Hey Doc, Why Am I Having Problems Seeing at Night?
By Timothy Earley, OD
Like a thief in the night; the first sign of AMD
When you think about night vision, think of AMD
Your patient reports having a hard time seeing at night and reading in dim light. They want to know what’s going on. In the past, optometrists would assume that these night vision complaints are due to early cataracts or the aging process. More recent evidence suggests that a night vision complaint is a red flag for the possibility of early age-related macular degeneration (AMD). It is surely a reason for us to dig deeper into whether the cause of this reduced night vision is poor dark adaptation.
According to the Beckman Classification scale early AMD has been traditionally diagnosed once medium-sized drusen (>63 and <125 µm) become evident upon clinical evaluation. Yet, studies have revealed drusen are just the tip of the iceberg.
Curcio et al discovered that an invisible layer of cholesterol builds up between the pigmented layer of the retina (RPE) and the elastic layer of Bruch’s membrane, before drusen are perceptible. These cholesterol deposits—basal laminar (BLamD) and basal linear (BLinD)—cause oxidative stress and inflammation, hindering nutrient transportation to photoreceptor cells. As photoreceptor cells die, it becomes harder for the eyes to adjust to darkness and night vision declines.
Subtle, yet progressive, night blindness is the earliest symptom of AMD. Research shows that dark adaptation, the ability of our eyes to adjust from light to darkness, is compromised from the earliest stages of AMD and impairment increases as the disease progresses. In fact, impaired dark adaptation indicates the presence of AMD at least three years before drusen are visible and is the first symptom of the disease.
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Nearly two-thirds of older adults will report having trouble seeing at night as they age, yet 78% are not diagnosed with AMD until irreversible vision loss occurs. How can we help prevent irreversible vision loss due to AMD? Early detection is key.
First things first
Identify symptoms. Rule of thumb: Ask all your patients over the age of 50 if they’re having trouble seeing at night.
Dig deeper. Is your patient experiencing worsened visual acuity? Loss of central vision?
What else is going on?
Identify risk factors. Some are modifiable; others are not.
Non-modifiable: The patient is over 50 years of age. Is there a family history of AMD? Is the person Caucasian?
Modifiable: Does the person smoke? Have high cholesterol, cardiovascular disease, or diabetes? Is the patient obese? Do they spend a lot of time in the sun?
If your patient is showing symptoms or has risk factors for AMD, it is well worth to examine retinal function. Your best bet: a dark adaptation test. Dark adaptation impairment is 90% sensitive and specific to AMD.
Hey doc, why am I having trouble seeing at night?
I make it a habit of asking all my patients over the age of 50 if they’re having trouble seeing at night. If they do, that is my cue to perform dark adaptation testing. They might have AMD.
About the Author
Dr. Timothy Earley joined Medina Vision Centre in 1998. He was born and raised in Honesdale, PA and earned his Bachelor’s degree in Biology/Pre-Med from the University of Scranton. He earned his Bachelor’s degree in Visual Science and his Doctorate in Optometry from the Pennsylvania College of Optometry. Dr. Earley is a national speaker and consultant on age-related macular degeneration, specialty contacts and practice management.