Stratus OCT in dominant optic atrophy: features differentiating it from glaucoma

Neuro-Ophthalmological Optic Nerve Cupping: An Overview

Optic nerve cupping or enlargement of the cup-to-disc ratio is widely recognized as a feature of glaucoma, however it may also occur in non-glaucomatous optic neuropathies. The most well-recognized non-glaucomatous optic neuropathies that cause cupping include compressive optic neuropathies, arteritic anterior ischemic optic neuropathies, hereditary optic neuropathies, and optic neuritis. Cupping is thought to consist of two main components: prelaminar and laminar thinning. The former is a shallow form of cupping and related to loss of retinal ganglion cells, whereas the latter involves damage to the lamina cribrosa and peripapillary scleral connective tissue. Differentiating glaucomatous and non-glaucomatous optic nerve cupping remains challenging even for experienced observers. Classically, the optic nerve in non-glaucomatous causes has pallor of the neuroretinal rim, but the optic nerve should not be examined in isolation. The patient’s medical history, history of presenting illness, visual function (visual acuity, color vision and visual field testing) and ocular examination also need to be considered. Ancillary testing such as optical coherence tomography of the retinal nerve fiber layer and ganglion cell layer-inner plexiform layer may also be helpful in localizing the disease. In this review, we review the non-glaucomatous causes of cupping and provide an approach to evaluating a patient that presents with an enlarged cup-to-disc ratio.

Comparison of Lamina Cribrosa Morphology in Normal Tension Glaucoma and Autosomal-Dominant Optic Atrophy

Purpose

To compare lamina cribrosa (LC) morphology in patients with normal tension glaucoma (NTG) and autosomal-dominant optic atrophy (ADOA).

Methods

This cross-sectional study matched 24 patients diagnosed with ADOA (24 eyes) by age and retinal nerve fiber layer thickness with 48 patients diagnosed with NTG (48 eyes) by age with 48 healthy controls (48 eyes). Optic nerve heads were scanned by enhanced-depth imaging (EDI) optical coherence tomography (OCT). The LC curvature index (LCCI) and LC depth (LCD) on B-scan images obtained using EDI-OCT were measured at seven locations spaced equidistantly across the vertical optic disc diameter and compared among the NTG, ADOA, and control groups.

Results

Mean LCCI and LCD were significantly greater in NTG than in ADOA and healthy eyes (P < 0.001 each) but did not differ significantly in ADOA and healthy eyes.

Conclusions

NTG eyes have a more posteriorly curved and deeper LC than ADOA and healthy eyes. This finding provides insight into the role of LC morphology in NTG and provides a clinical clue to distinguish between NTG and ADOA.

OCTA in neurodegenerative optic neuropathies: emerging biomarkers at the eye-brain interface

OCTA imaging in optic neuropathies.

Neuro-ophthalmic Disease in Pediatric Glaucoma Practice

PRECIS

Pediatric glaucoma referral to neuro-ophthalmology has a high yield for diagnosing neurological disease and neuroimaging in this cohort often uncovers intracranial abnormalities.

PURPOSE

Multiple studies have examined the utility of neuro-ophthalmology referrals in an adult glaucoma patient population. No similar studies in the pediatric glaucoma population have been completed. An analysis of pediatric referral patterns and clinical characteristics can serve to guide future physician referrals and improve patient outcomes.

MATERIALS AND METHODS

A retrospective review of medical records was conducted to identify pediatric patients evaluated by both glaucoma and neuro-ophthalmology services at Bascom Palmer Eye Institute from January 2013 to August 2018. Records were reviewed for clinical examination findings, demographics, ophthalmic imaging, neuroimaging, and ultimate diagnosis.

