The Rhese view Method (Parieto-Orbital Oblique Projection) is the primary radiographic view specifically engineered to project the optic canal (optic foramen) end-on, demonstrating its cross-sectional circular profile, bony margins, and surrounding sphenoid structures in the lower outer quadrant of the orbit.
Both the Right and Left orbits are routinely imaged for bilateral comparative analysis.
1. Clinical Indications & Contraindications
Detailed Indications:
- Optic Foramen Pathology & Neoplasms:
- Evaluation of asymmetric enlargement, erosion, or cortical thinning of the optic canal due to Optic Nerve Glioma or Meningioma of the optic nerve sheath.
- Bony narrowing/stenosis of the optic canal causing visual impairment or optic nerve compression.
- Orbital Apex Trauma & Fractures:
- Identification of fractures involving the lesser wing of the sphenoid bone, anterior clinoid process, and optic canal margins following blunt cranial trauma.
- Foreign Body Localization:
- High-detail localization of radiopaque metallic foreign bodies within the orbital apex or posterior orbital cavity prior to MRI clearance.
- Fibrous Dysplasia & Paget’s Disease:
- Assessment of hyperostosis, bony encroachment, or osteosclerosis encroaching upon the optic nerve pathways.
Contraindications & Limitations:
- Unstable Cervical Spine Injury: Prone or forward-rotated head positioning is strictly contraindicated. A Reverse Rhese (Orbito-Parietal Oblique / AP Axial Oblique) can be performed in the supine position without rotating the cervical spine, utilizing compensatory tube angulation.
- Severe Facial Bone Fractures: Direct pressure on the zygoma, nose, and chin against the Bucky can aggravate unstable facial fractures.
2. Technical Factors & Exposure Physics
| Parameter | Recommended Specification | Radiographic Rationale |
| Patient Posture | Erect (Seated) or Semi-Prone | Erect seated provides superior control over subtle angle adjustments |
| Image Receptor (IR) | 18 × 24 cm (Portrait) | Tight format centered on the affected orbit and optic apex |
| SID | 100 to 115 cm ( 40 to 44 inches) | Standard focal distance balances spatial resolution and beam divergence |
| Grid Ratio | 8 : 1 to 12: 1 focused grid | Essential to absorb scatter from dense cranial structures |
| Tube Potential (kVp) | 70 – 75 kVp | High-contrast resolution to define thin cortical margins of the foramen |
| mAs Range | 20 – 30 mAs | Calibrated for bony orbit and sphenoid strut (AEC center cell active) |
| Focal Spot | Small (0.6 mm) | High spatial sharpness required to visualize the tiny (4 to 5 mm) optic ring |
| Breathing | Suspended respiration | Eliminates respiratory motion and ocular movement blur |
3. Step-by-Step Patient & Part Positioning
[ Vertical Bucky Surface ]
║
(Affected Orbit Down) ◄─ ║ ◄── 3-Point Touch: Chin, Cheek & Nose
║
/──────║──────\
│ AML ║ │ ◄── Acanthiomeatal Line ⟂ IR
│ ──────║────── │
│ ║ │ ◄── MSP forms 53° to IR (Rotated 37°)
\ ║ /
║
▲
│
[ Central Ray: 0° ]
(Exits at Affected Orbit)
The “3-Point Touch” (Malar, Nose, Chin) Rule
- Starting Posture: Patient sits or stands erect facing the vertical Bucky (or lies semi-prone on the radiographic table). Place the orbit of interest closest to the image receptor.
- Reference Point Contact: Adjust the head so that the chin, cheek (malar prominence/zygoma), and tip of the nose rest firmly against the center of the vertical Bucky surface.
- Reference Line Alignment (AML):
- Adjust neck flexion/extension until the Acanthiomeatal Line (AML) is strictly perpendicular (90⁰) to the plane of the image receptor.
- Plane Rotation (MSP):
- Rotate the patient’s head away from the lateral position so that the Mid-Sagittal Plane (MSP) forms an angle of 53⁰ with the plane of the IR (which corresponds to rotating the head 37⁰ toward the affected side away from a standard PA projection).
4. Central Ray (CR), Centering & Collimation
- Central Ray (CR) Tube Angle: Strictly 0⁰ (Perpendicular) to the image receptor.
- CR Centering / Alignment:
- Enters the superior-posterior aspect of the skull (parietal region opposite the side of interest).
- Exits precisely through the center of the downside orbit (the orbit resting against the Bucky).
- Collimation: Four-sided collimation tightly restricted to a a 7.5 × 7.5 cm (3 × 3 inches) field over the orbit of interest to minimize secondary radiation scatter and optimize contrast resolution.
5. Positioning Errors & Diagnostic Corrective Actions
| Positioning Error | Morphological Appearance of Optic Foramen | Cause & Corrective Action |
| Over-Rotation of Head (37° /MSP < 53°) | Optic foramen projects into the lateral orbital margin or outside the orbit. | Head turned too far toward lateral; rotate head back toward the PA stance. |
| Under-Rotation of Head ( 37° /MSP > 53°) | Optic foramen projects into the medial orbital wall or ethmoidal sinus. | Head kept too close to PA; rotate head further toward the affected side. |
| Over-Extension of Neck (AML not 90°) | Optic foramen projects into the upper half/superior quadrant of the orbit. | Chin tilted too far up; flex neck slightly to restore AML perpendicularity. |
| Over-Flexion of Neck (Chin tucked too much) | Optic foramen projects inferior to the orbital floor into the maxillary antrum. | Chin tucked too low; extend head upward until AML is perpendicular. |
6. Radiographic Anatomy & Quality Evaluation Criteria
+───────────────────────────────────────────────────────────────────────────+
| |
| /─── SUPERIOR ORBITAL RIM ───\ |
| / \ |
| / \ |
| │ [ Upper-Inner ] │ |
| │ Quadrant │ |
| │ │ |
| │ (Ethmoid / Nose) │ |
| │ │ |
| │ \ (o) ◄─────┼── OPTIC FORAMEN |
| │ \ [Lower-Outer] │ (In Lower-Outer |
| \ \ Quadrant / Quadrant) |
| \ \ / |
| \─── INFERIOR ORBITAL RIM ────/ |
| |
+───────────────────────────────────────────────────────────────────────────+
- Target Quadrant Rule (Golden Benchmark):
- The optic foramen must be clearly projected in the lower-outer (inferolateral) quadrant of the orbit, adjacent to the junction of the lateral wall and orbital floor.
- Optic Ring Morphology:
- Optic foramen seen end-on as a clean, rounded radiolucent ring with distinct cortical margins.
- Clear visualization of the sphenoid strut (inferior root of the lesser wing of the sphenoid) forming the inferolateral border of the canal.
- Orbital Apex Clarity:
- Unobstructed view of the superior orbital fissure and lateral orbital wall free of movement blur or excessive collimator cut-off.
7. Comparison: PA Oblique (Rhese) vs. AP Oblique (Reverse Rhese)
| Feature | PA Oblique (Standard Rhese) | AP Oblique (Reverse Rhese) |
| Patient Stance | PA (Cheek, nose, chin touch IR) | AP (Back of head on IR, orbit away) |
| Lens Radiation Dose | Low (Ocular lens on exit side) | High (Ocular lens directly in entrance beam) |
| Geometric Magnification | Minimal (Low OID) | Increased (Higher OID of the orbit) |
| Primary Utility | Routine elective & diagnostic imaging | Trauma patients with immobilized C-spine |