Frontalis sling operation using silicone rod for the correction of ptosis in chronic progressive external ophthalmoplegia

Mitochondrial Chronic Progressive External Ophthalmoplegia

BACKGROUND

Chronic progressive external ophthalmoplegia (CPEO) is a rare disorder that can be at the forefront of several mitochondrial diseases. This review overviews mitochondrial CPEO encephalomyopathies to enhance accurate recognition and diagnosis for proper management.

METHODS

This study is conducted based on publications and guidelines obtained by selective review in PubMed. Randomized, double-blind, placebo-controlled trials, Cochrane reviews, and literature meta-analyses were particularly sought.

DISCUSSION

CPEO is a common presentation of mitochondrial encephalomyopathies, which can result from alterations in mitochondrial or nuclear DNA. Genetic sequencing is the gold standard for diagnosing mitochondrial encephalomyopathies, preceded by non-invasive tests such as fibroblast growth factor-21 and growth differentiation factor-15. More invasive options include a muscle biopsy, which can be carried out after uncertain diagnostic testing. No definitive treatment option is available for mitochondrial diseases, and management is mainly focused on lifestyle risk modification and supplementation to reduce mitochondrial load and symptomatic relief, such as ptosis repair in the case of CPEO. Nevertheless, various clinical trials and endeavors are still at large for achieving beneficial therapeutic outcomes for mitochondrial encephalomyopathies.

KEY MESSAGES

Understanding the varying presentations and genetic aspects of mitochondrial CPEO is crucial for accurate diagnosis and management.

An Adjustable Magnetic Levator Prosthesis for Customizable Eyelid Reanimation in Severe Blepharoptosis II: Randomized Evaluation of Angular Translation

Purpose

Examine the effect of force modulation via angular translation of a static magnetic field for customizable treatment of severe blepharoptosis.

Methods

Prototype adjustable-force magnetic levator prostheses (aMLP) consisted of a spectacle-mounted magnet in rotatable housing and small eyelid-attached magnets embedded in a biocompatible polymer. Interpalpebral fissure (IPF) of 17 participants with severe blepharoptosis was continuously measured for one minute at five spectacle magnet angles, with order randomized and participant and data analyst masked. The hypothesis that angular position affected opening IPF (o-IPF), minimum blink IPF (m-IPF), and comfort ratings (1-10) was tested.

Results

The aMLP improved o-IPF from 4.5 mm without the device to 6.2 mm on the lowest force setting (P < 0.001) and 7.1 mm on the highest setting (P < 0.001) and allowed for complete volitional blink regardless of setting (average m-IPF 0.4 mm and no change with aMLP; P = 0.76). Spontaneous blink without the device (2.0 mm) was affected on the highest force setting (m-IPF 3.9 mm; P < 0.001) but only marginally so on the lowest setting (3.0 mm; P = 0.06). Comfort (7.6/10) did not vary with the angle (P > 0.36). Profile analysis found substantial individual responses to angle (P < 0.001), confirming the value of customization.

Conclusions

Angular translation provided adjustable force, which had a statistically and clinically meaningful impact on eye opening and the completeness of the spontaneous blink. This quantitative evidence supports continued use of the angular translation mechanism for force adjustment in the customizable magnetic correction of severe blepharoptosis.

Translational Relevance

Evidence for the benefit of customizable magnetic force via angular translation in a larger sample of participants than reported previously.

Mitochondria and the eye-manifestations of mitochondrial diseases and their management

Historically, distinct mitochondrial syndromes were recognised clinically by their ocular features. Due to their predilection for metabolically active tissue, mitochondrial diseases frequently involve the eye, resulting in a range of ophthalmic manifestations including progressive external ophthalmoplegia, retinopathy and optic neuropathy, as well as deficiencies of the retrochiasmal visual pathway. With the wider availability of genetic testing in clinical practice, it is now recognised that genotype-phenotype correlations in mitochondrial diseases can be imprecise: many classic syndromes can be associated with multiple genes and genetic variants, and the same genetic variant can have multiple clinical presentations, including subclinical ophthalmic manifestations in individuals who are otherwise asymptomatic. Previously considered rare diseases with no effective treatments, considerable progress has been made in our understanding of mitochondrial diseases with new therapies emerging, in particular, gene therapy for inherited optic neuropathies.

