The nanophthalmic macula

Clinical update in nanophthalmos: Features, diseases and complications associated

Nanophthalmos is a rare congenital condition of the eyeball that is characterised by a smaller size of the anterior and posterior segments without associated ocular malformations. Typical features that have traditionally been described in these eyes are short axial length, thickened sclera, cornea with a smaller diameter, narrow anterior chamber, and an increased lens to globe volume ratio. However, at present, there is still a lack of recognised diagnostic criteria for nanophthalmos and a classification of its severity. Its clinical relevance stems from the increased risk of multiple ocular conditions, such as high hyperopia, amblyopia, angle-closure glaucoma, retinal detachment, and cataracts. Likewise, in relation to surgery in these eyes, there are particularities in cataract and glaucoma surgery and with a greater risk of associated intra- and postoperative complications. In this way, the treatment of nanophthalmos focuses on controlling the associated eye conditions and reducing and controlling surgical complications. This review aims to update what has been published in recent years regarding nanophthalmos.

Clinical spectrum of blunted foveal contour

Foveal hypoplasia is the absence of a foveal depression and the presence of the ganglion cell layer in the foveola. A spectrum of clinical characteristics, including normal or variably decreased visual acuity, has been described in patients with blunted foveal contours. Multiple systemic and ophthalmologic conditions including albinism, aniridia, nanophthalmos, prematurity, and fovea plana have been associated with this anomaly. This article illustrates select clinical conditions characterized by a blunted foveal contour. Given the heterogeneity of findings, a thorough medical history and detailed physical and ocular examinations are usually sufficient for the clinician to make the correct diagnosis.

Nanophthalmos: An Update on the Biological Parameters and Fundus Abnormalities

Nanophthalmos is a clinical phenotype of simple microphthalmos, in which the anterior and posterior segments of the eyeball do not develop into a normal size without other major ocular or systemic anomalies. Typical clinical manifestations of nanophthalmos include short axial length, thickened sclera, small cornea, shallow anterior chamber, and increased lens-to-eye volume ratio. Currently, there is a lack of recognized diagnostic criteria for nanophthalmos. With the development of eye examination technologies, such as biological measurement and imaging examination, visualization and quantification of the eyeball's shape and structure in nanophthalmos can be realized. New clinical features have been reported, which are of great significance for diagnosing and treating nanophthalmos. This review introduces the related concepts of nanophthalmos and the new developments in its clinical characterization.

Foveal structure in nanophthalmos and visual acuity

PURPOSE

To evaluate the fovea in nanophthalmic eyes using spectral domain optical coherence tomography (SD-OCT) and OCT angiography (OCTA), and to investigate the relationship between the macular microstructure and visual acuity.

METHODS

This is a retrospective case series of five nanophthalmic patients. The foveal avascular zone (FAZ) area was measured in superficial and deep vascular layers with OCTA. The thickness of the inner retinal layer (IRL) was measured with SD-OCT. The ratio of the foveal and parafoveal IRL thickness (fIRL/pIRL ratio) was calculated. The relationship between these parameters and visual acuity was then investigated.

RESULTS

Eight eyes were identified as nanophthalmic with a mean axial length of 17.19 ± 1.44 mm (range: 15.71 to 19.88 mm). The mean best-corrected visual acuity (BCVA) in the logarithm of the minimum angle of resolution (logMAR) was 0.12 ± 0.18 (range: - 0.18 to 0.40). OCTA showed that FAZs were either absent or undeveloped in the superficial and deep capillary plexuses. Two patients did not show any visual impairments despite small FAZ and a shallow foveal depression. Although the BCVA was significantly correlated with the deep FAZ size, it did not correlate with the superficial FAZ size, axial length, or fIRL/pIRL ratio. However, the refractive error, axial length, and deep FAZ size were all significantly correlated with the fIRL/pIRL ratio.

CONCLUSIONS

The FAZs were commonly found to be small in the superficial and deep capillary plexuses. Although the deep FAZ size correlated with visual acuity, it is unclear whether the retinal microstructure and the FAZ size are responsible for the visual impairments observed in the same individuals.

The majority of autosomal recessive nanophthalmos and posterior microphthalmia can be attributed to biallelic sequence and structural variants in MFRP and PRSS56

