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HomemipatientToxic Optic Neuropathy: An Unspoken Cause of Vision Loss

Toxic Optic Neuropathy: An Unspoken Cause of Vision Loss

An important piece of information provided by the husband of Vanessa*, a patient presenting with a puzzling decline in vision, was the key to her diagnosis.

Vanessa, a 51-year-old woman, returned for review complaining of reduced vision, photophobia and difficulty focussing after two years of working at home due to the COVID-19 pandemic. She was last seen six years prior, and at the time had been experiencing some difficulty at near. Progressive spectacles were discussed, however Vanessa elected to continue with single vision distance spectacles.

A thorough history should be taken when there is a suspected optic neuropathy – including substance use, environment, and diet

Vision with her spectacles of prescription R -5.25/-2.00×6 and L -5.25/-2.50×17 was R 6/30 and L 6/38. At her last review six years ago, spectacle acuities had been R & L 6/7.5.

Subjective refraction revealed no change, and no improvement was found with pinhole.

Colour vision was reduced slightly L>R, and pupil reactions were slightly sluggish, but there was no relative afferent pupil defect (RAPD) noted. Intraocular pressures were R & L 15mmHg.

Anterior eye examination revealed mild anterior cortical and nuclear lenticular changes in the right eye and moderate in the left. The tear film was mucoid, oily and unstable, with significant meibomian gland dysfunction in both eyes, but there was minimal corneal staining noted.

Figure 1 and 2. Mydriatic fundus examination
revealed healthy tilted optic nerves, maculae
and blood vessels.

Mydriatic fundus examination revealed healthy tilted optic nerves, maculae and blood vessels (Figures 1 and 2). No changes were noted from the last review. Optical coherence tomography (OCT) revealed no abnormalities with flat maculae in both eyes (Figure 3).

Visual field examination was normal, however reliability indices were poor (Figure 4).

Vanessa’s decline in vision was puzzling – the lenticular changes and ocular surface were impaired but not at the level to explain her decline in vision. She was advised to perform dry eye therapy in the form of hot compresses, lid scrubs and ocular lubrication, and was referred on for further investigation and consideration for possible cataract surgeries.

Her surgeon agreed that the bilateral decline in vision was unexpected – and MRI and CT testing was ordered to rule out compressive lesions in the visual pathway.

At this point, Vanessa’s husband, also a patient of the practice, made contact to inform us that she had been consuming alcohol heavily – at least one bottle of wine daily, but frequently more. She was diagnosed as having toxic optic neuropathy as a result of excessive alcohol consumption and referred on for blood tests to assess for nutritional or vitamin deficiencies and also referred for counselling.

She was reviewed six months later. She had ceased drinking and her tear film had improved slightly, however her vision only made a mild recovery to R 6/18 and L 6/24-.

TOXIC AND NUTRITIONAL OPTIC NEUROPATHIES

Toxic and nutritional optic neuropathies can arise from drug and substance abuse or malnutrition. They normally present bilaterally, producing a symmetric, painless, progressive loss of vision with dyschromatopsia. Pupil reactions may be sluggish, and a RAPD is not normally noted. The fundus may appear normal with few abnormalities noted – the optic nerve may appear normal, but may also present as swollen, hyperaemic and may produce temporal disc pallor in later stages. Visual acuities and contrast sensitivity are reduced and there may be central or centrocecal scotoma in the visual field. Loss of retinal nerve fibres on OCT may be observed. Sufferers may also experience photophobia and poor dark adaptation.

The pathophysiology of toxic optic neuropathy is multifactorial but not fully understood. Substances, such as alcohol and tobacco produce toxic effects, impairing the tissue’s vascular supply or metabolism, as well as leading to malnutrition by impairing the absorption of essential vitamins and nutrients. Chronic exposure to toxic agents can lead to malnutrition and vitamin B-complex vitamins – in particular cyanocobalamin (Vitamin B12) and thiamine (Vitamin B1) – and folate deficiencies. These deficiencies can cause formic acid and cyanide to accumulate, disrupting electron transport chain and mitochondrial function and subsequent optic neuropathy.

Figure 3. OCT revealed no abnormalities with flat maculae in both eyes.