Healthcare resource utilization of patients with mitochondrial disease in an outpatient hospital setting

BACKGROUND AND OBJECTIVES

Mitochondrial diseases present as multi-system disorders requiring a comprehensive multidisciplinary approach. The data on healthcare resource utilization associated with mitochondrial diseases and the clinical drivers of these costs are limited including for the out-patient setting where the majority of the clinical care for mitochondrial disease patients occurs. We performed a cross-sectional retrospective study of out-patient healthcare resource utilization and costs for patients with a confirmed diagnosis of mitochondrial disease.

METHODS

We recruited participants from the Mitochondrial Disease Clinic in Sydney and stratified them into three groups: those with mitochondrial DNA (mtDNA) mutations (Group 1), those with nuclear DNA (nDNA) mutations and the predominant phenotype of chronic progressive external ophthalmoplegia (CPEO) or optic atrophy (Group 2) and those without a confirmed genetic diagnosis but clinical criteria and muscle biopsy findings supportive of a diagnosis of mitochondrial disease (Group 3). Data was collected through retrospective chart review and out-patient costs were calculated using the Medicare Benefits Schedule.

RESULTS

We analyzed the data from 91 participants and found that Group 1 had the greatest average out-patient costs per person per annum ($838.02; SD 809.72). Neurological investigations were the largest driver of outpatient healthcare costs in all groups (average costs per person per annum:-Group 1: $364.11; SD 340.93, Group 2: $247.83; SD 113.86 and Group 3: $239.57; SD 145.69) consistent with the high frequency (94.5%) of neurological symptoms. Gastroenterological and cardiac-related out-patient costs were also major contributors to out-patient healthcare resource utilization in Groups 1 and 3. In Group 2, ophthalmology was the second-most resource intensive specialty ($136.85; SD 173.35). The Group 3 had the greatest average healthcare resource utilization per person over the entire duration of out-patient clinic care ($5815.86; SD 3520.40) most likely due to the lack of a molecular diagnosis and a less customized management approach.

CONCLUSION

The drivers of healthcare resource utilization are dependent on the phenotype-genotype characteristics. Neurological, cardiac, and gastroenterological costs were the top three drivers in the out-patient clinics unless the patient had nDNA mutations with predominant phenotype of CPEO and/or optic atrophy wherein ophthalmological-related costs were the second most resource intensive driver.

A review of surgical management of progressive myogenic ptosis

PURPOSE

Surgical correction of myogenic ptosis is a sophisticated endeavor, as the disease is progressive and the post-operative course is prone to significant complications. We sought to review the literature for repair techniques in different types of myogenic ptosis.

METHODS

A PubMed/MEDLINE literature search of publications pertaining to surgical outcomes of progressive myogenic ptosis repair was performed. Studies included were original retrospective studies with a minimum of four patients.

RESULTS

A total of 27 articles were identified and divided by etiology of myogenic ptosis; either chronic progressive external ophthalmoplegia (CPEO), oculopharyngeal muscular dystrophy (OPMD), myasthenia gravis (MG), or mixed. Surgical techniques predominantly involved levator advancement, levator resection, frontalis sling, blepharoplasty, and Fasanella-Servat. Success rates ranged from 60.5% to 100%. Significant postoperative complications included ptosis recurrence, under-correction, over-correction, keratopathy, lagophthalmos, sling exposure, and sling infection.

CONCLUSION

Like surgical repair for other forms of ptosis, correction of progressive myogenic ptosis is guided by levator excursion. However, myogenic ptosis is especially challenging as it is characterized by worsening ptosis and the loss of protective corneal mechanisms. The goals of care with myogenic ptosis involves repairing ptosis just sufficiently to alleviate visual obstruction while avoiding adverse post-operative complications. This intentional under-correction subsequently increases susceptibility for ptosis recurrence. Myogenic ptosis repair therefore requires delicate balancing between function, sustained repair, and corneal protection.

