Multimodal Imaging for Differential Diagnosis of Bietti Crystalline Dystrophy

Diagnostic and Management Strategies of Bietti Crystalline Dystrophy: Current Perspectives

Bietti crystalline dystrophy (BCD) is a rare, genetically determined chorioretinal dystrophy presenting with intraretinal crystalline deposits and varying degrees of progressive chorioretinal atrophy commencing at the posterior pole. In some cases, there can be concomitant corneal crystals noted first in the superior or inferior limbus. CYP4V2 gene, a member of the cytochrome P450 family is responsible for the disease and more than 100 mutations have been defined thus far. However, a genotype-phenotype correlation has not been established yet. Visual impairment commonly occurs between the second and third decades of life. By the fifth or sixth decade of life, vision loss can become so severe that the patient may potentially become legally blind. Multitudes of multimodal imaging modalities can be utilized to demonstrate the clinical features, course, and complications of the disease. This present review aims to reiterate the clinical features of BCD, update the clinical perspectives with the help of multimodal imaging techniques, and overview its genetic background with future therapeutic approaches.

Corneal deposits and nerve alterations in Bietti Corneoretinal Crystalline Dystrophy imaged using in vivo confocal microscopy

PURPOSE

To evaluate the imaging features of corneal deposits and nerve alterations in Chinese patients with Bietti Corneoretinal Crystalline Dystrophy (BCD) using in vivo confocal microscopy (IVCM).

METHODS

Twenty patients with BCD and 20 age- and sex-matched healthy controls were enrolled in this retrospective, observational study. Corneal deposits and sub-basal nerve plexus (SNP) were observed by IVCM. Parameters of SNP including total nerve density/number, main nerve trunk density/number, and branch nerve density/number were analyzed by Neuron J.

RESULTS

Corneal deposits were observed in both eyes of all patients by IVCM. These crystals appeared as dot-shaped, needle-shaped, and rod-shaped hyperreflective bodies and were located not only in the sub-epithelium and stroma of cornea, but in endothelium which were not reported before. There was a decrease of total nerve density (P < 0.001), main nerve trunk density (P = 0.007), and branch nerve density (P = 0.001), in BCD compared to controls. The number of total nerves/frame (P = 0.001), main nerve trunks/frame (P = 0.005), and branch nerves/frame (P = 0.006) in BCD were lower than controls.

CONCLUSION

New findings in locations of corneal crystals by IVCM expand the phenotype spectrum of BCD. Corneal deposits may be useful for diagnosis of BCD, especially ones without retinal deposits. Corneal nerve parameters were reduced in BCD, which may provide new insights to be further explored to contribute to our understanding of BCD. IVCM is a promising tool to evaluate corneal deposits and nerve alterations in BCD.

A patient advocating for transparent science in rare disease research

300 million people live with at least one of 6,000 rare diseases worldwide. However, rare disease research is not always reviewed with scrutiny, making it susceptible to what the author refers to as nontransparent science. Nontransparent science can obscure animal model flaws, misguide medicine regulators and drug developers, delay or frustrate orphan drug development, or waste limited resources for rare disease research. Flawed animal models not only lack pharmacologic relevance, but also give rise to issue of clinical translatability. Sadly, these consequences and risks are grossly overlooked. Nontransparency in science can take many forms, such as premature publication of animal models without clinically significant data, not providing corrections when flaws to the model are discovered, lack of warning of critical study limitations, missing critical control data, questionable data quality, surprising results without a sound explanation, failure to rule out potential factors which may affect study conclusions, lack of sufficient detail for others to replicate the study, dubious authorship and study accountability. Science has no boarders, neither does nontransparent science. Nontransparent science can happen irrespective of the researcher's senority, institutional affiliation or country. As a patient-turned researcher suffering from Bietti crystalline dystrophy (BCD), I use BCD as an example to analyze various forms of nontransparent science in rare disease research. This article analyzes three papers published by different research groups on Cyp4v3^-/-, high-fat diet (HFD)-Cyp4v3^-/-, and Exon1-Cyp4v3^-/- mouse models of BCD. As the discussion probes various forms of nontransparent science, the flaws of these knockout mouse models are uncovered. These mouse models do not mimic BCD in humans nor do they address the lack of Cyp4v3 (murine ortholog of human CYP4V2) expression in wild type (WT) mouse retina which is markedly different from CYP4V2 expression in human retina. Further, this article discusses the impact of nontransparent science on drug development which can lead to significant delays ultimately affecting the patients. Lessons from BCD research can be helpful to all those suffering from rare diseases. As a patient, I call for transparent science in rare disease research.

