Posterior polar cataract: A review

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. Different surgical strategies were described for the handling of this challenging entity, most of which emphasized the need for gentle maneuvering in dealing with these cases. It has a unique clinical appearance that should not be missed in order to anticipate, avoid, and minimize the impact of the complications associated with it.     

Posterior polar cataract surgery - a posterior segment approach

PURPOSE: To suggest a surgical approach that would pre-empt uncontrolled posterior capsular rupture and consequent posterior segment complications associated with posterior polar cataract surgery. DESIGN: An interventional case series. METHODS: This was a prospective, interventional study undertaken at a tertiary referral ophthalmic unit. Eleven eyes of eight patients underwent planned pars plana vitrectomy, lensectomy and posterior chamber sulcus fixated intra-ocular lens implantation. Demography, presenting features, pre- and post-operative visual acuities, complications and length of follow-up were recorded. A single surgical technique was performed in all the cases. RESULTS: Five male and three female patients with a mean age of 49.7 years, underwent this procedure. The median-corrected pre-operative visual acuity was 6/12 and the same post-operatively was 6/6. The only major per-operative complication was one case of accidental iridectomy. Post-operatively there were transient choroidal folds in one case, mild posterior segment haemorrhage in another and retinal detachment in one patient. The mean follow-up period was 13 months. CONCLUSIONS: This surgical technique offers a relatively controlled and predictable approach to posterior polar cataract surgery compared to others described in the literature. Although this technique is not without complications, the visual outcome is usually good.     

Posterior polar cataract: minimizing risk of posterior capsule rupture

PURPOSE: To study a preferred technique of phacoemulsification in eyes with posterior polar cataract and report its outcome. METHODS: Under topical anesthesia, phacoemulsification was carried out after hydrodelination in 23 cases (38 eyes) with ages ranging from 19 to 65 years (mean=33.5 years). Hydrodissection was not performed. RESULTS: Mean duration of follow-up was 9.5 months. None of the eyes developed posterior capsule rupture, but seven eyes (18.4%) revealed posterior capsule plaque postoperatively, which needed neodymium : YAG laser capsulotomy. Mean visual acuity improved significantly after surgery (P=0.0001, paired t-test); In all, 34 eyes achieved a best-corrected visual acuity of 20/40 or more (89.4%). However, the postoperative visual acuity was less than 20/25 in 11 eyes (28.9%). The causes of the low acuity were amblyopia in eight eyes (21.0%) and macular degeneration due to retinitis pigmentosa in two others (5.2%). CONCLUSION: Phacoemulsification is an effective and safe method to treat posterior polar cataract with gentle hydrodelination 'hydrodissection free phacoemulsification technique'. This is especially true when great attention is paid to the 'floppy' posterior capsule. Although previous amblyopia might interfere with excellent surgical outcome in patients with a unilateral or highly asymmetric bilateral cataract, visual acuity improved significantly in most cases.     

一个后极性白内障家系致病基因的筛查与鉴定

目的　对中国一个具有常染色体显性遗传特点的后极性白内障家系进行致病基因的筛查。方法　分别采集家系成员外周静脉血,提取基因组ＤＮＡ,根据临床表型选取６个候选基因（ＣＲＹＡＡ、ＣＲＹＡＢ、ＰＩＴＸ３、ＣＨＭＰ４Ｂ、ＭＩＰ、ＣＲＹＧＤ）设计引物,通过ＰＣＲ扩增ＤＮＡ片段,琼脂糖凝胶电泳分离ＤＮＡ片段,直接测序法寻找致病基因及突变位点。结果　该家系符合常染色体显性遗传家系特征,先证者表型为后极性白内障,通过候选基因外显子直接测序,发现家系内患者ＣＲＹＧＤ基因第２个外显子第１２７位碱基有１个Ｔ→Ｃ的点突变,此突变导致蛋白第４３位的色氨酸被精氨酸取代（Ｗ４３Ｒ）。结论　ＣＲＹＧＤ基因ｃ．Ｔ１２７Ｃ（ｐ．Ｗ４３Ｒ）突变是该后极性白内障家系的致病原因。     

Posterior polar cataract: Hydrodissection and nucleus rotation in manual small-incision cataract surgery not a taboo with proper fluidics

