Surgical technique (cataract surgery)
The phacoemulsification: technical reference for resection of the crystalline lens surgery
The phacoemulsification is currently the technique of reference for the cataract surgery.
Phacoemulsification: General information
The phacoemulsification (often abbreviated by the acronym PKE) is based on the fragmentation in situ before extra-capsulaire aspiration of lens clouded through a small limbic or corneal incision with the width between 1.8 mm (micro incision), 2 (mini-incision) mm and 3.2 mm (small incision), while the equatorial diameter of the lens is close to 12 mm on average. This low invasiveness authorizes the creation of a outpatient surgery.
The techniques preceding phacoemulsification consisted of the total resection cristallinienne (capsule, cortex and nucleus)-extraction intracapsular), or partial (cortex and nucleus-manual excapsular) but in all case Without fragmentation of the Crystalline lens and thus through a broad incision.
The term "extra-capsulaire" means that the posterior and the equator of the lens (capsule) bag are preserved extraction in order to provide anatomical support and accommodate the implant of artificial, thus placed in lens "anatomical" position in the posterior Chamber. The artificial lens implant is that of posterior Chamber (often used acronym: PKI for Implant of room rear - intervention being then summarized by the PKE + PKI formula!).
A page is devoted to the description in images of the modern in phaco emulsification cataract surgery.
The use of laser radiation is widespread in ophthalmology, but is not used in routine for resection of the crystalline lens surgery. An emerging technology is currently in evaluation: the cataract surgery femtosecond laser. To date, profits have not been clearly established, and if maneuvers like capsular cutting benefit of automation and precision of laser, some side effects such as reduction of the dilation of the iris may upset some steps. In the future, it seems that the possibility of the operating times of way 'external', automaisee and "more reproducible" way will certainly source of progress.
Phacoemulsification: surgical technique
The technique described here is called axial co: a main incision (micro incision: 1.8 mm) is performed to allow the passage of the emulsificateur phaco and some instruments. A lateral incision, or so-called ' service', allows the passage of micro-manipulator, which facilitates manoeuvres intra ocular.
The realization of a local anesthesia or topical combined with the reduction of the size of the eye incision helped speed Visual recovery, and reduce the rate of certain retinal or infectious complications. Thus, the cataract surgery can be done in routine with one outpatient management ; its duration is now close to 15 minutes on average.
Anesthesia for the phacoemulsification is essentially issued locally, except in special situations (cataract of the child of the deficient mental, etc...). It consists in the orbital injection of anesthetic products (injection peri or retro bulbar), either in the administration of local anesthetics (anaesthetic drops topical).
The cataract surgery is carried out under indirect Visual control through the eyepiece of the microscope. ¨Afin to reduce the risk of post-operative infection (endophthalmitis), this Act is done in the strict surgical asepsis conditions.
The corneal incision is made by a calibrated instrument: microincision, this incision is close: 1.8 mm. It permits the passage of instruments and cannulas used for surgery. A second lateral incision (< 1 mm) is made for the passage of the micro manipulator.
The capsulorhexis is the cutting of the anterior capsule: the capsule is 'torn' in the centre, then this tear is guided by a microclamp to achieve a centered circular opening whose diameter is close to 5.5 mm. This gesture is made while the anterior Chamber of the eye (space between the posterior face of the cornea and the lens) was previously filled by a transparent viscoelastic substance.
Fragmentation of the cristallinien kernel
The fragmentation of the cristallinien core is caused by the mechanical energy delivered to the contact of the lens in the form of vibrations of ultrasonic frequency by the metal head of the phacoemulsificateur. It is also helped by maneuvers surgical endoculaires so-called "cracking" or "chop". A permanent irrigation of isotonic saline solution avoids sagging of the prior and posterior Chambers. Vibrations, aspiration and irrigation can be introduced into the anterior Chamber of the eye by the end of a single hand (coaxial surgery), or can be performed by two tips separated and introduced by two lateral incisions (so-called two-hand surgery). Management intensity of ultrasound, of aspiration and irrigation fluid flow is controlled permanently by the phacoemulsification console, on which are connected manifolds and the power supply to the room to hand.
During the surgical procedure, the surgeon has viscoelastic injectable substances (sodium hyaluronates of varying molecular weight) involved in the maintenance of the ocular volumes and ensuring the protection of the endothelial layer corneal Lining the posterior side of the cornea. The respect of this fragile and regenerating cell tunic is essential to avoid transient or definitive corneal edema in postoperative.
