Examination Techniques for Accuracy and Efficiency Refractive Errors and Accommodative Control A VOSH-Florida Presentation

Important elements of Accommodation Myopia and accommodation Hyperopia and accommodation Age Factors and Accommodation Final Rx vs. Uncorrected Acuity Pseudomyopia Accommodative Spasms Latent Hyperopia Manifestations of Presbyopia Amblyopia – refractive vs. strabismic

Important elements of Accommodation Accommodation can be defined as the controlled flexing of the crystalline lens resulting in the increase of it’s dioptric power necessary to place a near object in sharp focus at the plane of the fovea. Types of Accommodative Responses: Reflex Vergence Proximal Tonic

Types of Accommodative Responses: Reflex: Largest accommodative response. Reaction to blur input Vergence: Second largest accommodative response. Neurological link to the convergence stimulus. Measured using the Accommodative Convergence/Accommodation ratio (AC/A).

Proximal: Accommodative response to the knowledge that an object is in close proximity (within 3 meters). Typically provides 4% - 10% of accommodative response to a near stimulus. Tonic: Basal neural input to crystalline lens resulting in a stable minimal accommodative tonicity. Results in a mean tonic accommodative level of between 1 – 2 diopters in young adults. Tonic accommodation decreases with age.

Amplitude of Accommodation: The maximum accommodative response measured in a fully corrected eye. At age 10, this is ~13.5 diopters. Amplitude of Accommodation decreases by ~0.3D/year. By age 40, near point asthenopia may develop indicating early presbyopia. Presbyopia is an inadequate amplitude of accommodation necessary to achieve or maintain a sharp focus at the normal reading position (usually 40cm).

Myopia and accommodation: Overcorrection of Myopia: Any increase in minus power that yields an increase in visual acuity is considered a correction of refractive error. Any increase in minus power that does not yield an increase in visual acuity is considered an overcorrection. Myopic overcorrection results in increased contrast due to minification, which the patient perceives as sharper vision.

Symptoms of overcorrection: Asthenopia Intermittent distance blur Nearpoint problems – blur, esophoria Accommodative/Convergence problems Managing an overcorrection problem: Patient may not accept reduced minus initially. Reduce the overcorrection slowly over time and as symptoms develop.

The Uncorrected Myope: Will try to take more minus correction than necessary. May have an underdeveloped accommodative response at near with correction, due to lack of demand for accommodation when uncorrected. May show a sudden increase in esophoria or esotropia at near when corrected for the first time, due to a poor AC/A relationship. Patient may need to increase the near working distance with a new myopic correction in order to reduce the accommodative demand. Bifocals or removing of glasses may be necessary at near.

Hyperopia and accommodation: Clinical Forms and Responses to Hyperopia: Facultative Hyperopia Absolute Hyperopia Latent Hyperopia Spasm of Accommodation Pseudomyopia

Facultative Hyperopia: The amount of hyperopia that can be overcome by accommodation. Generally asymptomatic at a younger age, unless high enough to create AC/A problems. Patient will often not accept the hyperopic correction until symptoms occur due to loss of accommodation with aging.

Absolute Hyperopia: The amount of hyperopia that cannot be overcome by accommodation. Near-point symptoms present first. Distance blur can present as intermittent or constant. Patients will usually accept only enough correction necessary to relieve symptoms. Requires increasing plus correction gradually over time.

Latent Hyperopia: Hyperopia that is present, but cannot be measured using routine refractive methods. Two Types: Tonic: Constant spasm of accommodation. May not be symptomatic until there is a sufficient loss of accommodation with aging, becoming absolute hyperopia. Clonic: Intermittent spasm of accommodation. May produce Pseudomyopia.

Pseudomyopia: Patient with latent hyperopia who over-accommodates on refraction yielding a false myopic correction. Correcting this patient for myopia may result in the following symptoms: Asthenopia Intermittent blur at distance Near point fatigue Esophoria/Esotropia

Refractive Presentations: Pseudomyopia: Refractive Presentations: Young, non-presbyopic patient with near point complaints. Presents with uncorrected 20/20 (6/6) acuity. Fluctuating light reflex on retinoscopy. Fluctuating results on repeated autorefractor readings. Low minus subjective refractive error (-0.25 – 0.50 x 180)

Pseudomyopia: Refraction Tips: Recognize the signs and symptoms of pseudomyopia. Examining instruments (autorefractors, phoropters) sometimes stimulate proximal accommodation. Do not prescribe minus lenses if distance acuity is 20/20. Look for astigmatism, anisometropia, or antimetropia. Prescribe for the symptoms.

Manifestations of Presbyopia: Results from a loss of flexibility of the crystalline lens, causing a gradual reduction in the Amplitude of Accommodation (AA). Onset of symptoms usually occurs when the AA is less than half of the accommodative demand. Generally, by age 40 the AA is <5.00 diopters and the accommodative demand at 40cm is 2.50 diopters, resulting in symptoms of presbyopia.

Symptoms of Presbyopia: Age of 40 years or older Asthenopia on near point tasks Near point blur Need for an increase in near working distance Intermittent distance blur due to accommodative spasms

Management of Presbyopia: Refraction tips: Prescribe for the symptoms. Don’t over-prescribe Latent hyperopes may require more Add power than age tables suggest. A myope that takes too much Add power may be overcorrected at distance.

Refraction tips: Consider separate near-only glasses if: there is significant anisometropia in the vertical meridian that may cause prism-induced diplopia through an Add. the patient has macular degeneration and must eccentrically view for optimal vision. the patient has a convergence insufficiency or high exophoria. Base-in prism readers may be indicated. The Add required is strong (>+3.00) and may interfere with walking and other tasks. Always recommend good lighting for reading.

Amblyopia Definition: A nonspecific loss of visual acuity of at least two lines that is not caused by pathology nor correctable by ordinary refractive means (Shapero et al., 1980)

Amblyopia – refractive vs. strabismic Results in poor macular development due to a significant anisometropia causing one eye to be essentially fogged at a young age. Strabismic: Results in poor macular development due to an inability to fuse the eyes at the point of fixation causing suppression of one eye at a young age.

Management tips to prevent amblyopia: Any child or young adult presenting with a tropia or significantly unequal acuities should be screened for: High hyperopia High myopia High astigmatism Restricted eye movements Eye disease, trauma, congenital anomalies Refer for cycloplegic refraction and possible neurological evaluation.