The role of near-infrared reflectance imaging in retinal disease: A systematic review

Near-infrared reflectance (NIR) retinal imaging aids in a better visualization of structures at the level of outer retina, retinal pigment epithelium, and choroid. It has multiple advantages, including easy acquisition in association with structural spectral domain optical coherence tomography, more comfort for patients, and enhanced contrast and spatial resolution. It helps in the diagnosis of chorioretinal diseases that present with minimal funduscopic findings and can be used to follow up many chorioretinal conditions. We describe the chorioretinal NIR imaging appearance and the clinical role of NIR imaging in ocular inflammatory disease, vascular and acquired disease, degenerative disease, tumors, associated systemic condition, toxic and traumatic disease, optic nerve head conditions, and physiological findings.

Presumed Bietti crystalline dystrophy with optic nerve head drusen: a case report

Background

Bietti crystalline dystrophy is primarily a retinal dystrophy caused by a CYP4V2 mutation and typically presents with crystalline retinal deposits in the posterior fundus.

Case presentation

We present the case of an otherwise healthy 39-year-old Iranian woman with no family history of ocular disease who suffered with progressive vision loss that had started 2 years prior to presentation. Ocular examination revealed blurry optic nerve head margin and diffuse retinal crystalline deposit in both eyes. Spectral domain optical coherence tomography images showed retinal crystals, located mostly in outer retinal layers, with some areas of outer retinal tubulation and attenuation of outer retinal layers. Crystalline deposits were better visualized on near-infrared images as hyperreflective spots. Fundus autofluorescence images showed hyperautofluorescence areas on optic nerve head consistent with optic nerve head drusen and large hypoautofluorescence areas in posterior retina consistent with retinal pigment epithelium atrophy. Cystinosis was ruled out by blood testing.

Conclusion

Bietti crystalline dystrophy may be associated with optic nerve head drusen.

Structural and functional phenotypic features and molecular analysis of Indian patients with Bietti crystalline dystrophy

Purpose:

Bietti crystalline dystrophy (BCD) is a rare retinal dystrophy, uncommon in Indians. This study describes the various phenotypic features seen in the Indian population.

Methods:

In this retrospective, descriptive case series, records of patients with either clinical or molecular diagnosis of BCD from 2009 to 2020 were perused. Phenotypic and genotype information was collected and analyzed.

Results:

This study included 58 patients of BCD (31 males) aged 21–79 years (mean: 47 ± 14 years). The age at onset ranged from 7 to 41 years (mean: 28.8 ± 5.1 years). Vision ranged from 20/20 to counting fingers. There were 18 (31%) patients with stage 1 with crystals and mild retinochoroidal atrophy, 22 (38%) with stage 2 with atrophy extending beyond arcades, and 18 (31%) with absent crystals and extensive atrophy of stage 3. Choroidal neovascular membrane was seen in four patients. The optical coherence tomography showed retinochoroidal thinning (84.6%), outer retinal tubulations (71.8%), and paradoxical foveal thickening with interlaminar bridges (7.7%). Electrophysiology and visual fields showed reduced responses in advanced retinochoroidal changes. Molecular confirmation was available in five patients; five mutations were seen in the CYP4V2.

Conclusion:

A wide variation is seen in the phenotypic picture of BCD. A molecular diagnosis is helpful in differentiating from other retinal dystrophies. The OCT shows the peculiar feature of the interlaminar bridge in early cases with photoreceptor loss. Further investigations into this OCT feature may provide insights into the pathogenesis of BCD. A genotype–phenotype correlation could not be done.

