Relative afferent pupillary defects in patients with Leber hereditary optic neuropathy and unilateral visual loss

Peripapillary microcirculation in Leber hereditary optic neuropathy

PURPOSE

In this prospective observational comparative case series, we aimed to study the peripapillary capillary network with spectral-domain optical coherence tomography angiography (OCT-A) in Leber hereditary optic neuropathy (LHON).

METHODS

Twelve eyes of six individuals, of these three males (five eyes) after clinical onset of visual impairment were imaged by OCT-A with scans centred on optic discs. Control group consisted of 6 eyes with no visual impairment.

RESULTS

The three affected individuals lost vision 6 years (at age 22 years), 2 years and 3 months (at age 26 years) and 1 year and 2 months (at age 30 years) prior to OCT-A examination. All five affected eyes had alterations in density of the radial peripapillary microvascular network at the level of retinal nerve fibre layer, including an eye of a patient treated with idebenone that underwent almost full recovery (best corrected visual acuity 0.87). Interestingly, the other eye showed normal ocular findings 14 months after onset. Results of OCT-A examination in this eye were unfortunately inconclusive due to a delineation error. At the level of the ganglion cell layer differences could be also noted, but only in two severely affected individuals. There were no differences between unaffected mutation carriers and control eyes.

CONCLUSION

Optical coherence tomography angiography scans confirmed that the peripapillary microvascular network is highly abnormal in eyes manifesting visual impairment due to LHON. These findings support the hypothesis that microangiopathy contributes to the development of vision loss in this mitochondrial disorder.

Leber hereditary optic neuropathy: current perspectives

Leber hereditary optic neuropathy (LHON) is one of the most common inherited optic neuropathies causing bilateral central vision loss. The disorder results from point mutations in mitochondrial DNA and subsequent mitochondrial dysfunction. The primary cell type that is lost in LHON is the retinal ganglion cell, which is highly susceptible to disrupted ATP production and oxidative stress. Inheritance of LHON follows that of mitochondrial genetics, and it has a highly variable clinical phenotype, as other genetic and environmental factors also play a role. Although LHON usually presents with isolated vision loss, some patients suffer other neurological sequelae. For ill-defined reasons, male LHON mutation carriers are more affected than females. Most LHON patients remain legally blind, but a small proportion can experience spontaneous partial recovery, often within the first year of symptom onset. Unfortunately, at this time there are no established curative interventions and treatment is largely supportive. Patients should be offered low vision services and counseled on mitigating risk factors for additional vision loss, such as smoking and consuming alcohol. Encouraging treatments currently undergoing investigation includes ubiquinone analogs, such as idebenone, as well as gene therapy and stem cells to restore ATP synthesis and provide neuroprotection to surviving retinal ganglion cells.

Unilateral visual loss in a previously healthy 15-year-old girl: monosymptomatic neuromyelitis optica?

We report a previously healthy 15 year old girl with acute onset of unilateral visual loss consistent with a diagnosis of monosymptomatic optic neuritis. Her symptoms responded well to the use of high-dose intravenous methylprednisolone. With very brief follow-up (2 months) she has had no subsequent difficulties. However, testing was positive for the presence of anti-aquaporin-4 antibodies in both serum and cerebrospinal fluid, which have been associated with neuromyelitis optica (NMO). While NMO antibodies lack complete sensitivity, there is high degree of specificity. Our patient does not meet currently accepted diagnostic criteria for NMO, but is likely at high-risk to develop myelitis or recurrent optic neuritis. There are no evidence-based guidelines for whether this patient should undergo disease-modifying treatment. Based upon the high-risk for clinical relapse, we have recommended immunosuppressive therapy with rituximab (anti-B cell monoclonal antibodies). While randomized trials for patients with this clinical scenario are unlikely, observational studies of a cohort of such patients would provide better guidance on the natural history and merits of disease-modifying therapy.

The pupil light reflex in Leber's hereditary optic neuropathy: evidence for preservation of melanopsin-expressing retinal ganglion cells

PURPOSE

To investigate the pupillary light reflex (PLR) of patients with severe loss of vision due to Leber's Hereditary Optic Neuropathy (LHON) in the context of a proposed preservation of melanopsin-expressing retinal ganglion cells (mRGCs).

METHODS

Ten LHON patients (7 males; 51.6 ± 14.1 years), with visual acuities ranging from 20/400 to hand motion perception and severe visual field losses, were tested and compared with 16 healthy subjects (7 males; 42.15 ± 15.4 years) tested as controls. PLR was measured with an eye tracker and the stimuli were controlled with a Ganzfeld system. Pupil responses were measured monocularly, to 1 second of blue (470 nm) and red (640 nm) flashes with 1, 10, 100, and 250 cd/m² luminances. The normalized amplitude of peak of the transient PLR and the amplitude of the sustained PLR at 6 seconds after the flash offset were measured. In addition, optical coherence topography (OCT) scans of the peripapillary retinal nerve fiber layer were obtained.

