FLUORESCENCE LIFETIME IMAGING OPHTHALMOSCOPY IN PATIENTS WITH MACULAR TELANGIECTASIA TYPE 2 WITH AND WITHOUT DIABETES

PURPOSE

Macular telangiectasia type 2 (MacTel) is a vision-altering retinal disease with a high prevalence of diabetes. Differences between patients with MacTel with and without diabetes were investigated using fluorescence lifetime imaging ophthalmoscopy (FLIO).

METHODS

Eighty-six patients with MacTel (59 ± 12 years) were included. 40 patients (46%) did not have diabetes, 16 patients (19%) were prediabetic, and 30 patients (35%) were diabetic. Of these, seven had diabetic retinopathy. 18 diabetic patients without MacTel and 42 age-matched healthy controls were included. FLIO lifetimes (FLTs) were obtained in short (SSC, 498-560 nm) and long (LSC, 560-720 nm) spectral channels from different areas of interest using a Heidelberg Engineering FLIO.

RESULTS

Fundus autofluorescece lifetimes did not show significant differences when comparing diabetic with nondiabetic MacTel eyes (MacTel zone, SSC, diabetic: 243 ± 65 ps; nondiabetic: 232 ± 51 ps; P = 1.0; LSC, diabetic: 327 ± 66 ps; nondiabetic: 309 ± 54 ps; P = 0.582). Longitudinal changes were similarly unrelated to diabetes status. A nonsignificant trend of increased FLT progression with higher body mass index was found. Fundus autofluorescece lifetimes in diabetic patients without MacTel were significantly shorter within the MacTel zone and longer in the periphery compared with diabetic patients with MacTel.

CONCLUSION

Although MacTel has a high prevalence of diabetes, FLTs from the MacTel zone are unrelated to diabetes. Fluorescence lifetime imaging ophthalmoscopy retains diagnostic abilities in patients with MacTel even in the presence of prediabetes, diabetes, and advanced diabetic retinopathy. The lack of diabetic FLT changes in the periphery of diabetic patients with MacTel is an interesting finding that needs further investigation.

Intravitreal Bevacizumab for Choroidal Neovascular Membrane in Macular Telangiectasia Type 2

We report a case of macular telangiectasia type 2 with an associated choroidal neovascular membrane and its treatment. A 54-year-old female presented with a history of gradual vision loss in both eyes. A physical exam showed visual acuity of 20/40 in both eyes and significant metamorphopsia in the right eye. A fundus examination of the right eye was remarkable for right-angled vessels in the juxtafoveal region and subretinal fibrosis temporal to the fovea. A fundus examination of the left eye revealed intraretinal crystals in the juxtafoveal region and right-angled vessels. Optical coherence tomography and angiography confirmed the diagnosis of macular telangiectasia type 2 as well as the presence of a choroidal neovascular membrane in the right eye. The patient was treated with 18 intravitreal injections of anti-vascular endothelial growth factor agent in the right eye for two years, with five to six weeks between each treatment, which resulted in the membrane's stability. Our report suggests that anti-vascular endothelial growth factor therapy via intravitreal injection may be beneficial in treating choroidal neovascular membranes in patients with macular telangiectasia type 2.

Macular Telangiectasia Type 2: A Comprehensive Review

Macular telangiectasia Type 2 (MacTel) is a gradually progressive disease that affects the quality of life by impairing both distant and near vision. It had previously been considered a vascular condition, but recent evidence suggests a neurodegenerative etiology, with primary involvement of Muller cells. Retinal pigment epithelium (RPE) hyperplasia and subretinal neovascularization (SNV) are responsible for most of the vision loss in advanced cases. Neurotrophic factors in the non-proliferative phase and intravitreal anti-Vascular Endothelial growth factor (VEGF) in the proliferative phase have shown to retard the progression of the disease. This review will discuss the pathophysiology, clinical features, important diagnostic imaging studies and available treatment options for MacTel.

Cell-specific cis-regulatory elements and mechanisms of non-coding genetic disease in human retina and retinal organoids

Cis-regulatory elements (CREs) play a critical role in the development and disease-states of all human cell types. In the retina, CREs have been implicated in several inherited disorders. To better characterize human retinal CREs, we performed single-nucleus assay for transposase-accessible chromatin sequencing (snATAC-seq) and single-nucleus RNA sequencing (snRNA-seq) on the developing and adult human retina and on induced pluripotent stem cell (iPSC)-derived retinal organoids. These analyses identified developmentally dynamic, cell-class-specific CREs, enriched transcription-factor-binding motifs, and putative target genes. CREs in the retina and organoids are highly correlated at the single-cell level, and this supports the use of organoids as a model for studying disease-associated CREs. As a proof of concept, we disrupted a disease-associated CRE at 5q14.3, confirming its principal target gene as the miR-9-2 primary transcript and demonstrating its role in neurogenesis and gene regulation in mature glia. This study provides a resource for characterizing human retinal CREs and showcases organoids as a model to study the function of CREs that influence development and disease.