Multimodal Imaging Observation in Different Progressive Types of Bietti Crystalline Dystrophy

Objective

The aim of the study is to observe the difference in progression between type 1 and type 2 Bietti crystalline dystrophy (BCD) using multimodal imaging.

Methods

A retrospective clinical study was performed with six BCD patients who underwent multimodal imaging twice in Hebei Provincial Eye Hospital from October 2015 to December 2020. Multimodal imaging includes color fundus photography, fundus autofluorescence (AF), infrared autofluorescence (IRAF), fundus fluorescein angiography (FFA), and spectral domain optical coherence tomography (SD-OCT). The fundus lesion progression difference was observed in 3 patients with type 1 BCD and 3 patients with type 2 BCD.

Results

In type 1 BCD, the range of hypoautofluorescence (hypo-AF), hypoinfrared autofluorescence (hypo-IRAF), and hypofluorescence in the posterior pole was enlarged, and FFA showed that the lesions in the posterior pole and periphery extended to the middle periphery. SD-OCT revealed retinal and choroidal thinning, progressive loss of the outer nuclear layer and ellipsoid zone, and reduction of the choroid macrovascular diameter. In type 2 BCD, the range of hypo-AF was enlarged, but there was no significant change in the macula area. The uniform hypo-IRAF in the posterior pole showed no significant change. FFA showed no significant change with the progression of the disease in the macula area and the hypofluorescence around it expanded. SD-OCT revealed no obvious change in the macula area.

Conclusions

The retinal choroid atrophy in the macula area of type 1 BCD continued to worsen, and the choroid great vessels became narrower. The macular lesions of type 2 BCD can remain unchanged for a long time.

Intereye Symmetry in Bietti Crystalline Dystrophy

PURPOSE

To evaluate anatomic and functional intereye symmetry among individuals with Bietti crystalline dystrophy (BCD) using clinical and multimodal imaging methods, with a focus on the number, area, and distribution of the characteristic retinal crystalline deposits.

DESIGN

Observational case series with prospective and retrospective data.

METHODS

Setting: Multicenter.

STUDY POPULATION

Thirteen Australian and New Zealand participants (26 eyes) with confirmed biallelic CYP4V2 mutations and a characteristic BCD fundus appearance. Procedures and main outcome measures: Crystals visible on color fundus photography were manually counted. Crystals were superimposed on aligned multimodal fundus images. Spearman's correlation coefficients (ρ), intraclass correlation coefficients (ICCs), and Bland-Altman plots were used to quantify symmetry between eyes.

MAIN OUTCOME MEASURES

Fundus crystal area and count, and absent-autofluorescence (absent-AF) area.

RESULTS

Median participant age was 48 years (interquartile range: 40-60 years). Intereye symmetry was high for fundus crystal area (ρ = 1.00, 95% confidence interval [CI]: 1.00-1.00; ICC = 0.97, 95% CI: 0.88-0.99), fundus crystal count (ρ = 0.98, 95% CI: 0.92-1.00; ICC = 0.97, 95% CI: 0.89-0.99), and absent-AF area (ρ = 0.88, 95% CI: 0.53-0.98; ICC = 0.98, 95% CI: 0.90-0.99). Average foveal volume, foveal crystal count and area, average and central foveal thickness, best corrected visual acuity, and average macular and central foveal sensitivity were not highly correlated between eyes.

CONCLUSIONS

This study demonstrated strong intereye symmetry measured by fundus crystal area, fundus crystal number, and absent-AF area. This may influence the choice of outcome measures for future therapeutic trials for BCD and provides valuable clinical information for ophthalmologists involved in the care and counseling of patients with BCD.

Utilizing Advanced Technology to Facilitate Diagnosis of Rare Retinal Disorders: A Case of Bietti Crystalline Dystrophy

SIGNIFICANCE

Optometrists, as primary eye care providers, encounter patients with rare ocular disease such as Bietti crystalline dystrophy from time to time. Using advanced technologies, which are also useful in managing common ocular conditions, to facilitate a prompt diagnosis is highly recommended.