Frontalis Suspension in Muscular Dystrophy: 16-years Follow-up

Acquired eyelid ptosis in adults, with complete loss of levator palpebrae superiosis function, can be a challenging problem to diagnose and treat. A 48-year-old woman with chronic bilateral severe blepharoptosis of 10 years duration is presented, whose neurological investigations excluded myasthenia gravis. The patient was preliminarily diagnosed with chronic progressive external ophthalmoplegia. The levator excursion was negligible, and a frontalis suspension procedure was considered using a conventional autogenous fascia lata graft. An optimal outcome was achieved with over 16-years follow-up. Although the patient was healthy otherwise upon first presentation, 10 years later, she developed other neurologic manifestations, including dysphagia and oral dryness. The fact that blepharoptosis did not recur over the years in this case differentiates an oculo-pharyngeal type of muscular dystrophy in this patient from other types and from the more frequent condition of chronic progressive external ophthalmoplegia.

Frontalis Sling Using a Silicone Rod for Ptosis in Third Nerve Palsy: Cosmesis Versus Safety

Purpose

To evaluate the results of the frontalis sling operation using a silicone rod for the correction of ptosis in patients with third nerve palsy with a focus on corneal safety.

Methods

Patients with third nerve palsy who underwent the frontalis sling operation using a silicone rod between 2008 and 2019 were included in this study. The medical records of all patients were reviewed, and their clinical characteristics and postoperative outcomes were analyzed. In this retrospective, interventional case series, the main outcome measures were eyelid contour, eyelid height by margin reflex distance, and corneal status.

Results

Twenty-four eyes of 18 patients (12 male and six female patients) were included. The mean age at the time of surgery was 35.1 years (range, 5–64 years). Twelve patients underwent a unilateral ptosis operation, and six patients received a bilateral ptosis operation. The mean follow-up period was 32.1 months (range, 2–87 months). Most patients (21 of 24 eyes, 88%) showed poor Bell’s phenomenon on preoperative examination. Satisfactory eyelid height and eyelid contour were achieved in almost all patients (mean postoperative margin reflex distance, +1.2 mm) postoperatively. Although corneal erosions were detected for several months in eight of 24 eyes after surgery, these findings were well controlled medically with artificial tear eye drops and ointments.

Conclusions

Frontalis sling surgery using a silicone rod can safely and effectively correct ptosis without severe corneal complications in patients with third nerve palsy. Our study outlines a new method to define the postoperative safety outcome by specifically focusing on categorized corneal status.

Strabismus in chronic progressive external ophthalmoplegia

PURPOSE

To elucidate the patterns of strabismus and ophthalmoplegia associated with chronic progressive external ophthalmoplegia (CPEO) confirmed by mitochondrial DNA (mtDNA) deletions in Asians.

METHODS

A total of 10 patients confirmed to have mtDNA deletion associated with CPEO were included. Long-range PCR encompassing the entire mtDNA was carried out. In the cases with mtDNA deletion, the exact deletion ranges of mtDNA were identified by sequencing. A full ophthalmologic examination including prism and alternate cover test in the primary position, evaluation of ductions and versions, and binocularity was performed in 10 patients with confirmed mtDNA deletions associated with CPEO.

RESULTS

All of the patients showed ophthalmoplegia as well as ptosis, even after eyelid surgeries. Ophthalmoplegia was symmetric between both eyes in nine patients (90%) while one patient (10%) showed asymmetric ophthalmoplegia with esotropia and left hypotropia. Among the nine patients with symmetric involvement, four patients (44%) showed exotropia, three (33%) had exotropia with vertical deviation, and the remaining two patients (22%) showed orthotropia. Five out of 10 patients (50%) complained of diplopia associated with strabismus, four of whom (80%) had vertical deviation. Three out of five patients (60%) without diplopia showed exotropia of 20 prism diopters (PD) to 50 PD.

