Foveal structure and visual function in nanophthalmos and posterior microphthalmos

BACKGROUND/AIMS

The reason for visual impairment in patients with nanophthalmos and posterior microphthalmos is not completely understood. Therefore, this study aims to investigate foveal structure, and the impact of demographic, clinical and imaging parameters on best-corrected visual acuity (BCVA) in these conditions.

METHODS

Sixty-two eyes of 33 patients with nanophthalmos (n=40) or posterior microphthalmos (n=22), and 114 eyes of healthy controls with high-resolution retinal imaging including spectral-domain or swept-source optical coherence tomography images were included in this cross-sectional case-control study. Foveal retinal layer thickness was determined by two independent readers. A mixed-effect model was used to perform structure-function correlations and predict the BCVA based on subject-specific variables.

RESULTS

Most patients (28/33) had altered foveal structure associated with loss of foveal avascular zone and impaired BCVA. However, widening of outer nuclear layer, lengthening of photoreceptor outer segments, normal distribution of macular pigment and presence of Henle fibres were consistently found. Apart from the presence of choroidal effusion, which had significant impact on BCVA, the features age, refractive error, axial length and retinal layer thickness at the foveal centre explained 61.7% of the variability of BCVA.

CONCLUSION

This study demonstrates that choroidal effusion, age, refractive error, axial length and retinal layer thickness are responsible for the majority of interindividual variability of BCVA as well as the morphological foveal heterogeneity in patients with nanophthalmos or posterior microphthalmos. This might give further insights into the physiology of foveal development and the process of emmetropisation, and support clinicians in the assessment of these disease entities.

Multimodal imaging in posterior microphthalmos

Purpose

To evaluate the multimodal imaging including optical coherence tomography angiography (OCTA) findings in patients with posterior microphthalmos (PM).

Methods

In an observational case series, four eyes of two patients, eight and twenty-three years old, with clinical proven PM underwent complete ophthalmic examination, including refraction, fluorescein angiography, optical coherence tomography (OCT), OCTA, B-scan ultrasonography, axial length measurement using IOL Master optical measuring, and Pentacam evaluation.

Results

Both patients were high hyperopic with partial thickness retinal fold in macula, retinoschisis, and foveal hypoplasia. Axial length was less than 17 mm with scleral thickening in all eyes. OCTA showed absence of foveal avascular zone (FAZ) in both superficial and deep capillary plexuses. Pentacam showed corneal steepness, shallow anterior chamber, and low anterior chamber volume.

Conclusion

OCTA findings showed absence of avascular zone in both superficial and deep capillary plexuses, while OCT shows partial thickness retinal fold and retinoschisis.

Novel truncation mutations in MYRF cause autosomal dominant high hyperopia mapped to 11p12-q13.3

High hyperopia is a common and severe form of refractive error. Genetic factors play important roles in the development of high hyperopia but the exact gene responsible for this condition is mostly unknown. We identified a large Chinese family with autosomal dominant high hyperopia. A genome-wide linkage scan mapped the high hyperopia to chromosome 11p12-q13.3, with maximum log of the odds scores of 4.68 at theta = 0 for D11S987. Parallel whole-exome sequencing detected a novel c.3377delG (p.Gly1126Valfs*31) heterozygous mutation in the MYRF gene within the linkage interval. Whole-exome sequencing in other 121 probands with high hyperopia identified additional novel mutations in MYRF within two other families: a de novo c.3274_3275delAG (p.Leu1093Profs*22) heterozygous mutation and a c.3194+2T>C heterozygous mutation. All three mutations are located in the C-terminal region of MYRF and are predicted to result in truncation of that portion. Two patients from two of the three families developed angle-closure glaucoma. These three mutations were present in neither the ExAC database nor our in-house whole-exome sequencing data from 3280 individuals. No other truncation mutations in MYRF were detected in the 3280 individuals. Knockdown of myrf resulted in small eye size in zebrafish. These evidence all support that truncation mutations in the C-terminal region of MYRF are responsible for autosomal dominant high hyperopia in these families. Our results may provide useful clues for further understanding the functional role of the C-terminal region of this critical myelin regulatory factor, as well as the molecular pathogenesis of high hyperopia and its associated angle-closure glaucoma.

Detailed ophthalmologic evaluation of posterior microphthalmos

We performed various ophthalmic investigations in order to confirm the diagnosis and document the various features of posterior microphthalmos in a 21-year-old male. Ophthalmic examination revealed low vision with high hyperopia, papillomacular folds, midperipheral pigmentary changes and crowded optic discs. The optic discs were small and crowded with increased nerve fiber layer thickness. Fundus fluorescein angiography showed reduced diameter of a capillary free zone. Anterior segment (AS) optical coherence tomography demonstrated near normal anterior chamber depths, but markedly diminished anterior chamber angles. In spite of the increased corneal thickness and steep corneas, lens thickness and endothelial cell counts were normal. Sclerochoroidal thickening and foreshortening of the globes were detected with B-scan ultrasonography. Electroretinographic findings and visual field tests were similar to those in pigmentary retinopathy. Posterior microphthalmos is a complex eye disorder, which affects predominantly the posterior segment but also involves the AS of the eye.

