Posterior polar cataracts
Everything you ever wanted to know about posterior polar cataracts
A: Posterior polar cataract; B: Hydrodissection is contraindicated. Only hydrodelineation is performed and the golden ring is seen; C: Cortex aspiration completed; D: A different case showing posterior capsular rent as cortex was attempted to be aspirated with the I/A port facing the posterior capsule
Posterior polar cataract, as the name implies, is located at the posterior pole of the crystalline lens at the nodal point. It is generally bilateral and has a unique, whorl-like appearance. It extends into the subcapsular and posterior cortical regions in the axial zone. It needs to be differentiated from the more anterior and larger, diffuse nature of a posterior subcapsular cataract, as the surgical techniques differ for each.
The posterior polar cataract may be stationary, associated with hyaloid artery remnants or may be of a progressive variety. Being at the nodal point, patients with the progressive variety present early with symptoms of progressively worsening glare and difficulty in reading. Interdigitation of the cataract with the posterior capsule causes a weakness in the capsule in the involved area.
In some cases, the capsule may be congenitally deficient. The remaining lens may be clear, associated with riders in the posterior cortex or have associated nuclear sclerosis. With dense nuclear sclerosis, the polar element may be undiagnosed, leading to intraoperative complications. Proper preoperative identification is therefore important to avoid posterior capsular rent and vitreous loss.
Cataract surgery may be planned as soon as there is interference with the patient’s visual requirements. However, proper preoperative counselling of the patient and an informed consent are important because of the increased risk associated with surgery. Adequate surgical precautions should be taken to decrease the risk of posterior capsular rent and its consequent complications. With better understanding and description of techniques, the rate of posterior capsular rent has decreased from about a third of cases to less than 10%.
Proper preoperative identification is therefore important to avoid posterior capsular rent and vitreous loss.
WHY, HOW, WHICH?
The capsulorhexis should be centred and sized to be suitable for optic capture in the eventuality of a sulcus placement of the intraocular lens (IOL). All surgical manoeuvres should be aimed at negating any stress or pressure on the weakened posterior capsule.
Hydrodissection should never be performed for posterior polar cataracts as it can cause a hydraulic perforation of the posterior capsule or enlargement of a pre-existing defect, generally at the border of the cataract. I prefer instead to perform a gentle multi-quadrant, limited viscodissection by injecting small aliquots of viscoelastic under the anterior capsule in multiple sites limited to a few millimetres beyond the rhexis and not crossing the equator.
This has the benefit of initiating a limited anterior cortical cleavage, while also acting as a barrier preventing accidental hydrodissection. A controlled hydrodelineation is then done to separate the epinucleus and the central nucleus. The hydro cannula is inserted into the nucleus in a plane away from the height of the polar cataract so that the fluid wave from hydrodelineation does not rupture the posterior capsule.
An inside-out hydrodelineation, as described by Vasavada et al, may also be performed after gently sculpting an initial groove in the nucleus followed by injection of fluid at the desired depth in the groove. A good hydrodelineation allows the generally small and soft nucleus to be lollipopped or speared out gently with the phaco probe. Iris plane or anterior chamber phacoemulsification can then be safely performed.
The epinuclear shell gives additional protection during nucleus removal. Slow-motion phacoemulsification with low power, flow rate, vaccum and infusion creates a highly stable intraocular environment.
Another technique that has been described for removing soft nuclei is by first performing hydro-free dissection using a blunt spatula that is passed up to the equatorial fornix to free cortico-capsular adhesions. The nucleus is then progressively debulked in the inferior half. The remaining superior nucleus is then brought to the centre with a combination of visco-displacement and manual manoeuvring and is then removed.
Though a gentle chop may be attempted for denser nuclei, care should be taken not to apply any posterior pressure. Femtodelineation using a cylindrical pattern of laser application, as described by Vasavada et al, creates multiple concentric layers that act as shock absorbers and prevent stress transmission to the posterior capsule during surgery.
However, care still needs to be taken that the intra-lenticular gas bubbles created by the femtosecond laser do not increase intra-lenticular pressure and cause a posterior capsular rent. A capsular block syndrome may also similarly occur causing a rent.
CORTEX REMOVAL AND
Chamber fluctuations can cause a dehiscence at the edge of the posterior polar cataract and this should be avoided at all times. Viscoelastic should be injected through the side port before removing the phaco or I/A probe to prevent forward movement of the lens-iris diaphragm.
This is especially important at the time of cortex aspiration, as the chamber can shallow, and with most of the lenticular material removed, the bag can move forwards substantially while removing the I/A probe, resulting in a posterior capsular dehiscence. Cortex aspiration should be done gently and by stripping the cortex carefully, and slowly by engaging it from under the rhexis. It is helpful to partially strip and loosen the cortex from all sides before finally removing the posterior polar element, though often the plaque comes loose and can then be aspirated.
Any residual posterior capsular opacity is best left for subsequent YAG capsulotomy. At no point should the cortex be attempted to be directly aspirated from the posterior capsule, even with capsule polishing mode, as this can cause a tear in the weakened capsule.
The IOL is finally implanted into the bag, avoiding direct contact of the leading edge of the IOL on the weakened posterior capsule and taking care that it slides gently into the distal fornix. An IOL that gently unfolds in the bag is preferred.
If a capsular tear does occur, a closed system should be maintained before retracting the phaco or I/A probe by injecting viscoelastic to avoid vitreous prolapse. Vitrectomy should be performed and the IOL placed into the ciliary sulcus with optic capture.
Dr Soosan Jacob is Director and Chief of Dr Agarwal’s Refractive and Cornea Foundation at Dr Agarwal’s Eye Hospital, Chennai, India