Anomalies of Accommodation

Definition

Classification (Duke-Elder)

ANOMALIES OF ACCOMMODATION
├── A. DIMINISHED / DEFICIENT ACCOMMODATION
│   ├── 1. Physiological  → Presbyopia
│   ├── 2. Pharmacological → Cycloplegia
│   └── 3. Pathological
│       ├── Insufficiency of accommodation
│       ├── Ill-sustained accommodation
│       ├── Inertia (infacility) of accommodation
│       └── Paralysis of accommodation
└── B. INCREASED ACCOMMODATION
    ├── 1. Excessive accommodation
    └── 2. Spasm of accommodation

Measuring the Near Point of Accommodation (NPA)

RAF rule for measuring the near point of accommodation - Kanski's Clinical Ophthalmology

A. DIMINISHED / DEFICIENT ACCOMMODATION

1. Presbyopia (Physiological)

• The crystalline lens gradually loses its pliability with age
• The zonular fibers attach to the ciliary body, which in youth can alter lens shape to increase near-focusing power
• As the lens hardens, this shape change becomes impossible regardless of how hard the ciliary muscle contracts
• A secondary role is played by weakening of the ciliary muscle itself

• Presents in the 4th to 6th decade of life
• Difficulty reading small print, eye strain, headaches
• Patient holds reading material progressively farther away
• NPA recedes with age - when it recedes to >46 cm, reading becomes difficult without correction

• Reading glasses (convex lenses / plus lenses) for near work
• Bifocal or progressive addition lenses (PALs) if distance correction also needed
• Surgical options: clear lens extraction with multifocal IOL implantation, monovision LASIK, corneal inlays (e.g., small aperture KAMRA inlay), conductive keratoplasty, presbyLASIK
• Scleral expansion surgery (results inconsistent)

2. Cycloplegia (Pharmacological)

• Tropicamide 1% - shortest acting (~4-6 hours)
• Cyclopentolate 1% - effective within 30 min, recovery in 2-3 hours; most commonly used clinically
• Homatropine 2%
• Atropine 1% - strongest, duration up to 2 weeks

• Refraction in children (to unmask hidden hypermetropia)
• Treatment of uveitis (to relieve ciliary spasm and prevent synechiae)
• Dynamic retinoscopy to confirm adequacy of cycloplegia

3. Pathological Forms

a. Insufficiency of Accommodation

• Systemic: anaemia, debilitating illness, diabetes mellitus, thyroid disease
• Local: after severe uveitis or ocular surgery
• Neurological: early paresis of the oculomotor nerve (III)
• Psychological: fatigue, stress, anxiety

• Blurred near vision
• Asthenopia (eye strain, headaches) with near work
• Reduced NPA for the patient's age

• Treat the underlying cause
• Convex (plus) lenses for near work
• Vision therapy / accommodative exercises
• Bifocals if distance glasses also needed

b. Ill-Sustained Accommodation

• Vision starts clear for near but blurs after prolonged near work
• Patient fails the ±2.00 D flipper test (accommodative facility test)
• Decreased positive relative accommodation (PRA)
• Common in debilitating systemic illness and after prolonged near work

c. Inertia (Infacility) of Accommodation

• Blurred distance vision immediately after sustained near work
• Slow transition between near and distance focus
• Fails the ±2.00 D flipper test (monocularly and binocularly)
• Normal amplitude of accommodation
• Some consider it a precursor to myopia

d. Paralysis of Accommodation

• III nerve palsy (most important): interruption of parasympathetic fibers travelling with CN III - presents with dilated fixed pupil, ptosis, and divergent strabismus alongside cycloplegia
• Adie's tonic pupil: post-ganglionic parasympathetic denervation, gives sluggish/absent pupil response + loss of accommodation
• Trauma to the ciliary ganglion or ciliary nerves
• Cycloplegic drugs (atropine, scopolamine, tricyclics, antihistamines)
• Toxins: diphtheria toxin (classically causes bilateral post-diphtheritic paralysis), botulinum toxin, lead poisoning
• Systemic diseases: multiple sclerosis, encephalitis, syphilis

• Chief complaint: blurred near vision
• Micropsia (objects appear smaller)
• May be associated with a fixed dilated pupil (mydriasis + cycloplegia = internal ophthalmoplegia)

• Identify and treat the underlying cause
• Reading glasses (convex lenses) while awaiting recovery
• Recovery is variable; post-diphtheritic paralysis generally recovers fully

B. INCREASED ACCOMMODATION

1. Excessive Accommodation

• Young uncorrected hyperopes (must over-accommodate constantly to see clearly at any distance)
• Young myopes doing prolonged near work with associated excessive convergence
• Children with undetected astigmatism
• Early presbyopes straining to maintain near focus

• Eye strain (asthenopia), headache, browache
• Blurred distance vision after prolonged near work
• Difficulty relaxing accommodation when shifting from near to far
• Often accompanied by accommodative esotropia (convergent squint) in hyperopic children

• Reduced ability to relax accommodation on accommodative facility testing
• High lag of accommodation on dynamic retinoscopy

• Full optical correction of the underlying refractive error (especially hyperopia)
• Vision therapy
• Cycloplegic eye drops (low-dose atropine or cyclopentolate) to break the cycle of over-accommodation

2. Spasm of Accommodation

• Functional/psychosomatic (most common in young patients) - stress, anxiety, exam pressure
• Excessive near work in poor illumination
• Organic: miotic eye drops (pilocarpine, carbachol), organophosphate poisoning
• Part of Spasm of the Near Reflex triad: overaccommodation + overconvergence (esotropia) + miosis

• Blurred distance vision (pseudomyopia)
• Diplopia (from associated convergence spasm)
• Headache, browache, eye pain
• Miotic pupils (small pupils with near triad spasm)

• Cycloplegic refraction: the induced myopia disappears after cycloplegia, revealing the true refraction (which may even show hyperopia)
• This distinguishes spasm (pseudomyopia) from true myopia

• Cycloplegic drops (cyclopentolate, atropine) to break the spasm
• Correct any underlying refractive error
• Prescribe appropriate glasses (especially full plus correction for hyperopes)
• Vision therapy and behavioural modification (reduce excessive near work)
• Address psychological factors in functional cases
• Treat causative miotic drug if applicable

Summary Table

Key Points for 15 Marks

1. Accommodation anomalies are classified as diminished (physiological, pharmacological, pathological) or increased (excessive, spasm).
2. Presbyopia is the most common - physiological, due to lens sclerosis, presenting in the 4th-6th decade; treated with plus lenses.
3. Paralysis of accommodation (cycloplegia) may signal serious pathology - always exclude CN III palsy and diphtheria.
4. Spasm of accommodation causes pseudomyopia; cycloplegic refraction is diagnostic.
5. Ill-sustained accommodation and inertia have a normal amplitude but differ in facility and sustainability.
6. The spasm of the near reflex triad = overaccommodation + convergence spasm + miosis - often functional/psychogenic.
7. The RAF rule is the standard clinical tool for measuring the NPA and amplitude of accommodation.