Pupillary reflexes, Accomodation, PD

Clinical Foundations I

What are the two methods of PD Measurement?

• Sight Method

• CRP (Corneal Reflection Pupilometer)

What is Pupillary Distance (PD)?

Pupillary Distance (PD) is the distance between the right and left eye in millimeters. It can be measured for Distance or Near.

Why is Pupillary Distance important?

Misalignment of lenses with the optical axis of the eye results in prism being induced. This prism induces errors in eye position and refraction.

What are the normal values of PD?

• Distance:
    • Adults = 55–75 mm
    • Children = 43–58 mm

• Near: 2–5 mm shorter than distance

What are the methods for measuring interpupillary distance (IPD) with a PD stick?

• Center to center – Hard to estimate exact center; can introduce at least a 1 mm error.

• Margin to margin (pupil) – Pupil not stable; it moves.

• Temporal limbus to nasal limbus (cornea) – More consistent, but ignores the fact that pupils may not be centered in the cornea.

When do you measure interpupillary distance with a pupillometer?

Most accurate (±0.5 mm); a MUST for Progressive and High Index lenses.

How is the Sight Method for measuring PD performed?

• At 40 cm, hold the PD stick across the bridge of the nose.

• Close your right eye; have the patient fixate on your open left eye.

• Align the “zero” point of the ruler with the patient’s right pupil. Estimate where the center of the left pupil falls on the ruler → this is Near PD.

• Keep the ruler in place, open your right eye, and ask the patient to look at it. Estimate where the left pupil falls again → this is Distance PD.

How should PD values be recorded?

• Always record Distance/ Near PD in mm.

• Average PD is 64/60 mm.

• Near PD should be 2–5 mm smaller than distance.

• Expect measurements to be accurate within ±1–2 mm error.

• If examiner and patient PD differ by more than 8 mm, error can increase up to 3 mm.

What are common sources of error in PD measurement?

• Tolerance: ±2 mm (only acceptable for low Rx, not for PALs or high index lenses).

• Closer than 40 cm from patient: Near PD will be too small.

• Moving the ruler after zeroing.

• Incorrect centration.

• Parallax error – occurs if examiner is not directly in line with the patient’s sight.

What does the Corneal Reflection Pupillometer (CRP) measure?

• Monocular PDs (OD, OS) and Binocular PD (OU).

• Measures both distance and near PDs

In what cases must CRP be used?

• High spectacle corrections

• Progressive (PAL) lenses

• High index lenses

How is the CRP set up before use?

• Remove the patient’s glasses.

• Lighting should be full/bright.

• Set the focusing distance on the pupillometer to infinity (∞).

• Set the view switch on top to the straight (vertical) position

What should you say to the patient when using CRP?

“I’ll put this on your nose like a pair of binoculars.”

How should the CRP be positioned on the patient?

• Pads rest on the patient’s nose.

• Patient must fixate on the rings/bulls-eye inside the pupillometer.

How is PD measured with the CRP?

• Examiner looks into the opposite end through one peephole.

• Adjust the vertical crosshairs/reticles until each overlaps the corneal reflex of the patient’s eyes.

• Flip the instrument to read monocular and binocular PDs.

• Repeat for confirmation; if readings match, record distance PD.

How is Near PD measured with CRP?

• Reset the focusing distance to 40 cm (or patient’s working distance).

• Have the patient tip the pupillometer slightly downward for easier viewing.

• Repeat the measurement steps as done for distance PD.

How should CRP be recorded?

• Record near PD under distance PD.

• Example: 65/61 mm.

How should the CRP be stored?

• Store bottom side (scale and knob side) up → shuts off automatically.

• Do not store right side up → instrument stays on, battery drains, bulb life shortens.

What errors can still occur with CRP?

• Over-convergence due to closeness of instrument/target (especially in high AC/A patients).

• Strabismic or suppressing patients.

• Corneal pathology interfering with proper reflection.

What are the key procedures when testing pupils?

• Size/anisocoria (in light and dark)

• Color/Shape

• Direct response

• Consensual response

• APD (Afferent Pupillary Defect)

• Accommodative response

How does aging affect pupils?

• Smaller diameter with age

• Reaction to light is:
   • Reduced in amplitude
   • Less rapid

• Changes are due to ischemia and structural abnormalities.

What is “hippus”?

• A normal pulsating movement of the pupil.

• Rhythmic over seconds.

• Amplitude of 1–2 mm.

• Always bilateral.

• Caused by balance between parasympathetic and sympathetic nervous systems.

• Exact significance is unknown.

