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OP9.1-5 | Retina, Optic Nerve and Visual Pathway — PBL Case

CLINICAL SETTING

Mr Suresh Balan, a 55-year-old schoolteacher, is brought to the ophthalmology casualty by his wife at 9 pm. She noticed that he was struggling to read the evening newspaper, holding it very close, and that his right eye seemed to be drifting. He reports that over the past 3 months he has seen occasional floaters in the right eye which he ignored. This evening he noticed a dark curtain moving inward from the upper right side of his vision in that eye. He has had type 2 diabetes for 12 years, managed on metformin and glipizide; his last HbA1c 3 months ago was 9.4%. He also has hypertension on amlodipine. He has never had an eye check. His wife is 7 months pregnant and has been told by her obstetrician that she has gestational diabetes and should also see an ophthalmologist.

Trigger 1: The First Consultation

On examination, Mr Balan's visual acuity is 6/9 left and 1/60 right. A right relative afferent pupillary defect is present. Anterior segment is normal bilaterally. Fundoscopy (dilated, right eye): the optic disc has a frond of new vessels (NVD) covering approximately one-third of the disc area. Extending from the disc superiorly there is a dense red mass filling the vitreous cavity in the upper half of the visual field (vitreous haemorrhage). Temporal retina is obscured. The left eye shows scattered microaneurysms, a few dot-blot haemorrhages, and three small hard exudates within one disc diameter of the fovea. The foveal reflex appears dull. OCT of the left macula reveals central subfield thickness of 395 micrometres with subretinal fluid.

DISCUSSION POINTS

  • What is the most likely cause of the sudden visual loss in the right eye, and how does the fundoscopy support your diagnosis? Use the NPDR/PDR distinction precisely.
  • Why does new vessel formation (neovascularisation) occur in diabetic retinopathy? Explain the pathogenesis from pericyte loss through VEGF upregulation to new vessel formation.
  • Classify the retinopathy severity in each eye. For the right eye, describe the high-risk PDR criteria that are met. For the left eye, identify whether macular disease is present and how it should be classified.
  • What does the right RAPD indicate, and why is it present in this patient?
  • Mr Balan's wife has gestational diabetes. What is the recommended ophthalmology screening protocol for a pregnant woman with diabetes, and why does pregnancy worsen diabetic retinopathy?
Click to reveal Trigger 2: Management Decisions (discuss previous trigger first!)

Trigger 2: Management Decisions

The on-call ophthalmologist explains the situation to Mr Balan. He is told the right eye has a vitreous haemorrhage and new vessel growth that has bled; the left eye has diabetic changes near the centre that need treatment. The right eye: PRP is not possible immediately due to the dense vitreous haemorrhage obscuring the view. B-scan ultrasonography is performed and shows a clear vitreous haemorrhage with no underlying retinal detachment; the retina is flat. The left eye: the ophthalmologist recommends a treatment for the left macular oedema. Mr Balan asks: 'My friend had a laser done for his diabetes eye. Will I also need laser? Is it just one sitting?' He is also worried because he is a schoolteacher and needs his vision for reading and writing on the blackboard.

DISCUSSION POINTS

  • For the right eye vitreous haemorrhage: (a) What is the immediate management? (b) The patient asks when the haemorrhage will clear and when he will see again — how do you counsel him? (c) Under what circumstances would surgery (pars plana vitrectomy) be required?
  • For the left eye: compare panretinal photocoagulation (PRP) and intravitreal anti-VEGF. Which is indicated for (a) the macular oedema and (b) PDR? Why are these different treatment targets?
  • Mr Balan's HbA1c is 9.4%. What is the evidence that glycaemic control affects the progression of diabetic retinopathy? Which landmark trials support this? What target HbA1c would you recommend?
  • Outline the multi-disciplinary team (MDT) approach to managing this patient. Who should be involved and what are their specific contributions?
  • How would you explain the difference between NPDR and PDR to a patient who has no medical background, using a simple analogy?
Click to reveal Trigger 3: A Month Later: New Symptom (discuss previous trigger first!)

Trigger 3: A Month Later: New Symptom

Mr Balan returns 4 weeks later. His right eye vitreous haemorrhage has partially cleared, and the ophthalmologist can now see the peripheral fundus more clearly; PRP is scheduled. The left eye received an intravitreal anti-VEGF injection 2 weeks ago and the macular OCT shows improvement (central subfield thickness now 280 micrometres). However, Mr Balan now reports a new concern: he has noticed that the upper half of his vision in the right eye has a shadow across it, and he can see what looks like a grey curtain even when the vitreous is slightly clearer today. B-scan USS today shows a highly reflective membrane extending from the disc toward the superior retina. Fundoscopy of the right eye (partial view): a pale grey elevated area of retina is visible superiorly through a gap in the remaining haemorrhage. Examination of the left eye also reveals a visual field abnormality: on confrontation testing, Mr Balan cannot see fingers in the right half of his left visual field. MRI brain performed urgently shows a small acute infarct in the right occipital cortex.

DISCUSSION POINTS

  • What complication has occurred in the right eye? Classify this complication and explain its relationship to the underlying proliferative diabetic retinopathy. How is it distinguished from a rhegmatogenous retinal detachment?
  • What are the indications for pars plana vitrectomy in diabetic eye disease? List them in order of priority.
  • Interpret the visual field defect in the left eye. Where is the lesion? Explain using visual pathway anatomy why the occipital cortex infarct produces this specific field pattern and not monocular blindness.
  • Mr Balan has now had a cerebral infarct. What shared vascular risk factors link diabetic retinopathy, retinal vascular occlusion, and cerebrovascular disease? How does this change his systemic management?
  • Reflect on the entire case from the perspective of preventability. At what point(s) could appropriate screening and early treatment have changed the outcome for Mr Balan? Design a district-level diabetic retinopathy screening programme that would have detected his disease at an earlier stage.

Learning Issues

Research these questions and bring your findings to the discussion.

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