This study aimed to genetically and clinically characterize a unique cohort of 25 individuals from 21 unrelated families with autosomal recessive nanophthalmos (NNO) and posterior microphthalmia (MCOP) from different ethnicities. An ophthalmological assessment in all families was followed by targeted MFRP and PRSS56 testing in 20 families and whole-genome sequencing in one family. Three families underwent homozygosity mapping using SNP arrays. Eight distinct MFRP mutations were found in 10/21 families (47.6%), five of which are novel including a deletion spanning the 5' untranslated region and the first coding part of exon 1. Most cases harbored homozygous mutations (8/10), while a compound heterozygous and a monoallelic genotype were identified in the remaining ones (2/10). Six distinct PRSS56 mutations were found in 9/21 (42.9%) families, three of which are novel. Similarly, homozygous mutations were found in all but one, leaving 2/21 families (9.5%) without a molecular diagnosis. Clinically, all patients had reduced visual acuity, hyperopia, short axial length and crowded optic discs. Retinitis pigmentosa was observed in 5/10 (50%) of the MFRP group, papillomacular folds in 12/19 (63.2%) of MCOP and in 3/6 (50%) of NNO cases. A considerable phenotypic variability was observed, with no clear genotype-phenotype correlations. Overall, our study represents the largest NNO and MCOP cohort reported to date and provides a genetic diagnosis in 19/21 families (90.5%), including the first MFRP genomic rearrangement, offering opportunities for gene-based therapies in MFRP-associated disease. Finally, our study underscores the importance of sequence and copy number analysis of the MFRP and PRSS56 genes in MCOP and NNO.

Clinical features of posterior microphthalmic and nanophthalmic eyes

AIM

To clinically differentiate nanophthalmos (NO) and posterior microphthalmos (PM) and to explore the mechanisms related to papillomacular folds (PMF).

METHODS

Medical records of 34 unrelated patients with microphthalmos (54 eyes) from April 2009 to October 2017 were retrospectively reviewed.

RESULTS

Fourteen eyes of 7 unrelated patients with NO and PM were included in the study. The presenting age of the NO cohort was significantly higher compared with the PM cohort (NO: 27±16y; PM: 3.7±0.6y). PMF was more likely to occur in cases with PM than in NO (25% in NO, 100% in PM). The anatomic features of PMF from optical coherence tomography (OCT) included: ganglion cell layer, inner plexiform layer, inner nuclear layer, outer plexiform layer and outer nuclear layer. In eyes without an apparent PMF (these were all NO eyes), rudimentary fovea without a foveal pit was noted. Four eyes that were NO developed angle closure glaucoma. Three NO eyes developed exudative retinal detachment and were successfully treated with lamellar sclerectomy.

CONCLUSION

Posterior segment changes are pervasive both in PM and NO. Complications like angle closure glaucoma and exudative retinal detachment are likely to occur in eyes with NO but not with PM. Detailed OCT analysis found that PMF was partially a neural retinal issue, suggesting that redundancy of retinal issues involved only inner retinal layers.

Loss of Zebrafish Mfrp Causes Nanophthalmia, Hyperopia, and Accumulation of Subretinal Macrophages

Purpose

Mutations in membrane frizzled-related protein (MFRP) are associated with nanophthalmia, hyperopia, foveoschisis, irregular patches of RPE atrophy, and optic disc drusen in humans. Mouse mfrp mutants show retinal degeneration but no change in eye size or refractive state. The goal of this work was to generate zebrafish mutants to investigate the loss of Mfrp on eye size and refractive state, and to characterize other phenotypes observed.

Methods

Clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 methods were used to generate multiple frameshift mutations in zebrafish mfrp causing premature translational stops in Mfrp. Spectral-domain optical coherence tomography (SD-OCT) was used to measure eye metrics and refractive state, and immunohistochemistry was used to study adult eyes. Gene expression levels were measured using quantitative PCR.

Results

Zebrafish Mfrp was shown to localize to apical and basal regions of RPE cells, as well as the ciliary marginal zone. Loss of Mfrp in mutant zebrafish was verified histologically. Zebrafish eyes that were mfrp mutant showed reduced axial length causing hyperopia, RPE folding, and macrophages were observed subretinally. Visual acuity was reduced in mfrp mutant animals.

Conclusions

Mutation of zebrafish mfrp results in hyperopia with subretinal macrophage infiltration, phenocopying aspects of human and mouse Mfrp deficiency. These mutant zebrafish will be useful in studying the onset and progression of Mfrp-related nanophthalmia, the cues that initiate the recruitment of macrophages, and the mechanisms of Mfrp function.

High-hyperopia database, part I: clinical characterisation including morphometric (biometric) differentiation of posterior microphthalmos from nanophthalmos

PURPOSE To characterise and differentiate posterior microphthalmos (PM) and nanophthalmos (NO) using morphometric parameters.Patients and methodsConsecutive case database of patients with hyperopia >+7.00 D sphere was analysed retrospectively for clinical and biometric characterisation. Thirty-eight consecutive high-hyperopic subjects (75 eyes) with axial lengths <20.5 mm underwent uniform comprehensive ocular evaluation. Twenty-five subjects were diagnosed as PM and 13 as NO based on the horizontal corneal diameter. Parameters analysed included visual acuity, refraction, horizontal corneal diameter, anterior chamber depth, lens thickness, axial length, fundus changes, and associated ocular pathology.

PRIMARY OUTCOME MEASURES

ocular biometry difference between PM and NO.

