High-Resolution In Vivo Imaging in Achromatopsia
Ophthalmology Group, School of Medicine, University of Leicester, Leicester, United Kingdom. Ophthalmology
(Impact Factor: 6.14).
05/2011; 118(5):882-7. DOI: 10.1016/j.ophtha.2010.08.053
To characterize the retinal changes in patients with achromatopsia using an ultrahigh-resolution (UHR) spectral-domain optical coherence tomography (OCT) to examine how human achromatopsia corresponds to its animal model.
Comparative case series.
Ultrahigh-resolution OCT (Copernicus; OPTOPOL Technology S.A., Zawiercie, Poland; 3-μm axial resolution) was used to obtain scans from 13 patients (26 eyes) with achromatopsia and from 20 controls (40 eyes).
A 3-dimensional scan program (743×75; A×B scan) sampling a 7×7-mm retinal area centered at the fovea was used to obtain tomograms of the fovea. Individual B-scans at the fovea were exported and analyzed using ImageJ (Wayne Rasband, National Institute of Health) for reflectance profiles and morphologic abnormalities.
Gross morphologic changes in OCT were characterized. Specifically, inner segment and outer segment (IS/OS) junction and cone outer segment tip (COST) disruption was noted. Using the reflectance profiles, foveal depth, thickness of the outer nuclear layer (ONL), and retinal thickness (RT) were measured.
A characteristic so-called punched out hyporeflective zone (HRZ) was noted in 7 of 13 patients; this was age-dependent (P = 0.001). The area of the HRZ was asymmetric with the nasal area being significantly greater than the temporal area (P = 0.002). In all patients, there was disruption of the IS/OS junction at the foveal or parafoveal regions, or both. Five of 13 patients also had a disrupted COST reflectivity. There was significant (P = 1.1×10(-6)) ONL thinning in the achromats compared with controls, which was age-dependent (P = 0.0002). Foveal maldevelopment was seen in 9 of 13 patients. The achromats also had a significantly reduced foveal depth (P = 7.7×10(-6)) and RT (P = 1.46×10(-9)) compared with controls.
A range of signs in achromatopsia are described that can be detected using UHR OCT. The IS/OS junction and COST reflectivity disruption and presence of HRZ and ONL thinning are signs of cone photoreceptor degeneration. The latter 2 are age-dependent, which suggests that achromatopsia is a progressive disorder. In addition, foveal maldevelopment is described; this represents a fetal developmental defect linked to cone photoreceptor degeneration.
Available from: Rebecca Jane Mclean
- "The fact that most forms of infantile nystagmus arise due to mutations of genes expressed within the developing retina would argue in favor of an afferent abnormality. Moreover, abnormal retinal phenotypes have been described in most of these disorders (6–8). However, in IIN, other than reduced visual acuity and an abnormal optokinetic response (9,10), no overt ocular abnormality has been described. "
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ABSTRACT: Idiopathic infantile nystagmus (IIN) is a genetically heterogeneous disorder, often associated with FRMD7 mutations. As the appearance of the retina is reported to be normal based on conventional fundus photography, IIN is postulated
to arise from abnormal cortical development. To determine whether the afferent visual system is involved in FRMD7 mutations, we performed in situ hybridization studies in human embryonic and fetal stages (35 days post-ovulation to 9 weeks post-conception). We show a
dynamic retinal expression pattern of FRMD7 during development. We observe expression within the outer neuroblastic layer, then in the inner neuroblastic layer and at
9 weeks post-conception a bilaminar expression pattern. Expression was also noted within the developing optic stalk and optic
disk. We identified a large cohort of IIN patients (n = 100), and performed sequence analysis which revealed 45 patients with FRMD7 mutations. Patients with FRMD7 mutations underwent detailed retinal imaging studies using ultrahigh-resolution optical coherence tomography. The tomograms
were compared with a control cohort (n = 60). The foveal pit was significantly shallower in FRMD7 patients (P < 0.0001). The optic nerve head morphology was abnormal with significantly decreased optic disk area, retinal nerve fiber
layer thickness, cup area and cup depth in FRMD7 patients (P < 0.0001). This study shows for the first time that abnormal afferent system development is associated with FRMD7 mutations and could be an important etiological factor in the development of nystagmus.
Available from: Michel Michaelides
Available from: Frank A Proudlock
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ABSTRACT: To characterize and grade the spectrum of foveal hypoplasia based on different stages of arrested development of the fovea. Grading was performed using morphologic findings obtained by ultra high-resolution spectral-domain optical coherence tomography. Best-corrected visual acuity (BCVA) was calculated for different grades.
Observational case series.
Sixty-nine patients with foveal hypoplasia (albinism, n = 34; PAX6 mutations, n = 10; isolated cases, n = 14; achromatopsia, n = 11) and 65 control subjects were examined.
A 7×7-mm retinal area was sampled using a 3-dimensional scanning protocol (743×75, A scans×B scans) with ultra high-resolution spectral-domain optical coherence tomography (SOCT Copernicus HR; 3-μm axial resolution). Gross morphologic abnormalities were documented. B-scans at the fovea were segmented using a longitudinal reflectivity profile. Logarithm of the minimum angle of resolution BCVA was obtained.
Grading was based on presence or absence of foveal pit and widening of the outer nuclear layer (ONL) and outer segment (OS) at the fovea. Quantitative measurements were obtained for comparing atypical foveal hypoplasia in achromatopsia. Best-corrected visual acuity was compared with the grade of foveal hypoplasia.
Four grades of foveal hypoplasia were distinguished: grade 1, shallow foveal pit, presence of ONL widening, presence of OS lengthening; grade 2, grade 1 but absence of foveal pit; grade 3, grade 2 but absence of OS lengthening; grade 4, grade 3 but absence of ONL widening. There was significant difference in visual acuity (VA) associated with each grade (P<0.0001). Grade 1 was associated with the best VA (median VA, 0.2), whereas grades 2, 3, and 4 were associated with progressively poorer VA with a median VA of 0.44, 0.60, and 0.78, respectively. The atypical features seen with foveal hypoplasia associated with achromatopsia were characterized by decreased retinal and ONL thickness and deeper foveal depth.
A structural grading system for foveal hypoplasia was developed based on the stage at which foveal development was arrested, which helps to provide a prognostic indicator for VA and is applicable in a range of disorders associated with foveal hypoplasia. Atypical foveal hypoplasia in achromatopsia shows different characteristics.
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