RESULTS

A total of 59 patients, average age 10 years old, were included for analysis. The majority of patients were referred from pediatric glaucoma to neuro-ophthalmology (n=52, 88.1%). The most common reasons for referral included suspected nonglaucomatous optic neuropathy (n=14), optic disc swelling (n=7), color vision deficiency (n=6), and nonglaucomatous visual field defect (n=4). Referral to neuro-ophthalmology resulted in neuro-imaging in 22 patients (22/52, 42.3%), with 7 patients (7/52, 13.7%) having pathology on the scan. Ultimately, 38 patients (73.1%) referred to neuro-ophthalmology had an ultimate diagnosis unrelated to glaucoma. Color vision abnormality, optic nerve pallor, and/or retinal nerve fiber layer <70 µm in at least 1 eye were associated with a diagnosis unrelated to glaucoma. Of the 7 patients referred from neuro-ophthalmology to pediatric glaucoma, none were diagnosed with glaucoma or started on intraocular pressure lowering therapy.

CONCLUSIONS

Patients referred from pediatric glaucoma to neuro-ophthalmology often have nonglaucomatous disease requiring subspecialty evaluation and neuroimaging. Neuroimaging in this cohort is high yield for uncovering intracranial pathology.

Optical Coherence Tomography of the Retinal Ganglion Cell Complex in Leber's Hereditary Optic Neuropathy and Dominant Optic Atrophy

Background: Mitochondrial optic neuropathies such as Leber's Hereditary Optic Neuropathy (LHON) and Dominant Optic Atrophy (DOA) have been shown to produce an optic neuropathy secondary to retinal ganglion cell loss with thinning of the retinal ganglion cell complex (RGCC). Methods: We performed a retrospective analysis assessing the thicknesses of the peripapillary retinal nerve fiber layer (pRNFL) along with the macular retinal ganglion cell-inner plexiform layer (RGC-IPL) using optical coherence tomography (OCT). We compared these changes among acute and chronic LHON, DOA, and normal healthy control patients. Results: Patients with chronic LHON exhibited statistically significant thinning of the RNFL in the superior, nasal, and inferior quadrants of the retina. In acute LHON, the RNFL was relatively thicker in all but the temporal quadrant when compared with respective quadrants in normal eyes; however, statistical significance was not achieved. In DOA, the RNFL was thinnest in the superior and inferior quadrants of the retina, measuring between acute and chronic LHON thickness values. In chronic LHON and DOA, both the pRNFL and RGC-IPL were significantly thinner in all four retinal quadrants relative to controls. Conclusions: This article represents the first comparative study of the RGCC between LHON and DOA. Our findings demonstrated significant thickness reductions in pRNFL and macular RGC-IPL in patients with LHON and DOA, with different specific patterns consistent with the general patterns of thinning classically observed. This study suggests the usefulness of the RGCC as a potential in vivo biomarker for assessing disease in patients with LHON and DOA.

Are All Retinal Nerve Fiber Layer Defects on Optic Coherence Tomography Glaucomatous?

Objectives

In this study, we investigated the patients who were referred to our clinic with a prediagnosis of glaucoma based on retinal nerve fiber layer (RNFL) defects on optic coherence tomography (OCT) but were determined to have nonglaucomatous RNLF defects upon detailed examination.

Materials and Methods

The ophthalmic examination notes, OCT images, Heidelberg retinal tomography (HRT) II and fundus photographs of 357 patients were retrospectively evaluated. Final diagnoses of these patients were investigated.

Results

Of the 357 patients, 216 (60.5%) were diagnosed as open angle glaucoma, 33 (9.2%) as low-tension glaucoma, 39 (10.9%) as pre-perimetric glaucoma. The ophthalmic examinations of 14 patients (3.9%) were normal and there were no RNFL defects in OCT examinations after dilatation. In 39 patients (10.9%), the ophthalmic and optic disc examinations were completely normal and no etiologic factor explaining RNFL defects was found. Twenty-two eyes of 16 patients (4.5%) were included in this study (the mean age was 53.8±11.5 years; 9 men and 7 women). After detailed questioning of the medical history and systemic and neurologic examinations, a diagnosis of ischemic optic neuropathy was made in 11 eyes (10 patients) (2.8%), optic neuritis in 3 eyes (2 patients) (0.6%), optic disc drusen in 4 eyes (2 patients) (0.6%), pseudotumor cerebri in 2 eyes (1 patient) (0.3%), and cerebral palsy in 2 eyes (1 patient) (0.3%).