SECONDARY OUTCOME MEASURES

differences in associated ocular pathologies between PM and NO.RESULTS Hyperopia ranged from +7 to +17 D and was similar in the two groups. Lens thickness was statistically more in NO than in PM group (4.53±0.75 mm vs 3.82±0.48 mm, P <0.001), whereas anterior chamber depth was more in the PM than in NO group (3.26±0.36 mm, vs 2.59±0.37 mm, P<0.001). NO had higher association with angle-closure glaucoma (66.7% vs 0%) and pigmentary retinopathy (38.5 vs 8.0%) but lesser association with macular folds (0% vs 24%) as compared with PM. NO was associated with poorer visual acuity.CONCLUSION PM and NO have significant differences in lens thickness, anterior chamber depth, prevalence of glaucoma, pigmentary retinopathy, macular pathology, and visual acuity while being similar in hyperopic refraction.

Analysis of corneal topography in patients with pure microphthalmia in Eastern China

OBJECTIVES

To determine the typical corneal changes in pure microphthalmia using a corneal topography system and identify characteristics that may assist in early diagnosis.

METHODS

Patients with pure microphthalmia and healthy control subjects underwent corneal topography analysis (Orbscan IIZ® Corneal Topography System; Bausch and Lomb, Bridgewater, NJ, USA) to determine degree of corneal astigmatism (mean A), simulation of corneal astigmatism (sim A), mean keratometry (mean K), simulated keratometry (sim K), irregularities in the 3 - and 5-mm zone, and mean thickness of nine distinct corneal regions.

RESULTS

Patients with pure microphthalmia (n = 12) had significantly higher mean K, sim K, mean A, sim A, 3.0 mm irregularity and 5.0 mm irregularity, and exhibited significantly more false keratoconus than controls (n = 12). There was a significant between-group difference in the morphology of the anterior corneal surface and the central curvature of the cornea.

CONCLUSIONS

Changes in corneal morphology observed in this study could be useful in borderline situations to confirm the diagnosis of pure microphthalmia.

Optical coherence tomography of bilateral nanophthalmos with macular folds and high hyperopia

Importance. There is a conflict about the content of the macular folds in nanophthalmic eyes in the literature. Our study clearly demonstrated that papillomacular folds seen in nanophthalmos or posterior microphthalmos were only composed of neurosensory retina without involvement of retinal pigment epithelium and choroid. Observations. This is a report of two consecutive nanophthalmic patients with macular folds at Maltepe University School of Medicine, Department of Ophthalmology, from January to June 2012. Anterior segment dimensions were near normal. The axial lengths of the eyes were short with markedly shortened posterior segment. A macular fold extending from the center of the fovea towards the optic nerve head was present in all eyes. Optic coherence tomography clearly demonstrated that folds were only composed of neurosensory retina. Binocular visual acuities and refractive errors of the cases were 0.3, 0.2 and +16.00, +15.75 diopters, respectively. Conclusions and Relevance. Our study proposes a surgical option to treat these folds like serous retinal detachments by showing the true content of the folds, although there is not any surgical operation accepted for this condition yet. Further studies dealing with the surgical interventions of these folds should be performed to support this option.

Novel membrane frizzled-related protein gene mutation as cause of posterior microphthalmia resulting in high hyperopia with macular folds

PURPOSE

We present a genetic and clinical analysis of two sisters, 3 and 4 years of age, with nanophthalmos and macular folds.

METHODS

Ophthalmological examination, general paediatric examination and molecular genetic analysis of the MFRP gene were performed in both affected siblings.

RESULTS

Clinical analysis showed high hyperopia (+11 D and +12 D), short axial lengths (15 mm) and the presence of macular folds and optic nerve head drusen. Autofluorescence of the retina was generally normal with subtle macular abnormalities. Sequence analysis showed compound heterozygosity for severe MFRP mutations in both sisters: a previously reported p.Asn167fs (c.498dupC) and a novel stop codon mutation p.Gln91X (c.271C>T).

CONCLUSION

These are the youngest nanophthalmos patients in the literature identified with severe loss of MFRP function, showing already the known structural abnormalities for this disease. Adult patients affected by homozygous or compound heterozygous MFRP mutations generally show signs of retinal dystrophy, with ERG disturbances and RPE abnormalities on autofluorescence imaging. ERG examination could not be performed in these children, but extensive RPE abnormalities were not seen at this young age.

Biometric and molecular characterization of clinically diagnosed posterior microphthalmos

PURPOSE

To biometrically and molecularly characterize clinically diagnosed posterior microphthalmos.

DESIGN

Prospective case series.

METHODS

Twenty-five affected patients from 13 families diagnosed by ophthalmologists experienced with the condition at the King Khaled Eye Specialist Hospital were studied. All participants underwent axial length measurement, keratometry, corneal pachymetry, and candidate gene analysis (MFRP, PRSS56). Main outcome measures were the results of ocular biometry and gene analysis.