PURPOSE

This report describes a patient with clinically diagnosed Bietti crystalline dystrophy with findings on funduscopy, multimodal imaging, and visual electrophysiology.

CASE REPORT

A 41-year-old Chinese woman who had subjectively progressing dimmed vision (especially in the left eye) for 9 months was referred to our clinic to test for retinitis pigmentosa. Best-corrected visual acuities were 6/6 and 6/7.6 in the right and left eyes, respectively. Funduscopy revealed multiple crystalline deposits on the posterior pole in both eyes. The 30-2 perimetry displayed bi-inferotemporal scotoma (left > right eye). Scotopic flash electroretinogram (ERG) yielded a normal result, whereas photopic ERG was slightly attenuated. Electro-oculogram showed an abnormal adaptation time course of the retinal pigmented epithelium (RPE). Multifocal ERG revealed a decreased central retinal response, but paracentral responses were relatively better preserved. Optical coherence tomography showed multiple patches of RPE atrophy, with disruption of the left ellipsoid zone. Outer retinal tubulations, hyperreflective dots on RPE-Bruch's membrane interface, and intraretinal bright spots were also identified.

CONCLUSIONS

Rare ocular diseases like Bietti crystalline dystrophy can be encountered by optometrists. This case report shows the ophthalmic findings of a rare chorioretinal dystrophy and provides insight on how to better use advanced equipment in an optometric practice to facilitate prompt diagnoses.

Near-Infrared Reflectance Imaging in Retinal Diseases Affecting Young Patients

Near-infrared reflectance (NIR) is a noninvasive, contactless, and rapid in vivo imaging technique for visualizing subretinal alterations in the photoreceptor layer, retinal pigment epithelium, and choroid. The present report describes the application of this imaging method in retinal and choroidal pathologies affecting young patients where scarce cooperation, poor fixation, and intense glare sensation can result in a challenging clinical examination. A literature search of the MEDLINE database was performed using the terms "near-infrared reflectance" and "spectral-domain optical coherence tomography." Articles were selected if they described the diagnostic use of NIR in children or young adults. Of 700 publications, 42 manuscripts published between 2005 and 2020 were inherent to children or young adults and were considered in this narrative literature review. The first disease category is the phakomatoses where NIR is essential in visualizing choroidal alterations recognized as cardinal biomarkers in neurofibromatosis type 1, microvascular retinal alterations, and retinal astrocytic hamartomas. Another diagnostic application is the accurate visualization of crystals of various nature, including the glistening crystals that characterize Bietti crystalline dystrophy. Acute macular neuropathy and paracentral acute middle maculopathy represent a further disease category with young adulthood onset where NIR is not only diagnostic but also essential to monitor disease progression. A further interesting clinical application is to facilitate the detection of laser-induced maculopathy where funduscopic examination can be normal or subnormal. In conclusion, NIR imaging has a noninterchangeable role in diagnosing certain retinal diseases, especially in children and young adults where there is scarce collaboration and a lack of evident clinical findings. Moreover, this technique can reveal unique retinal and choroidal biomarkers highly specific to rare conditions.

Fundus Autofluorescence and Clinical Applications

Fundus autofluorescence (FAF) has allowed in vivo mapping of retinal metabolic derangements and structural changes not possible with conventional color imaging. Incident light is absorbed by molecules in the fundus, which are excited and in turn emit photons of specific wavelengths that are captured and processed by a sensor to create a metabolic map of the fundus. Studies on the growing number of FAF platforms has shown each may be suited to certain clinical scenarios. Scanning laser ophthalmoscopes, fundus cameras, and modifications of these each have benefits and drawbacks that must be considered before and after imaging to properly interpret the images. Emerging clinical evidence has demonstrated the usefulness of FAF in diagnosis and management of an increasing number of chorioretinal conditions, such as age-related macular degeneration, central serous chorioretinopathy, retinal drug toxicities, and inherited retinal degenerations such as retinitis pigmentosa and Stargardt disease. This article reviews commercial imaging platforms, imaging techniques, and clinical applications of FAF.