Conclusion

Decrease in RNFL thickness on OCT images alone may be misleading in glaucoma examination. In cases where optic disc cupping is not evident, diagnosis should not be based on OCT RNFL examinations alone, and the patient's medical history, detailed ophthalmic examination, OCT optic disc parameters, HRT, and visual field tests should all be carefully evaluated together.

A Review of Mitochondrial Optic Neuropathies: From Inherited to Acquired Forms

In recent years, the term mitochondrial optic neuropathy (MON) has increasingly been used within the literature to describe a group of optic neuropathies that exhibit mitochondrial dysfunction in retinal ganglion cells (RGCs). Interestingly, MONs include genetic aetiologies, such as Leber hereditary optic neuropathy (LHON) and dominant optic atrophy (DOA), as well as acquired aetiologies resulting from drugs, nutritional deficiencies, and mixed aetiologies. Regardless of an inherited or acquired cause, patients exhibit the same clinical manifestations with selective loss of the RGCs due to mitochondrial dysfunction. Various novel therapies are being explored to reverse or limit damage to the RGCs. Here we review the pathophysiology, clinical manifestations, differential diagnosis, current treatment, and promising therapeutic targets of MON.

Lateral thinking - Interocular symmetry and asymmetry in neurovascular patterning, in health and disease

No biological system or structure is likely to be perfectly symmetrical, or have identical right and left forms. This review explores the evidence for eye and visual pathway asymmetry, in health and in disease, and attempts to provide guidance for those studying the structure and function of the visual system, where recognition of symmetry or asymmetry may be essential. The principal question with regards to asymmetry is not 'are the eyes the same?', for some degree of asymmetry is pervasive, but 'when are they importantly different?'. Knowing if right and left eyes are 'importantly different' could have significant consequences for deciding whether right or left eyes are included in an analysis or for examining the association between a phenotype and ocular parameter. The presence of significant asymmetry would also have important implications for the design of normative databases of retinal and optic nerve metrics. In this review, we highlight not only the universal presence of asymmetry, but provide evidence that some elements of the visual system are inherently more asymmetric than others, pointing to the need for improved normative data to explain sources of asymmetry and their impact on determining associations with genetic, environmental or health-related factors and ultimately in clinical practice.

Assessment of the retinal posterior pole in dominant optic atrophy by spectral-domain optical coherence tomography and microperimetry

Background

To assess posterior pole (PP) retinal structure in patients with genetically confirmed autosomal dominant optic atrophy (ADOA) using new spectral domain optical coherence tomography (SD-OCT) segmentation technology. To analyze retinal PP thickness in relation to retinal sensitivity data from microperimetry (MP) in ADOA patients.

Methods and findings

This prospective cross-sectional study included 11 patients with ADOA and 11 age-matched healthy subjects. All participants underwent both a “Posterior Pole” and “peripapillary RNFL (pRNFL)” scanning protocol using SD-OCT. Functional mapping of the PP was also performed using MP. A customized program was implemented in order to achieve accurate superimposition of MP sensitivity map onto SD-OCT map. The thickness of the PP different retinal layers and pRNFL was obtained and measured for each eye. Mean retinal sensitivity values and fixation stability were obtained and compared between ADOA patients and healthy subjects. Correlation analysis was performed on a point-to-point basis to evaluate the association between mean thickness and retinal sensitivity of each retinal layer. Total retinal thickness (TRT), Retinal Nerve Fiber Layer (RNFL), Ganglion Cell Layer (GCL), Inner Plexiform Layer (IPL), Inner Nuclear Layer (INL) and Inner Retinal Layers (IRL) at the posterior pole as well as pRNFL were significantly thinner in ADOA patients (P < 0.0001). On the contrary, the Outer Plexiform Layer (OPL) and the Outer Nuclear Layer (ONL) were significantly thicker in the ADOA group (P < 0.001). No significant differences were found in Retinal Pigment Epithelium (RPE) and Outer Retinal Layers (ORL) thickness between ADOA and controls. The average PP retinal sensitivity was significantly reduced in ADOA patients compared with controls (P < 0.001), as measured by microperimeter Nidek MP-1 (MP1). Fixation stability was significantly worse in the ADOA group (P = 0.01). The most severe sensitivity defects in ADOA patients were found at the level of the papillo-macular bundle (PMB).