RESULTS

All patients (2-47 years of age) had high hyperopia, normal-appearing anterior segments, posterior chamber foreshortening, and characteristic papillomacular folds/wrinkles. For the right eye, mean cycloplegic refraction was +15.09 diopters (D) (range 9.88-18.75). Axial length (mean 16.25 mm [range 14.88-19.88]) had strong inverse correlation (Pearson coefficient -0.88, P < .0001) with corneal power (mean 48.89 D [range 41.91-52.25]) and a positive correlation with corneal diameter (Pearson 0.64, P = .001). Corneal thickness and anterior chamber dimensions were within normal ranges. Left eye data were similar. Nineteen Saudi patients (8/13 families) harbored 4 different homozygous PRSS56 mutations, 1 Indian and 1 Saudi patient harbored 2 different homozygous MFRP mutations, and 4 Saudi patients (3/13 families) had no detectable mutation in either gene. Patients with MFRP mutations were not clinically different from patients with PRSS56 mutations or no identified mutation. Truncating PRSS56 mutations were associated with shorter axial lengths (mean 15.72 mm) than missense PRSS56 mutations (mean 16.37 mm) or no identified mutation (mean 17.57 mm).

CONCLUSIONS

These data define posterior microphthalmos biometrically and reveal that corneal steepening proportional to the degree of axial foreshortening is part of the phenotype. Corneal diameter decreases with decreasing axial length, suggesting posterior microphthalmos and nanophthalmos represent a spectrum of high hyperopia rather than distinct phenotypes. In the Saudi population PRSS56 mutations are the major cause, and in our cohort truncating mutations were associated with a more severe phenotype.

Optical coherence tomography findings of retinal folds in nanophthalmos

Aim. To report the optical coherence tomography (OCT) findings in three members of the same family with nanophthalmos associated with elevated papillomacular retinal fold. Methods. Complete ophthalmic examination as well as ultrasonography and OCT was performed in all patients. Results. Axial lengths ranged from 16.75 mm to 17.48 mm and refractive errors ranged from +17.50 D to +20.50 D. Main fundus findings were the hyperopic crowded, cupless optic disc, and retinal fold through papillomacular region. Macular OCT scans revealed retinal fold with normal retinal pigment epithelium and choriocapillaris. Interpretation. It is presumed that the retinal folds in nanophthalmos result from a redundancy of the retinal layer caused by retarded growth of the scleral, choroidal, and retinal pigment epithelial layers. The anatomic information provided by the current study is consistent with this thesis.

Chronic central serous choroidopathy with severe visual loss in hyperopic microphthalmic identical twins

OBJECTIVE

To report chronic central serous choroidopathy with severe visual loss in hyperopic microphthalmic identical twins.

METHODS

The index patient was first examined in 1994, at age 31, and has been followed up closely for 17 years. He had repeated fluorescein and indocyanine green angiograms, OCT, ultrasound biometry, and recently also autofluorescence and EDI OCT. His twin brother was first examined in 2010, at age 47, and had a similar extensive exploration.

RESULTS

The index patient had a mean refractive error of +6 D OU and VA was 20/32++ in the RE and 20/200 in the LE in 1994. Vision slowly went down to 20/800+ in the RE and 20/600 in the LE in 2011. His twin brother has a mean refractive error of +6 D OU and VA 20/400 OU. Both have a short axial length of the eye, a thick choroid with dilated vessels, and central serous choroidopathy with cystic degeneration of the macula and retina in the posterior pole.

CONCLUSIONS

We add to the reported complications of microphthalmos, chronic central serous choroidopathy.

Mutations in a novel serine protease PRSS56 in families with nanophthalmos

PURPOSE

Nanophthalmos is a rare genetic ocular disorder in which the eyes of affected individuals are abnormally small. Patients suffer from severe hyperopia as a result of their markedly reduced axial lengths, but otherwise are capable of seeing well unlike other more general forms of microphthalmia. To date one gene for nanophthalmos has been identified, encoding the membrane-type frizzled related protein MFRP. Identification of additional genes for nanophthalmos will improve our understanding of normal developmental regulation of eye growth.

METHODS

We ascertained a cohort of families from eastern Canada and Mexico with familial nanophthalmos. We performed high density microsatellite and high density single nucleotide polymorphism (SNP) genotyping to identify potential chromosomal regions of linkage. We sequenced coding regions of genes in the linked interval by traditional PCR-based Sanger capillary electrophoresis methods. We cloned and sequenced a novel cDNA from a putative causal gene to verify gene structure.

RESULTS

We identified a linked locus on chromosome 2q37 with a peak logarithm (base 10) of odds (LOD) score of 4.7. Sequencing of coding exons of all genes in the region identified multiple segregating variants in one gene, recently annotated as serine protease gene (PRSS56), coding for a predicted trypsin serine protease-like protein. One of our families was homozygous for a predicted pathogenic missense mutation, one family was compound heterozygous for two predicted pathogenic missense mutations, and one family was compound heterozygous for a predicted pathogenic missense mutation plus a frameshift leading to obligatory truncation of the predicted protein. The PRSS56 gene structure in public databases is based on a virtual transcript assembled from overlapping incomplete cDNA clones; we have now validated the structure of a full-length transcript from embryonic mouse brain RNA.