Differential diagnoses include non-arteritic anterior ischemic optic neuropathy, Leber’s hereditary optic neuropathy, lesions in the optic chiasm, inflammatory or demyelinating optic neuropathies, maculopathies or macular dystrophies and retinal degenerations.

The Australian National Health and Medical Research Council recommend no more than ten standard drinks a week and no more than four standard drinks in any one day. Each bottle of wine contains between 7.5–8 standard drinks. For someone who enjoys a glass of wine, the maths is glaringly too simple.

The COVID-19 pandemic turned our worlds upside-down, causing stress, fear and anxiety in many. Heightened stress levels can result in behavioural changes such as increase in alcohol, smoking and other substance consumption, with women being generally more likely to drink in response to stress.

One in five adults in Australia reported increased alcohol consumption during the COVID-19 pandemic. Increased consumption was reported to be higher in women than men, with the greatest increase being those in the mid-age range, and associated with those suffering from depression and anxiety.3

Figure 4. Visual field examination was normal.

Toxic and nutritional optic neuropathies present a diagnostic challenge in many cases as the symptoms often far outweigh the signs. A thorough history should be taken when there is a suspected optic neuropathy – including substance use, environment, and diet. Alcoholics may not be forthcoming or be defensive about their drinking habits due to the stigma associated. However, many may not realise they have a problem and while there is knowledge that heavy alcohol consumption can cause other severe health complications including stroke, liver damage, development of cancers, disorders of the heart and cardiovascular system, peripheral and central nervous system including optic neuropathy, many may believe they will be unaffected, especially as alcohol in moderation in Australia is an accepted social norm.

Treatment of toxic optic neuropathy includes abstinence from the toxic agent as well as vitamin supplementation. In cases detected early enough, vision may recover, however the damage may be irreversible, as it was in Vanessa’s case. Prognosis is dependant on the extent of exposure, duration of symptoms and time before treatment initiation.

Much of our diagnosis occurs before we even measure vision or look at the eye, as we have been trained to be diagnostic detectives. Careful history can usually point us towards the solution, and I have to admit that after history, I thought Vanessa was a simple case of presbyopia, myopic progression and dry eye from prolonged time indoors and near work. However, her case simply did not make sense – the degree of vision loss was not accounted for by the slightly abnormal signs, and further investigation was required. Unfortunately for Vanessa, her drinking habits caused irreversible damage to her eyes but, fortunately, it was the impetus to give up alcohol and she is now in a better space mentally and physically.

Vanessa’s husband, Jason*, is a long-standing keratoconic patient of our practice who I have gotten to know well as he attends frequently for his contact lenses. I see their two sons and have literally watched them grow from shorter than me to towering over me in physical stature. As we had an established relationship, Jason felt comfortable speaking to me about his wife’s drinking habits.

As an optometrist, asking about someone’s drinking habits may not come intuitively, however the eyes that we care for are connected to a body and that body belongs to a person. The world we live in right now holds great uncertainty and trepidation for many. We are health care professionals and play an important role in many of our patients’ lives. Today there is much conversation about mental health and there will be times when we need to be comfortable with asking our patients if they ‘are ok?’. We also need to be ok with dealing with the uncomfortable situation when they are not.

* Patient names changed for anonymity. 

Jessica Chi is the director of Eyetech Optometrists, an independent speciality contact lens practice in Melbourne. She is the current Victorian, and a past national president of the Cornea and Contact Lens Society, and an invited speaker at meetings throughout Australia and beyond. She is a clinical supervisor at the University of Melbourne, a member of Optometry Victoria Optometric Sector Advisory Group and a Fellow of the Australian College of Optometry, the British Contact Lens Association and the International Academy of Orthokeratology and Myopia Control. 

References 

  1. Baj J, Forma A et al. “Toxic and Nutritional Optic Neuropathies – An Updated Mini-Review“ Int. J. Environ. Res. Public Health 2022, 19, 3092. 
  2. Chiotoroiu SM et al. Tobacco-alcohol optic neuropathy – clinical challenges in diagnosis. Journal of Medicine and Life. 7(4)Oct-Dec 2014 pp.472-476 
  3. Tran, T. et al. (2020), “Alcohol use and mental health status during the first months of COVID-19 pandemic in Australia”, Journal of Affective Disorders, Vol. 277, pp. 810-813,