Careful evaluation for diabetics with cataracts

By Sean Henahan

Which diabetic patient should be considered a potential candidate for cataract surgery and which should be excluded? The answers come from a careful preoperative evaluation and, if necessary, referral to a retina specialist for further studies.
"When I see a diabetic patient, I feel that patient should have a more significant decrease in visual acuity and symptoms related to the cataract than a non-diabetic patient before going ahead with surgery.

"That's because the prognosis is not as good. I have a thorough discussion of the increased risks of surgery to the retina, including the increased incidence of CME and possible increase in the retinopathy," according to James J. Salz MD, Clinical Professor of Ophthalmology at the University of Southern California, Los Angeles County Medical Centre.

Many, but not all, patients with diabetes have related eye problems, particularly macular oedema and/or proliferative retinopathy. These pathologies are associated with worse postoperative visual outcomes. A thorough examination of the retina preoperatively can eliminate disasters later, he noted.

If preoperative examination reveals pre-existing macular oedema, Dr Salz refers the patient to a retinal specialist to see if they are candidates for laser therapy and to rule out epiretinal membrane as a possible cause of the oedema.
If the patient has significant background retinopathy or proliferative retinopathy, the retinal surgeon may want to perform laser treatment first. Cataract surgery can then be reconsidered once the retinal surgeon feels the patient is stable.

"The key thing is for the surgeon to look very carefully at the retina. However, when a patient has a cataract, the view to the back of the eye is not crystal clear. If the view is not good or you are not sure, then you can send the patient to the retina specialist," said William R. Freeman MD, Co-Chief of the Retina Division at the Shiley Eye Center in La Jolla, California.

Fluorescein angiography
Fluorescein angiography can be a very helpful test when the view is obscured. The nature of this technique allows the surgeon to see vessel leakage, aneurysms and neovascularisation in cases where the view might be very hazy under the ophthalmoscope, he noted.

Angiography can also help screen for diabetic macular oedema. The macular oedema may be relatively subtle preoperatively and might be difficult to see if the cataract is dense. If there is retinopathy with macular oedema preoperatively, Dr Freeman advises treating it ahead of time because of the known risk that cataract surgery can exacerbate the problem.

Experience has shown that if patients with macular oedema undergo cataract surgery, the condition can worsen dramatically and become more difficult to treat, he stressed.

"There is no question that cataract surgery exacerbates the situation in some patients. We don't really understand the process completely. If a patient has proliferative retinopathy, the vessels grow from the retina into the vitreous. When you remove the cataract - even if you don't rupture the capsule - you still end up moving the vitreous body forward because the lens is no longer there.

"We know that most patients who have cataract surgery end up with posterior vitreous detachments. When that occurs in a diabetic with neovascularisation, it will tear the neovascularisation and cause haemorrhaging. It can also turn an area of flat neovascularisation into an area of tractional retinal detachment," Dr Freeman said.
In such cases, the cataract surgeon will notice that suddenly there is a vitreous haemorrhage after surgery. Further evaluation reveals traction retinal detachment, fronds of neovascularisation and so on.

At that point it becomes clear that the underlying pathology was pre-existing and doing the cataract surgery converted it to a more active form, he explained.
While many cataract surgeons refer these high-risk patients to the retinal surgeon and wait until the underlying conditions are treated and stable, others will do the cataract procedure and have the retina specialist see the patient very shortly after the surgery.
Modern cataract surgery techniques utilising contact lens bandaging postoperatively allow the retinal surgeon to treat the eye the next day if necessary, he noted.

A combined cataract and vitrectomy procedure might be contemplated in cases where
the pathology is complicated, for example a traction retinal detachment and neovascularisation. This can be done by both surgeons together or by a retinal specialist who is comfortable doing the whole thing.

"This approach virtually guarantees that the pathology is going to be controlled because you are back there and dealing with it. When that operation is done you know you have fixed the problem," Dr Freeman said.

IOL choice important
Choosing which IOL to implant is also a critical decision when treating patients with diabetes. Because of the increased risk of CME and the possibility of future vitrectomy, Dr Salz said he avoids silicone IOLs in diabetic patients out of concern for an increased risk of CME and retinal detachment. He recommended using a square edge design acrylic lens, such as the Alcon SA60AT, single piece acrylic IOL.

Dr Freeman agreed: "Silicone IOLs are a big problem for vitreoretinal surgeons. The foldable acrylic lenses tend to be much better because if the patient is going to need retinal surgery, the silicone lenses make it very difficult.

"It is not easy to see through them when you do the gas-fluid exchange. If you are dealing with an eye that is predisposed to retinal problems which might need retinal surgery, then you should avoid the silicone lenses."

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