Conclusions

Inner retinal layers showed pathological changes in ADOA patients. In addition, the whole retinal PP (not only the PMB) was significantly altered in ADOA, both in terms of retinal thickness and sensitivity.

Genotype-phenotype heterogeneity of ganglion cell and inner plexiform layer deficit in autosomal-dominant optic atrophy

PURPOSE

To describe the thickness of the combined ganglion cell and inner plexiform layers (GC-IPL) and the peripapillary retinal nerve fibre layer (RNFL) in patients with OPA1 c.983A>G or c.2708_2711delTTAG autosomal-dominant optic atrophy (ADOA).

METHODS

The study included 20 individuals with c.983A>G and nine individuals with c.2708_2711delTTAG. Data for comparison were drawn from 49, previously published, individuals with OPA1 c.2826_2836delinsGGATGCTCCA and 51 individuals with no OPA1 mutation. Subjects underwent refraction, best-corrected visual acuity assessment, axial length measurement and high-definition optical coherence tomography.

RESULTS

There was overlap in GC-IPL thickness in subjects younger than 20-30 years between the two new groups of ADOA patients and controls. Numerical decreases in GC-IPL thickness with age did not reach statistical significance in individuals with c.983A>G (p = 0.18) or in healthy controls (p = 0.22), but it did in individuals with c.2708_2711delTTAG (p = 0.02). Visual acuity decreased with decreasing GC-IPL thickness (p = 0.0006 in c.983A>G and p = 0.0084 in c.2708_2711delTTAG). Unlike c.2826_2836delinsGGATGCTCCA, individuals with c.983A>G or c.2708_2711delTTAG did not show a pattern of maximum GC-IPL deficit inferonasal of the fovea.

CONCLUSION

Genotype-phenotype heterogeneity in OPA1 ADOA is evident when inner retinal atrophy is examined as a function of age. Thus, a pronounced decline with age in GC-IPL thickness is observed in c.2708_2711delTTAG ADOA, an intermediate decline with age is observed in c.983A>G ADOA, whereas little or no change with age is observed in c.2826_2836delinsGGATGCTCCA ADOA. This genotype-phenotype heterogeneity may explain why some patients have progressive visual loss while others have a relatively stable prognosis.

OCT: New perspectives in neuro-ophthalmology

Optical coherence tomography (OCT) has become essential to evaluate axonal/neuronal integrity, to assess disease progression in the afferent visual pathway and to predict visual recovery after surgery in compressive optic neuropathies. Besides that OCT testing is considered a powerful biomarker of neurodegeneration and a promising outcome measure for neuroprotective trials in multiple sclerosis (MS). Currently, spectral-domain OCT (SD-OCT) technology allows quantification of retinal individual layers. The Ganglion Cell layer (GCL) investigation has become one of the most useful tools from a neuro-ophthalmic perspective. It has a high correlation with perimetry, is predictive of future progression and is a highly sensitive, specific of several neuro-ophthalmic pathologies. Moreover the superior correlation with clinical measures compared to peripapillary retinal nerve fiber layer (pRNFL) suggests that GCL analysis might be a better approach to examine MS neurodegeneration. In disorders with optic disk edema, such as ischemic optic neuropathy, papillitis and papilledema, reduction in RNFL thickness caused by axonal atrophy is difficult to distinguish from a swelling resolution. In this setting, and in buried optic nerve head drusen (ONHD), GCL analysis may provide more accurate information than RNFL analysis and it might be an early structural indicator of irreversible neuronal loss. Enhanced depth imaging OCT (EDI-OCT) provides in vivo detail of ONHD, allowing to evaluate and quantify the drusen dimensions. OCT is improving our knowledge in hereditary optic neuropathies. Furthermore, there is growing evidence about the role of OCT as an adjunctive biomarker of disorders such as Alzheimer and Parkinson's disease.