RESULTS

The patient's peak PLR responses were on average 15% smaller than controls (P < 0.05), but 5 out of 10 patients had amplitudes within the range of controls. The patients' sustained PLRs were comparable with controls at lower flash intensities, but on average, 27% smaller to the 250 cd/m² blue light, although there was considerable overlap with the PLR amplitudes of control. All patients had severe visual field losses and the retinal nerve fiber layer thickness was reduced to a minimum around the optic disc in 8 of the 10 patients.

CONCLUSIONS

The PLR is maintained overall in LHON patients despite the severity of optic atrophy. These results are consistent with previous evidence of selective preservation of mRGCs.

Disorders of the pupil

Pupil size is determined by the interaction of the parasympathetic and the sympathetic nervous system. The parasympathetic system conducts the light reaction with its major center in the dorsal midbrain. The sympathetic nervous system acts either directly on the dilator muscle (peripherally) or centrally by inhibiting the Edinger-Westphal nucleus. Psychosensory reactions are transmitted via the sympathetic system. The afferent input of the light reflex system in humans is characteristically wired, allowing a detailed analysis of a lesion of the afferent input. Even in humans a subgroup of ganglion cells containing melansopsin plays an important role as a light sensor for the pupillary system. To diagnose normal pupillary function, pupils need to be isocoric and react bilaterally equally to light. Anisocoria indicates a problem of the efferent pupillary pathway. Pupillary disorders may involve the afferent pathways (relative afferent pupillary defect) or the efferent pathways. Physiological anisocoria is a harmless condition that has to be distinguished from Horner's syndrome. In this case pharmacological testing with cocaine eye-drops is helpful. Disorders of the parasympathetic system will impair the light response. They include dorsal midbrain syndrome, third-nerve palsy, and tonic pupil. Tonic pupils are mainly idiopathic and do not need imaging. Disorders of the iris, including application of cholinergic agents, need also to be considered in impaired pupillary light reaction.

The neuro-ophthalmology of mitochondrial disease

Mitochondrial diseases frequently manifest neuro-ophthalmologic symptoms and signs. Because of the predilection of mitochondrial disorders to involve the optic nerves, extraocular muscles, retina, and even the retrochiasmal visual pathways, the ophthalmologist is often the first physician to be consulted. Disorders caused by mitochondrial dysfunction can result from abnormalities in either the mitochondrial DNA or in nuclear genes which encode mitochondrial proteins. Inheritance of these mutations will follow patterns specific to their somatic or mitochondrial genetics. Genotype-phenotype correlations are inconstant, and considerable overlap may occur among these syndromes. The diagnostic approach to the patient with suspected mitochondrial disease entails a detailed personal and family history, careful ophthalmic, neurologic, and systemic examination, directed investigations, and attention to potentially life-threatening sequelae. Although curative treatments for mitochondrial disorders are currently lacking, exciting research advances are being made, particularly in the area of gene therapy. Leber hereditary optic neuropathy, with its window of opportunity for timely intervention and its accessibility to directed therapy, offers a unique model to study future therapeutic interventions. Most patients and their relatives benefit from informed genetic counseling.

Prophylaxis for second eye involvement in leber hereditary optic neuropathy: an open-labeled, nonrandomized multicenter trial of topical brimonidine purite

PURPOSE

To test a topical agent with purported antiapoptotic properties as prophylactic treatment after first eye involvement in Leber hereditary optic neuropathy (LHON), a maternally-inherited disorder characterized by bilateral, often sequential, visual loss.

DESIGN

Open labeled, nonrandomized prospective pilot study.

METHODS

Nine primary mutation molecularly confirmed LHON patients with one eye vision loss for less than 6 months and normal visual function in the fellow eye were treated with brimonidine purite 0.15% (Alphagan P) 4 times daily in the unaffected eye for up to 2 years. Visual acuity was the primary efficacy outcome. Secondary measures included changes on automated perimetry and quantification of the relative afferent pupillary defect.

RESULTS

There were 8 men and 1 woman enrolled, aged 13 to 54 years (mean 32 years), eight with the 11778 mitochondrial DNA (mtDNA) mutation, and one with the 3460 mutation. Despite normal visual acuity at baseline in all patients, 7 patients had some minimal changes in the central visual field of the study eye. All patients had deterioration of vision in their second eye. In 1 of the 2 patients who had treatment initiated within 16 days after first eye involvement, good visual acuity was maintained in the study eye at 15 month followup, despite a mildly abnormal study eye baseline visual field.

