Shedding light on cataract surgery in opaque corneas
Björn Bachmann MD, FEBO
Performing cataract surgery in the presence of an opaque cornea can be successfully achieved with a combination of rigorous surgical techniques and by respecting certain guidelines, according to Björn Bachmann MD, FEBO.
Speaking at the joint ESCRS/EuCornea Symposium on cataract surgery in eyes with diseased corneas at the 37th Congress of the ESCRS, Dr Bachmann said that key steps in a successful procedure included localisation of the key incision site, good control of the red reflex, optimal illumination using a variety of light sources and the application of appropriate staining to enhance visualisation.
“The main incision should be placed opposite the clean work zone, and we can try to improve the red reflex by using coaxial instead of full-field illumination and by enlarging the pupil. It is also advisable to avoid contact of dye with diseased endothelium when staining the anterior capsule,” he said.
Dr Bachmann, consultant at the Department of Ophthalmology, University of Cologne, Germany, noted that there are certain situations where it is advisable to perform cataract surgery in the presence of an opaque cornea before or without corneal surgery.
“This would include cases of mild or peripheral corneal opacification or in patients where there is a high risk of corneal graft failure after penetrating keratoplasty. If there is a history of good visual acuity before cataract formation it might not be necessary to perform corneal surgery before, or in eyes with low expectations in visual acuity such as amblyopia or post retinal detachment,” he said.
Combination surgery is also possible for a large percentage of patients, noted Dr Bachmann.
“We usually perform a combined procedure with the cataract removal coming before the Descemet membrane endothelial keratoplasty (DMEK) within the same surgery. When we looked at the data for our clinic in Cologne it amounted to 931 combined procedures (triple DMEKs) or 37% out of the 2,531 DMEK cases, which represents a high proportion,” he said.
Let there be light
It is important to understand the different sources of light available in the operating field in order to maximise visualisation, said Dr Bachmann.
“The operating microscope delivers front light which visualises the ocular structures by reflection. It also creates stray light from incident rays, which are increased in opaque corneas. The red reflex visualises ocular structures by shading and gives much better contrast to these ocular structures and causes minimal stray light,” he said.
The red reflex can be improved by influencing the pupil diameter and using appropriate illumination techniques, said Dr Bachmann.
“The intensity of the red reflex is influenced by the diameter of the pupil, so try to make it as large as possible by dilating it either pharmaceutically or surgically. We can experiment with different lighting techniques including full-field, coaxial and intracameral or even intravitreal illumination to obtain the best visualisation possible. The intensity of the light is also important in order to minimise stray light while still obtaining the best possible red reflex during the surgery,” he said.
Although full-field illumination is most commonly used in cataract surgery, it tends to increase stray light and reflection and results in a reduced red reflex. By contrast, employing a coaxial light source can greatly increase the red reflex and ensure good visualisation during capsulorhexis creation, said Dr Bachmann.
“It gives a sharper contrast in the area of opacification and also behind the cornea,” he said.
Intracameral light sources can also be helpful when placed in the anterior chamber, allowing visualisation of the ocular structures by reflection. This usually works best when placed directly adjacent to the structures that the surgeon wants to visualise, he explained.
Intravitreal light sources are ideally used in combination procedures and produce reduced stray light, little reflection and high contrast, he added.
“The downside is that there is a risk of the light source tearing the posterior lens capsule so it needs to be maintained a safe distance from the posterior capsule. It also delivers reduced 3D perception,” he said.
For patients with corneal endothelial disease, removal of the oedematous corneal epithelium rapidly improves visualisation and usually works best in combined procedures, said Dr Bachmann.
“This can result in wound healing problems if the epithelium is diseased and we proceed with cataract surgery without endothelium transplantation. An alternative approach is to apply glycerine eye drops, which clears the oedema quickly and should give enough time to perform the cataract surgery,” he said.
A time to dye
Although some concerns have been raised about potential toxicity to the cornea from using trypan blue to stain the anterior capsule, a recent study from Nagashima et al. suggests that the limited exposure time means that it is probably safe to continue to use such dyes, said Dr Bachmann.
“This was a prospective randomised trial study of both brilliant blue and trypan blue in 150 cataract patients, which found no statistically significant difference between the two dyes in terms of endothelial cell loss over the follow-up period,” he said.
He stressed, however, that contact between staining dyes and diseased endothelium is best avoided as it leads to increased corneal opacification.
“Techniques to avoid contact of dyes with corneal endothelium include filling the anterior chamber with an air bubble or viscoelastic material, he concluded.
Björn Bachmann: email@example.com