CONCLUSIONS

Exotropia with/without vertical deviation is the most common form of strabismus in Asian patients with CPEO and only one of them showed a small angle of esotropia. Ophthalmoplegia could be asymmetric in 10% of CPEO patients.

Neuro-ophthalmic manifestations of mitochondrial disorders and their management

The visual system has high metabolic requirements and is therefore particularly vulnerable to mitochondrial dysfunction. The most commonly affected tissues include the extraocular muscles, photoreceptors, retinal pigment epithelium, optic nerve and visual cortex. Hence, the most common manifestations of mitochondrial disorders are progressive external ophthalmoplegia, macular pattern dystrophy, pigmentary retinopathy, optic neuropathy and retrochiasmal visual field loss. With the exception of Leber hereditary optic neuropathy and stroke-like episodes seen in mitochondrial encephalopathy, lactic acidosis and stroke-like episodes, the majority of neuro-ophthalmic manifestations have an insidious onset. As such, some patients may not recognize subtle progressive visual symptoms. When mitochondrial disorders are highly suspected, meticulous examination performed by an ophthalmologist with targeted ancillary testing can help confirm the diagnosis. Similarly, neuro-ophthalmic symptoms and signs may be the first indication of mitochondrial disease and should prompt systemic investigations for potentially life-threatening associations, such as cardiac conduction defects. Finally, the ophthalmologist can offer symptomatic treatments for some of the most disabling manifestations of these disorders.

Safety and Efficacy of the Under-Corrected Frontalis Sling in Myogenic Ptosis Accompanying Extraocular Muscle Paralysis

OBJECTIVE

The surgical treatment of myogenic ptosis accompanying extraocular muscle paralysis is an intractable problem in the field of oculoplastic surgery due to the severe complications such as exposure keratopathy. It is promising to find an appropriate procedure to treat this kind of patients, which is able to ensure the safety and efficacy.

METHODS

The authors retrospectively reviewed 12 eyes of 6 patients who underwent the under-corrected "double V-Loop" frontalis suspension sling procedure for myogenic ptosis accompanying extraocular muscle paralysis and access the safety and efficacy of this kind of surgery. All the patients underwent corneal fluorescein staining and confocal microscopy before and after the surgery to inspect the corneal condition. The density of central corneal epithelial cells and endothelial cells were observed.

RESULTS

After the surgery, the eyelids contour was natural, and the symmetry was achieved in these cases. The average palpebral fissures height changed from 2.75 ± 1.41 mm to 4.50 ± 0.35 mm (P = 0.0007) and margin reflex distance 1 changed from -1.25 ± 1.22 mm to +0.50 ± 0.35 mm (P = 0.0002). Out of 12 operated eyes, mild postoperative lagophthalmos was present in 4 cases but without exposure keratopathy during the follow-up, the confocal microscopy showed that there were no significant differences in central corneal superficial epithelial cells (P = 0.93) and endothelial cells (P = 0.90) before and after the surgery.

CONCLUSION

The under-corrected "double V-Loop" frontalis suspension sling is a proper surgery in myogenic ptosis accompanying extraocular muscle paralysis, which leads to a low occurrence of exposure keratopathy, maintains the integrity of the cornea, and remains the patients' vision function.

Frontalis Linkage Without Intraoperative Eyelid Elevation for the Management of Myopathic Ptosis

PURPOSE

To report the effect of frontalis linkage without intraoperative eyelid elevation for the management of myopathic ptosis.

METHODS

Retrospective analysis of 21 (42 eyelids) myopathic patients with bilateral ptosis who were operated between 1999 and 2017. All patients had orbicularis weakness and poor or absent Bell's phenomenon. Surgery consisted of using an autogenous fascia sling to link the tarsal plate to the frontalis muscle without any degree of intraoperative eyelid elevation. The main outcome measures were margin reflex distance, brow height and degree of brow excursion and degree of lagophthalmos, and exposure keratitis.