CONCLUSIONS

PRSS56 is a good candidate for the causal gene for nanophthalmos in our families.

Autosomal-recessive posterior microphthalmos is caused by mutations in PRSS56, a gene encoding a trypsin-like serine protease

Posterior microphthalmos (MCOP) is a rare isolated developmental anomaly of the eye characterized by extreme hyperopia due to short axial length. The population of the Faroe Islands shows a high prevalence of an autosomal-recessive form (arMCOP) of the disease. Based on published linkage data, we refined the position of the disease locus (MCOP6) in an interval of 250 kb in chromosome 2q37.1 in two large Faroese families. We detected three different mutations in PRSS56. Patients of the Faroese families were either homozygous for c.926G>C (p.Trp309Ser) or compound heterozygous for c.926G>C and c.526C>G (p.Arg176Gly), whereas a homozygous 1 bp duplication (c.1066dupC) was identified in five patients with arMCOP from a consanguineous Tunisian family. In one patient with MCOP from the Faroe Islands and in another one from Turkey, no PRSS56 mutation was detected, suggesting nonallelic heterogeneity of the trait. Using RT-PCR, PRSS56 transcripts were detected in samples derived from the human adult retina, cornea, sclera, and optic nerve. The expression of the mouse ortholog could be first detected in the eye at E17 and was maintained into adulthood. The predicted PRSS56 protein is a 603 amino acid long secreted trypsin-like serine peptidase. The c.1066dupC is likely to result in a functional null allele, whereas the two point mutations predict the replacement of evolutionary conserved and functionally important residues. Molecular modeling of the p.Trp309Ser mutant suggests that both the affinity and reactivity of the enzyme toward in vivo protein substrates are likely to be substantially reduced.

Pseudopapilledema in Kenny-Caffey syndrome

A 21-year-old man with Kenny-Caffey syndrome had been observed since 1993 for hyperopia. Fundus examination revealed swollen optic disks. Further examinations (fluorescein angiography, B-scan ultrasonography, and optical coherence tomography) confirmed the optic nerve head elevation. The authors report a rare case of Kenny-Caffey syndrome with extreme pseudopapilledema. Although uncommon, ophthalmologists should be mindful of this disorder when a patient presents with characteristic findings because severe electrolyte disturbances may complicate the clinical course.

Choroidal Effusion with Serous Retinal Detachment as a Complication of Strabismus Surgery

A 12-year-old girl was referred because of unilateral visual loss in the right eye 5 days after uneventful strabismus surgery for a divergent squint. She had hypermetropia of +8 diopters and the axial length of both eyes was below normal for that age. Investigation with funduscopy, central visual field examination, optical coherence tomography, and fluorescein angiography revealed choroidal edema in the affected eye. The macular edema responded well to parabulbar and topical steroids and vision recovered completely within 2 weeks. Strabismus surgery in highly hypermetropic eyes with a small axial length can be complicated by choroidal edema.

Hereditary High Hypermetropia in the Faroe Islands

PURPOSE

To characterize the phenotype of two families with high hypermetropia from the Faroe Islands.

METHODS

Ophthalmologic evaluation including ultrasound oculometry and anthropometric measurements.

RESULTS

Of the 40 examined family members, 15 individuals (8 males, 7 females; ages: 6-77 years; mean: 36.5 years) had small deep-set eyes with high hypermetropia (median: + 16.5 D; range: + 7.75 to + 22), short axial eye length (< 21 mm), and a thickened eye wall. The median corrected visual acuity was 0.4 (0.2-0.9). Ocular complications included angle-closure glaucoma in six eyes, uveal effusion in three eyes, cataract in two eyes, and esotropia with amblyopia in three eyes. An emergency case of uveal effusion and retinal detachment after Yag iridotomy eventually responded to systemic corticosteroids and scleral resection surgery with a slow visual recovery. No associated ocular or systemic malformations were found in the series. In addition to the two examined families, six smaller Faroese families with high hypermetropia are briefly reported.

CONCLUSIONS

The study highlights the signs and symptoms of a rare hereditary phenotype characterized by a short axial length mainly confined to the posterior segment of the eye, a shallow anterior chamber, and a thickened eye wall. The morphological characteristics predispose for sight-threatening complications such as angle-closure glaucoma, chorioretinal pathology including uveal effusion, and amblyopia. Regular ophthalmic follow-up is therefore of obvious importance in families known to have small eyes/high hypermetropia. An endemic high prevalence in the Faroe Islands suggests the presence of a founder effect, and further genetic research would probably indicate pseudodominant rather than dominant transmission

Optical coherence tomography findings for nanophthalmic eyes

PURPOSE

To describe the optical coherence tomography (OCT) findings for nanophthalmic eyes.

