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Cell loss varies with nuclear density post phaco
Almost twice as much cell loss was seen in very hard nuclei as in milder cataracts after phacoemulsification.
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Disruption of corneal endothelium function after cataract surgery results in corneal edema, decreased cell density and hexagonal cell change, although the return to the normal state is rapid in most cases.
Specular microscopy has become a standard technique to determine endothelial cell density and cell morphology in vivo.
We know the endothelium recovery time after phacoemulsification depends upon several factors: nuclear density, phaco technique, irrigating solution, viscoelastic, type of IOL, etc.
Advances in endocapsular phacoemulsification procedures, instruments, IOLs and related materials, such as viscoelastic substances, have helped to decrease the endothelial damage.
Considering viscoelastic agents, our preference has always been to use dispersive viscoelastics, which present lower molecular weight, tend to stay in the anterior chamber, provide a better endothelial protection and tend to increase the intraocular pressure in the immediate postoperative period, thus requiring a more careful and complete removal at the end of the surgery.
Changes in endothelial cells
---Dissection toward the clear cornea with a crescent knife.
The purpose of our study was to evaluate changes in central corneal endothelial cells according to the nuclear density performing the same surgical technique.
The patients were divided into two series. In the first series, the nuclear density was one plus to three plus. Divide and conquer was the surgical technique used on all 50 eyes. Patients ranged in age from 59 to 85 years. Average age was 73.8 years.
In the second series, the nuclear density was 4 plus. Divide and conquer was the surgical technique used on all 35 eyes. Patients ranged in age from 63 to 88 years. Average age was 74.54 years.
All surgeries were uneventful and were performed by Dr. Ghiaroni.
Specular microscopy was performed preoperatively and 12 months postoperatively in all patients with a SP-1000 Topcon specular microscope (Paramus, N.J.). Dr. Daher performed all the measurements.
There were no significant differences between the two series regarding gender and age of the patients and the interval of time between the date of the surgeries and the moment the endothelial cell count was repeated.
Surgical technique
The surgical technique consisted basically of the following:
- Small fornix-based conjunctival flap.
- 50% thickness scleral groove centered at the 11 o'clock meridian performed with a diamond knife 1 mm from the limbus.
- Dissection toward the clear cornea with a crescent knife.
- Paracentesis with a straight 3.2-mm knife immediately anterior to the corneal vascular arcade.
- Capsulorrhexis with Masket forceps having the anterior chamber fully filled with sodium hyaluronate (Vitrax; Allergan).
- Hydrodissection.
- Emulsification of the nucleus (divide and conquer) using a Prestige AMO phacoemulsifier.
- Insertion of a foldable IOL (SI40 Allergan) with the Unfolder.
- Careful removal of the viscoelastic.
Surgical parameters included the following:
- Sculpt (grooves): power - 70% linear; vacuum (mm Hg) - zero; flow (mL/min) - 22.
- Quadrant emulsification: power - 50 to 70, pulse; vacuum (mm Hg) - 200; flow (mL/min) - 22.
- Epinucleus: power - 50, pulse; vacuum (mm Hg) - 200; flow (mL/min) - 22.
- Cortex removal: vacuum (mm Hg) - 400; flow (ml/min) - 22.
---Paracentesis with a 3.2-mm straight knife immediately anterior to the anterior corneal vascular arcade.
The preoperative endothelial cell evaluation must be routinely performed and is extremely important in the indication of the surgical technique to be chosen by the surgeon.
Concerning the divide and conquer technique and according to our results, the surgeon must be prepared to have a much higher endothelial cell loss when dealing with harder nuclei, so it is important to know, depending upon the case and upon the surgeon's experience, when it is better to indicate an extracapsular procedure.
If a surgeon in his or her learning curve faces a patient with a very dense nucleus, a shallow anterior chamber and a low endothelial cell count, he or she must have the ability to choose the technique that will decrease the risks of the facectomy in the case of that patient.
Hard nuclei
---Capsulorrhexis with Masket forceps having the anterior chamber fully filled with viscoelastic.
Sometimes, it may be hard, even for a beginning phaco surgeon, to be humble enough to recognize that he or she is not yet prepared to face hard nuclei; however, we cannot minimize the risks of a severe trauma to the cornea, leading to an important endothelium cell loss, especially in countries where the availability of corneas to be transplanted is still a big problem.
It is important to note that the machine used in this study did not allow us to increase the vacuum above 250 mm Hg without having surge. Based on that, we have already begun another similar study using a phacoemulsifier that allows us to work with a vacuum as high as 500 mm Hg. We have also begun to study a series of patients who underwent extracapsular cataract extraction and who had 4 plus nuclei. Our initial results seem to show a much lower endothelial cell loss compared to the series of patients with 4 plus nuclei who underwent phacoemulsification.
It would be interesting to see the results of a similar study using a phaco chop technique that minimizes the ultrasound energy used and to observe if the endothelial cell loss would be lower with very dense nuclei.
The endothelial cell loss in cataract surgery is an aspect that must be carefully valorized by the surgeon and that represents an indication of the safety of the surgical technique performed.
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For Your Information:
- Almir Ghiaroni, MD, can be reached at R. General Venancio Flores, 305 Sala 309, Rio de Janeiro 22441-090, Brazil; 55-21-259-2099; fax: 55-21-512-8947. Dr. Ghiaroni does not have a direct financial interest in any product mentioned in this article, nor is he a paid consultant for any company mentioned.