The Management of Strabismus in Patients with Chronic Progressive External Ophthalmoplegia

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.

Botilinum toxin in the treatment of strabismus

Introduction: Strabismus is an oculomotor imbalance that occurs in 0.5 to 5% of the population. There are various etiopathogenetic theories and several modalities of treatment. One of these modalities is the application of botulinum toxin intramuscularly. This chemodenervation causes temporary muscle paresis which acts as a recession while its antagonist contracts. This achieves a temporary correction of strabismus. However, further research is needed. The aim of the paper was evaluation of published research studies on botulinum toxin as a treatment option in strabismus, as a primary and adjuvant therapy and as a preventive therapy in patients with abducens nerve palsy. For this purpose, we searched the major databases of the medical publications Medline and Pubmed, using keywords: strabismus, botulinum toxin. We found more than 50 articles related to our search for the last 30 years, 30 of which have been used for this review. In this review paper we have presented the most important insights from the literature, as well as our opinions and insights on the topic. Although further studies are needed regarding dosing as well as avoiding side effects, botulinum toxin has been shown to be a good alternative and adjunctive therapy to strabismus surgery, with the downside being that the effect is temporary. Positive effects and faster recovery have also been shown in patients with abducens nerve palsy.

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.

Clinical features of mtDNA-related syndromes in adulthood

Mitochondrial diseases are the most common inheritable metabolic diseases, due to defects in oxidative phosphorylation. They are caused by mutations of nuclear or mitochondrial DNA in genes involved in mitochondrial function. The peculiarity of "mitochondrial DNA genetics rules" in part explains the marked phenotypic variability, the complexity of genotype-phenotype correlations and the challenge of genetic counseling. The new massive genetic sequencing technologies have changed the diagnostic approach, enhancing mitochondrial DNA-related syndromes diagnosis and often avoiding the need of a tissue biopsy. Here we present the most common phenotypes associated with a mitochondrial DNA mutation with the recent advances in diagnosis and in therapeutic perspectives.

Mitochondrial disorders and the eye

Mitochondria are cellular organelles that play a key role in energy metabolism and oxidative phosphorylation. Malfunctioning of mitochondria has been implicated as the cause of many disorders with variable inheritance, heterogeneity of systems involved, and varied phenotype. Metabolically active tissues are more likely to be affected, causing an anatomic and physiologic disconnect in the treating physicians' mind between presentation and underlying pathophysiology. We shall focus on disorders of mitochondrial metabolism relevant to an ophthalmologist. These disorders can affect all parts of the visual pathway (crystalline lens, extraocular muscles, retina, optic nerve, and retrochiasm). After the introduction reviewing mitochondrial structure and function, each disorder is reviewed in detail, including approaches to its diagnosis and most current management guidelines.

The Use of Botulinum Toxin in Strabismus Treatment

There is a long and extensive experience with the use of Botulinum Toxin type A (BoNT-A) injection in the treatment of different types of strabismus and oculomotor palsies. The frequency of its use varies depending on the country and institution. It is a short procedure, may reduce general anesthesia exposure, causes minimal scarring compared to surgery, and can be proposed as an early treatment in unstable strabismus. Over many years, the experience of using BoNT-A indications has been refined and new applications have been reported. The use of BoNT-A in the postoperative period, after strabismus surgery or during surgery, can also be beneficial.

Strabismus surgery for diplopia in chronic progressive external ophthalmoplegia

BACKGROUND

To report midterm outcomes of strabismus strategy for management of diplopia in chronic progressive external ophthalmoplegia and specific surgical planning rationale.

DESIGN

Retrospective interventional case series.

RESULTS

Two patients, a 26-year-old male and a 36-year-old female, diagnosed with chronic progressive external ophthalmoplegia presented with blepharoptosis and intermittent diplopia. Ocular motility examination was significant for bilateral profound impairment of adduction with relative preservation of abduction, infraduction and elevation. Control of intermittent exotropia gradually worsened over 3 and 1.5 years of follow-up, respectively, in the presence of documented stability of the angle of exodeviation. Strabismus surgery involving modest amounts of bilateral medial rectus resection and lateral rectus recessions was undertaken. Surgical intervention was successful in controlling alignment in primary position and alleviating diplopia and asthenopia after 9 and 8 years of follow-up time, respectively, despite slow progression of ophthalmoplegia.

CONCLUSION

Bilateral selective impairment of adduction and intermittent exotropia may be the presenting ocular motility disturbance in chronic progressive external ophthalmoplegia. Properly designed strabismus surgery may provide sustainable, in the midterm, control of alignment and symptomatic relief in selected patients with CPEO.