Macular Telangiectasia type 2: multimodal assessment of retinal function and microstructure

PURPOSE

To assess the impact of neurodegenerative morphologic alterations due to macular telangiectasia type 2 (MacTel) on microperimetry (MP) and multifocal electroretinography (mfERG).

METHODS

Thirty-five eyes of 18 patients with MacTel were examined using spectral domain optical coherence tomography (SD-OCT), fundus autofluorescence (FAF), mfERG and MP. Software was used to match SD-OCT B-scans with the corresponding retinal sensitivity map and multifocal electroretinograms (mfERGs), thus enabling direct structure/function correlation.

RESULTS

Loss of the ellipsoid zone (EZ) had the strongest negative association with retinal sensitivity (16.77 dB versus 4.58 dB, adj. p < 0.001) of all parameters examined, and a limited negative effect on mfERGs (0.32 SD versus -1.97 SD adj. p = 0.121). Ellipsoid zone (EZ) irregularity was associated with reduced MP values but preserved mfERGs. There was a significant association between areas of inner retinal hyporeflectivity and loss of MP sensitivity (adj. p < 0.001) but the reduction in sensitivity was less than in locations with EZ loss. Areas of mfERG abnormality showed similar sensitivity loss with either inner retinal hyporeflectivity or EZ loss (adj. p = 0.063). In areas with EZ loss alone, preservation of the external limiting membrane (ELM) was associated with higher MP values than in areas with additional ELM loss; the integrity of the ELM alone was not associated with changes either in MP or mfERG. Increased FAF was observed in 51% of eyes, mixed/reduced FAF in 40%, and no abnormality was detected in 9% of eyes.

CONCLUSION

The data suggest both MP and mfERG to be useful non-invasive modalities for detecting localised macular dysfunction in MacTel. The findings suggest a different sensitivity of the two modalities to inner and outer retinal changes in macular function and are therefore complementary.

An unusual presentation of macular telangiectasia type 2 with a large pigment deposit

Macular telangiectasia type 2 (MacTel) is a bilateral retinal disease that seems to be limited to the juxtafoveal region of the macula. We herein report an unusual presentation of MacTel with a large pigment deposit at the macula. Fundus of the right eye showed a large pigment deposit at the macula and right-angled venule. The left eye fundus showed a grayish discoloration due to subretinal fibrosis, dark pigment clumps and right-angled venule in the macula. Lesions were highlighted on multicolor imaging and blue reflectance imaging. Spectral domain optical coherence tomography (SD-OCT) of both eyes showed hyperreflectivity on the inner aspect of the retina corresponding to the area of pigment clumping.

A connectomics approach to understanding a retinal disease

Macular telangiectasia type 2 (MacTel), a late-onset macular degeneration, has been linked to a loss in the retina of Müller glial cells and the amino acid serine, synthesized by the Müller cells. The disease is confined mainly to a central retinal region called the MacTel zone. We have used electron microscopic connectomics techniques, optimized for disease analysis, to study the retina from a 48-y-old woman suffering from MacTel. The major observations made were specific changes in mitochondrial structure within and outside the MacTel zone that were present in all retinal cell types. We also identified an abrupt boundary of the MacTel zone that coincides with the loss of Müller cells and macular pigment. Since Müller cells synthesize retinal serine, we propose that a deficiency of serine, required for mitochondrial maintenance, causes mitochondrial changes that underlie MacTel development.

FLUORESCENCE LIFETIME IMAGING OPHTHALMOSCOPY (FLIO) PATTERNS IN CLINICALLY UNAFFECTED CHILDREN OF MACULAR TELANGIECTASIA TYPE 2 (MACTEL) PATIENTS

PURPOSE

Macular telangiectasia Type 2 (MacTel) is an inherited retinal disease following an autosomal dominant pattern with late onset and reduced penetrance. Fluorescence lifetime imaging ophthalmoscopy (FLIO) enhances diagnosis by showing distinct changes in MacTel. This study investigates FLIO-associated changes in clinically unaffected family members.

METHODS

Eighty-one patients with MacTel (61 ± 12 years), 33 clinically healthy children under age 40 years of these MacTel patients (MacTel-C; 31 ± 6 years), 27 other family members (children over age 40 years, siblings, and parents) and 30 controls were investigated with the Heidelberg FLIO. All subjects underwent multimodal conventional imaging, including optical coherence tomography, blue-light reflectance, fluorescein angiography, and macular pigment imaging.