Observation of the characteristics of the natural course of Bietti crystalline dystrophy by fundus fluorescein angiography

Background

Bietti crystalline dystrophy (BCD) is an autosomal recessive genetic disorder that causes progressive vision loss. Here, 12 patients were followed up for 1–5 years with fundus fluorescein angiography (FFA) to observe BCD disease progression.

Methods

FFA images were collected for 12 patients with BCD who visited our clinic twice or more over a 5-year period. Peripheral venous blood was collected to identify the pathogenic gene related to the clinical phenotype.

Results

We observed two types in FFA images of patients with BCD. Type 1 showed retinal pigment epithelium (RPE) atrophy in the macular area, followed by choriocapillaris atrophy and the subsequent appearance of RPE atrophy appeared at the peripheral retina. Type 2 showed RPE atrophy at the posterior pole and peripheral retina, followed by choriocapillaris atrophy around the macula and along the superior and inferior vascular arcades and the nasal side of the optic disc. The posterior and peripheral lesions of both type 1 and type 2 BCD subsequently extended to the mid-periphery; finally, all the RPEs and choriocapillaris atrophied, exposing the choroid great vessels, but type 2 macular RPE atrophy could last longer.

Conclusions

The characterization of two different types of BCD development provides a better understanding of the phenotype and the progression of the disease for a precise prognosis and prediction of pathogenesis.

Expanding the Phenotypic and Genotypic Spectrum of Bietti Crystalline Dystrophy

The rare form of retinal dystrophy, Bietti crystalline dystrophy, is associated with variations in CYP4V2, a member of the cytochrome P450 family. This study reports patients affected by typical and atypical Bietti crystalline dystrophy, expanding the spectrum of this disease. This is an observational case series of patients with a clinical and molecular diagnosis of Bietti crystalline dystrophy that underwent multimodal imaging. Four unrelated patients are described with two known variants, c.802-8_810del17insGC and c.518T > G (p.Leu173Trp), and one novel missense variant, c.1169G > T (p.Arg390Leu). The patient with the novel homozygous variant had the most severe phenotype resulting in macular hole formation and retinal detachment in both eyes. To the best of our knowledge, there is no association of these features with Bietti crystalline dystrophy. Patient 1 was the youngest patient and had the mildest phenotype with crystals in the retina without chorioretinal atrophy and visual complaints. Patients 2 and 3 presented with fewer crystals and chorioretinal atrophy. These three patients presented a classic phenotype. The fourth patient presented with an atypical and severe phenotype. This study reveals a new genotype and new phenotype associated with this disorder.

Genotype and Long-term Clinical Course of Bietti Crystalline Dystrophy in Korean and Japanese Patients

PURPOSE

To investigate the genotype and long-term clinical phenotype of patients with Bietti crystalline dystrophy (BCD) in Korea and Japan.

DESIGN

Retrospective case series.

PARTICIPANTS

We analyzed 62 patients with clinical features of BCD who harbor pathogenic biallelic CYP4V2 variants in their homozygote or compound heterozygote.

METHODS

Data were collected from patient charts, including age, best-corrected visual acuity (BCVA), Goldmann perimetry results, fundus photography, OCT findings, fundus autofluorescence results, and electroretinography findings. We compared the clinical course of the patients with homozygous c.802-8_810de117insGC [exon7del], the most common mutation in the East Asian population, with those of the patients with other genotypes.

MAIN OUTCOME MEASURES

Best-corrected visual acuity, visual field (VF), and their changes during follow-up.

