21.2 Core Workflows and Decision Points
Key Takeaways
- Refraction follows a fixed order: history, lensometry of current glasses, objective starting point (retinoscopy/autorefractor), then subjective refinement.
- Retinoscopy at a 67 cm working distance requires subtracting +1.50 D of working-distance power from the gross finding.
- 'With' motion means add plus; 'against' motion means add minus; neutralization is the endpoint.
- Spherical equivalent = sphere + (cylinder/2); transposition flips cylinder sign, adds it to sphere, and rotates the axis 90 degrees.
21.2 Core Workflows and Decision Points
A clean refraction is a sequence, and the COA exam rewards knowing the order. Skipping a step or doing it out of sequence is a common wrong answer.
The refraction workflow in order
| Step | Action | Why it matters |
|---|---|---|
| 1. History | Chief complaint, last exam, current symptoms | Frames whether the goal is distance, near, or both |
| 2. Lensometry | Read the power of current glasses (sphere, cyl, axis, add, prism) | Gives a baseline and detects an outdated Rx |
| 3. Objective | Retinoscopy or autorefractor to find a starting point | Produces a number even for a non-verbal patient |
| 4. Subjective | Refine sphere, then cylinder/axis, then binocular balance, then add | Tailors the Rx to what the patient actually sees |
| 5. Record | Write sphere -cyl x axis, add; verify | Physician signs the final prescription |
Retinoscopy and the working-distance lens
Retinoscopy is the objective technique of shining a streak or spot of light into the eye and watching the reflex (the red glow) move. The examiner sits at a fixed working distance, typically about 67 cm (two-thirds of a meter), and adds lenses until the reflex fills the pupil and stops moving, the neutralization point. Because the examiner is 67 cm away rather than at infinity, the gross finding contains extra plus power equal to 1 / 0.67 m, about +1.50 D. You must subtract +1.50 D from the gross retinoscopy value to get the true distance refraction. A 50 cm working distance would instead require subtracting +2.00 D.
Reading reflex motion
- 'With' motion (reflex moves the same direction as the streak): the eye is under-plussed. Add plus lenses until neutral. Pure hyperopes and low myopes show with motion.
- 'Against' motion (reflex moves opposite the streak): the eye is over-minus or myopic beyond the working distance. Add minus lenses until neutral.
- Neutrality: the pupil fills with light and the reflex no longer moves. This is the endpoint where you record the gross value and subtract the working-distance lens.
Two calculations the exam loves
Spherical equivalent (SE) estimates the single sphere power that best replaces a sphero-cylindrical lens: SE = sphere + (cylinder / 2). For -3.00 -2.00 x 090, SE = -3.00 + (-1.00) = -4.00 D. SE is used for soft contact-lens estimates and for dilated patients who cannot refine cylinder.
Transposition converts between plus-cylinder and minus-cylinder notation without changing the lens. Three steps: (1) algebraically add sphere and cylinder for the new sphere; (2) reverse the cylinder sign; (3) change the axis by 90 degrees. Example: +2.00 -1.00 x 180 transposes to +1.00 +1.00 x 090. The optical lens is identical; only the notation changed.
Subjective refinement endpoints
During subjective refraction, refine sphere with the rule 'maximum plus, maximum acuity' to avoid over-minusing a patient into accommodative fatigue. Refine cylinder axis and power with the Jackson cross cylinder (JCC), flipping the handle to find the axis where both choices look equally blurred, then adjusting power. End with a binocular balance and a near add for presbyopes. Recording in the wrong order, or over-minusing, are the workflow traps the exam plants.
Using the Jackson cross cylinder correctly
The JCC is a lens with equal plus and minus power on perpendicular axes (commonly +/-0.25 D), mounted so it can be flipped about a handle. Refine axis first, then power. For axis, align the JCC handle with the current cylinder axis, flip, and rotate the cylinder axis toward the position of the plus (or minus, depending on cylinder sign) that the patient prefers, in decreasing steps until the two flips look equal. For power, align the JCC axes with the cylinder axis, flip, and add cylinder when the patient prefers the matching side or reduce it when they prefer the opposite. The endpoint is when both flips appear equally blurred.
A common exam point: always refine axis before power, never the reverse.
Choosing a near add for presbyopes
The near add is estimated from age and confirmed by the patient's preferred working distance. A reasonable starting add by age: about +1.00 to +1.25 D at 45, +1.50 to +2.00 D at 55, and +2.25 to +2.50 D at 65 and beyond. Always verify against the actual reading distance, because someone who reads at 33 cm needs about +3.00 D of total near power.
| Age band | Typical starting add |
|---|---|
| 40-45 | +0.75 to +1.25 D |
| 46-55 | +1.50 to +2.00 D |
| 56-65 | +2.00 to +2.25 D |
| 66+ | +2.25 to +2.50 D |
The add is added to the distance sphere to give the near sphere; it is never recorded as the full near power. Confirm comfortable near acuity binocularly before finalizing, because an add that is too strong shortens the focal range and frustrates the patient.
Pupil and accommodation control during the workflow
Whether the eye is dilated changes which steps are valid. A cycloplegic drop (cyclopentolate, tropicamide, or atropine) paralyzes accommodation, so a wet refraction reveals latent hyperopia but cannot use the patient's accommodation for the add. A dry (manifest) refraction lets accommodation operate, which can hide hyperopia and lead to over-minusing in young patients. The COA must know which condition the patient is in before interpreting findings. When a stem mentions dilation and then asks for a near add, the answer recognizes that you cannot finalize the add under full cycloplegia.
Document the drop, the time given, and whether the refraction was manifest or cycloplegic so the physician interprets the numbers correctly.
During retinoscopy at a 67 cm working distance, the gross neutralizing lens reads +2.00 D. What is the patient's true distance refraction?
Transpose +2.00 -1.00 x 180 into plus-cylinder form.