RESULTS

All 81 patients with MacTel showed typical FLIO patterns. Of the 33 investigated MacTel-C with completely normal eye examinations and conventional imaging, 12 (36%) show FLIO patterns consistent with early MacTel.

CONCLUSION

Prolonged FLIO lifetimes in the parafoveal area within the short spectral channel, especially temporally, are MacTel-specific. Fluorescence lifetime imaging ophthalmoscopy detects these lifetime patterns in over one-third of clinically unaffected MacTel-C. Although further studies will be necessary to determine the specificity of FLIO, it may help diagnose MacTel before conventional imaging modalities show changes or patients experience visual disturbances. Early detection may facilitate future gene discovery studies and interventional trials.

Perivenular Capillary Loss: An Early, Quantifiable Change in Macular Telangiectasia Type 2

Purpose

To evaluate differences in parafoveal vascular density surrounding arterioles and venules in type 2 macular telangiectasia (MacTel).

Methods

Thirty-seven eyes (20 subjects) diagnosed with MacTel and 16 healthy eyes (10 subjects) were imaged with optical coherence tomography angiography between March 2016 and June 2019 in this single-center, observational, cross-sectional study. Arterioles and venules were manually identified, and perivascular density was generated using a custom MATLAB code. The primary outcome measure was the ratio of periarteriolar to perivenular vascular density (arteriovenous [A/V] capillary ratio) in the superficial and deep capillary plexuses across MacTel stages. The main secondary outcome measures were overall parafoveal vascular density (VD), periarteriolar VD, and perivenular VD.

Results

In the superficial capillary plexus (SCP), the A/V capillary ratio was significantly higher in MacTel subjects than controls (0.914 vs. 0.892; P = 0.0044). The greatest differences occurred between controls and nonproliferative MacTel subjects without optical coherence tomography evidence of disease (P = 0.0055). A/V capillary ratios progressed in a nonlinear fashion with MacTel severity, increasing from nonproliferative disease (0.912) to intraretinal proliferative disease (0.931), then decreasing in subretinal proliferative disease (0.905). Parafoveal VD in the SCP was lower in MacTel subjects than controls only in subretinal proliferative disease (P = 0.0130).

Conclusions

The A/V capillary ratio of the SCP is a quantifiable metric of vascular pathology in MacTel that occurs earlier than decline in parafoveal VD. Elevated A/V capillary ratios in MacTel are consistent with an early, disproportionately perivenular disruption in the SCP.

Translational Relevance

Findings inform MacTel pathogenesis through revealing early perivenular capillary loss and offer a new quantitative metric for earliest stage MacTel.

Progression characteristics of ellipsoid zone loss in macular telangiectasia type 2

PURPOSE

To investigate the progression characteristics of ellipsoid zone (EZ) loss in eyes with macular telangiectasia type 2 (MacTel) as reflected by area and linear measurements, and their relevance for visual acuity.

METHODS

Participants were selected from the MacTel Study cohort. Linear and area measurements of EZ loss were performed in Spectral-Domain Optical Coherence Tomograph (SD-OCT) volume scans. Progression characteristics and correlations between linear and area measurements were analysed using linear mixed effects models.

RESULTS

A total of 134 eyes of 70 patients were included (85 eyes with follow-up, mean 4.7 years, range: 1.4-8 years). Ellipsoid zone (EZ) loss significantly progressed at a mean annual increment of 0.057 mm² (p = 0.005). The progression rate was non-linear and interacted significantly with initial EZ lesion size indicating an exponential growth before reaching a plateau. There was a strong heterogeneity in area sizes between fellow eyes. EZ break length had a significant linear effect on EZ break area (b = 1.06, p < 0.001) and could predict it. The location of the EZ break had a significant impact on visual acuity.

CONCLUSION

Ellipsoid zone (EZ) loss in MacTel has a non-linear progression characteristic, and its rate depends on area size at baseline, which must be taken into account at sample selection in clinical trials. Our results show a good correlation of linear and area measures of EZ loss and a segregation of best-corrected visual acuity by EZ location, which may help routine clinical practice.

Fluorescence Lifetime Imaging Ophthalmoscopy (FLIO) of Macular Pigment

Purpose

To describe different patterns of macular pigment (MP) seen in fluorescence lifetime imaging ophthalmoscopy (FLIO) and to analyze ex vivo fluorescence characteristics of carotenoids.

