13.4 Visual Acuity, Over-Refraction & Gross Evaluation Techniques

Visual Acuity, Over-Refraction & Gross Evaluation Techniques

Quick Answer: Every CLRE follow-up follows a structured evaluation: measure visual acuity with lenses in place, perform over-refraction if acuity is below baseline, conduct a gross evaluation without instrumentation, then proceed to slit-lamp biomicroscopy with fluorescein. Documentation of all findings at every visit is non-negotiable, and distinguishing normal adaptation from abnormal findings determines whether the patient continues the lens, modifies the fit, or discontinues wear.

Visual Acuity (Measured at Every Follow-Up)

Visual acuity is the single most important functional outcome at a follow-up visit. It is measured at every follow-up without exception.

Protocol

1. Measure acuity with the contact lenses in place — distance (and near for presbyopic or multifocal patients) using the patient's current correction
2. Compare to baseline — the acuity recorded at the dispensing visit; any drop of one line or more requires investigation
3. If acuity is reduced, perform over-refraction — a sphero-cylindrical over-refraction determines whether the drop is refractive or lens-related
4. If over-refraction improves acuity to baseline, the lens power or fit is the problem; if it does not, the cause is ocular (edema, staining, ulcer, dryness)
5. Document — record acuity with lenses, the over-refraction result, and the final acuity after any in-office modification

A two-line drop from baseline at a follow-up is never normal. Even if the patient reports good comfort, reduced acuity with the lens in place is a sign of lens flexure, rotation, deposits, drying, fit change, or ocular disease. Skipping acuity measurement at a follow-up is the most common reason lens-related problems are missed.

Over-Refraction at Follow-Up

Over-refraction is the act of placing trial lenses (loose lenses or a phoropter) over the patient's contact lens to determine the additional refractive correction required. At follow-up, it serves two purposes: detect power changes, and isolate lens versus ocular causes of reduced acuity.

RGP Over-Refraction

For rigid gas-permeable lenses, the over-refraction is particularly informative because an RGP creates a tear lens that masks corneal astigmatism and irregularity:

• A stable, reproducible over-refraction near plano indicates the lens power and corneal shape are stable
• A power shift in the same direction as the original refractive error suggests corneal shape change — the cornea has warped under the lens (from a tight fit, over-wear, or flexure) and the tear lens is no longer compensating correctly
• A fluctuating over-refraction that changes between blinks suggests lens flexure on the cornea

A new RGP over-refraction of more than approximately ±0.50 D from baseline warrants corneal topography or keratometry to rule out warpage.

Soft Lens Over-Refraction

For soft lenses, the over-refraction is less informative about corneal shape but tells you about the lens:

• A stable over-refraction with reduced acuity suggests the lens power is wrong or the lens is damaged
• A fluctuating over-refraction suggests lens flexure or drying — the front surface curvature is changing with hydration
• A cylindrical over-refraction in a spherical lens patient suggests the lens is flexing and inducing astigmatism, or the lens has rotated (in a toric)

Toric Lens Over-Refraction

For a toric soft lens, an over-refraction that varies as the lens rotates between blinks confirms rotation. Check the orientation marks at the slit lamp, and if rotation is more than approximately 10 to 15 degrees, the lens axis must be adjusted (use the manufacturer's rotation chart or the LARS rule: left add, right subtract).

Always record the over-refraction in the chart: the spherical and cylindrical components, the visual acuity with the over-refraction in place, and the interpretation. The next follow-up will be judged against this finding.

Gross Evaluation (Without Instrumentation)

Before touching the slit lamp, a gross evaluation of the patient provides information that instrumentation can miss. This is the clinician's first look at how the patient is doing in real life.

What to Observe

Gross evaluation often catches problems that a slit-lamp exam alone would miss: the patient who is comfortable at the slit lamp but visibly squinting in the waiting room, the incomplete blink that exposes the inferior lens edge, the head tilt that signals an optical problem.

Slit-Lamp Evaluation with Fluorescein

After gross evaluation, the slit-lamp biomicroscope with fluorescein is the core instrument for follow-up:

1. Without fluorescein first — assess lens fit, movement, centration, deposits, and any visible corneal opacity or infiltrate
2. Instill fluorescein with a moistened strip or drop
3. Assess with a yellow barrier (Wratten) filter — punctate staining, abrasions, 3 and 9 o'clock staining, infiltrates, and edema become visible
4. Assess tear film — tear break-up time (TBUT) and tear meniscus height
5. Evert the lids — inspect the tarsal conjunctiva for papillae, follicles, and foreign bodies

For RGP lenses, fluorescein patterns reveal the central pooling (steep), central touch (flat), and edge lift that define the fit. For soft lenses, fluorescein reveals staining patterns and tear exchange.

Adaptation Assessment

At a follow-up, the clinician must distinguish normal adaptation from abnormal findings that require intervention.

Normal Adaptation Findings

These findings in the first one to two weeks of wear are expected and do not require lens change:

• Mild lid awareness that diminishes over the wearing day
• Mild bulbar injection at the end of the day
• Variable vision in the first few days with an RGP as the tear lens stabilizes
• Excess tearing during the first few days of RGP wear
• Mild superficial punctate staining under a soft lens in the first week, if it resolves by the next visit

Abnormal Findings (Require Intervention)

• Persistent or worsening awareness beyond two weeks
• Moderate to severe injection, especially circumciliary
• Vision that does not stabilize or that declines from baseline
• Persistent staining at any location
• Corneal edema (striae, folds, cloudiness)
• Infiltrates or ulcers
• GPC with large papillae and reduced wearing time

Documentation

Every follow-up note must include: subjective findings (verbatim complaint, onset, wear time, environment, solution); visual acuity with lenses and after any over-refraction; gross evaluation findings (comfort, appearance, lens position, tearing, blink, posture); slit-lamp findings without and with fluorescein (fit, movement, staining, deposits, edema, infiltrates, lid eversion); adaptation assessment (normal versus abnormal); diagnosis and management plan (continue, modify, discontinue, refer); patient instructions and follow-up interval.

Documentation is not optional. A follow-up visit that is not documented did not happen, from a regulatory and patient-safety perspective. The CLRE blueprint expects you to know that records must be thorough at every visit.

Key Takeaways

• Visual acuity is measured at every follow-up with the lenses in place, with over-refraction if acuity is below baseline, and the result is documented and compared to baseline
• Over-refraction at follow-up detects power changes; RGP shifts suggest corneal warpage or flexure, soft lens shifts suggest flexure or drying, and toric shifts suggest rotation
• Gross evaluation without instrumentation observes general comfort, eye appearance, lens position, tearing, blink quality, and compensatory head posture
• Slit-lamp evaluation with fluorescein follows gross evaluation and confirms staining, fit, deposits, edema, and infiltration
• Distinguishing normal adaptation from abnormal findings at follow-up determines whether to continue, modify, or discontinue lens wear, and every visit is documented thoroughly