Anterior segment OCT imaging in mucopolysaccharidoses type I, II, and VI.

PURPOSE: To describe the anterior segment optical coherence tomography (AS-OCT) characteristics of patients with ocular manifestations of mucopolysaccharidoses type I (Hurler), II (Hunter), and VI (Maroteaux-Lamy). METHODS: Prospective, observational study of nine consecutive patients with variants of mucopolysaccharidosis (MPS) attending the Paediatric Ophthalmology service at Manchester Royal Eye Hospital, UK. All patients underwent Visante AS-OCT imaging as part of their ophthalmic assessment. RESULTS: Ocular involvement tended to be symmetrical. Angle-to-angle distance was significantly lower in MPS VI than in MPS I (P=0.04). Anterior chamber depth, angle opening distance, trabecular-iris space area, and scleral spur angle tended to be lower in MPS VI than in MPS I, but did not reach statistical significance. Corneal thickness in the central 0-2 mm zone was greater in MPS VI than in MPS I, approaching but not attaining statistical significance (P=0.07). The 2-5 and 5-7 mm zones were significantly thicker in MPS VI than MPS I (P=0.04, P=0.04). There was no difference in corneal thickness between MPS I and MPS VI in the peripheral 7-10 mm zone (P=0.57). Measurements of the patient with MPS II resembled the mean values of the MPS I group. CONCLUSION: AS-OCT is valuable in quantifying anterior segment pathology in MPS. It suggests more crowded anterior segments and greater corneal thickness in patients with MPS VI than MPS I. AS-OCT is useful in evaluating the risk and mechanism of glaucoma in MPS patients, and may improve our assessment of the efficacy of systemic treatment.

Refractive outcomes after primary intraocular lens implantation in infants.

BACKGROUND: Intraocular lens (IOL) implantation is becoming increasingly accepted as a primary procedure in infants. AIM: To evaluate the accuracy of IOL power calculation, the rate of myopic shift and the refractive outcome after primary IOL implantation in infants aged <12 months at the time of cataract surgery. METHOD: A retrospective case review of 25 patients (8 with bilateral cataracts and 17 with unilateral cataracts) who underwent cataract surgery with primary IOL implantation at <12 months of age. Outcomes measured were actual early postoperative refraction, lens power calculation error, myopic shift and refractive outcome. RESULTS: In 83% of cases, actual postoperative refraction was within 2 dioptres (D) of the target refraction. Lens power calculation error did not depend on axial length, age at surgery or target refraction. Mean (SD) myopic shift was 5.43 (3.7) D in the first 12 months after surgery, but was significantly greater when surgery was performed at <10 weeks of age. CONCLUSION: This study demonstrates that IOL power can be calculated with reasonable accuracy in infants using current formulas. Factors such as age at the time of surgery, axial length, whether surgery is unilateral or bilateral, and the presence of systemic pathologies do not seem to influence the accuracy of lens power calculation or myopic shift up to 36 months of age.

The ocular features of the mucopolysaccharidoses.

AIMS: The mucopolysaccharidoses (MPS) are a heterogeneous group of rare disorders characterised by accumulation of glycosaminoglycans within multiple organ systems. This study aimed to determine the prevalence and severity of ocular complications in patients with MPS. METHODS: Clinical ophthalmic features and electrodiagnostic results of 50 patients with a diagnosis of MPS were retrospectively reviewed. RESULTS: A total of 79% of MPS IH patients had a visual acuity of less than 6/12 equivalent in their better eye, compared to 44% of MPS IH/S and 25% of MPS VI patients. In total, 16% of MPS IH and 25% of MPS IH/S had severe corneal opacification, compared to 38% of MPS VI patients. 16% of MPS IH patients had optic atrophy; 21% of MPS VI patients had mild disc swelling, 29% had markedly swollen discs, and 14% had optic atrophy. One patient with MPS IH, one with MPS IH/S and six with MPS VI had ocular hypertension. One MPS VI patient had glaucoma that required topical therapy. Nine patients with MPS IH had electrodiagnostic evidence of retinopathy, as did one MPS VI patient. CONCLUSIONS: Ocular complications causing significant reduction in vision are common in MPS. The majority of MPS I and MPS VI patients have corneal opacification, which can lead to difficulties in diagnosis and monitoring of glaucoma, optic disc changes, and retinopathy.

Regulation of fibrillin carboxy-terminal furin processing by N-glycosylation, and association of amino- and carboxy-terminal sequences.

