and I wanted to discuss the issue of the small pupil in cataract surgery.

Just before cataract surgery, all my patients receive four sets of dilating eye drops to temporarily enlarge the pupil of the eye. This is to ensure that the eye surgeon has easy access to the cataract. Normally the iris is constricted over the cataract as it is constantly adjusting to different lighting conditions – the pupil is small in bright light and large in dim light.

If dilation with drops was not performed before cataract surgery, the light from the operating microscope would automatically constrict the pupil. The access to the cataract would be difficult.

However, some patients’ pupils may not dilate well despite administering drops before their surgery. This may be because the iris is stuck down to the front of the capsular bag (that encases the cataract) as a result of previous inflammation known as uveitis. Pupils often remain small in dark eyed patients who have large amounts of iris melanin pigment, which prevents eye drops from infiltrating the iris muscles. Some of my diabetic patients do not dilate well, possibly as a result of high blood sugars causing eye nerve problems. Eyes that have pseudo-exfoliation or trauma can also have poor dilation.

The small pupil therefore presents a challenge to a cataract surgeon. How do we gain access to the cataract if the pupil opening remains small? Well thankfully, there are extra steps that can be incorporated into cataract surgery that can overcome this problem.

If the pupil dilation is moderate, the eye surgeon can inject some further dilating drugs into the eye (eg phenylnephrine), which can act directly on the iris muscles. In some cases, this is enough to open up the pupil enough to perform safe cataract surgery. However, there are cases where the eye surgeon may need to use physical methods to open up the pupil.

Iris stretching refers to the process of manually opening up the iris at the beginning of cataract surgery. This ensures safe and controlled access to the patient’s cataract.

One method of iris stretching is to insert iris hooks. I will place the Iris hooks, small plastic hooks, through very small side openings at the edge of the cornea. They are carefully inserted and each hook pulls the edge of the iris out to enlarge the pupil. Usually the eye surgeon puts 4 or 5 iris hooks into the eye to ensure a regular iris stretch. The result is a rectangular shaped or pentagonal shaped iris, which looks quite odd.

The regular steps of cataract surgery can now take place. The iris hooks remain in place until the end of the cataract operation. They are then carefully removed one at a time and the pupil returns to its normal shape. The iris hook ends are very soft in order to cause minimal damage to the iris edge. The eye surgeon should always check that all hooks are removed from the eye and the nurse scrub assistant should count them out with the surgeon.

More recently, surgeons perform iris stretching by using a Malyugin Ring invented by Boris Malyugin. This device can be inserted through one of the existing openings in the eye. Thus there is no need for more openings, compared to more traditional iris hooks. It may also cause less stress on the iris edge as its stretching effect is more even. Its other main advantage is that it can be inserted and removed in one go.

An illustration of a Malyugin ring being inserted to stretch a poorly dilating pupil in cataract surgery.

Stretching the iris in eyes that do no dilate well in cataract surgery has enhanced our ability to continue producing excellent visual outcomes in difficult cataract cases. I have used various iris stretching techniques on hundreds of patients in the past and achieved excellent results.

If you have cataracts or would like to discuss any aspects of cataract surgery, please feel free to call me on 07919 895 448. I would be very happy to discuss any of your specific needs.