21 Steps Normal Range Values and Diagnostic Norms

A complete set of vocabulary practice cards detailing the standard Morgan / Scheiman & Wick 21-step optometric norms, expected findings, and clinical interpretations.

Step 1: Ophthalmoscopy

Qualitative evaluation showing clear media, a normal red reflex, and a healthy disc and macula, with vertical C/D typically $\approx 0.3$ and normal value $< 0.7$.

Step 2: Keratometry

Measures corneal curvature with a mean of $43.00\text{ to }44.00\,\text{D}$ ($7.85\text{ to }7.67\,\text{mm}$), an overall range of $40\text{ to }47\,\text{D}$, and with-the-rule corneal astigmatism of $\le 1.00\,\text{D}$.

Step 3: Habitual Phoria, Far

Distance phoria measured at $6\,\text{m}$ with habitual correction; normal is $1\Delta\text{ exo} \pm 2\Delta$ (range $-3\Delta$ to $+1\Delta$).

Step 4: Static Retinoscopy

Objective distance refraction with no fixed norm; expected to agree with subjective refraction within $\pm 0.50\,\text{D}$ after removing the working-distance lens.

Step 5: Dynamic Retinoscopy (20 in)

Objective accommodative evaluation performed at $20\,\text{in}$; normal lag is $+0.25\text{ to }+0.75\,\text{D}$ with a mean of $+0.50\,\text{D}$.

Step 6: Dynamic Retinoscopy (50 in)

Dynamic retinoscopy performed at $50\,\text{in}$; secondary sources report no published norm, with an expected lag of $\approx 0\text{ to }+0.25\,\text{D}$.

Step 7: Subjective Refraction, Far

Subjective distance refraction endpoint yielding best visual acuity of $6/6$ ($20/20$) or better.

Step 7A: Subjective Refraction, Near

Near subjective visual acuity evaluation achieving $\text{J1 / N5}$ at $40\,\text{cm}$.

Step 8: Induced Phoria, Far

Distance phoria measured through the subjective refraction; normal is identical to Step 3 at $1\Delta\text{ exo} \pm 2\Delta$ (range $-3\Delta$ to $+1\Delta$).

Step 9: True Adduction, Far (BO)

Distance base-out vergence testing to blur; normal blur occurs at $9\Delta \pm 4\Delta$ (range $5\Delta\text{ to }13\Delta$).

Step 10: Convergence, Far (BO)

Distance base-out vergence testing; normal break is $19\Delta \pm 8\Delta$ (range $11\Delta\text{ to }27\Delta$) and recovery is $10\Delta \pm 4\Delta$ (range $6\Delta\text{ to }14\Delta$).

Step 11: Abduction, Far (BI)

Distance base-in vergence testing; normal break is $7\Delta \pm 3\Delta$ (range $4\Delta\text{ to }10\Delta$) and recovery is $4\Delta \pm 2\Delta$ (range $2\Delta\text{ to }6\Delta$).

Step 12A: Vertical Phoria, Far

Distance vertical ocular alignment; normal is orthophoria ($\pm 0.5\Delta$).

Step 12B: Vertical Duction, Far

Distance vertical vergence break value of approximately $2\text{ to }3\Delta$ base-up (BU) and base-down (BD).

Step 13A: Habitual Phoria, Near

Near phoria measured at $40\,\text{cm}$ with habitual correction; normal is $3\Delta\text{ exo} \pm 3\Delta$ (range $-6\Delta$ to $0\Delta$).

Step 13B: Induced Phoria, Near

Near phoria measured through subjective refraction at $40\,\text{cm}$; normal is identical to Step 13A at $3\Delta\text{ exo} \pm 3\Delta$ (range $-6\Delta$ to $0\Delta$).

Step 13B+1: Gradient AC/A

Accommodative convergence per dioptre of accommodation measured using lenses; normal is $4\Delta/\text{D} \pm 2\Delta/\text{D}$ (range $2\Delta/\text{D}\text{ to }6\Delta/\text{D}$).