RESULTS

After surgery, there were significant changes (p <0.0001) in both margin reflex distance and brow position. Mean margin reflex distance increased to 1.4 mm ± 1.34 DP and with full frontalis contraction, it reached 3.0 mm ± 1.73 DP, while mean brow position decreased 1.6 mm ± 1.59 SD, p < 0.0001. Postoperative lagophthalmos was not detected in 31 (74%) eyes. In the remaining 11 eyes (26%), lagophthalmos ranged from 1.2 to 5.2 mm (mean = 1.7 mm ± 0.74 DP). Mild inferior superficial keratitis was detected in 14 eyes (33.3%) of 7 patients only 3 of which had lagophthalmos. One patient needed additional surgery to correct unilateral eyelid retraction. Overall, 81.81% of the patients were pleased with the procedure.

CONCLUSIONS

Myopathic ptosis can be alleviated with a minimal amount of lagophthalmos by just linking the tarsal plate to the frontalis muscle without lifting the eyelid margin intraoperatively.

Efficacy of frontalis suspension with silicone rods in ptosis patients with poor Bell's phenomenon

PURPOSE

The purpose of the study was to evaluate the efficacy of silicone rods as frontalis sling for correction of ptosis associated with poor Bell's phenomenon in specific situations.

MATERIALS AND METHODS

A retrospective interventional case series of 25 eyes of 19 patients who underwent frontalis suspension surgery with silicone rods for ptosis correction from May 2006 to April 2011, was performed. Inclusion criteria included severe ptosis with poor Bell's phenomenon. Patient evaluation included clinical history and other relevant parameters of ptosis measurement. Final outcome measurements included postoperative lid height, lagophthalmos, complications, need for reoperation, and patient satisfaction.

RESULTS

Mean age at presentation was 25.72 ± 2.2 years. The sex ratio of male: female was 1.11. The causes of ptosis included chronic progressive external ophthalmoplegia (CPEO) in 11 eyes (44%), oculopharyngeal dystrophy in 2 (8%), third cranial nerve palsy in 7 (28%), traumatic in three eyes (12%), and iatrogenic postoperative ptosis (after orbital tumor excision) in two eyes (8%). The postoperative palpebral fissure height and margin reflex distance improved significantly (P = 0.0001). Extrusion of the sling and granuloma formation occurred in two eyes each, and these patients had to undergo sling removal. One patient developed mild exposure keratopathy and was managed conservatively.

CONCLUSION

Silicone is an effective material for use in frontalis suspension in the management of severe ptosis with poor Bell's phenomenon. The elastic nature of silicone rod makes it an ideal suspensory material for patients with CPEO or third nerve palsy.

Mitochondrial disease: genetics and management

Mitochondrial disease is one of the most common groups of genetic diseases with a minimum prevalence of greater than 1 in 5000 in adults. Whilst multi-system involvement is often evident, neurological manifestation is the principal presentation in most cases. The multiple clinical phenotypes and the involvement of both the mitochondrial and nuclear genome make mitochondrial disease particularly challenging for the clinician. In this review article we cover mitochondrial genetics and common neurological presentations associated with adult mitochondrial disease. In addition, specific and supportive treatments are discussed.

Levator resection in the management of myopathic ptosis

Purpose

To evaluate the results of levator resection in patients with myopathic ptosis.

Methods

The medical records of consecutive patients who underwent levator resection surgery performed for myopathic ptosis between October 2009 and March 2013 were reviewed. Indications for surgery were ptosis obscuring the visual axis and margin-reflex distance ≤2 mm. Surgical success was defined as clear pupillary axis when the patient voluntarily opened his eye and margin-reflex distance ≥3 mm. We analyzed the effect of levator function and Bell's phenomenon on the rates of success and corneal complication.

Results

This series included six male and six female patients. Levator function was between 4 and 12 mm. We performed bilateral levator resection surgery in all patients. The mean follow-up time was 14.8 months (range, 6 to 36 months). No patient was overcorrected. Adequate lid elevation was achieved after the operation in 20 eyes. Ptosis recurred in three out of 20 eyes after adequate lid elevation was achieved. Our overall success rate was 70.8%. In three eyes with poor Bell's phenomenon, corneal irritation and punctate epitheliopathy that required artificial eye drops and ointments developed in the early postoperative period, although symptoms resolved completely within 2 months of the resection surgery. No patients required levator recession or any other revision surgery for lagophthalmos or corneal exposure after levator resection.

