Congruous homonymous hemianopia due to occipital lobe infarction

Optic disorder in which the visual fi eld defects in both eyes are completely symmetric in extent and intensity are defi ned as Congruous homonymous hemianopia. Here is such a case that I followed early this year. A sixtyfi ve years old male, diabetic since 1994, Hypertensive for 14 years and ischemic heart disease for 10 years under ayurvedic treatment reported with a history of fall from the bed while sleeping in the midnight 11th &12th February 2020 and found himself fully blurred bilateral vision with severe headache on the morning of 15th. After a local consultation and laser therapy attempt did not benefi t, he landed in Bangalore. Suspecting diabetic Retinopathy, we took him to Narayana Netralaya a super-specialty eye hospital. Detailed examination by a retina specialist confi rmed right homonymous hemianopia with no signifi cant Retinal fi ndings to explain the defective vision. An MRI Brain and Orbit plain and contrast was ordered, that revealed Subacute Ischemic Infarct in Bilateral PCA territory. Other investigations did indicate uncontrolled diabetes hypertension and evidence of Ischemic Heart Diseases S/P PTCA. The case was referred to a neuro-physician who put him on Inj. Perfalgan 1 G IV SOS, Inj. PAN-40 Mg IV once a day x3, Inj. Emeset 4 mg IV SOS, Tab Clopilet A 150 mg once a day in the afternoon and other supportive treatment. There was an improvement in the vision within 24 hours as he could count fi ngers at 1 foot. Hospital stay lasted for 3 days and the vision was improving day by day. The second follow-up was uneventful but before a bit delayed third follow-up the patient died of cardiac arrest within 2 months of the fi rst episode. Case Study


Background
The vision can be affected from a myriad of local ophthalmologic conditions and those affecting the neural structures conveying visual information from retina to brain.
Such neuro-ophthalmologic diseases can be due to damage at any location from optic disc, optic nerve, optic chiasm, optic tract to optic radiation and occipital cortex. Various

Case presentation
A cousin of mine, a male of sixty-fi ve years known Diabetic for over 26 years, Hypertensive for last 15 years, and under treatment for Ischaemic heart disease for last 4 years landed on the morning of 18 February 2020 in Bengaluru seeking my professional support. His main complaint was sudden bilateral blindness following a fall from a bed in the midnight of 11/2/20. and was able to recognize the faces of family members by then and walk around without any support though the clarity was around 50%. He was discharged on the 4 th day with continued medication and follow-up after a fortnight on 2 March 2020.

Outcome & Follow-up
The second follow-up on 2 nd March was uneventful and the Neurologist was also fully satisfi ed with the progress. The On 14 th April 2020 he had a sudden discomfort when he went for an early evening walk and died of Cardiac arrest before reaching the nearest hospital.

Causes of sudden blindness
Migraines are the most common causes of temporary vision loss. They cause blind spots, or one may feel like one is seeing when there is blockage due to a clot in a blood vessel [1].
In a study with a prevalence of visual impairment of 24.5% (95% CI: 20.9% -28.1%), Cataract was the leading cause of visual impairment (50.7%), followed by uncorrected refractive error (36.8%). Despite a reportedly high CSR, cataract remains the predominant cause of blindness [2].
In another study where a total of 900 eyes were examined.
Visual impairment and blindness were, seen in 135 (30%) and 36 (8%) individuals, respectively. The most common cause of blindness was cataract, followed by corneal opacity, glaucoma, refractive error, diabetic retinopathy, macular scar, age related macular degeneration, retinal detachment, retinitis pigmentosa. There is an increase in blindness and visual impairment due to corneal diseases and glaucoma which was not seen a decade ago. The availability and accessibility to eye care particularly for corneal diseases and glaucoma need augmentation in Northern India [3].
4. Congruous homonymous hemianopia due to occipital lobe infarction -Up to 8%-25% of patients who had a stroke can develop visual fi eld loss. Stroke is the most common causative factor for HH and correspondingly, HH is the most common form of visual fi eld loss following stroke Visual disturbance induced by bilateral LGB infarction is a rare occurrence [2].

The importance of congruous homonymous hemianopia
Congruous homonymous hemianopia due to occipital lobe infarction is estimated to be 8%-25% of patients who had a stroke that can develop visual fi eld loss. A large portion of the central nervous system is dedicated to vision and therefore strokes have a high likelihood of involving vision in some way.
Vision loss can be the most disabling residual effect after a cerebral infarction. Transient vision problems can likewise be a harbinger of stroke and prompt evaluation after recognition of visual symptoms can prevent future vascular injury [6].

Diffi culties in diagnosing or treatment
The most common cause of HH in adults is stroke.
Approximately 8%-25% of stroke patients have permanent HH, and 52%-70% of hemianopias are caused by stroke. As the population ages and stroke patients live longer, the incidence of stroke and resultant HH is likely to increase [7,8].
Visual fi elds, particularly when correlated with other symptoms, provide valuable information regarding the location of brain lesions. Goldmann perimetry is useful in detecting neurologic visual fi eld loss. Humphrey automated perimetry is widely used for assessing visual fi eld defects. Confrontation visual fi eld testing is not sensitive at detecting visual fi eld loss, but it may be the only method available. The most sensitive individual method of confrontation visual fi eld testing is kinetic testing using a 5 mm red bead. This picks up 43% of mild defects and 89% of severe defects. The overall sensitivity using the kinetic red bead is 74%, but this improves to 78% when combined with static fi nger wiggle testing [8][9][10] Study inferred that lesions involving the occipital lobe produce congruent HH, at least 50% of lesions in other locations also produced congruent HH [10,11].
A well conducted visual fi eld testing and careful evaluation of the visual fi eld defect pattern can localize the lesion site approximately along the optic pathway that can be confi rmed by modern imaging modalities, reported Shikha Baisakhiya and Amit Agrawal in a case report where the lesion was localized more anteriorly where anatomically the peripheral vision function in the cerebral cortex is located, sparing of the occipital pole was responsible for macular sparing in the patient [12,13].

Take home messages
• Strokes could involve vision in some way as large portion of central nervous system is dedicated to vision. • Post-chiasmal strokes occur secondary to ischaemia in the LGB, optic radiations, or occipital lobe and can manifest as sector anopias, quadrantanopias, or hemianopias, either congruous or incongruous.
• Homonymous Hemianopia is the most common form of visual fi eld loss following stroke • Congruous homonymous hemianopia due to occipital lobe infarction -8%-25% of patients who had a stroke can develop visual fi eld loss.