Step 14A: Unfused Cross Cylinder, Near

Endpoint near add test with no fixed norm; tentative adds by age are $+1.00\,\text{D}$ (ages $40\text{--}44$), $+1.25\text{ to }+1.50\,\text{D}$ (ages $45\text{--}49$), $+1.75\,\text{D}$ (ages $50\text{--}54$), $+2.00\,\text{D}$ (ages $55\text{--}59$), and $+2.25\text{ to }+2.50\,\text{D}$ (age $\ge 60$).

Step 14B: Fused Cross Cylinder, Near (FCC)

Near cross-cylinder test evaluating accommodative response under binocular conditions; normal lag is $+0.50\,\text{D}$ (range $+0.25\text{ to }+0.75\,\text{D}$).

Step 15A: Induced Phoria through 14A

Near phoria measured through the unfused cross cylinder net; normal is $3\Delta\text{ exo} \pm 3\Delta$ (range $-6\Delta$ to $0\Delta$).

Step 15B: Induced Phoria through 14B

Near phoria measured through the fused cross cylinder net; normal is $3\Delta\text{ exo} \pm 3\Delta$ (range $-6\Delta$ to $0\Delta$).

Step 16A: Positive Relative Convergence (Near BO)

Near base-out vergence test; normal blur is $17\Delta \pm 5\Delta$ ($12\Delta\text{ to }22\Delta$), break is $21\Delta \pm 6\Delta$ ($15\Delta\text{ to }27\Delta$), and recovery is $11\Delta \pm 7\Delta$ ($4\Delta\text{ to }18\Delta$).

Step 16B: Positive Fusional Reserve (Near BO)

Follows Step 16A near base-out norms: blur $12\Delta\text{ to }22\Delta$, break $15\Delta\text{ to }27\Delta$, and recovery $4\Delta\text{ to }18\Delta$.

Step 17A: Negative Fusional Convergence (Near BI)

Near base-in vergence test; normal blur is $13\Delta \pm 4\Delta$ ($9\Delta\text{ to }17\Delta$), break is $21\Delta \pm 4\Delta$ ($17\Delta\text{ to }25\Delta$), and recovery is $13\Delta \pm 5\Delta$ ($8\Delta\text{ to }18\Delta$).

Step 17B: Negative Fusional Reserve (Near BI)

Follows Step 17A near base-in norms: blur $9\Delta\text{ to }17\Delta$, break $17\Delta\text{ to }25\Delta$, and recovery $8\Delta\text{ to }18\Delta$.

Step 18A: Vertical Phoria, Near

Vertical ocular alignment at $40\,\text{cm}$; normal is orthophoria ($\pm 0.5\Delta$).

Step 18B: Vertical Duction, Near

Vertical vergence break value at near of approximately $2\text{ to }3\Delta$ base-up (BU) and base-down (BD).

Step 19: Hofstetter's Amplitude of Accommodation

Formulas for amplitude: minimum ($15 - 0.25 \times \text{age}$), mean ($18.5 - 0.30 \times \text{age}$), and maximum ($25 - 0.40 \times \text{age}$); yields $10 / 12.5 / 17\,\text{D}$ at age $20$, and $5 / 6.5 / 9\,\text{D}$ at age $40$.

Step 20: Positive Relative Accommodation (PRA)

Measurement of maximum accommodation stimulation under fixed convergence using minus lenses; normal is $-2.37\,\text{D} \pm 1.00\,\text{D}$ (range $-3.37\text{ to }-1.37\,\text{D}$).

Step 21: Negative Relative Accommodation (NRA)

Measurement of maximum accommodation relaxation under fixed convergence using plus lenses; normal is $+2.00\,\text{D} \pm 0.50\,\text{D}$ (range $+1.50\text{ to }+2.50\,\text{D}$).

Low NRA Clinical Finding

An NRA measurement below $+1.50\,\text{D}$, which indicates accommodative excess or that the patient is over-minused.

High NRA Clinical Finding (> +2.50 D)

An NRA measurement exceeding $+2.50\,\text{D}$, which leads the practitioner to suspect latent hyperopia.