Toxic optic neuropathies

PURPOSE OF REVIEW

Many causes of toxic optic neuropathy have been described to date and novel causes of toxicity are continuously being added to the current literature. The pathophysiological basis for the toxicity or a direct causal relationship is yet to be determined for many of these agents. This review highlights the reports made over the last year about the commonly reported agents, with emphasis on the mechanisms of toxicity.

RECENT FINDINGS

Mitochondria of retinal ganglion cells and papillomacular bundle in particular could be the common target of many causes of toxic optic neuropathy, if not all. Agents or their metabolites responsible for the toxicity seem to interfere with the oxidative phosphorylation in mitochondria, causing a buildup of reactive oxidation species, energy depletion, oxidative stress, and activation of apoptosis.

SUMMARY

Further data are still necessary to understand how some of the usual suspects cause damage to the optic nerve or whether they indeed cause damage or not. A basic algorithm, as proposed, could be a useful addition to discriminate the novel causes of toxic optic neuropathy.

VIDEO ABSTRACT

See the Supplemental Digital Content 1 (http://links.lww.com/COOP/A11).

Optical coherence tomography findings in spinocerebellar ataxia-3

PURPOSE

To report optical coherence tomography (OCT) findings in order to detect subclinical alterations of the afferent visual pathways in spinocerebellar ataxia 3 (SCA-3).

PATIENTS AND METHODS

Nine genetically confirmed patients (18 eyes) were evaluated with a complete ophthalmologic examination including visual acuity, colour vision, visual field test, and retinal nerve fibre layer (RNFL) and macular thickness with OCT Cirrus HD. A neurological examination was performed and the Scale for the Assessment and Rating of Ataxia (SARA score) was determined in all patients.

RESULTS

The mean RNFL thickness was 77.39 microns, standard deviation (SD) was ± 5.93. In 15 eyes (83.33%), the mean RNFL thickness was lower than the population average considering age and sex. In 10 cases, there was a reduction of the RNFL thickness in the superior sector, eight in the inferior and four in the nasal. Temporal sector RNFL thickness was preserved in all eyes. RNFL thickness was inversely correlated to SARA score (r=-0.64, P=0.012). The mean macular thickness was 252.61 microns, SD ± 22.80, being inferior respecting average population in only two eyes (11.11%). In four patients, (eight eyes) OCT studies were performed during a mean follow-up of 14.25 months, and in five eyes (62.50%) there was a mild trend to a RNFL thickness decrease in this period.

CONCLUSION

A mild and progressive decrease in RNFL thickness can be observed in SCA-3 patients. A negative correlation exists between an anatomic marker (RNFL thickness) and a clinical severity scale (SARA score); thus, RNFL thickness could be considered as a promising biomarker of the disease.

Optic disc rim area to retinal nerve fiber layer thickness correlation: comparison of diabetic and normal tension glaucoma eyes

PURPOSE

To compare the correlation between optic disc rim area and retinal nerve fiber layer thickness (rim-RNFL correlation) in diabetic eyes with non-progressive RNFL defects and normal tension glaucoma (NTG) eyes.

METHODS

Seventy-three eyes of 73 patients with preperimetric or early NTG and 25 eyes of 25 type II diabetes patients with a non-progressive RNFL defect for ≥5 years were enrolled in this retrospective cohort study. Rim areas and RNFL thicknesses were measured by Heidelberg retina tomography (HRT II) and by optical coherence tomography (Cirrus OCT), in global and 12 clock-hour parameters. Diabetic eyes were evaluated whether they were above the 95 % prediction interval (PI) for the rim-RNFL correlation of NTG.

RESULTS

A significant linear rim-RNFL correlation was observed in NTG eyes globally and at all clock-hours, except in the 4 and 9 o'clock areas, (0.08 < r (2) < 0.56, P < 0.05). Eighty-four percent of the diabetic eyes were above the 95 % PI of the rim-RNFL correlation of NTG in ≥2 clock-hours, as compared with 36 % of the eyes in the global parameter.

CONCLUSIONS

The eyes of diabetic patients with non-progressive RNFL were well-differentiated from NTG eyes by the rim-RNFL correlation.