RESULTS

The mean age at the first visit was 55.2 years, with a mean follow-up of 7.1 years. The mean BCVAs at the first and last visits were 0.28 logarithm of the minimum angle of resolution (logMAR) and 0.89 logMAR, respectively. In genetic testing, c.802-8_810de117insGC was detected in 86 of 124 alleles of the patients, and 36 patients were homozygous for this mutation. The age, BCVA, VF area, central foveal thickness, and abnormal hypoautofluorescent area at either the first or last visit were not different between the exon7del homozygotes and the others. The mean BCVA changes per year were 0.089 logMAR in the exon7del homozygotes and 0.089 logMAR in the others. An age- and gender-adjusted linear regression analysis showed no association between the exon7del homozygote status and the rate of vision loss. Characteristic crystalline deposits in the posterior pole were generally observed in younger patients and disappeared over time along with progressive retinochoroidal atrophy.

CONCLUSIONS

Patients with BCD and a homozygote for c.802-8_810de117insGC accounted for more than 50% of this cohort of Korean and Japanese patients, and the clinical effect of this deleterious variant was not severe in the spectrum of CYP4V2 retinopathy.

Predicting visual acuity in Bietti crystalline dystrophy: evaluation of image parameters

BACKGROUND

To analyze multiple imaging modalities in patients with Bietti crystalline dystrophy (BCD) and to investigate which factors from these modalities are associated with best corrected visual acuity (BCVA).

METHODS

In this retrospective study, 40 eyes from 22 patients with BCD were included and were separated into group 1 (BCVA ≤20/200) and group 2 (BCVA > 20/200). Data including BCVA and characteristic findings from near-infrared reflectance (NIR) imaging, fundus autofluorescence (FAF), and spectral domain-optic coherence tomography (SD-OCT) were analyzed and compared. The outcome measures of multimodal imaging were evaluated for correlation with BCVA.

RESULTS

NIR is a good diagnostic tool for detecting either crystalline or sclerotic vessels in BCD. Patients in group 1 tended to have a thinner choroid (P = 0.047) with ellipsoid zone (EZ) disruption (P = 0.011). Calculation of the area under the curve indicated that EZ disruption detected on SD-OCT could be a good predictor of legal blindness in BCD.

CONCLUSION

For the diagnosis of BCD, NIR could be a good diagnostic tool. Of the studied imaging modalities, we found that EZ disruption at the fovea were strongly associated with legal blindness, which could be easily assessed by SD-OCT.

Autofluorescence of choroidal vessels in Bietti's crystalline dystrophy

Objective

To describe the pattern of fundus autofluorescence (FAF) in Bietti’s crystalline dystrophy (BCD).

Methods and analysis

From the National Institutes of Health EyeGene database of 2769 patients with known pathogenic mutations, 5 patients with BCD-causing CYP4V2 mutations who had FAF images were selected. Demographic and genetic information and imaging files were obtained. From the FAF imaging files, unique autofluorescence (AF) patterns and correlation with retinal structures were assessed by three investigators for clinical significance.

Results

Five patients (four males, one female; mean age 56 years, range 42–76 years) were included, all with different CYP4V2 mutations. All patients displayed varying degrees of hypo-AF in the posterior pole. In four out of five patients, there was a relative hyper-AF of choroidal vessels within the hypo-AF area; this feature was limited to sclerotic vessels only. A transitional zone of speckled AF was visible around the hypo-AF area. This zone corresponded to the area containing retinal crystals on colour fundus photography; however, retinal crystals did not demonstrate hyper or hypo-AF.

Conclusions

This study presents a previously unreported characteristic finding in patients with BCD with CYP4V2 mutations. AF of choroidal vessels may aid in differentiating BCD from other retinal dystrophies.

Multimodal imaging features and genetic findings in Bietti crystalline dystrophy

Background

Bietti crystalline dystrophy (BCD) is a distinct entity of retinitis pigmentosa with a wide range of genotypic and phenotypic variabilities. The goal of the present study was to investigate the morphological, functional and genetic features of BCD.

Methods

A full series of multimodal imaging was performed in four Chinese patients with BCD, including fundus photography, fundus autofluorescence, fundus fluorescein angiography (FFA), indocyanine green (ICG) angiography, optical coherence tomography (OCT) and microperimetry. Electrophysiological tests including full-field electroretinography (ERG) and multifocal ERG were employed. CYP4V2 gene sequencing was performed.