The molecular mechanisms of fibrillin assembly into microfibrils are poorly understood. In this study, we investigated human fibrillin-1 carboxy-terminal processing and assembly using a recombinant approach. Processing of carboxy-terminal fibrillin-1 was strongly influenced by N-glycosylation at the site immediately downstream of the furin site, and by association with calreticulin. The carboxy terminus of fibrillin-2 underwent less efficient processing than carboxy-terminal fibrillin-1 under identical conditions. Size fractionation of the amino-terminal region of fibrillin-1, and of unprocessed and furin-processed carboxy-terminal region of fibrillin-1, revealed that the amino terminus formed abundant disulphide-bonded aggregates. Some association of unprocessed carboxy-terminal fibrillin-1 was also apparent, but processed carboxy-terminal sequences remained monomeric unless amino-terminal sequences encoded by exons 12-15 were present. These data indicate the presence of fibrillin-1 molecular recognition sequences within the amino terminus and the extreme carboxy-terminal sequence downstream of the furin site, and a specific amino- and carboxy-terminal association which could drive overlapping linear accretion of furin-processed fibrillin molecules in the extracellular space. Differences in processing of the two fibrillin isoforms may reflect differential abilities to assemble in the extracellular space.

Fibrillin assembly: dimer formation mediated by amino-terminal sequences.

We have investigated recombinant fibrillin-1 (profib-1) and fibrillin-2 (glyfib-2) molecules encoding the proline- or glycine-rich regions with flanking domains (exons 9-11), in order to establish whether these sequences might mediate specific molecular recognition events important in fibrillin assembly. Our data demonstrate that both recombinant molecules can form extracellular dimers, but highlight subtle differences in the stability of these dimers. Following expression in COS-1 cells, SDS-PAGE analysis showed that glyfib-2 was present intracellularly as monomers, and extracellularly as monomers and disulphide-bonded dimers. Size fractionation in native non-reducing conditions prior to SDS-PAGE analysis highlighted that glyfib-2 also formed non-covalent associations. In contrast, profib-1 appeared monomeric in cells and medium. Using an in vitro translation system supplemented with semipermeabilised HT1080 cells together with chemical crosslinking, dimers of the fibrillin-1 and fibrillin-2 molecules were detected. Dimerisation was not cell-dependent since molecules translated in the absence of cells dimerised, and was not an intracellular event as judged by proteinase K digestions. A crosslinking and coimmunoprecipitation strategy provided a means of investigating whether molecular chaperones might be involved in preventing dimerisation of translocated molecules. Proteinase K-resistant recombinant molecules associated rapidly with BiP, and thereafter with protein disulphide isomerase and calreticulin. Differences between the two fibrillin isoforms in ability to form stable dimers prompted investigation of the proline- and glycine-rich sequences. Differences in solubility and pI were apparent that may contribute to reduced stability of proline-rich region interactions. These studies suggest that extracellular dimer formation mediated by interactions of the proline- and glycine-rich regions may be a crucial early step in the extracellular assembly of fibrillin into microfibrils.

Fibrillin degradation by matrix metalloproteinases: identification of amino- and carboxy-terminal cleavage sites.

Fibrillin molecules form the structural framework of elastic fibrillin-rich microfibrils of the extracellular matrix. We have investigated the proteolysis of recombinant fibrillin molecules by five matrix metalloproteinases. Cleavage sites were defined at the carboxy-terminal end of the fibrillin-1 proline-rich region and the corresponding fibrillin-2 glycine-rich region (exon 10), and within exon 49 towards the carboxy-terminus of fibrillin-1. Cleavage at these sites is predicted to disrupt the structure and function of the fibrillin-rich microfibrils.

Fibrillin degradation by matrix metalloproteinases: implications for connective tissue remodelling.