Neuro-ophthalmic disease and optical coherence tomography: glaucoma look-alikes

PURPOSE OF REVIEW

The use of optical coherence tomography (OCT)-measured retinal nerve fiber layer (RNFL) thickness in neuro-ophthalmic disease has grown since its first use in glaucoma and retinal diseases. OCT-measured RNFL in nonglaucomatous optic neuropathies shows thinning, which may mimic those seen in glaucoma. This article aims to provide insight regarding the use of OCT in nonglaucomatous optic neuropathies and sheds light on common patterns of RNFL loss in different nonglaucomatous optic neuropathies.

RECENT FINDINGS

RNFL thinning is most likely to occur in the temporal peripapillary quadrant than in other quadrants in nonglaucomatous optic neuropathies. The pattern of RNFL thinning in ischemic optic neuropathy and optic nerve head drusen is more likely to mimic the pattern found in glaucoma due to the superior and inferior quadrant predilection. OCT-measured RNFL thickness in Alzheimer's disease reveals thinning superiorly and inferiorly, whereas superior and temporal thinning is seen in Parkinson's disease. The thinning observed in neurodegenerative diseases is believed to be multifactorial including causes such as axonal degeneration and retrograde degeneration. However, more studies are needed to further study these changes.

SUMMARY

OCT is a valuable tool in evaluating the peripapillary RNFL in both glaucomatous and nonglaucomatous optic neuropathies. This technology may be used for both research and clinical purposes to assess disease progression in optic neuropathies and diseases that affect the central nervous system. OCT-measured RNFL thickness remains complimentary to the clinical examination skills in the evaluation of nonglaucomatous optic neuropathies.

Use of optical coherence tomography to evaluate papilledema and pseudopapilledema

Idiopathic intracranial hypertension (IIH), or pseudotumor cerebri, describes a condition of elevated intracranial pressure (ICP) that typically presents in obese women of childbearing age with symptoms and signs of posture-dependent headaches, pulsatile tinnitus, visual changes, and papilledema. Optical coherence tomography (OCT) has begun to be utilized as an adjunctive, quantitative tool in the evaluation of patients with IIH to help distinguish between true optic nerve head edema and pseudopapilledema, and to contribute to our understanding of the consequences of prolonged optic nerve edema. Although few longitudinal studies of patients with IIH have been published to date, it appears that there may be a correlation between retinal nerve fiber layer (RNFL) thickness and visual function. With the new spectral domain OCT, additional parameters of the optic nerve imaging, including volume and height measurements, might provide greater sensitivity of the response to treatment and the long-term visual outcome in patients with IIH.

Pattern of retinal ganglion cell loss in dominant optic atrophy due to OPA1 mutations

PURPOSE

The majority of patients with autosomal dominant optic atrophy (DOA) harbour pathogenic OPA1 mutations. Although DOA is characterised by the preferential loss of retinal ganglion cells (RGCs), about 20% of patients with OPA1 mutations will develop a more severe disease variant (DOA+), with additional neuromuscular features. In this prospective, observational case series, optical coherence tomography (OCT) was used to define the pattern of retinal nerve fibre layer (RNFL) loss in patients with both the pure and syndromal forms of DOA.

METHODS

Forty patients with a molecular diagnosis of DOA due to OPA1 mutations were prospectively recruited from our neuro-ophthalmology clinic: 26 patients with isolated optic atrophy and 14 patients manifesting DOA+ features. Peripapillary RNFL thickness was measured with the Fast RNFL (3.4) acquisition protocol on a Stratus OCT.

RESULTS

There was a statistically significant reduction in average RNFL thickness in the OPA1 group compared with normal controls (P<0.0001). The percentage decrease was greatest in the temporal quadrant (59.0%), followed by the inferior (49.6%), superior (41.8%), and nasal (25.9%) quadrants. Patients with DOA+ features had worse visual outcomes compared with patients with pure DOA. Except in the temporal quadrant, RNFL measurements were significantly thinner for the DOA+ group. There was an inverse correlation between average RNFL thickness and logarithm of the minimum angle of resolution (LogMAR) visual acuity (P<0.0001).

