What are the diagnostic steps and treatment options for decreased visual acuity?

Diagnostic Approach to Decreased Visual Acuity

Begin with standardized visual acuity testing under proper lighting conditions, measuring both uncorrected and best-corrected vision with pinhole testing and manifest refraction, as this identifies correctable refractive errors in approximately 11% of low-vision patients and up to one-third of older adults with presenting acuity worse than 20/40. 1, 2

Initial Visual Acuity Assessment

• Measure visual acuity at distance (2 meters) and near (40 cm and preferred reading distance) using standardized charts (Snellen or ETDRS), testing both monocularly and binocularly 1
• Perform pinhole testing and manifest refraction for any patient with acuity worse than 20/40 to assess best-corrected visual potential 1
• In patients with nystagmus, prioritize binocular testing as monocular occlusion can worsen nystagmus amplitude and artificially reduce measured acuity 1
• Consider glare testing when symptoms suggest disability in bright lighting conditions, as cataracts may produce normal acuity in darkened rooms but significant impairment with glare 1

Comprehensive Ophthalmic Examination

After establishing best-corrected visual acuity, perform slit-lamp biomicroscopy through dilated pupils to identify the anatomic cause, focusing on corneal clarity, lens opacity, and macular/retinal pathology. 1

External and Anterior Segment Evaluation

• Assess for lagophthalmos, blepharoptosis, floppy eyelid syndrome, or facial asymmetry that may cause corneal exposure 1
• Examine cornea for edema (epithelial vs stromal), guttae, Descemet membrane abnormalities, or scarring using sclerotic scatter and specular reflection techniques 1
• Evaluate pupil size, shape, and reactivity; look for sphincter rupture, iris transillumination defects, or posterior synechiae as evidence of trauma or inflammation 1
• Assess lens for cataracts (nuclear, cortical, or posterior subcapsular opacities) and document severity 1

Posterior Segment Evaluation

• Perform dilated fundus examination with indirect ophthalmoscopy to evaluate macula, peripheral retina, and optic nerve 1
• Look specifically for drusen, pigmentary changes, geographic atrophy (dry AMD), or subretinal fluid/hemorrhage (wet AMD) 3
• Assess for diabetic retinopathy, retinal vein occlusion, or other vascular pathology 4

Supplemental Diagnostic Testing

Optical coherence tomography (OCT) should be performed when macular pathology is suspected to identify subretinal fluid, intraretinal fluid, or geographic atrophy. 3

• Visual field testing (Goldmann or automated perimetry) is indicated when field defects are suspected or when acuity loss is disproportionate to clinical findings 1
• Contrast sensitivity testing may reveal functional impairment not captured by standard acuity testing, particularly in early cataract or AMD 1
• Potential acuity meter testing helps predict visual potential before cataract surgery 1

Common Etiologies by Age Group

Older Adults (≥65 years)

Refractive errors, cataracts, age-related macular degeneration, and glaucoma account for the majority of visual impairment in older adults, with AMD being the leading cause of blindness in those over 65. 1

• Uncorrected refractive error is the most common cause worldwide and improves to 20/40 or better with refraction in one-third of cases 1
• Cataracts affect 50% of adults ≥75 years and cause approximately half of bilateral low vision cases in adults ≥40 years 1
• AMD prevalence is 6.5% in adults ≥40 years, increasing to 13.4% in those ≥60 years 1
• African Americans have disproportionately higher rates of blindness from cataract (2.7% vs 1.1%), glaucoma (0.9% vs 0.1%), and diabetic retinopathy (1.2% vs 0.2%) compared to whites 5

Preschool Children

Amblyopia related to refractive error is the most common cause of decreased visual acuity in preschool children, affecting 1.5-1.9% of African-American and Hispanic children. 6

• Uncorrected refractive error causes decreased presenting vision in 4.3-5.3% of minority preschool children 6
• Leber congenital amaurosis presents with severe visual impairment and the oculodigital sign (eye pressing), which increases risk for keratoconus 1

Treatment Algorithm

Refractive Error

Prescribe corrective lenses immediately for any refractive error causing visual impairment, as this provides immediate improvement in 11% of low-vision patients. 1, 2

• Retest the worse-seeing eye after refraction, as it may become the better-seeing eye in 6% of cases 2
• Consider LASIK or LASEK for appropriate candidates, though these carry risks of infectious keratitis and corneal ectasia 1

Cataracts

Recommend cataract surgery with intraocular lens implantation when visual symptoms interfere with daily activities, as surgery achieves visual acuity >20/40 in approximately 90% of patients. 1, 3

• Do not base surgical decision solely on Snellen acuity; incorporate patient-reported functional impairment using validated questionnaires (VF-14, NEI-VFQ, Catquest-9SF) 1
• Potential complications include posterior capsular opacification and endophthalmitis 1

Age-Related Macular Degeneration

Dry AMD

Prescribe AREDS2 formulation (vitamin C, vitamin E, zinc 25mg, copper, lutein 10mg, zeaxanthin 2mg) for patients with intermediate AMD or advanced AMD in one eye, as this reduces progression risk by up to 36% over 10 years. 3

• Avoid beta-carotene formulations in current or former smokers due to 18% increased lung cancer incidence (RR 1.28) 3
• Coordinate with primary care physicians before initiating long-term supplementation due to increased genitourinary hospitalizations with zinc 3
• Mandate smoking cessation as it is the key modifiable risk factor 3

Wet AMD

Initiate intravitreal anti-VEGF therapy (aflibercept, ranibizumab, or bevacizumab) immediately upon diagnosis with three loading doses at 4-week intervals, as early treatment within 2 years significantly reduces legal blindness. 3, 4

• Ranibizumab 0.5mg monthly dosing results in 61-98% of patients losing <15 letters and 37-48% gaining ≥15 letters at 12 months 4
• After loading doses, maintenance options include aflibercept every 8 weeks, treat-and-extend, PRN, or monthly injections based on OCT findings 3
• Risks include endophthalmitis, uveitis, increased intraocular pressure, traumatic cataract, and retinal detachment 1
• Continue AREDS2 supplementation concurrently with anti-VEGF therapy 3

Corneal Edema

Identify and treat underlying cause (endothelial dysfunction, elevated IOP, contact lens overwear, medication toxicity from amantadine, bupropion, or chlorhexidine exposure). 1

• Consider topical or systemic carbonic anhydrase inhibitors for symptomatic relief 1
• Corneal transplantation may be necessary for irreversible endothelial failure 1

Vision Rehabilitation Referral

Refer patients with persistent visual impairment (best-corrected acuity <20/40) to vision rehabilitation services immediately, as optical/electronic magnifying devices, bright lights, and reading aids optimize remaining visual function. 1, 3

• Counsel that central vision loss is common in AMD but total blindness is extremely rare, as peripheral vision is typically preserved 3
• Address increased fall risk and screen for depression, which frequently accompanies severe central vision loss 3
• Educate about Charles Bonnet syndrome (visual hallucinations), which does not represent psychosis or mental deterioration 3

Critical Pitfalls to Avoid

• Never skip refraction in low-vision patients assuming the underlying disease is solely responsible, as 11% achieve significant improvement 2
• Do not rely on visual acuity screening alone in primary care settings, as sensitivity ranges only 27-75% compared to comprehensive ophthalmologic examination 1
• Avoid delaying cataract surgery in favor of lutein supplementation, as surgery is highly effective while lutein has no proven benefit for cataracts 3
• Do not prescribe multifocal lenses without counseling about increased fall risk during adaptation period 1