Results

Intraretinal crystalline deposits were observed in fundus photographs in all patients. The crystals were better appreciated in infrared images. Autofluorescence imaging demonstrated multifocal patchy hypofluorescence, suggesting massive RPE atrophy. FFA and ICG angiography further confirmed atrophy of the RPE and the underlying choroidal vessels. OCT revealed disruption of the photoreceptors, RPE and the choroid. Outer retinal tubulations (ORTs) confining to the outer nuclear layer were detected in three out of four patients. Full-field ERG showed markedly diminished responses. Multifocal ERG displayed reduced central and peripheral responses in a patient with normal vision. Gene sequencing identified two deletion mutations in CYP4V2, c.802_807del and c.810delT. BCD complicated by choroidal neovascularization (CNV) was diagnosed in one patient, and intravitreal anti-vascular endothelial growth factor (VEGF) injection was given with favorable response.

Conclusions

Multimodal imaging features and electrophysiological findings of BCD patients were comprehensively discussed. A novel deletion mutation, c.802_807del, in the CYP4V2 gene was reported. ORTs are important changes in the outer retina of BCD patients, further investigation of this structure may provide insights into pathology of BCD. Intravitreal anti-VEGF therapy was effective for treatment of BCD complicated by CNV.

Role of red free imaging, retinal reflectance and fundus autofluorescence in Bietti crystalline dystrophy: case report

Bietti crystalline dystrophy (BCD), a rare autosomal recessive hereditary disorder, is identified by its clinical features. It is characterised by crystalline deposits and hence called crystalline retinopathy. The retinopathy progresses with age, showing a decrease in the number of crystalline deposits and increase in the area of chorioretinal degeneration, which spreads in a centrifugal pattern. Thus, BCD can be confused with other disorders with crystalline-like deposits and chorioretinal degenerations. The red-free and near-infrared reflectance allows prominent visualisation of crystalline deposits that may be missed. The non-inferiority of red-free imaging and its wider availability could allow its use as a screening tool. The enhanced depth imaging optical coherence tomography shows crystalline deposits throughout the retina and outer retinal tubulation. Thus, multimodality imaging can act as an adjunct in diagnosis, monitoring and follow up in these cases, acting not only as a teaching tool but also giving an insight into the underlying pathophysiology of the disorder.

Plain language summary

Use of imaging in diagnosis of Bietti crystalline dystrophy Bietti crystalline dystrophy is a rare familial disorder but is not shown in all family members and may skip generations, as it has an autosomal recessive pattern of inheritance. It shows refractile yellow-white crystalline deposits and degenerative changes in the retina. These crystalline deposits disappear with age while degenerative changes increase and spread from centre to the periphery. This may cause difficulty in early detection, and confusion with similar degenerative diseases of the retina. The use of various imaging modalities can help in diagnosis and follow up of these cases. These modalities also provide understanding of the basic disease process.

Current perspectives in Bietti crystalline dystrophy

Bietti crystalline dystrophy (BCD) is a rare-inherited disease caused by mutations in the CYP4V2 gene and characterized by the presence of multiple shimmering yellow-white deposits in the posterior pole of the retina in association with atrophy of the retinal pigment epithelium (RPE) and chorioretinal atrophy. The additional presence of glittering dots located at the corneal limbus is also a frequent finding. The CYP4V2 protein belongs to the cytochrome P450 subfamily 4 and is mainly expressed in the retina and the RPE and less expressed in the cornea. The disease has its metabolic origin in the diminished transformation of fatty acid substrates into n-3 polyunsaturated fatty acids due to a dysregulation of the lipid metabolism. In this review, we provide updated insights on clinical and molecular characteristics of BCD including underlying mechanisms of BCD, genetic diagnosis, progress in the identification of causative genetic and epigenetic factors, available techniques of exploration and development of novel therapies. This information will help clinicians to improve accuracy of BCD diagnosis, providing the patient reliable information regarding prognosis and clinical prediction of the disease course.