OPT 015: Clinical Refraction Module 1

Clinical Refraction Overview

• Optometers serve as autorefractors and visual analyzers, utilizing infrared light for refraction.
• Retinoscopes are objective instruments assessing refractive status through fundus reflex observation.
• Refraction is defined by Michel Millodot as measuring and correcting eye refractive errors.

Types of Refraction

• Subjective Refraction: Based on patient feedback; involves comparing lenses to determine the best visual acuity.
• Cycloplegic Refraction: Utilizes cycloplegics to paralyze ciliary muscles, facilitating accurate eye state determination.
• Stenopaic Refraction: Involves using a stenopaic slit for refraction assessment.
• Automated Refraction: Computerized measurements of refractive errors, emphasizing both objective and subjective accuracy.

Process and Techniques

• The objective is to align the retina with optical infinity, achieving clear visual outcomes.
• Includes three divisions: Starting Point (info gathering), Refinement (testing predictions), Endpoint Techniques (binocular balance).
• Employs various methods including phoropter tests and trial frame techniques.

Retinoscopy Insights

• Provides an objective assessment of refractive status without needing subjective patient input, critical for uncooperative individuals.
• Can determine lag of accommodation and detect ocular media opacities.
• Key historical contributors like Sir William Bowman and Parent popularized retinoscopy techniques.

Retinoscopy Advantages

• Acts as a reliable starting point for subjective refraction.
• Effective in detecting latent hyperopia and various accommodation dysfunctions.
• Offers an independent basis for comparison against subjective refraction results.

Instrumentation and Techniques in Retinoscopy

• Illumination Systems: Can use an external light source or self-illuminating designs for reflex observation.
• Observation Systems: Include a peephole to gauge the fundus light reflex and assess the refractive condition.
• Types of Retinoscopes: Varies based on light sources (luminous or non-luminous) and usage of different mirrors.

Static vs. Dynamic Retinoscopy

• Static Retinoscopy: Patient focuses on a distance object, evaluating the far point of vision.
• Dynamic Retinoscopy: Patient focuses on near objects, engaging accommodation, easing measurements of lag.

Factors Affecting Retinoscopic Results

• Clarity, intensity, speed of reflex motion, and the form and shape of pupil reflex significantly influence outcomes.
• Fundamentally important to adjust mirror types and distances during examination for accuracy.

Final Insights

• Point of Neutrality: Indicates where the reflex motion changes from 'with' to 'against', essential in determining true refractive error.
• Retinoscopy remains a cornerstone in optometric assessments, especially for patients with compromised ability to provide subjective feedback.### Static Retinoscopy Overview
• Adjust interpupillary distance (IPD) for accurate distance measurement.
• Instruct the patient to keep both eyes open during retinoscopy; ask about obstructions to fixation target.
• Examiner also keeps both eyes open; uses right eye for patient’s right eye and vice versa.

Static Retinoscopy Procedure

• Hold the retinoscope 20 inches (or 16 inches) from the patient's eye.
• Use retinoscopic lens in the phoropter to eliminate the unexamined eye.
• Scope both vertical (90th meridian) and horizontal (180th meridian) meridians.

Error Detection

• Continuous reflex indicates spherical error; observe movement with plus or minus lens to determine error type.
• Spherical errors detected involve reflex motion's direction:
  • Plus lens indicates "with" motion.
  • Minus lens indicates "against" motion.

Working Distance Lens (WDL)

• WDL is the distance of the examiner from the patient, expressed in diopters.
• Formula: D = 1/f; for example, 40 inches corresponds to 2.50D.

Break Phenomenon

• Observed when reflex within the pupil is not continuous with the streak on the eye, indicating astigmatic error.

Thickness Phenomenon

• Changes in reflex thickness during rotation hint at astigmatic versus spherical error; constant thickness indicates spherical error.

Skew Phenomenon

• Disalignment of streak with principal meridians points to astigmatic errors; if aligned, reflex moves parallel to the streak.