What does anisocoria mean?

Unequal pupil sizes between the two eyes.

What are the possible causes of anisocoria?

• Normal variant (physiological)

• Disturbance in parasympathetic or sympathetic pathways

• Structural disorder in the iris itself

What size of anisocoria can be normal?

A small difference of ≤1 mm, called physiologic anisocoria.

When does anisocoria suggest pathology?

If the difference is larger or new-onset → may suggest neurological, ocular, or drug cause.

How does light vs. dark testing help localize anisocoria?

• Worse in bright light → larger pupil is abnormal → parasympathetic issue.

• Worse in dim light → smaller pupil is abnormal → sympathetic issue.

What are the features of normal/physiological anisocoria?

• Present in ~50% of normal population.

• Typical difference of 0.3–0.4 mm.

• Inequality is the same under all conditions.

• May occasionally switch sides or be transient.

What is the conclusion if anisocoria is physiologic?

If pupils are structurally normal, react normally to light and near, and the anisocoria remains stable in dark and bright → no further workup needed.

What role does the autonomic nervous system play in pupil control?

• Parasympathetic system: “Rest and digest” → causes pupil constriction.

• Sympathetic system: “Fight or flight” → causes pupil dilation.

• Pupil control is autonomic in nature (no voluntary control).

• Pupil assessment is a powerful clinical tool because it reveals autonomic function.

What is the pathway for the pupillary light reflex?

• Light enters the eye → Retina → Optic nerve (CN II).

• Signal travels to the midbrain (pretectal + Edinger–Westphal nuclei).

• Outflow through Oculomotor nerve (CN III) → Ciliary ganglion → Short ciliary nerves → Iris sphincter.

• Result: Pupil constricts (miosis).

• Both pupils constrict because signals cross in the midbrain → Direct and consensual responses.

What are the three components of the near reflex pathway?

When shifting from far to near:

• Convergence: CN III → Medial rectus muscles.

• Accommodation: Ciliary muscle contracts → lens accommodates.

• Miosis: Pupil constricts via sphincter.

What is the near reflex triad?

Convergence + Accommodation + Miosis.

What is light-near dissociation (LND)?

• When afferent fibers are disrupted in the pretectal region.

• Light response is diminished, but near response is preserved.

• Near fibers outnumber light fibers by ~30:1.

• There is no condition where light reflex is present but near is absent.

What conditions can cause light-near dissociation?

(Don’t need to memorize these)

• Argyll-Robertson pupil

• Dorsal midbrain syndrome

• Encephalitis/meningitis

• Demyelination

• Pretectal lesions (e.g., pineal tumor)

• Diabetes

• Aberrant CN III regeneration

• Bilateral afferent disease

What are the clinical features of Argyll-Robertson pupil?

• Bilateral, asymmetrical miosis.

• Pupils often irregular, respond poorly to dilating agents.

• Light-near dissociation: virtually no response to light, but brisk near response.

• Normal visual acuity.

Where is the lesion in Argyll-Robertson pupil?

• Lesion in the pretectal area of the midbrain, interrupting the light reflex pathway before Edinger–Westphal nuclei.

• Near reflex fibers bypass this lesion and still reach EW nuclei via a different cortical pathway.

What is the result in Argyll-Robertson pupil?

• Light response: Absent

• Near response: Intact

What does a “fixed pupil” mean?

No reaction to light or accommodation.

What are possible etiologies of a fixed pupil?

• Pharmacologic blockade (reduced near VA)

• Trauma or inflammatory causes

• Glaucoma

• Structural abnormalities

• Adie’s tonic pupil

What are examples of afferent pupil defects?

• Afferent Pupillary Defect (APD)

• Light-near dissociation

• Argyll-Robertson pupil

What are examples of efferent pupil defects?

• Adie’s tonic pupil

• Horner’s syndrome

• Midbrain lesions

• Third nerve palsy

What is the purpose of pupil testing?

To assess the afferent and efferent neurological pathways responsible for pupillary function.

What equipment is needed for pupil testing?

• Pupil gauge

• Transilluminator

• Distant fixation target (20/400 letter)

How should the lighting be set up for pupil testing?

• Start with all lights on.

• Stand light should be to the side but still illuminating the face equally.

• Patient’s glasses must be removed.

How is pupil size measured in full light?

• Patient looks toward distance chart.

• Illuminate face tangentially with transilluminator.

• Use the 20/400 target.

• Note iris color and pupil shape.

• Using the pupil gauge, match the half circle that best fits pupil size.

• Record size to the nearest 0.5 mm.

