Vision Issues, Part 1

Good vision is imperative for success in survival settings. Vision problems are varied, but many can be identified in early childhood or even infancy. In this series, we’ll discuss eye anatomy, early childhood issues, eye infections, and traumatic injuries affecting vision.

Eye Anatomy

To understand the eye, we should review its anatomy. The human eye is a spherical organ designed to capture light and convert it into signals which the brain interprets as images. The eye consists of three main layers (also called “tunics”): A fibrous tunic (outer layer), a vascular tunic (middle layer), and the retina (inner layer).

Major Eye Structures and Their Functions

• The “cornea” (outer layer): The clear, dome-shaped membrane that covers the iris and pupil (see below). It provides most of the eye’s focusing power.
• The “sclera” (outer layer): The tough “white of the eye” that maintains the eye’s shape and protects internal structures.
• The “conjunctiva” (outer layer): A thin, transparent membrane covering the sclera and inner eyelids, providing lubrication and protection.
• The “iris” (middle layer): The colored part of the eye, made of muscle that controls the pupil’s size to regulate light entry (dilates in dim light, constricts in bright light).
• The “pupil” (middle layer): The black central opening in the iris through which light enters.
• The “lens” (between middle and inner layers): A flexible, transparent structure behind the pupil. It fine-tunes focus for near or distant vision.
• The “ciliary body” (middle layer): Contains muscles that adjust the lens shape.
• The “choroid” (middle layer): A vascular layer supplying blood to the retina.
• The “retina” (inner layer): A light-sensitive inner lining with structures called “photoreceptors.” There are two types: “Rods’ for low-light, peripheral vision and “cones” for color and detailed central vision.
• The “macula” and “fovea” (inner layer): Central retinal region that allows sharp, detailed vision.
• Other important structures include:
• The “optic nerve”: The nerve that carries signals from the retina to the brain.
• The “Vitreous humor”: Clear gel filling the main cavity of the eye, maintaining its shape and allowing the passage of light.
• The “Aqueous humor”: Clear fluid in the front chambers, nourishing the cornea/lens and maintaining pressure.

Perhaps the first vision abnormalities we humans have to deal with occurs in early childhood or even infancy has the colorful name “Lazy Eye.” In medical-ese, it’s called “amblyopia.” It’s common, affecting three percent of the general population.

What is Lazy Eye?

Lazy eye or amblyopia is a vision impairment in which one eye fails to achieve normal visual acuity, even with corrective lenses. It is the leading cause of vision loss in children, affecting up to 3% of the U.S. population.

What Happens in Amblyopia?

From birth until around age 7 or 8, a child’s eyes and brain form all-important connections. Anything that blocks or blurs vision in one or both eyes can slow down and prevent these connections.

If that happens, the brain might not fully recognize the images it sees. The brain learns to ignore the images seen by the eye in question and it becomes weaker, losing vision strength (also called acuity) over time.

So What Causes Amblyopia?

Strabismus

The three main causes are:

Eye misalignment, also called “strabismus”: In strabismus, the eyes do not line up in the same direction, may be crossed or appear to “wander.” This causes double vision, something the brain doesn’t tolerate well. In response, the brain suppresses the image from the misaligned eye.

Refractive error: A major difference in acuity (let’s say nearsightedness, farsightedness, or astigmatism) between the two eyes is called  “refractive error.” The brain favors the eye with the clearer image, ignoring the blurry one.

Deprivation: Deprivation refers to a physical obstruction that blocks light from entering the eye. This could be due to being born with a cloudy lens (a “cataract”) or a droopy eyelid (a condition called ptosis). This is the most severe and, luckily, least common type.

Signs of Amblyopia

Can the average person identify a lazy eye before an eye professional checks it? Maybe. Symptoms can be hard to notice, and kids don’t often complain because they adapt to the vision in their stronger eye.

Possible signs include:

• (As previously mentioned,) an eye that wanders inward or outward or eyes that do not appear to move in unison.
• Poor depth perception.
• Squinting or tilting the head.
• Rubbing the same eye frequently.

Regular vision screenings are essential for early diagnosis in normal times.

How Is A Lazy Eye Treated?

In amblyopia, the goal of treatment is to force the brain to use the weaker eye so that the nerve pathways develop properly. The earlier treatment begins, the better the outcome. Optimal results occur if the child is treated before age 6 or 7, though some improvement is possible in older children and teens.

Treatment options include:

Corrective eyewear: Glasses or contact lenses to correct near- or farsightedness sometimes resolves the amblyopia entirely.

Eye patches: Placing an opaque patch over the stronger eye for several hours each day forces the brain to rely on the weaker eye, strengthening its vision.

Medicated eye drops: Atropine drops placed in the stronger eye can temporarily blur vision, serving the same purpose as a patch without the physical discomfort or embarrassment.

In rare cases, surgery may be needed to correct underlying causes, such as removing a cataract, fixing a droopy eyelid, or realigning eye muscles to correct strabismus. Surgery alone. However, doesn’t treat the amblyopia itself, which usually still requires follow-up with patching or drops.

There are also newer methods, including programs using virtual reality (VR) headsets to encourage both eyes to work together. This is called “dichoptic therapy” and is receiving wider acceptance.

With an early diagnosis, the odds of success in treating lazy eye is very high. In the next part of this series, I’ll discuss other eye problems in survival settings such as common acuity deficits like nearsightedness, farsightedness, astigmatism, plus eye infections and traumatic injuries.

Joe Alton MD

Dr. Alton