METHODS

: In this retrospective, single-center, observational case series, 15 patients (28 eyes) with axial lengths of <or=20.5 mm were included. Ultrasonography (A- and B-scans), keratometry, and OCT were performed. The main outcome measures were average foveal thickness, foveal center point thickness, total macular volume, and a new quantitative measure of foveal depression, relative foveal depression (RFD). Reference values for RFD were obtained by examining 57 healthy eyes with axial lengths of 21.5 mm to 27 mm.

RESULTS

The foveae of nanophthalmic eyes had diminished foveal depression due to thickened outer retinal layers. One patient with papillomacular folds was identified as having posterior microphthalmos. There was a good correlation between axial length on one hand and foveal thickness, foveal center point thickness, macula volume, and RFD on the other hand (r = -0.58, -0.61, -0.56, and -0.70 with P = 0.003, 0.001, 0.004, and 0.000, respectively). The average RFD for eyes with normal axial lengths was 0.43.

CONCLUSIONS

OCT findings for nanophthalmic eyes with foveal underdevelopment are different from posterior microphthalmos and foveal hypoplasia seen in other disorders. The new measure RFD is a useful tool in ocular tomography.

Developmental basis of nanophthalmos: MFRP Is required for both prenatal ocular growth and postnatal emmetropization

BACKGROUND

Nanophthalmos is a genetic disorder characterized by very small, hyperopic eyes that are without gross structural defects. Recessive nanophthalmos is caused by severe mutations in the MFRP gene, which encodes a Frizzled-related transmembrane protein that is selectively expressed in the retinal pigment epithelium (RPE) and ciliary body.

RESULTS

For two MFRP -/- adults, we have obtained records of refraction that begin in early childhood. At the age of 6 months, one patient's eyes already had a refractive error of +12.25 D, and over the next 20 years this slowly increased to +17.50 D. Adults homozygous for null mutations in MFRP have eyes with axial lengths shorter than those of normal newborns. Furthermore, the unusually high curvature of their corneas is consistent with eyes that had been smaller than normal during late fetal development. MFRP protein was first detected at 14 weeks of gestation, when it was restricted to the posterior pole RPE. By 20 weeks gestation, MFRP expression had spread laterally, and was found throughout the RPE. MFRP protein was detected in both posterior and lateral RPE of the adult eye.

CONCLUSIONS

Embryonic function of the MFRP gene appears necessary for the eye to reach its full size at birth. Its onset of expression in the RPE during mid-gestation suggests that MFRP does not participate in early formation of the optic cup, and is consistent with a role in later growth and development of the eye. Patients without MFRP gene function exhibit no correction of refractive error during childhood, which suggests that this gene is essential for emmetropization, a complex process by which vision regulates axial growth of the eye.

Abnormal foveal avascular zone in nanophthalmos

PURPOSE

To evaluate the foveas of nanophthalmic patients.

DESIGN

Retrospective observational case series.

METHODS

Four nanophthalmic patients examined between April 2005 and April 2006 were included. Visual acuity (VA), refractive correction, axial length, corneal diameter, presence or lack of foveal light reflex, as well as fluorescein angiograms (FAs), and optical coherence tomography (OCT) scans of the maculae were evaluated.

RESULTS

None of the eight eyes had a foveal light reflex, corresponding to lack of a normal foveal pit on OCT. Fluorescein angiography showed no normal foveal avascular zones; all were either completely absent or small and rudimentary.

CONCLUSIONS

Nanophthalmic patients rarely have best-corrected visual acuity (BCVA) better than 20/40 at any point in their lives, even with an absence of known complications, such as uveal effusion or glaucoma. In many patients, this visual deficiency may correspond to an absent or rudimentary foveal avascular zone and lack of a normal foveal pit.

Characterization of optical coherence topography findings in Kenny-Caffey syndrome

An unusual congenital syndrome was first reported in 1966 by Kenny and Linarelli, who described two patients with dwarfism, cortical thickening of the long bones, transient hypocalcemia, and normal intelligence,(1) the radiological features in the condition being reported by Caffey.(2) The constellation of dwarfism, medullary stenosis, transient hypocalcemia, and ophthalmologic abnormalities has been classically recognized as Kenny-Caffey syndrome with additional manifestations ranging from hypoplastic nails, persistent neutropenia, abnormal T-cell function, and neonatal liver disease.(3) Ocular findings range from uncomplicated nanophthalmos with hypermetropia to extreme pseudopapilloedema, vascular tortuosity, and macular crowding. Other reported ophthalmic findings include bilateral band keratopathy,(4) bilateral optic atrophy,(5) and myelinated nerve fibers.(6) We report two cases of Kenny-Caffey syndrome with an ellipsoid macular fold orientated horizontally involving the fovea and document this unusual feature with optical coherence topography (OCT).

Nanophthalmos in a Melanesian population

PURPOSE

To characterize the ophthalmic features and causes of visual loss in a cohort of Melanesians living in New Caledonia with nanophthalmos.