A posterior polar cataract is a discoid posterior polar plaque-like cataract with a thin and fragile to absent posterior capsule with adherent acellular opacity to the capsule reported in the literature. It is a stationary or slowly progressive opacity. A higher risk of complications such as posterior capsular tear and nucleus drop makes this a challenging surgery. The techniques described in the literature include bimanual irrigation aspiration, leaving the plaque for later Yag, bimanual micro phaco, Lambda technique with dry aspiration, Phaco if opacity <4 mm and soft nucleus, pars plana vitrectomy (PPV), pars plana lensectomy (PPL) if opacity >4 mm and soft nucleus, intra-capsular cataract extraction (ICCE) and scleral fixated intraocular lens (IOL) if opacity >4 mm with the hard nucleus, viscodissection, 3 ports PPL, PPV, low parameters phaco, modified epinucleus removal, inverse horse-shoe technique, standard phacoemulsification, chip and flip for soft cataracts, stop and chop for hard cataracts, layer-by-layer phacoemulsification, standard lens aspiration, pars plicata posterior vitrecto-rhexis, manual small-incision cataract surgery, and conventional extracapsular extraction. A posterior capsule rupture rate of 0 to 36% is reported in different series for cataract extraction. To prevent this dreaded complication, surgeons used many modifications. Minimal hydrodissection in posterior polar cataract extraction was described by Fine et al. The authors describe a technique of low flow manual small-incision cataract surgery with minimal hydrodissection and nucleus rotation with no associated posterior capsule rent. This demonstrates that if the fluidics is understood and corrected, then minimal hydrodissection and nucleus rotation is not taboo in posterior polar cataract extraction by manual small-incision cataract surgery.     

先天性后极性白内障致病基因研究进展

先天性白内障是儿童最常见的致盲眼病,后极性白内障在先天性白内障中不少见,其混浊位于视轴上,在跟屈光系统的结点附近,对视力有显著影响.本文就目前已发现的导致人类先天性后极性白内障的致病基因作一综述.     

Genetically distinct autosomal dominant posterior polar cataract in a four-generation Japanese family

PURPOSE: To describe the clinical findings of a form of posterior polar cataract in a large Japanese family and to determine whether the posterior polar cataract is causally related to other autosomal dominant cataracts with known genes, chromosomal locations, or both. METHODS: Systemic and ocular histories were obtained and comprehensive ophthalmic examinations were performed in 15 of 37 members of the Japanese family. The posterior polar cataract was transmitted in an autosomal dominant manner through four generations. Although there is some variation in the degree of opacification, the posterior polar cataract in this family is characterized by progressive disk-shaped posterior subcapsular opacities. Genetic linkage analysis was performed with 41 polymorphic microsatellite markers located in chromosomal regions known for linkage to cataracts. Genomic DNA extracted from the 15 individuals was amplified by polymerase chain reaction, the genotype at the marker loci was determined in each family member, and the lod score was calculated at each locus. RESULTS: Significant linkage of the posterior polar cataract was ruled out from the following 10 loci or chromosomal regions: 16q22 and 1p36, to which two forms of autosomal dominant posterior polar cataract have been assigned: 1q21-q25, 2q33-q35, 13cen, 17p13, 17q11-q12, 17q24, 21q22, and 22q, which are the regions responsible for other autosomal dominant congenital cataracts. CONCLUSIONS: This study confirms the genetic heterogeneity of autosomal dominant posterior polar cataracts and demonstrates that the posterior polar cataract in this Japanese family is phenotypically and genetically distinct from previously mapped cataracts.     

先天性后极性白内障超微结构分析及突变基因筛查

目的 探讨一先天性后极性白内障家系晶状体的超微结构改变,并初步筛查其致病基因.方法 收集一常染色体显性遗传性先天性后极性白内障家系资料,对家系成员行眼部检查;在透射电镜下观察晶状体细胞超微结构的改变;选择CRYAB、CRYBA1/A3、CRYBB2、GJA8、CHMP4B、PITX3和EPHA2这7个热点基因进行突变位点筛查.结果 根据家系图分析该家系为垂直遗传,符合单基因常染色体显性遗传特点.裂隙灯显微镜下检查示全部患者晶状体混浊形态完全相同.透射电镜下发现患者前囊面晶状体上皮细胞排列紧密,结构完整,未见特异性病理变化;前皮质晶状体纤维细胞排列紧密,细胞内密度均一一致,但后皮质晶状体纤维细胞内出现斑驳状中高密度异常颗粒沉着.热点基因筛查显示:7个候选基因的外显子及其邻近内含子序列与基因库对照未发现任何突变.结论 本研究将后极性白内障病变定位于后皮质晶状体纤维细胞,排除了前囊面晶状体上皮细胞及前皮质晶状体纤维细胞.此家系携带的遗传突变位点位于尚未见报道的与后极性白内障相关的致病基因上.     