Injection of artificial lens implant
Once the cortex and the nucleus of the lens fragmented then evacuated, then empty capsular bag is unpleated by viscoelastic substance injected to better accommodate theimplant of artificial lens. In order not to increase the size of the incision, the majority of implants, (with the optical diameter close to 6 mm and the diameter of 11 to 12 mm) are injected into the posterior Chamber.
The implant is above all a lens whose optical power was calculated prior to intervention from the corneal power and Ocular axial Length (examination of the echobiometry or optical biometrics by interferometry), so as to Allow the focus of light rays on the most sensitive part of the retina for discrimination of details (fovea).
Control of the waterproofness of the incision
The corneal incisions of small size (less than or equal to 3.2 mm) do not require generally No wire sutureprovided that their geometry allows a good coaptation of the corneal banks at the end.
Phaco emulsification: postoperative
The first postoperative control must take place within the first 72 hours after the surgery, and is in practice often performed the day after the operation. It is intended to check the tightness of the incision, the good position of the implant and the absence of infection or inflammation.
If necessary, the renewal of glasses correctors is usually accomplished after a period of about three weeks.
Postoperative treatment is most often topical and consists in the daily administration of steroidal or nonsteroidal anti-inflammatory eye drops, antibiotics, and iris dilator agents. The total duration of the local treatment is between three weeks and one month.
Some prophylactic therapeutic protocols involve peri-operative supervision with administration of corticosteroids and or anti-inflammatory drugs by local or general means. They are the prerogative of the cataract surgery of the fragile patient (Diabetes bad balanced or complicated, immunodeficiency) or presenting a particular local or general field (history of uveitis, glaucoma, etc...).
Hypotonisants Eye Drops (beta blockers) can be prescribing in the absence of contraindications for patients with post-operative ocular Hypertonia.
Recent developments of phaco-emulsification technique (the lens extraction)
Unlike the benefits brought about by the passage of intra capsular extraction extra capsular extraction, recent progress in the field of phacoemulsification technique do not fundamentally alter patient management. These advances are intended to facilitate the surgical execution and/or to make the lens of less and less invasive surgery.
This progress is linked to the improvement of the surgical instrumentation, contemporary of the reduction of its congestion. It is now possible to achieve incisions of less than 2 mm wide (micro incision) for the extraction of the crystalline and implantation of an artificial lens. This reduction however imposes restrictions increased in terms of flow of fluids for irrigation and cooling. New techniques to reduce the issuance of ultrasonic vibration in contact with the lens: temporal modulation of ultrasonic vibration (micro pulse, micro burst), optimal management of the movements of the head of the phacoemulsificateur (pendulum oscillations: Ozil® technology), continuous injection of irrigation fluid swirling under pressure to replace the mechanical vibratory effect of ultrasound (Aqualase® technology), etc...
Reduction of the time of use of ultrasound helps minimize endothelial risk. Finally, new operating microscopes facilitate visualization of the previous eye structures for the surgeon and improve safety during surgery. Some systems allow the projection of Visual cues (augmented reality) to facilitate and increase the orientation of the implants-rings for example.
Cataract surgery and special situations
Surgery of cataract and cornea also (of Fuchs dystrophy)
The Fuchs dystrophy is endothelial dystrophy whose origin is unknown. It is related to the presence of abnormal deposits in the posterior part of the cornea, which form the "drops")cornea also); There is a gradual reduction in the density of corneal endothelial cells. THEcorneal endothelium is a single cell layer lining the back (inside) of the cornea; These cells are responsible for ensuring that the hydration of the cornea remains controlled. In adults; the endothelial cells density is greater than 2000 cells per mm2. When the number of cells per square millimetre of endothelium decreases (ex: less than 1000 cells per mm2), increases the risk of swelling of the cornea. This edema is maximum in the morning, because the evaporation of a part of the water contained in the stromal tissue in the air is no longer possible due to occlusion of the eyelids for sleep. The Fuchs dystrophy is characterized by a low maximum vision in the morning.
The cataract surgery induced endothelial cell loss, estimated at 5 per cent on average. The modern treatment of the Fuchs dytrophie is the pure endothelial graft (DMEK) or associated with a strip of tissue stromal (DSEK).
When the patient reached cataract presents visual impairment linked to Fuchs Dystrophy (decrease of Visual acuity in the morning), it is almost inevitable that endothelial cells transplantation will be necessary, and it can be done jointly at the cataract operation (triple procedure: removal of the lens, put an implant, endothelial graft).
When the patient is asymptomatic, it is in practice lawful to perform only the cataract operation, especially if the endothelial density is greater than 1000 cells per mm2, and corneal thickness is less than 600 microns (absent or moderate edema). In these conditions, a simple cataract surgery should be attempted, but by the decompensation case endothelial post operative, with low vision and chronic edema, a cell transplant endothelial (technical DMEK) must be made to restore the transparency of the cornea.