METHODS

In this observational study, axial length, visual acuity (VA), cycloplegic autorefraction were assessed and dilated fundus examination was performed. Visual impairment was defined as VA<6/12 in the better eye, hypermetropia as >+1.0 dioptre (D), astigmatism as >or=1.0 D and anisometropia as >or=1.0 D difference between both eyes. Unilateral amblyopia was defined as at least a two-line difference in VA between both eyes and bilateral amblyopia as VA<6/12 in both eyes which was not adequately explained by refractive error and macular folds.

RESULTS

Seventeen community-dwelling participants (aged 1.1-45.3 years) with short axial length (range from 16.1 to 21.6 mm) were identified. Of the 17 subjects, 14 were found to have crowded optic discs, three with papillomacular folds, three with a papillomacular band and three with macular radial folds. Further, all subjects demonstrated bilateral hypermetropia (range from +1.3 D to +15.1 D). A high proportion of subjects had astigmatism (12) and anisometropia (nine) in at least one eye. Visual impairment was found in nine subjects: five bilateral and four unilateral. Causes of visual impairment included amblyopia (seven), ametropia (seven) and macular folds (two). Amblyopia was attributed to several factors, including hypermetropia, anisometropia, astigmatism and esotropia.

CONCLUSIONS

In this sample of Melanesians with nanophthalmos, a spectrum of ophthalmic features that was consistent with intraocular crowding was found. Over half of the subjects were visually impaired, mostly due to amblyopia and ametropia. Further characterization of the underlying genetic cause of nanophthalmos in this cohort will be the focus of future studies.

Management of glaucoma in patients with nanophthalmos

AIMS

In this retrospective study, we aimed to evaluate the results of glaucoma surgery in patients with nanophthalmos.

METHODS

Twenty-eight bilateral nanophthalmic patients, of whom 20 patients underwent trabeculectomy+Mitomycin-C (MMC)+inferior sclerotomy between 1996 and 2004, were included in this study. Records of patients with nanophthalmos were reviewed. Intraocular pressure (IOP), glaucoma medications, surgical success, visual acuity and complications were analyzed.

RESULTS

The mean IOP was 34.6+/-5.3 mm Hg preoperatively. At the final follow-up visit, the mean IOP dropped to 21.41+/-7.34 mm Hg (P<0.05). The cumulative probability of success was 85% at 1 year, 78.5% at 2 years, 76.9% at 3 years, 70.6% at 4 years and 47% at 5 years after surgery. Visual acuity decreased in 13 (65%) patients but no eye lost vision. Sequels of choroidal detachment (five patients 25%) and retinal folds (four patients 20%) were the most frequent reason for visual decrease. Uveal effusion (10 patients 50%) and cataract formation (seven patients 35%) were major late postoperative complications.

CONCLUSIONS

Results indicate that trabeculectomy+MMC+inferior sclerotomy procedure was effective and safe for glaucoma control in patients with nanophthalmos, but uveal effusion is a major problem and cataract surgery is expected in the long run.

Nanophthalmos: Ultrasound biomicroscopy and Pentacam assessment of angle structures before and after cataract surgery

We report a case of nanophthalmos with intractable secondary glaucoma. Bilateral cataract extraction with intraocular lens implantation was used as definitive treatment for the chronic angle-closure glaucoma. The changes in angle and ciliary body anatomy were well documented with preoperative and postoperative Pentacam assessment (Oculus Optikgeräte GmbH) and ultrasound biomicroscopy (Paradigm Medical Industries) images. We believe these are the first diagnostic and prognostic images of this kind in a nanophthalmic eye.

Extreme hyperopia is the result of null mutations in MFRP, which encodes a Frizzled-related protein

Nanophthalmos is a rare disorder of eye development characterized by extreme hyperopia (farsightedness), with refractive error in the range of +8.00 to +25.00 diopters. Because the cornea and lens are normal in size and shape, hyperopia occurs because insufficient growth along the visual axis places these lensing components too close to the retina. Nanophthalmic eyes show considerable thickening of both the choroidal vascular bed and scleral coat, which provide nutritive and structural support for the retina. Thickening of these tissues is a general feature of axial hyperopia, whereas the opposite occurs in myopia. We have mapped recessive nanophthalmos to a unique locus at 11q23.3 and identified four independent mutations in MFRP, a gene that is selectively expressed in the eye and encodes a protein with homology to Tolloid proteases and the Wnt-binding domain of the Frizzled transmembrane receptors. This gene is not critical for retinal function, as patients entirely lacking MFRP can still have good refraction-corrected vision, produce clinically normal electro-retinograms, and show only modest anomalies in the dark adaptation of photoreceptors. MFRP appears primarily devoted to regulating axial length of the eye. It remains to be determined whether natural variation in its activity plays a role in common refractive errors.

Oculometric Characteristics of Extreme Hypermetropia in Two Faroese Families

PURPOSE

To describe and analyze the oculometric features of small eyes with high hypermetropia in two Faroese families, with emphasis on refractive components.