先天性前极白内障家系致病基因的定位与候选基因突变检测

目的 对中国一常染色体显性遗传先天性前极白内障家系进行致病基因的定位与候选基因突变检测.方法 采集家系成员外周静脉血,提取基因组DNA.选用ABI公司提供的约400个遗传标记物进行基因扫描.基因扫描分初步扫描和精细扫描两步进行.首先对已报道的先天性白内障候选区域进行初步扫描,之后在阳性区域内进行精细扫描.数据经连锁分析,初步确定致病基因所在染色体区域.在阳性区域内选取更高密度的荧光标记物进行精细扫描,并进行单体型分析.候选基因直接测序检测基因突变.结果 两点间连锁分析在微卫星标记D21S1252处获得最大对数优势计分(LOD)值Zmax=3.23(θmax=0.00).精细定位和单体型分析将致病基因定位于微卫星标记D21S263和D21S266之间,遗传距离约18.47厘摩(cM),染色体位置为21q22.11-q22.3.候选基因直接测序发现CRYAA基因第3外显子第347碱基一个G→A的点突变.结论 本研究将一中国先天性前极白内障家系的致病基因定位于21号染色体21q22.11-q22.3区域内,并在CRYAA基因发现一个点突变与此家系共分离.

Abstract：

Objective To map the gene mutation responsible for autosomal dominant inherited congenital anterior polar cataract in a Chinese family. Methods Peripheral blood samples were collected from the members in this congenital cataract family. DNA was extracted from the blood samples. A genescan was performed using approximately 400 microsatellite markers (ABI). Linkage analysis was processed to define the region of mutated gene. High density primers labeled with fluorescent stain for the positive region were adopted for fine targeting and haplotype analysis was performed. Mutation detection was carried out by sequencing candidate genes. Results The maximum two-point LOD score was obtained at D21S1252,Zmax = 3. 23 ( θmax = 0. 00). After fine targeting and haplotype analysis,the mutated gene was located within a 18. 47 cM region between D21S263 and D21S266 on chromosome 21q22.11 -q22.3. Direct sequencing of the candidate gene revealed a G→ A transition in exon 3 of CRYAA. Conclusion The present study has identified a missense mutation in CRYAA associated with congenital anterior polar cataract in a Chinese family.     

Validity of a personal and family history of cataract and cataract surgery in genetic studies

PURPOSE: To determine the accuracy of a history of cataract and cataract surgery (self-report and for a sibling), and to determine which demographic, cognitive, and medical factors are predictive of an accurate history. METHODS: All participants in the Salisbury Eye Evaluation (SEE) project and their locally resident siblings were questioned about a personal and family history of cataract or cataract surgery. Lens grading at the slit lamp, using standardized photographs and a grading system, was performed for both SEE participants (probands) and their siblings. Cognitive testing and a history of systemic comorbidities were also obtained for all probands. RESULTS: Sensitivity of a history of cataract provided on behalf of a sibling was 32%, specificity 98%. The performance was better for a history of cataract surgery: sensitivity 90%, specificity 89%. For self-report of cataract, sensitivity was also low at 55%, with specificity at 77%. Self-report of cataract surgery gave a much better performance: sensitivity 94%, specificity 100%. Different cutoffs in the definition of cataract had little impact. Factors predicting a correct history of cataract included high school or greater education in the proband (odds ratio [OR] = 1.13, 95% confidence interval [CI]1.02-1.25) and younger sibling (but not proband) age (OR = 0.94 for each year of age, 95% CI 0.90-0.99). Gender, race and Mini-Mental Status Examination (MMSE) result were not predictive. CONCLUSIONS: Whereas accurate self and family histories for cataract surgery may be obtainable, it is difficult to ascertain cataract status accurately from history alone.     