How is pupil size measured in dim light?

• Reduce room lights and check pupil size again.

• If light-dark difference is ≤1 mm, possible errors are:
   1) Room lighting was too bright for dark measurement.
   2) Light measurement was too dim.

• Adjust lighting and re-measure.

What if you cannot see the pupil in dim light?

Hold a penlight slightly in front and below the chin, pointing upward.

• This lights the eye without affecting pupil reaction.

How is pupil color recorded?

Right eye over left, using abbreviations:

• Bl = Blue, Gr = Green, Hz = Hazel, Br = Brown.
  Example: Gr/Gr.

How is pupil shape recorded?

Right eye over left, using:

• R = Round, O = Oval, Irg = Irregular.
  Example: R/R.

How is pupil size recorded?

• Either: Right eye over left, in light over dark.
   Example: 5mm/5mm 7mm/7mm.

• Or: Each eye’s size in light over dark.
   Example: OD 5/7 mm, OS 5/7 mm.

How is the direct response tested?

• Hold light under line of sight (LOS), pointed at one pupil from 5–6 cm for 2 seconds.

• Observe constriction speed in the eye receiving light.

• This is the direct response of that eye.

How is the consensual response tested?

• Hold light under LOS, pointed at pupil.

• Remove light and allow recovery.

• Reintroduce light quickly.

• Observe the other eye’s pupil (no direct stimulus).

• This is the consensual response.

• Repeat for both eyes.

• Grade response speed on a 0–4 scale:
   0 = no movement, 4 = very rapid.

How are direct and consensual responses recorded?

Two options:

• Right eye over left, direct then consensual.
   Example: 3+/3+ 3+/3+.

• Or each eye’s direct over consensual.
   Example: OD 3+/3+, OS 3+/3+.

What is an APD and how is it tested?

• APD = Afferent Pupillary Defect, also called the Swinging Flashlight Test or Pupillary Escape Test.

• Positive APD is called a Marcus Gunn pupil.

How is the Swinging Flashlight Test performed?

• Reduce room lights.

• Shine light under LOS of one eye for 2 seconds.

• Observe for hippus (normal rhythmic pupil movement).

• Quickly swing light to the other eye and hold 3+ seconds.

• A normal pupil bounces, then constricts again.

• Must swing light quickly to avoid false positives.

• Repeat at least 3 times.

What indicates a positive APD?

If the pupil dilates when directly illuminated, APD is present in that eye.

How should APD be recorded?

• Positive: APD+ OD (eye that dilates).

• Negative: APD –.

What causes an APD?

• Impaired function of sensory retina or optic nerve.

• Can also be optic tract lesion (complete homonymous hemianopia).

• Less stimulation reaches EW nucleus when light shines in affected eye.

What ocular conditions can cause APD?

• Optic neuropathies (neuritis, ischemic, traumatic, compressive, drusen, asymmetric glaucoma).

• Retinal conditions (detachment, macular disease, central retinal artery occlusion).

What ocular conditions do NOT cause APD?

• Refractive error

• Corneal opacities

• Lens or vitreous opacities

• Malingering / hysteria

How can a neutral density filter help confirm APD?

• Place a 0.3 log ND filter over each eye during the test.

• A normal eye shows a slight symmetric APD.

• A mild APD eye will show a magnified defect.

How is APD quantified with ND filters?

• Use filters in 0.3 log unit steps over the normal eye.

• Perform swinging test until defect disappears.

• Bleach retina and retest several times to confirm.

What happens when an object is brought close to the eyes?

Eyes converge, pupils constrict, and accommodation occurs in a yoked response.

How is the accommodative pupil response tested?

• Usually not needed if other pupil responses are normal.

• Tested with full light, Rx off (unless response is abnormal).

• Patient shifts gaze rapidly from distance chart to near target (10 cm below LOS).

• Both pupils should constrict equally and quickly.

How is accommodative response recorded?

• As +/+ (right over left).

• Very rapid responses may be noted as ++/++.

What is the full format for recording pupil findings?

• Color: e.g., Bl/Bl

• Shape: e.g., R/R

• Direct (D) and Consensual (C) responses: e.g., 3/3 3/3

• Accommodative response (ACC): e.g., +/+

• APD: – or APD+ OD or OS

• Size (light/dark): e.g., 5/5 mm, 7/7 mm

What does PERRLA mean?

Pupils are Equal, Round, and Reactive to Light and Accommodation.

What does PERRL mean?

Pupils are Equal, Round, and Reactive to Light (accommodation not tested).