Posterior polar cataract
Posterior polar cataract
Description, Causes and Risk Factors:
Posterior polar cataract is a rare form of congenital cataract. It is usually inherited as an autosomal-dominant disease, yet it can be sporadic. Five genes have been attributed to the formation of this disease. It is highly associated with complications during surgery, such as posterior capsule rupture and nucleus drop. The reason for this high complication rate is the strong adherence of the opacity to the weak posterior capsule.
It has been recognized that posterior polar cataracts seemed to follow an autosomal-dominant inheritance pattern, and although it is occasionally sporadic. Positive family history was found in 40-55% of the patients and Molecular genetic analyses have demonstrated that an autosomal-dominant posterior polar cataract is a genetically heterogenous disease.
The direct cause of the lenticular fiber malformation during lens development has not been well understood. There are five genes attributed to posterior polar cataract (CTTP) that have been identified. CTPP1 has been mapped to 1p36, CTPP2 has been associated with CRYAB on 11q22-q22.3, and a Pro20Ser mutation and a deletion mutation (450delA) have also been highlighted. The CHMP4B gene on chromosome 20p12-q12 is responsible for CTPP3. Three mutations of PITX3 gene on chromosome 10q25, 38G > A mutation, 17-bp insertion, and 650delG have been reported to cause CTPP4. Two loci with unknown genes have similarly been reported, 14q22-q23 for CTPP5 and 16q22.
Posterior polar cataract is a true challenge for Cataract surgeons associated with a higher risk for surgical complication. Different techniques have been described to minimize this risk and improve its final outcome. All these techniques reflect that this type of cataract needs more gentle maneuvering with avoidance of chamber collapse or overinflation, low parameters, avoidance of hydrodissection, nucleus rotation, posterior capsule polishing, and excessive intraocular lens manipulation during surgery and should not be performed with same techniques as any standard cataract surgery. For larger opacities (>4 mm), one might consider going directly to posterior approach. Genetic studies have revealed the responsible genes in certain populations and this should guide the proper counseling of the patients in addition to screening the family members at risk.
Most patients with posterior polar cataracts present with symptoms as they start to become presbyopic because the loss of accommodation teams with the evolving cataract near the nodal point to significantly reduce reading ability.
The diagnosis of a posterior polar cataract is self-evident on slit-lamp examination and does not require special diagnostic procedures beyond a full ophthalmic examination. Slit-lamp examination and pupillary retroillumination allow a good evaluation of the visual significance of the opacity. Posterior polar cataract is easily identified by the slit-lamp and often clearly delineated.
Posterior polar cataract surgery is challenging, even with the most advanced techniques available. The surgical pitfalls have been well documented in the Ophthalmic literature. The importance of being aware of these surgical pitfalls and avoiding them cannot be overemphasized. It has been suggested that where hydrodelineation is difficult, pre-chopping of the anterior nucleus should be initially performed and any cracking of the nucleus should be limited so as to not involve the area near the poster pole or the capsule. Hydrodissection should be avoided because it can, in itself, cause the abnormally weakened posterior capsule to tear.
Posterior polar cataract surgery is associated with an increased incidence of posterior capsular rupture (PCR). Undue stress on the capsule must be minimized. The main difficulty is the adherence of the abnormally formed lens fibers to the posterior capsule and its associated weakness. Once the surgeon is aware of these dangers, the technique can be altered to meet these challenges.
NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.
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