How is the near response of vision assessed and managed?

Assessment and Management of Near Response of Vision

The near response of vision should be comprehensively assessed through testing of accommodation and convergence, including measurement of near point of accommodation, convergence, and determination of accommodative and fusional convergence amplitudes to properly identify and manage vision disorders affecting near visual function. 1

Assessment Components of Near Response

Visual Acuity Testing

• Near visual acuity should be measured at 14-16 inches (35-40 cm) using standardized high-contrast charts with black optotypes on white background 1
• For near visual acuity measurements, specify:
  • Reading add used (if any)
  • Letter size
  • Reading distance 1
• Visual acuity testing conditions should be standardized to allow comparison of results across visits 1

Accommodation Assessment

1. Near Point of Accommodation Testing:

   • Determines how close an object can be brought to the eyes while maintaining clear vision
   • Particularly important in children with reading concerns 1

2. Noncycloplegic Retinoscopy:

   • Provides rapid assessment of accommodation
   • Helpful for evaluating:
     • Children with asthenopia and high hyperopia
     • Children at risk for accommodative dysfunction (cerebral palsy, Down syndrome, developmental delay)
     • Accurate accommodation is indicated by neutral retinoscopic reflex or small "with" movement 1

3. Dynamic Retinoscopy:

   • Evaluates change in retinoscopic reflex from "with" motion toward neutrality when patient shifts fixation from distance to near target 1
   • Helps identify accommodative insufficiency, which affects approximately 10% of school-age children 1

Convergence Assessment

1. Near Point of Convergence:

   • Measures how close an object can be brought to the nose while maintaining single binocular vision
   • Critical for identifying convergence insufficiency, present in 2-6% of school-age children 1

2. Fusional Vergence Testing:

   • Measures the eyes' ability to maintain fusion while overcoming increasing prismatic demand
   • Can be assessed using prism bar or rotary prism 1

Binocular Vision Assessment

1. Sensory Fusion Testing:

   • Worth 4-Dot Test evaluates sensory fusion capacity 1
   • Should be performed before any dissociating examination techniques 1

2. Stereoacuity Testing:

   • Randot Stereo Test evaluates depth perception ability 1
   • High-grade stereoacuity is associated with normal alignment 1

Management Approaches

Refractive Correction

1. Accurate Refraction:

   • Subjective refinement of refraction using phoropter or trial lens set is preferred 1
   • Reproducibility of subjective refraction is typically within 0.50 diopters for spherical equivalent, spherical power, and cylindrical power 1
   • For near vision problems, determine near-vision add at the reading/working distance preferred by the patient 1

2. Prescribing Guidelines:

   • For patients with exodeviations:
     • Correct clinically significant refractive errors that cause reduced vision 1
     • Consider correcting even mild myopia as improved retinal image clarity often improves control of exotropia 1
     • For hyperopia, prescribe the least amount needed to promote good vision while still promoting accommodative convergence 1

3. Special Considerations:

   • In low vision patients, refraction can improve visual acuity by 2 lines or more in 11% of cases 2
   • For patients with accommodative dysfunction, appropriate refractive correction is essential 1

Management of Accommodative and Vergence Disorders

1. Accommodative Insufficiency:

   • Reading glasses or bifocals may be prescribed to reduce accommodative demand 1
   • Vision therapy exercises may improve accommodative amplitude and facility

2. Convergence Insufficiency:

   • Vision therapy with convergence exercises
   • Base-in prism glasses for symptomatic relief
   • Consider part-time patching in children (2-6 hours daily) to improve fusional control 1

3. Stimulating Accommodative Convergence (for exodeviations):

   • Increase myopic correction in myopes
   • Reduce hyperopic correction in hyperopes
   • Consider prescribing myopic correction in emmetropes 1
   • Overcorrecting minus-lens therapy may stimulate accommodation but can be associated with a myopic shift 1

Clinical Pitfalls and Considerations

1. Avoiding Misdiagnosis:

   • The AC/A ratio (accommodative convergence/accommodation) varies among refractive groups, with early-onset myopes exhibiting significantly higher response AC/A ratios 3
   • Accommodative and vergence responses develop with age and can be affected by conflicting blur and disparity stimuli 4

2. Testing Considerations:

   • Testing of sensory function should be performed before using any dissociating examination techniques 1
   • For children, avoid rushed testing as fixation and acuity may vary with time 1
   • Consider the crowding phenomenon in amblyopia assessment - single optotype testing may overestimate visual acuity 1

3. Refractive Correction Timing:

   • For vision rehabilitation patients, consider delaying new distance eyeglasses prescription until after occupational therapy training with devices 1
   • In low vision patients, always refract both eyes as the worse-seeing eye at presentation may become the better-seeing eye after refraction 2

4. Contrast Sensitivity Considerations:

   • Patients with poor contrast sensitivity may require devices that supply illumination or contrast enhancement (illuminated magnifiers, video magnifiers, computers, electronic tablets) 1
   • Contrast sensitivity testing provides insight into patient performance beyond standard visual acuity testing 1

By systematically assessing and managing the near response of vision, clinicians can effectively identify and treat disorders affecting near visual function, improving patients' quality of life and functional vision for reading, computer use, and other near tasks.