Identification of a CRYAB mutation associated with autosomal dominant posterior polar cataract in a Chinese family

PURPOSE: A four-generation Chinese family with 13 members affected with autosomal dominant congenital posterior polar cataract was studied. The purpose of this study was to identify the disease-causing gene in the family and to validate that mutations in CRYAB, the alphaB-crystallin gene, cause the congenital cataract. METHODS: Linkage analysis was performed with a panel of microsatellite markers flanking candidate genetic loci for cataracts, including 14 known autosomal dominant congenital cataract (ADCC) genes. For mutation analysis, the complete coding region and exon-intron boundaries of CRYAB were sequenced with DNA from the proband. Single-strand conformation polymorphism (SSCP) analysis for exon 1 of CRYAB was performed in all family members and 200 normal control subjects. RESULTS: The disease gene in the Chinese family was mapped to chromosome 11 in region q22-22.3 with a maximum lod score of 4.52. Direct DNA sequence of CRYAB revealed a heterozygous C-->T transition at nucleotide 58, resulting in a novel 58 C-->T (Pro20Ser) mutation. The Pro20Ser mutation cosegregated with all affected individuals and was not present in unaffected members in the family or in 200 normal control subjects. The mutation occurs at the evolutionarily conserved residue Pro20 in the N-terminal region of alphaB-crystallin. CONCLUSIONS: To date, only one CRYAB mutation has been associated with congenital isolated cataract. This study identified a second novel mutation in CRYAB in a large Chinese cataract family. Together, these results provide strong evidence that CRYAB is a pathogenic gene for congenital cataract.     

Approaches to a posterior polar cataract

Posterior polar cataracts present special challenges to the cataract surgeon. These are often associated with weakness/dehiscence of the posterior capsule and thus have a higher rate of intraoperative posterior capsule rupture. The surgeon needs to adhere to special surgical strategies to minimize the risk of a posterior capsule rupture. These include, adhering to the principles of closed chamber technique, avoiding hydrodissection – instead performing ‘inside-out’ hydrodelineation and using modest to low phaco parameters and reducing these stepwise. This article provides important pearls on how to approach a posterior polar cataract.     

Surgical approaches to posterior polar cataract: a review

The aim of this study is to provide a comprehensive overview of surgical methods used in the emulsification of posterior polar cataracts (PPCs) that have been devised to minimize the risk of posterior capsule rupture (PCR) and its consequences. A Pubmed and Medline search of relevant literature on PPC was done. Only articles relevant to the treatment of PPC were included. The posterior capsule in eyes with PPC are known to have an abnormal adhesion to the polar opacity or a pre-existing weakness of the capsule that predisposes the eye to PCR. To circumvent the consequences of cleaving the abnormal adhesion, a majority of the surgeons use the anterior approach through the limbus, whereas some advocate the posterior approach through the pars plana. Emulsifying the nucleus and cleaving the central opacity of the PPC off the posterior capsule without disrupting its integrity provides optimal surgical outcomes. To achieve this, various modifications have been applied by surgeons during different phases of surgery. The advantages, disadvantages, complications, and results of each method have been discussed. Phacoemulsification is the preferred technique for removing PPC. This review will provide methods to avoid and /or deal with intraocular surgical difficulties that can arise during emulsification. Employing these would result in least ocular morbidity and satisfactory visual outcomes for the patient. This is particularly relevant given the major advancements in technology and refinements in surgical techniques in phacoemulsification.     

Posterior polar cataracts: a predisposition to intraoperative posterior capsular rupture

We performed phacoemulsification or planned extracapsular cataract extraction on posterior polar cataracts in 31 eyes of 22 patients and experienced eight cases of posterior capsular rupture (26%). Capsular rupture occurred during removal of the posterior polar opacity or during cleaning of the posterior capsule after the opacity had been removed. We believe that excessive adherence of the opacity to the posterior capsule and unusual thinness of the capsule predisposed these eyes to posterior capsular rupture.     

Management of posterior polar cataract

In this technique for managing posterior polar cataract, extreme care is taken not to overpressurize the anterior chamber or capsular bag to prevent posterior capsule rupture. Minimal hydrodissection and hydrodelineation are performed. The nucleus is extracted using minimal ultrasound energy. Viscodissection is used as a primary technique to mobilize the epinucleus and cortex. A protective layer is preserved over the posterior polar region until the conclusion of the extraction procedure to minimize the risk of loss of lens material into the vitreous cavity in the case of a capsule defect.     

一个常染色体显性遗传先天性白内障家系致病基因筛查

目的: 对中国一个常染色体显性遗传先天性白内障家系(ADCC)的已知候选基因进行筛查以寻找致病位点。方法: 收集一个ADCC家系的临床资料并采集静脉血。在24个已知与ADCC相关基因附近选择微卫星标记,利用Linkage软件Mlink软件包进行连锁分析计算Lod值。结果: 此家系白内障类型为核性白内障,24个候选基因附近50个微卫星Lod值均小于0,微卫星所在区域与此家系致病基因无连锁关系。结论: 此ADCC家系致病基因不是已知的与ADCC相关基因,可能是一个新的致病基因突变导致此家系疾病发生。