In a 48-year-old woman with hyperlipidemia, hypothyroidism, migraine, rheumatoid arthritis, and type 1 diabetes mellitus who presents with sudden painless monocular vision loss described as a dark shadow moving from the peripheral visual field to the center of the right eye, which past medical condition most likely increased her risk for this event?

Type 1 Diabetes Mellitus Most Likely Increased This Patient's Risk

Type 1 diabetes mellitus is the condition in this patient's history that most significantly increased her risk of retinal detachment, which is the diagnosis suggested by her presentation of painless monocular vision loss described as a "dark shadow" moving from periphery to center.

Clinical Presentation Analysis

The patient's description is pathognomonic for retinal detachment, not retinal vascular occlusion:

• The "dark shadow" or "curtain" moving from peripheral to central vision over hours is the classic presentation of rhegmatogenous retinal detachment 1
• Painless progressive vision loss over three hours (not seconds or minutes) rules out arterial occlusion, which occurs instantaneously 1, 2
• Central retinal artery occlusion presents with sudden vision loss over seconds, not hours, and is described as complete blackout rather than a progressive shadow 1, 2

Why Type 1 Diabetes is the Primary Risk Factor

Diabetic retinopathy creates the pathophysiologic substrate for retinal detachment through multiple mechanisms:

• Proliferative diabetic retinopathy causes vitreoretinal traction from neovascular membranes, directly predisposing to tractional and rhegmatogenous retinal detachment 1
• Diabetic patients have significantly higher rates of posterior vitreous detachment, which is the initiating event in most rhegmatogenous retinal detachments 1
• The chronic microvascular changes in diabetes weaken retinal architecture and increase susceptibility to retinal breaks 1

Why Other Conditions Are Less Relevant

Hyperlipidemia, hypothyroidism, and rheumatoid arthritis:

• These conditions are risk factors for retinal vein occlusion (not detachment), which presents differently with hemorrhages and venous engorgement rather than a progressive shadow 1
• Hyperlipidemia and hypertension are associated with branch retinal vein occlusion at arteriovenous crossing points 1
• The patient's presentation does not match vein occlusion, which typically has better initial visual acuity and visible hemorrhages on fundoscopy 1

Migraine:

• Migraine aura is transient (5-60 minutes), features positive visual phenomena (scintillations, zigzag lines), and resolves completely without permanent vision loss 2
• This patient's progressive, persistent vision loss over three hours with a negative scotoma (dark shadow) is incompatible with migraine 2

Critical Diagnostic Distinction

If this were central retinal artery occlusion (CRAO):

• Vision loss would occur over seconds, not hours 1, 2
• The patient would describe complete blackout or "lights going out" 2
• Risk factors would include hyperlipidemia, hypertension, and carotid disease 1, 2
• This would require immediate stroke center transfer within 4.5 hours for potential thrombolysis 1, 2

However, the three-hour progressive "curtain" presentation definitively indicates retinal detachment, making diabetes the culprit condition.

Common Pitfall to Avoid

Do not confuse the time course of different causes of monocular vision loss:

• Retinal detachment: Progressive over hours to days with "curtain" or "shadow" 1
• Arterial occlusion: Instantaneous (seconds) with complete blackout 1, 2
• Venous occlusion: Acute but not instantaneous, with better initial acuity 1
• Migraine: Transient (minutes), with positive phenomena and complete resolution 2