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.

Spectral domain optical coherence tomography findings in retinal folds associated with posterior microphthalmos

Posterior microphthalmos is a rare congenital malformation characterized by normal anterior segment dimensions with an abnormally small posterior segment resulting in high hyperopia. Reduced visual acuity in these cases is sometimes caused by the presence of papillomacular retinal folds. We report two cases of posterior microphthalmos in which the papillomacular folds could be visualized on spectral domain optical coherence tomography with sufficient detail to illustrate that only the layers of neural retina within the external limiting membrane were involved.

Spectral domain optical coherence tomography finding in posterior microphthalmos

An eight-year-old boy presented with decreased vision in both eyes. At presentation, the visual acuity was 6/60 in both eyes with high plus spheres. Anterior segment examination was normal. Fundus examination and spectral domain optical coherence tomography were consistent with posterior microphthalmos and showed an elevated foveal contour and fold in the outer plexiform layer. External limiting membrane, photoreceptor and retinal pigment epithelium were not involved in the fold. To the best of our knowledge this is the first such case report with optical coherence tomography imaging of the retinal layer involved in a case of posterior microphthalmos.

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.

Assessment of anterior segment tumors with ultrasound biomicroscopy versus anterior segment optical coherence tomography in 200 cases

PURPOSE

To compare ultrasound biomicroscopy (UBM) versus anterior segment optical coherence tomography (AS-OCT) for imaging of tumors of the anterior segment of the eye.

DESIGN

Retrospective, noninterventional case series.

PARTICIPANTS

We included 200 patients.

METHODS

Review of medical records of patients who underwent both UBM and AS-OCT for evaluation of anterior segment tumors.

MAIN OUTCOME MEASURES

Comparison of tumor surface and internal visualization.

RESULTS

There were 200 eyes with anterior segment tumors involving the iris stroma in 96 (48%), ciliary body in 14 (7%), combined iris and ciliary body in 32 (16%), iris pigment epithelium (IPE) in 44 (22%), conjunctiva in 6 (3%), sclera in 4 (2%), and others in 6 (1% each). The diagnoses included nevus in 75 eyes (38%), melanoma in 47 (24%), cyst in 48 (24%), epithelioma (adenoma) in 5 (3%), metastasis, melanocytosis and melanocytoma in 4 eyes each (2%), and others (1% each). Image analysis (UBM vs AS-OCT) revealed adequate visualization of all tumor margins (189 [95%] vs 80 [40%]), posterior tumor shadowing (9 [5%] vs 144 [72%]), and high overall image quality (159 [80%] vs 136 [68%]). Comparison for better image resolution (UBM vs AS-OCT) disclosed UBM provided better overall tumor visualization (138 [69%] vs 62 [31%]) and better resolution of the posterior margin (147 [74%] vs 53 [27%]), whereas AS-OCT provided better resolution of the anterior margin (40 [20%] vs 160 [80%]) as well as better overall resolution of anterior segment anatomy (41 [21%] vs 159 [80%]). Better resolution was found with UBM for pigmented tumors (n = 162; 107 [66%] vs 55 [34%]) as well as for nonpigmented tumors (n = 38; 23 [61%] vs 15 [39%]). Regarding location, iris tumor resolution was similar with each technique (49 [52%] vs 45 [48%]).

CONCLUSIONS

For anterior segment tumors, UBM offers better visualization of the posterior margin and provides overall better images for entire tumor configuration compared with AS-OCT.

Childhood macular dystrophies

PURPOSE OF REVIEW

The aim of this review is to highlight recent advances in our understanding of the molecular genetic basis and phenotype of childhood onset macular dystrophies and to summarize current attempts to develop novel therapies for this group of disorders.

RECENT FINDINGS

The genes associated with the major causes of childhood onset macular dystrophies have now been identified and current research efforts have been focused on understanding the function of the encoded protein, how the mutant protein leads to photoreceptor cell death and investigation of the range of retinal phenotypes that result from mutations in these genes. Assessment of the phenotype has been greatly helped by improvements in retinal imaging such as spectral domain optical coherence tomography and fundus autofluorescence imaging. The development of animal models has, despite their limitations, helped understanding of disease mechanisms and allowed assessment of new therapeutic approaches such as gene replacement therapy and pharmacological treatments.

SUMMARY

Molecular diagnosis and improvements in retinal imaging have greatly improved the accuracy of diagnosis in paediatric macular disease and allowed better genetic counselling and information about prognosis to be given to children and their families. Advances in basic understanding of disease mechanism will lead to the development of clinical trials of novel therapies in the near future.