METHODS

Members of the two families (N=40; age, 1 to 77 years), including 15 cases of extreme hypermetropia (+7.5 to +19.25 D), had an ophthalmic evaluation including refractometry, keratometry, and axial ocular measurements using A-scan ultrasound. Eye-wall thickness was assessed using B-scan. Nonparametric statistics were used, mainly the Mann-Whitney U test.

RESULTS

In the two families, there were six and nine probands, respectively, with hypermetropia more than +7 D and short eyes as defined by axial eye lengths <21 mm. The median corrected visual acuity was 0.4 (range, 0.2 to 0.9). Gross fundus abnormalities were not observed. All 15 had a short posterior segment with a thick eye wall and a relatively thick lens. Furthermore, steep and rather small corneas were present. In one of the families, 70% of the affected had a corneal curvature radius of < or =7.0 mm. Five probands from family 2 were labeled as possibly affected because of hypermetropia and borderline axial length findings (21 to 22 mm). The remaining 20 subjects had visual acuity and oculometric findings within physiologic limits.

CONCLUSIONS

The axial measurement features in our series of highly hypermetropic eyes mainly presented as an extension downward from the hypermetropic bottom line of the normal distribution. The axial shortness of the eyes was primarily the result of a short posterior eye segment ("posterior microphthalmos"). A steep cornea was a feature in most small eyes in our series, particularly in one family branch.

Management of strabismus in nanophthalmic patients: a long-term follow-up report

PURPOSE

The purpose of this study is to identify the characteristics of strabismus that coexist with nanophthalmos and to report the results of strabismus surgery performed on these small eyes.

DESIGN

Retrospective, consecutive, noncomparative interventional case series.

PARTICIPANTS

Fifteen bilateral nanophthalmic patients, of whom five underwent horizontal muscle surgery, were included in this study.

METHODS

Chart review. The clinical examination included visual acuity assessments using the linear Snellen and the Lea charts, slit-lamp and fundus examinations, intraocular pressure, and axial length measurements. The orthoptic examination consisted of measurements of ocular deviations using the prism cover test with an accommodative target at both near and distance with and without refractive correction, assessment of ocular motility with ductions and versions, binocularity with Worth's four-dot test, and the Titmus test. Amblyopia was treated with part-time occlusion. Surgery for the correction of esotropia included bilateral medial rectus recessions or recess-resect procedures.

MAIN OUTCOME MEASURES

Magnitude of strabismic deviation, best-corrected visual acuity, and the level of binocular vision achieved were monitored.

RESULTS

The average age of enrollment in the study was 4.7 (range, 1-12) years. The patients were followed for an average of 7.0 (range, 4-14) years. The mean axial length was determined as 18.4 mm (range, 15.5-20.7). The mean refractive error in spherical equivalents was measured as +9.9 and ranged between +4.0 and +15.0 diopters. Five patients (33%) had nonaccommodative esotropia, four (27%) had partially refractive esotropia, four (27%) had microesotropia, and two (13%) had exotropia. Five patients, all having nonaccommodative esotropia, underwent surgery for the correction of ocular misalignment. Diminishing the surgical dose in these small eyes resulted in undercorrections. Despite patching, 3 patients (20%) had unilateral and 12 patients (80%) had bilateral amblyopia at the conclusion of the study.

CONCLUSIONS

Strabismus in nanophthalmos usually manifests as nonaccommodative and partially refractive esotropia. Medial rectus recession should be applied with care to prevent adduction deficit and convergence insufficiency. Otherwise, there seems to be no need for decreasing the surgical dose with regard to the smaller axial length. Amblyopia tends to be persistent in these patients.

A clinical and molecular genetic study of a rare dominantly inherited syndrome (MRCS) comprising of microcornea, rod-cone dystrophy, cataract, and posterior staphyloma

AIM

To phenotype and genetically map the disease locus in a family presenting with autosomal dominant microcornea, rod-cone dystrophy, cataract, and posterior staphyloma.

METHODS

Six affected and three unaffected members of the pedigree were examined. All individuals provided a history and underwent a full clinical examination with A-scan and B-scan ultrasonography and electrophysiological testing where appropriate. PCR based microsatellite marker genotyping using a positional candidate gene approach was then performed on DNA samples extracted from venous blood provided by each subject.

RESULTS

The disorder is inherited as an autosomal dominant trait with variable expressivity and has a complex phenotype. Affected individuals had bilateral microcornea, pulverulent-like lens opacities, a rod-cone dystrophy and posterior staphyloma (MRCS). Using a positional candidate gene approach, the authors have evidence suggestive of linkage of this disorder to a region on 11q13 within the nanophthalmos 1 (NNO1) genetic interval. The small family size militates against achieving a LOD score of 3, but the haplotype data and the position of the putative MRCS locus within a known nanophthalmos locus are suggestive of linkage. A candidate gene within this region (ROM1) was screened and no mutations were found in affected members of the family.

CONCLUSION

This rare developmental disorder has some phenotypic similarities to nanophthalmos and possibly maps to a locus within the genetic interval encompassing the NNO1 locus. Screening of candidate genes within this region continues.