Neutralizing Astigmatic Errors

• Identify principal meridians, neutralize using a combination of spherical and cylindrical lenses based on motion detected.
• Record findings to adjust refractive status accurately.

Dynamic Retinoscopy

• Conducted to assess the lag of accommodation at near.
• A lag greater than +0.75D indicates insufficient accommodative response, while under +0.50D suggests over-accommodation.

Measurement Techniques

• Nott Technique: Neutralizes reflex with a card at 40 cm, moving closer to determine neutrality.
• Mohindra’s Near Retinoscopy: Examines distance refractive error using light from the retinoscope as a target, useful for infants.
• MEM Retinoscopy: Measures accommodative response using monocular estimation, focusing on the fixation target.

Key Considerations

• Dim lighting enhances pupil dilation for better observation.
• Proper understanding of eye movement and lens effect is crucial for accurate retinoscopy findings.
• Different methods serve various patient needs and conditions (e.g., adults vs infants).

FAQs

• Astigmatism affects nearly 2/3 of the population, often asymptomatic.
• Importance of understanding reflex movements for diagnosing refractive errors effectively.### Retinoscopy Techniques
• Chrome Retinoscopy: Introduced by Bobier and Sivak in 1980, it measures accommodative lag using a mobile target.
• Bell Retinoscopy: Developed by Apell in 1975, this method uses a filter to limit light wavelengths entering the examiner's eye.
• Radical Retinoscopy: Used when the retinoscopic reflex is faint; performed closer than usual (as close as 20 cm or 10 inches) to address issues from small pupils or cataract.

Testing for Accommodative Insufficiency

• Lag can be measured using binocular cross-cylinders and near point retinoscopy.
• A lag of +1.00 or greater indicates possible accommodative insufficiency.

Subjective Refraction

• Determines the necessary combination of spherical and cylindrical lenses to achieve best visual acuity at infinity.
• Phoropter: A lens holder with controls for spherical and cylinder adjustments, allowing efficient lens changes.
• Fogging Technique: Uses plus lenses to relax accommodation, assessing the patient's refractive error.

Lens Controls in the Phoropter

• Spherical Lens Control: Range of +20D to -20D; controls for adding plus or minus sphere.
• Minus Plano-Cylinder Control: Adjusts cylindrical lenses, displaying cylinder and axis settings.
• Auxiliary Lens Knob: Includes different apertures for controlling viewing conditions.

Monocular Subjective Refraction Steps

• Fogging: Observe visual acuity (VA) before applying the strongest plus lens until vision is slightly worse.
• Tentative Diagnosis: After fogging, if plus lenses improve vision, suspect hyperopia, if minus improves, suspect myopia.
• Visual acuity checking and adjusting lenses continue until best possible VA is established.

Determination of Cylinder Under Fog

• Astigmatic charts help assess if a patient is astigmatic by evaluating clarity of lines.
• Different chart types include Fixed Clock Dial, Sunburst Dial, and Fan Chart.

Confirmation of Cylinder Axis

• After establishing a tentative axis, the Jackson-Cross Cylinder (JCC) verifies the correct cylinder axis by rotating it until all lines appear equally blurred.

Common Cases and Prescriptions

• Patient Examples:
  • An 18-year-old male with 20/50 visual acuity; tentative diagnosis of myopia with a prescription of -1.00sph.
  • A 25-year-old female with headaches related to vision, presenting hyperopia with a proper fogging lens of +1.25sph.

Additional Considerations

• Importance of subjective refraction in optometry for accurate prescriptions.
• Quality patient experience leads to repeat visits and referrals, enhancing clinic reputation.
• Educating patients on relaxation techniques, such as the 20-20-20 rule, helps improve comfort during assessments.

Test your knowledge of Clinical Refraction in Optometry with this quiz focused on Module 1. This module introduces autorefractors and the basics of refraction. Prepare for your Doctor of Optometry studies in the third year, first semester.