CONCLUSIONS

RGC loss in DOA is characterised by severe involvement of the temporal papillomacular bundle, with relative sparing of the nasal fibres. RNFL thinning is more pronounced in patients with DOA+ phenotypes.

Mitochondrial optic neuropathies - disease mechanisms and therapeutic strategies

Leber hereditary optic neuropathy (LHON) and autosomal-dominant optic atrophy (DOA) are the two most common inherited optic neuropathies in the general population. Both disorders share striking pathological similarities, marked by the selective loss of retinal ganglion cells (RGCs) and the early involvement of the papillomacular bundle. Three mitochondrial DNA (mtDNA) point mutations; m.3460G>A, m.11778G>A, and m.14484T>C account for over 90% of LHON cases, and in DOA, the majority of affected families harbour mutations in the OPA1 gene, which codes for a mitochondrial inner membrane protein. Optic nerve degeneration in LHON and DOA is therefore due to disturbed mitochondrial function and a predominantly complex I respiratory chain defect has been identified using both in vitro and in vivo biochemical assays. However, the trigger for RGC loss is much more complex than a simple bioenergetic crisis and other important disease mechanisms have emerged relating to mitochondrial network dynamics, mtDNA maintenance, axonal transport, and the involvement of the cytoskeleton in maintaining a differential mitochondrial gradient at sites such as the lamina cribosa. The downstream consequences of these mitochondrial disturbances are likely to be influenced by the local cellular milieu. The vulnerability of RGCs in LHON and DOA could derive not only from tissue-specific, genetically-determined biological factors, but also from an increased susceptibility to exogenous influences such as light exposure, smoking, and pharmacological agents with putative mitochondrial toxic effects. Our concept of inherited mitochondrial optic neuropathies has evolved over the past decade, with the observation that patients with LHON and DOA can manifest a much broader phenotypic spectrum than pure optic nerve involvement. Interestingly, these phenotypes are sometimes clinically indistinguishable from other neurodegenerative disorders such as Charcot-Marie-Tooth disease, hereditary spastic paraplegia, and multiple sclerosis, where mitochondrial dysfunction is also thought to be an important pathophysiological player. A number of vertebrate and invertebrate disease models has recently been established to circumvent the lack of human tissues, and these have already provided considerable insight by allowing direct RGC experimentation. The ultimate goal is to translate these research advances into clinical practice and new treatment strategies are currently being investigated to improve the visual prognosis for patients with mitochondrial optic neuropathies.

Optic disc evaluation in optic neuropathies: the optic disc assessment project

OBJECTIVE

Optic nerve morphology is affected by genetic and acquired disease. Glaucoma is the most common optic neuropathy; autosomal-dominant optic atrophy (ADOA) and Leber's hereditary optic neuropathy (LHON) are the most prevalent hereditary optic neuropathies. These 3 entities can exhibit similar topographical changes at the optic nerve head. Both ADOA and LHON have been reported to be misdiagnosed as glaucoma. Our aim was to determine whether glaucoma subspecialists and neuro-ophthalmologists can distinguish these diagnoses on optic disc assessment alone.

DESIGN

Observational study.

PARTICIPANTS

Twenty-three optic nerve experts.

METHODS

We randomized and masked 60 high-resolution stereoscopic optic disc photographs (15 ADOA images, 15 LHON, 15 glaucoma, and 15 normal controls). Experts were asked to assess the discs on 12 conventional topographic features and assign a presumptive diagnosis. Intra- and interanalysis was performed using the index of qualitative variation and absolute deviation.

MAIN OUTCOME MEASURES

Can glaucoma specialists and neuro-ophthalmologists distinguish among the disease entities by optic nerve head phenotype.

RESULTS

The correct diagnosis was identified in 85%, 75%, 27%, and 16% of the normal, glaucoma, ADOA, and LHON disc groups, respectively. The proportion of correct diagnoses within the ADOA and LHON groups was significantly lower than both normal and glaucomatous (P<0.001). Where glaucoma was chosen as the most likely diagnosis, 61% were glaucomatous, 34% were pathologic but nonglaucomatous discs, and 5% were normal. There was greater agreement for individual parameters assessed within the normal disc set when compared with pathologic discs (P<0.05). The only parameter to have a significantly greater agreement within the glaucomatous disc set when compared with ADOA or LHON disc sets was pallor, whereby experts agreed on is absence in the glaucomatous discs but were not in agreement on its presence or its absence in the ADOA and LHON discs (P<0.01).

