Vision, explained: “pie in the sky,” “pie on the floor,” and how we avoid both in surgery.
Post 5: Occipital Lobe
About this series. Plain-English guides to where adult gliomas begin and which brain networks are at risk—so patients and families understand planning, mapping, and recovery.
Why the occipital lobe matters
The occipital lobe is the brain’s primary vision center. Tumors here don’t usually change personality or speech—but small missteps can cost visual fields you use every minute of the day. Planning routes around the optic radiations and calcarine cortex (V1) lets teams remove tumor while protecting functional sight.
Takeaway: Occipital tumors threaten visual field clarity—not the eyeball. The goal is to keep the “wiring” for sight intact while pushing resection safely.
Occipital networks in plain English
1) Primary visual cortex (V1 around the calcarine fissure) — the pixel map
What it does: First stop for visual information from the eyes. It’s laid out like a map of the visual world (retinotopy).
Common signs if affected: A clean “cut” in part of the visual field (often the same side in both eyes), sometimes with macular sparing.
2) Optic radiations — the cables to V1
White-matter “cables” that carry vision signals from the lateral geniculate nucleus (LGN) to V1 in three major bundles:
Meyer’s loop (anterior/temporal) — carries upper-field info.
If injured: Superior quadrantanopia (“pie in the sky”).
Superior parietal bundle — carries lower-field info.
If injured: Inferior quadrantanopia (“pie on the floor”).
Direct posterior bundle — feeds the central (macular) map in V1.
If injured: Dense central field loss.
3) Dorsal vs ventral visual streams — “where/how” and “what”
Dorsal (“where/how”): from occipital → parietal; guides reaching, spatial attention, motion.
If affected: Trouble tracking moving objects, misjudging where things are.
Ventral (“what”): from occipital → temporal; links to object/face recognition and reading.
If affected: Harder time recognizing complex objects or fast visual word recognition (when lesions extend forward).
Common signs you might notice
A missing corner or half of vision on eye testing (often noticed when reading or driving).
“I bump the same side of doorframes,” “I miss cars coming from the right/left.”
Skipping words at line ends; losing place on the page.
Trouble with fast visual tasks (sports, crossing streets) when motion processing is stressed.
If spread into streams: difficulty with object recognition (ventral) or spatial tracking (dorsal).
How teams plan surgery (Before • During • After)
Before surgery
Map the roads: Tractography of optic radiations (pay special attention to Meyer’s loop), plus proximity to V1 along the calcarine fissure.
Field testing: Confrontation fields at bedside; formal perimetry when time allows to document a baseline.
Corridor planning: Choose angles that skirt the radiations; consider prone vs lateral positioning and sulcal corridors that minimize fiber crossing.
Set expectations: Discuss risks of quadrantanopia/hemianopia and the difference between attention problems vs visual wiring loss.
During surgery
Navigation: Use tractography to avoid radiations. We rarely do surgery awake for optic radiations. Cortical/subcortical stimulation doesn’t work well here and isn’t utilized frequently.
Tissue-sparing technique: Work along sulci, preserve veins, and avoid long instrument paths across predicted radiation arcs—especially anteriorly where Meyer’s loop swings forward.
After surgery
Field reassessment: Early confrontation fields, then formal perimetry if any concern.
Vision rehab: Scanning strategies, boundary training, and reading tricks (line guides, larger fonts).
Safety coaching: Stepwise return to driving or sports following local regulations and therapy guidance.
Ask your surgeon (patient-facing)
Are my optic radiations close—especially Meyer’s loop?
Will the plan spare the central (macular) visual map in V1?
What is my risk of a quadrantanopia or hemianopia, and how would we detect it early?
Which surgical corridor minimizes radiation injury for my tumor’s location?
Bottom line
Occipital gliomas put vision wiring at risk. When teams plan corridors around optic radiations and V1, and verify fields before/after surgery, they can push resection safely—protecting the sight you rely on all day.
Fast FAQ
Is vision loss from occipital tumors an eye problem?
No. The eyes can be normal. The issue is the brain pathways that carry and map vision.
What’s the difference between “pie in the sky” and “pie on the floor”?
Injury to Meyer’s loop (temporal) causes upper-field loss; injury to superior parietal fibers causes lower-field loss.
Can field cuts improve?
Sometimes swelling-related deficits improve. Fixed cuts from pathway damage can persist; rehab helps people compensate.