Conclusions

Levator resection seems to be a safe and effective procedure in myopathic patients with moderate or good Bell's phenomenon and levator function greater than 5 mm.

The 18-gauge needle: an innovative simple tool for frontalis sling surgery

PURPOSE

The aim of this study was to introduce the use of the 18-gauge hypodermic needle as a simple and cost-effective alternative tool in frontalis silicone suspension ptosis surgery.

METHODS

A retrospective, interventional, noncomparative case study was performed by reviewing 64 patients (82 eyes) who underwent this technique between February 2010 and January 2011. Patients with simple, severe congenital ptosis with poor levator excursion were included in the study. Patients with prior sling and levator resection surgery were excluded. All patients underwent unilateral or bilateral frontalis sling surgery with a silicone rod placed via a closed-incision pentagonal configuration. All surgeries were performed by a single surgeon at a tertiary referral institute using the 1.5 inch hypodermic 18-gauge needle as an insertion guide for the silicone rod. Intraoperative technique, ease of surgical maneuverability, operative time, and postoperative results and complications were noted.

RESULTS

The mean patient age was 10.3 years (range: 1-28 years). Fifty-six of 64 patients (87.5%) were between the ages of 1 and 18 years (mean: 8.5 years), and 8 of 64 (12.5%) between 9 and 28 years (mean: 23 years). Forty-two of 64 (65.7 %) patients were female and 22 of 64 (34.4%) were male. Forty-six of 64 (71.9%) patients underwent unilateral frontalis sling surgery and 18 of 64 (28.1%) patients underwent bilateral surgery. Follow up ranged from 12 to 18 months. In 2 of the 82 eyes (2.4%), the sharp end of the needle cut the silicone rod while introducing the needle from the medial suprabrow stab incision to the eyelid margin end in a closed technique, requiring replacement of the silicone rod. Average surgical time was 15 minutes for unilateral cases and 30 minutes for bilateral cases. The main advantages noted intraoperatively were the small incisions that allowed for less operative time and minimal bleeding, easy maneuverability and control of the needle during tissue passage, and smooth threading of the silicone rod. Blunting of the tip is also eliminated as the needles are disposable.

CONCLUSIONS

The 18-gauge hypodermic needle is a simple and cost-effective alternative to other needles used in frontalis silicone sling ptosis surgery. Its low cost and easy accessibility make it a particularly quick and useful option in community-based practices, tertiary referral centers, and large medical eye camps globally.

Exposure keratopathy following silicone frontalis suspension in adult neuro- and myogenic ptosis

PURPOSE

To evaluate the incidence of exposure keratopathy following silicone frontalis suspension in adult neuro- and myogenic blepharoptosis.

METHOD

Retrospective noncomparative analysis of the charts of 69 cases (101 eyelids) of silicone frontalis suspension.

RESULTS

Sixty-one patients (93 eyelids) had myogenic ptosis, and eight patients (eight eyelids) had neurogenic ptosis. Preoperative diagnoses included chronic progressive external ophthalmoplegia, myotonic dystrophy, oculopharyngeal dystrophy, third cranial nerve palsy because of trauma or other causes. Average age at the time of operation was 54. Mean interval between the intervention and the first and second postoperative control was 8 and 28 months, respectively. Thirty-one patients (31 eyelids) needed a second follow-up visit. Postoperative punctate epithelial erosions (PEE) were encountered most frequently in patients with Steinert's disease (42% of eyes) and congenital ptosis (33% of eyes). Patients with oculopharyngeal dystrophy did not develop PEE. Corneal ulceration developed in three eyes (two patients): one eye was successfully treated with local antibiotic ointments and lubricants, a bilateral corneal ulceration in the second patient was successfully treated with partial conjunctival grafts.

CONCLUSION

This study cohort demonstrated a 26% risk of exposure keratopathy following silicone frontalis suspension. The risk of major corneal complications, such as ulceration, was low (3%).

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.

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.