CONCLUSIONS

Optic neuropathies can result in similar topographic changes at the optic disc, particularly in late-stage disease, making it difficult to differentiate ADOA and LHON from glaucoma based on disc assessment alone. Other clinical parameters such as acuity, color vision, history of visual loss, and family history are required to make an accurate diagnosis.

First-visit diagnosis of preperimetric glaucoma

Purpose:

To present a revised interpretation of the work-up data that enabled diagnosis of preperimetric glaucoma (PPG) at the first examination.

Methods:

a) Literature analysis on PPG; b) 6-year follow-up of a glaucoma-suspect patient.

Results:

Two new concepts may be adapted: (a) the objective finding of retinal nerve fiber layer (RNFL) thinning below the normal border in the opposing typical glaucoma locations, the inferior and superior quadrants, and in a non-diffuse pattern, appears asymptomatically and simultaneously only in glaucoma; and (b) the imaging-related RNFL thickness may be considered the reference glaucoma standard, whereas the suspicious early glaucomatous optic neuropathy, having a potential diagnostic inaccuracy, would serve as a complementary revealing finding. That approach enabled, in retrospect, a first-visit diagnosis of low-tension PPG in the patient. Diagnosis was confirmed after 6 years, when cecocentral scotoma and further RNFL thinning emerged despite treatment.

Conclusions:

A revised approach enabled PPG diagnosis during the first visit.

Ophthalmic features of spinocerebellar ataxia type 7

BACKGROUND

Patients with spinocerebellar ataxia 7 (SCA7) are known to develop ocular abnormalities. The purpose of this study was to characterize these abnormalities in greater detail and with the aid of newer quantitative technologies.

METHODS

Seven patients with SCA7 diagnosed by genetic analysis at La Paz Hospital (Madrid, Spain), a country-wide referral center for ataxias, were included in the study. Demographic data and ocular features were recorded from a complete ophthalmologic examination, specular microscopy, corneal topography (Pentacam), and optical coherence tomography (OCT).

RESULTS

All 7 patients had decreased visual acuity associated with varying degrees of macular pigmentary changes on ophthalmoscopy. All 7 had lower corneal endothelial cell densities than expected for their age, and 5 had increased corneal volume, although none had corneal edema. Patients with mild disease showed retinal thinning at the fovea. In patients with more advanced disease, retinal thinning was present also in the outer zone of the macula. Mean peripapillary retinal nerve fiber layer thickness was decreased in all patients; however, the temporal quadrant was spared except in advanced disease.

CONCLUSIONS

This study of 7 patients with SCA7 amplifies previous reports of ophthalmic abnormalities in this condition by providing data from specular microscopy, corneal topography, and OCT. Abnormalities were present in the anterior and posterior ocular segments, as well as in eye movements and pupillary reactions. Visual dysfunction, present in all patients, was associated with retinal thinning. Decreased endothelial cell density and increased corneal thickness were common.

Inherited mitochondrial optic neuropathies

Leber hereditary optic neuropathy (LHON) and autosomal dominant optic atrophy (DOA) are the two most common inherited optic neuropathies and they result in significant visual morbidity among young adults. Both disorders are the result of mitochondrial dysfunction: LHON from primary mitochondrial DNA (mtDNA) mutations affecting the respiratory chain complexes; and the majority of DOA families have mutations in the OPA1 gene, which codes for an inner mitochondrial membrane protein critical for mtDNA maintenance and oxidative phosphorylation. Additional genetic and environmental factors modulate the penetrance of LHON, and the same is likely to be the case for DOA which has a markedly variable clinical phenotype. The selective vulnerability of retinal ganglion cells (RGCs) is a key pathological feature and understanding the fundamental mechanisms that underlie RGC loss in these disorders is a prerequisite for the development of effective therapeutic strategies which are currently limited.