Methods

A total of 31 eyes of young healthy subjects, 4 eyes from patients with albinism, 36 eyes with macular telangiectasia type 2 (MacTel), 24 eyes with retinitis pigmentosa, and 1 eye with a macular hole were included in this clinic-based, cross-sectional study. All subjects underwent Heidelberg Engineering FLIO and MP measurements (dual-wavelength autofluorescence). Fundus autofluorescence (FAF) lifetimes of a 30° retinal field were detected in two spectral channels (SSC: 498-560 nm; LSC: 560-720 nm), and amplitude-weighted mean fluorescence lifetimes (τm) were calculated. Additionally, autofluorescence lifetimes of known dilutions of lutein and zeaxanthin were measured in a cuvette in free- and protein-associated states.

Results

MP shows a significant inverse correlation to foveal FAF lifetimes measured with FLIO (SSC: r = -0.608; P < 0.001). Different distribution patterns can be assigned to specific disease-related changes. Two patients with albinism, who did not have MP, were found to be missing short FAF lifetimes. In solvent, lutein and zeaxanthin show very short autofluorescence lifetimes (∼50-60 ps; SSC), as do their respective binding proteins (∼40-50 ps; SSC). When combining carotenoids with their specific binding proteins, the decay times shift to longer means (∼70-90 ps; SSC).

Conclusions

This study expands upon previous findings of an impact of MP on short FAF lifetimes by describing ex vivo autofluorescence lifetimes of carotenoids and different in vivo autofluorescence patterns that can be associated with certain diseases.

Electrophysiological findings show generalised post-photoreceptoral deficiency in macular telangiectasia type 2

BACKGROUND

Photoreceptor damage, reported in single observations, has been suggested to contribute to the disease pathogenesis in macular telangiectasia type 2 (MacTel2). The purpose of this study was to ascertain whether the photoreceptor or post-photoreceptoral function is affected in MacTel2 and could be detected using electrophysiological examination.

METHODS

Thirty-five eyes from 18 patients (15 men, aged 60.1±9.6 years, range 38-77 years) with MacTel2 were included in the study. All patients underwent standard ophthalmic examination followed by pattern electroretinography (PERG) and full-field ERG. The data were compared against 22 normal control subjects (10 men, age 59.83±6.28 years, range 48-76).

RESULTS

Mean PERG P50 amplitude and peak time in patients with MacTel2 did not differ significantly from control values (p>0.2) but P50 amplitude was subnormal in three patients. The mean scotopic rod b-wave amplitude was significantly lower in patients than in healthy controls (p=0.027). A lower dark-adapted 10.0 b-wave (p=0.06) but not a-wave amplitude (p=0.58) was present in patients with MacTel2. Photopic single-flash a-wave and b-wave amplitudes did not differ between patient and control groups (p=0.2 and 0.3), but 30 Hz flicker peak time was significantly later in patients with MacTel2 with no effect on amplitude (p=0.04 and 0.7).

CONCLUSION

Both scotopic (rod system dominated) and photopic ERGs (cone system) are consistent with post-photoreceptoral dysfunction. There was no electrophysiological evidence of dysfunction at the level of the photoreceptor.

Anti-retinal antibodies in patients with macular telangiectasia type 2

PURPOSE

Macular telangiectasia type 2 (MacTel-2) is a retinal disease that can cause loss of central vision. To gain better understanding of the etiology and pathogenesis of MacTel-2, we investigated antigens that prompt the generation of retinal autoantibodies in the serum of patients with MacTel-2.

METHODS

We screened for the presence of retinal autoantibodies in 45 serum samples collected from patients with MacTel-2 and 58 serum samples from healthy control subjects by Western blot. We then isolated and identified three retinal proteins that are putative targets of three of the most frequently detected autoantibodies in the serum of patients with MacTel-2 using chromatographic fractionation and liquid chromatography coupled to tandem mass spectrometry. We also validated the retinal location of the three antigens by immunohistochemisty using MacTel-2 sera as primary antibodies and commercial antibodies.

RESULTS

Retinal autoantibodies were detected in a significantly higher proportion of patients with MacTel-2 than in controls (31 of 45 [69%] vs. 9 of 58 [16%], P < 0.0001). The three antigens that were targeted by the most frequently detected MacTel-2 autoantibodies were identified as glycogen debranching enzyme (hereafter AGL, named for the gene symbol AGL), retinol-binding protein 3 (RBP3), and creatine kinase type B (CK-B); autoantibodies against these antigens were found in four, eleven, and nine MacTel-2 serum samples, respectively.

CONCLUSIONS

We found that most patients with MacTel-2 possess retinal autoantibodies, the most prevalent of which were directed against AGL, RBP3, and CK-B. The localization of retinal proteins bound by AGL, RBP3, and CK-B autoantibodies is consistent with their putative physiological functions. These findings provide potentially novel mechanisms for the etiology and pathogenesis of MacTel-2.