When the endothelial density is less than 1000 cells per mm2 and there is corneal edema)Center thickness greater than 650 microns), the realization of a joint (or performed secondarily) endothelial cell transplant to the cataract surgery may be offered.
Cataract surgery and diabetes
While the cataract surgery performed in patient with a well-balanced diabetes and diabetic retinopathy absent or minimal results in a low rate of complications, the surgical management of severe and complicated diabetes patients is more problematic.
The balance of diabetes must be obtained preferably several months before the completion of the surgical procedure. Elevation of HbA1c is a risk factor for worsening diabetic retinopathy during cataract surgery. The modern and non-invasive techniques of vitreous retinal imaging such as the OCT (Optical Coherence Tomography) allow to objectify the relationship between vitreous and macula, and to consider the realization of a combined surgery (ablation of the Cataract and Vitrectomy) in some case of persistent macular edema.
Diabetes would be the first risk factor for infectious complication after cataract surgery (endophthalmitis) which is part of nosocomial infections. The antibiotics is controversial; the fluoroquinolone systemically administered 2 hours before the gesture and possibly completed by a new 24 hours after is recommended in patients at risk. More preventive measures (asepsis and antisepsis), early follow-up during the first days and diabetic patients adequate information are important for preventing infectious complications. Injection into the anterior Chamber of a solution of antibiotic (cefuroxime) at the end is some European studies an effective prophylactic method at the cataract operation, but some results are challenged especially in the USA.
Surgery of cataracts and age-related macular degeneration (AMD)
The progression of AMD increased after the cataract surgery has been reported. The Framigham study showed that nuclear cataract patients (particularly filtering short close radiation of light blue) had an lower than those with macular reworking rate of cortical cataract. These elements suggest the deleterious role for retinal macular short (300-400 nm, or near ultraviolet) light radiation.
On the contrary, some studies find no significant link between exposure to light and AMD. The potential risk associated with short-wavelength retinal exposure in cataract-operated patients justifies, however, the presence of a UV filter (< 400nm).
The implants 'yellow '. because filtering some of blue light were introduced on the market. They mimic the properties of absorption of a moderately aged crystalline by reducing light radiation between 400 and 500 nm (peak light blue is situated around 430 nm).
The benefit provided by these yellow implants remains speculativein the absence of clinical findings found on randomised studies. The blue light on the retinal level reduction could reduce Visual performance in reduced lighting (status scotopiques), and disrupt circadian rhythms by the reduction in the secretion of melanopsin (this protein found in certain photosensitive ganglion cells inhibits the secretion of melatonin by the pineal gland).
Cataract surgery and corneal refractive surgery history
Refractive surgery for the correction of the optical eye defects (myopia, astigmatism, and presbyopia) knows a growing success, enjoyed every year more than a million to American eyes at least 100 000 french eyes.
Corneal surgery Techniques (PKR for procedures to Refractive aiming, Laser Assisted In Situ Keratomileusis; LASIK) alter the optical power of the cornea in a controlled manner. During the 80's and 90's, the technique of radial keratotomy was based on the realization of peripheral incisions to correct myopia through central flattening.
If cataract surgery in patients with corneal refractive surgery does not pose any particular technical problems, the previously generated contact geometric changes make the optical power measurement of the cornea possible Prove to be wrong with standard measurement techniques (keratometry). Some formulas used to accurately predict the potency of the Cristallinien implant in subjects without surgical history may also lead to errors in patients operated of refractive surgery.
Cataract surgery and tamsulosin decision-making
Tamsulosin is an alpha 1 adrenergique antagonist that allows the preferential blocking alpha 1 receptors prostatic (subtype 1 (A) with limited vascular receptors alpha A action (under type 1 B). This molecule is indicated in BPH.
The syndrome of the " IRIS flask intraoperative "(floppy iris syndrome) is observed in patients taking tamsulosin and is characterized by a triad of intraoperative which combines a flaccid irien stroma, a prolapse of the iris to the suction tube and the incision, and progressive pupillary constriction despite an appropriate expansion Protocol. Taking tamsulosin for two weeks just to induce this syndrome, which can also be observed 3-5 years after cessation of the treatment. This peculiarity is that tamsulosin remained linked for a long time to the post synaptic ends of the iris dilator.
The recommendations regarding the operative strategy are the continuation of the treatment but the use of a Protocol of preoperative dilation specific herbal cyclopentolate 0.5% and the instillation of atropine 1% three times a day one to two days before surgery. Research in the questioning of tamsulosin decision-making must be systematic questioning before cataract surgery.