CONCLUSIONS

LHON may be a bilateral condition at onset more frequently than appreciated, with asymmetric severity at presentation. Topical brimonidine purite in this dosage was unsuccessful in preventing second eye involvement in recently monocularly-symptomatic LHON.

Relative post-mortem sparing of afferent pupil fibers in a patient with 3460 Leber's hereditary optic neuropathy

BACKGROUND

Relative sparing of the pupillary reflexes in patients with leber's hereditary optic neuropathy (LHON) has been observed clinically. This study sought to test histologically whether retino-pupillary fibers are spared in LHON.

METHODS

Di-I, a fluorescein dye that allows anterograde labeling of axons, was injected into the brachium of the superior colliculus in post-mortem brain from a patient diagnosed with LHON (3460 mutation) and a normal control brain. After 4 weeks, serial fragmatome sections were obtained in the pretectal area and further stained with propidium iodide (PI stains DNA) to delineate the pretectal nuclei in the dorsal midbrain. Examination was performed under a confocal microscope. Optic nerves obtained from the above subjects were cut, mounted and stained with p-phenylenediamine (PPD) and trichrome stain for digital morphometry.

RESULTS

Di-I-labeled fibers were visible on all sections from the superior colliculus to the pretectum in the LHON and the control specimens, as were the nuclei in the cell bodies stained with PI. There was mild attenuation of the afferent pretectal fibers in LHON, but this was not as dramatic as the attenuation of the total population of fibers in the LHON optic nerve.

CONCLUSIONS

In our LHON patient, the preservation of retinofugal fibers to the pretectum lends support to the clinical observation of relatively preserved pupillary function in LHON.

Hereditary optic neuropathies

AIMS

To provide a clinical update on the hereditary optic neuropathies.

METHODS

Review of the literature.

RESULTS

The hereditary optic neuropathies comprise a group of disorders in which the cause of optic nerve dysfunction appears to be hereditable, based on familial expression or genetic analysis. In some hereditary optic neuropathies, optic nerve dysfunction is typically the only manifestation of the disease. In others, various neurologic and systemic abnormalities are regularly observed.

CONCLUSION

The most common hereditary optic neuropathies are autosomal dominant optic atrophy (Kjer's disease) and maternally inherited Leber's hereditary optic neuropathy. We review the clinical phenotypes of these and other inherited disorders with optic nerve involvement.

Pupil assessment in optic nerve disorders

BACKGROUND

The normal pupillary constriction to light is an involuntary reflex that can be easily elicited and observed without specialized equipment or discomfort to the patient. Attenuation of this reflex in optic nerve disorders was first described 120 years ago. Since then, pupil examination has become a routine part of the assessment of optic nerve disease.

CLINICAL TECHNIQUES

The original cover/uncover test compares pupillomotor drive in the two eyes, but requires two working pupils and is relatively insensitive. The swinging flashlight test is now the standard clinical tool to detect pupillomotor asymmetry. It requires only one working pupil, is easily quantified, and has high sensitivity in experienced hands, but interpretation of the results needs care. Measurement of the pupil cycle time is the only clinical test that does not rely on comparison with the fellow eye, but it can only be measured in mild to moderate optic nerve dysfunction, is more time consuming, and less sensitive.

LABORATORY TECHNIQUES

Infrared video pupillography allows recordings to be made of the pupil responses to full-field or perimetric light stimulation under tightly controlled conditions with a high degree of accuracy. Frustratingly, there is a wide range in reflex gain in normal subjects limiting its usefulness unless comparison is made with the fellow eye or stimulation of unaffected adjacent areas of the visual field.

CORRELATION WITH OTHER TESTS

In general, pupillomotor deficit shows good correlation with visual field deficit. However, some diseases of the optic nerve are associated with relative sparing either of pupil function or visual function implying that pupil tests and psychophysical tests may assess function in different subpopulations of optic nerve fibres. Less is known of the relationship between pupil measurements and electrodiagnostic tests.

USES IN CLINICAL PRACTICE

Pupil assessment is invaluable when distinguishing functional from organic visual loss. Its usefulness in distinguishing between different causes of optic neuropathy and as a prognostic sign is gradually emerging.

Clinical assessment of optic nerve disorders

Optic nerve disorders range from the manifestations of life-threatening intracranial or systemic disease, to minor congenital anomalies. Careful clinical assessment, which relies upon a thorough evaluation of symptoms as well as signs, is essential for effective and timely investigation and treatment. Examination methods and pitfalls to be avoided are discussed.

Physiology, assessment, and disorders of the pupil

Proper examination of the pupil provides an objective measure of the integrity of the pregeniculate afferent visual pathway and allows assessment of sympathetic and parasympathetic innervation to the eye. Infrared videography and pupillography are increasingly used to study the dynamic behavior of the pupil in common disorders, such as Horner's syndrome and tonic pupil.