Fibrillin is the principal structural component of the 10-12 nm diameter elastic microfibrils of the extracellular matrix. We have previously shown that both fibrillin molecules and assembled microfibrils are susceptible to degradation by serine proteases. In this study, we have investigated the potential catabolic effects of six matrix metalloproteinases (MMP-2, MMP-3, MMP-9, MMP-12, MMP-13 and MMP-14) on fibrillin molecules and on intact fibrillin-rich microfibrils isolated from ciliary zonules. Using newly synthesized recombinant fibrillin molecules, major cleavage sites within fibrillin-1 were identified. In particular, the six different MMPs generated a major degradation product of approximately 45 kDa from the N-terminal region of the molecule, whereas treatment of truncated, unprocessed and furin-processed C-termini also generated large degradation products. Introduction of a single ectopia lentis-causing amino acid substitution (E2447K; one-letter symbols for amino acids) in a calcium-binding epidermal growth factor-like domain, predicted to disrupt calcium binding, markedly altered the pattern of C-terminal fibrillin-1 degradation. However, the fragmentation pattern of a mutant fibrillin-1 with a comparable E-->K substitution in an upstream calcium-binding epidermal growth factor-like domain was indistinguishable from wild-type molecules. Ultrastructural examination highlighted that fibrillin-rich microfibrils isolated from ciliary zonules were grossly disrupted by MMPs. This is the first demonstration that fibrillin molecules and fibrillin-rich microfibrils are degraded by MMPs and that certain amino acid substitutions change the fragmentation patterns. These studies have important implications for physiological and pathological fibrillin catabolism and for loss of connective tissue elasticity in ageing and disease.

A clinical study of the hydroxyapatite orbital implant.

The hydroxyapatite orbital implant has been used in the anophthalmic patient to give good motility of the artificial eye and a cosmetic result which matches that of the natural eye. It is thought to reduce the unacceptable complication rate that has been associated with other implants, as its buried, vascularized state deters extrusion and migration of the implant. Eighty consecutive patients were followed, 33 of whom had been referred for primary enucleation or evisceration, and 47 for secondary implant surgery. Thirteen of the secondary patients already had implants in situ. There were 44 males and 36 females in the study. The age range was 2.5 to 72 years with a mean of 36 years. The follow-up time was 2 to 30 months with a mean of 15 months. Twenty patients had been pegged at the time of review. A standardised operative and post-operative protocol was followed. The patients were assessed for the results of the motility of the artificial eye for both smooth pursuit and saccades, and for the cosmetic result. The amount of upper lid sulcus deformity was assessed to give an indication of volume replacement by the implant. The nature of any complications was noted as well as any further surgical procedures undertaken. The results show the hydroxyapatite orbital implant to give good cosmetic results with good motility of the artificial eye and to be associated with a low rate of complications. Drilling of the implant is simple to perform and also not associated with any significant complications. The hydroxyapatite orbital implant can be used successfully not only as a primary but also as a secondary or exchange implant with very few contraindications.

Correction of blepharoconjunctivitis-related upper eyelid entropion using the anterior lamellar reposition technique.

Upper eyelid entropion is a complication of chronic blepharoconjunctivitis which may be easily missed unless careful examination of the lid margin of patients with trichiasis is carried out. Many patients undergo years of unsuccessful treatment for trichiasis because the underlying upper eyelid entropion has not been detected. We would like to recommend the already established procedure of anterior lamellar repositioning as a more permanent solution to this distressing condition and present the results of this procedure on 19 consecutive patients (28 lids). Our surgical technique is described and the results in this group of patients reported. The procedure was successful in 24 of 28 eyelids (85%), with success being defined as complete resolution of symptoms for a follow-up period of at least 10 months. Anterior lamellar repositioning is easy and relatively quick to perform and provides good functional and cosmetic results.

The hydroxyapatite orbital implant: a prospective study.

The hydroxyapatite orbital implant was first released for use as an orbital implant in humans in August 1989. It has been shown to be well tolerated, providing good motility of the artificial eye with a low complication rate when used as a primary implant. This prospective study evaluated the hydroxyapatite orbital implant used as both a primary and a secondary implant. Sixty patients were implanted between October 1992 and November 1994, 28 being implanted as a primary procedure at the time of enucleation or evisceration, and 32 as a secondary procedure. Seven patients underwent second-stage drilling and pegging of the implant. The mean follow-up time was 13 months (range 2-26 months). A standardised operative and post-operative protocol was followed. The patients were evaluated post-operatively for the amount of enophthalmos, degree of upper lid sulcus deformity, motility of the prosthesis, location of the implant in the socket, socket status and the presence or absence of discharge, position of the drill hole and coverage of the implant. Complications and their management were documented. Both patient and surgeon made a subjective assessment of cosmesis and the patient's satisfaction with the overall result was noted. The results of this study show the hydroxyapatite orbital implant to provide excellent motility of the artificial eye and good cosmesis with a low rate of complications when used both as a primary and as a secondary implant.