Near Vision Assessment and Accommodation

Near Vision Assessment

• Near vision assessment involves evaluating accommodative status, dynamic retinoscopy, presbyopia, and near addition range.

Near Vision Triad

• The near vision triad involves convergence, accommodation, and miosis.

Accommodation

• Accommodation is the eye's ability to focus at varying distances.
• The near point of accommodation is the shortest distance at which the eyes can focus when fully accommodated.
• Presbyopia is a physiological condition where accommodation gradually declines with age.
• A table shows the amplitude of accommodation and near point for various ages.

Accommodative Dysfunction

• Causes: systemic and ocular medication, ocular trauma, inflammatory disease, metabolic disorders (e.g., diabetes), Down syndrome, cerebral palsy (reduced amplitude), idiopathic.
• Symptoms: headaches, asthenopia (eyestrain), near vision blur, difficulty in reading, difficulty in changing focus.

Assessment of Accommodative Status

• Recommended tests for suspected accommodative dysfunction include:
  • Amplitude of accommodation using the push-up and pull-down method, which involves determining the furthest distance at which a patient can clearly focus on an object, thereby assessing the extent of their accommodative能力.
  • Accommodative facility using +/-2.00D spherical flippers, a dynamic test that evaluates the speed and flexibility of the eye's focusing response by alternating the lenses rapidly to challenge the visual system.
  • Positive and negative relative accommodation tests, which help to assess how well the eyes can adjust focus to different distances while measuring the amount of accommodative power that is being utilized.
  • Dynamic retinoscopy is employed to observe real-time accommodation changes as the patient fixates on moving targets, which provides insight into the accuracy of their refocusing mechanism.

Static vs. Dynamic Retinoscopy

• Static retinoscopy measures accommodation as relaxed, estimating refraction. It's done by having the patient look at a specific part of a duochrome or using cyclopentolate eye drops.
• Dynamic retinoscopy measures accommodation while it is active, assessing the accuracy of accommodation. It uses measurement while the patient focuses on a near target.

Dynamic Retinoscopy Methods

• Dynamic retinoscopy is sometimes used with young children when other methods are not possible.
  • Monocular estimation method (MEM)
  • Modified Nott method
• Principles include neutralizing the reflex, and with or against movement, determining the appropriate lens to add.

Accommodative Lag

• Accommodative lag occurs when the accommodative response is less than the accommodative stimulus.
• Normal accommodative lag ranges from +0.25 to +0.75DS

Accommodative Lead

• Accommodative lead occurs when the accommodative response is greater than the accommodative stimulus.

Monocular Estimation Method (MEM)

• Equipment: retinoscope, budgie stick or near chart, anglepoise lamp (if needed)
• Procedure:
  • Dim the room lights.
  • Use additional lighting if necessary.
  • Patient wears distance correction.
  • Retinoscope collar is down (max divergence).
  • Explain the procedure to the patient.
  • Hold the budgie stick or near chart and retinoscope at 40cm from patient.
  • Point to Snellen letters, ask patient to focus using both eyes.
  • Perform retinoscopy along the horizontal meridian (with the streak vertical) on the right eye.
  • Record dioptric power for neutrality.
  • Repeat on the left eye.
  • Record findings.
• Clinical notes:
  • Plus lenses indicate accommodative lag.
  • Minus lenses indicate accommodative lead.
  • Most pre-presbyopes have lags of +0.25 to +0.75DS using MEM.

Interpreting MEM Results

• Values above +1.00DS may indicate near esophoria due to convergence system trying to compensate for insufficient accommodation.
• Values above this may also indicate accommodative dysfunction (paresis or fatigue) or an undercorrected hyperope or overcorrected myope.
• Higher positive diopters might suggest presbyopia signs.
• Values below +0.25DS might indicate near exophoria, accommodation spasm, or undercorrected myopia.
• Values below this may also indicate latent hyperopia.

Nott Dynamic Retinoscopy

• An alternative if MEM is not suitable.
• Follow similar settings as with MEM.
• Ask patient to focus on letters or targets.
• Perform retinoscopy along the horizontal meridian (with streak vertical) on the right eye starting from 40cm.
• Perform retinoscopy as quickly as possible, minimize binocular interference.
• Determine the distance where neutrality is reached.
• If not achieved at 40cm, move the retinoscope further away or closer as indicated

Presbyopia

• A refractive condition where the eye's accommodative ability decreases for near vision.
• The crystalline lens loses flexibility.
• Clinically significant in the fifth decade; earlier in people with hot climates, people with short arms/work distances, and hyperopes.
• May affect emmetropes, astigmats, myopes, and hyperopes.

Comfortable Near Point

• Patients cannot continuously exert full accommodative effort for long periods without experiencing asthenopia.
• The entire accommodation range can be used for short tasks.
• Extended periods of near work can lead to eye strain and headaches.
• Usually 2/3 or 1/2 of accommodation is used.

Near Vision Measurement

• Near visual acuity is often not measured letter by letter. Instead, sentences or paragraphs at a preferred working distance are used on near charts like N-point or LogMAR. Equivalent Snellen charts are also used.

Tips for Testing

• For children, ask them to read or describe details for proper fixation and accommodation.
• Only present lenses for a brief time during retinoscopy (~0.5 seconds).
• Tables exist showing the dioptric values for various distances.

How to Approach the Patient

• Listen to patient needs (work, hobbies).
• Take a detailed history and symptom record.

Additional Power

• Age and working distance are the simplest and quickest methods for determining tentative add.

Determining Tentative Add

• Determine working distance requirements
• Calculate appropriate add based on age and working distance. The table demonstrates how tentative add is calculated with age and distance factors for the 33, 40, and 50–60 cm working distances.

Determining the Final Add

• Room lights should be on.
• Explain that the add will be determined.
• Adjust the trial frame, set the distance correction, and insert the tentative add.
• Provide the patient with reading charts.
• Have the patient read the smallest letters visible at normal reading distance.
• Determine the range and check for clarity using +/− .25 steps.

Determining the Range of Clear Vision

• Explain what will be done.
• Have the patient move the chart towards and away until letters blur.
• Record the distance measurements.
• Ask if the patient is happy with the determined range for the add.

Common Errors

• Assessing near add without the distance correction in place.
• Not insisting that the patient can read the lower line(s).
• Presenting the positive side of the flippers when negative side is needed to refine the final add.
• Not considering the patient's hobbies or occupation.

Additional Notes

• The specific terminology used in the PowerPoint slides is followed.

This quiz explores the essential concepts of near vision assessment, focusing on accommodative status, its dysfunctions, and the physiological changes with aging such as presbyopia. It also delves into the near vision triad involving convergence, accommodation, and miosis, highlighting their roles in near vision performance. Assess your understanding of these critical aspects of vision science.