refraction 2 k n jha 25.08.16
TRANSCRIPT
Learning Aims
• Hyperopia: Definition, optics, clinical features,
diagnosis, treatment of hyperopia.
• Accommodation: Definition, mechanism,
measurement.
• Presbyopia ( Physiological failure of
accommodation)
• Treatment of presbyopia
Hyperopia
Hyperopia
Total hypermetropia comprises of
• Latent hypermetropia (portion of hypermetropia which
can be revealed only under cycloplegia)
• Manifest hypermetropia
Facultative hypermetropia , the portion which can be
overcome by accommodation.
Absolute hypermetropia , The part that cannot be
compensated by accommodation.
Clinical features
• In young:
-asymptomatic
-asthenopia, burning in the
eyes
-chronic conjunctival
congestion
- Esotropia( convergent
squint)
• In older patients:
Asymptomatic
Early presbyopic symptoms
Examination of the eye
• Small axial length
• Small corneal diameter
• Shallow anterior chamber
• Fundus: Normal, or may suggest features of
pseudopapillitis.
• Predisposition to angle closure glaucoma.
Diagnosis of Hyperopia in Young: Cycloplegic Refraction
• Cycloplegia is the temporary paralysis of the ciliary
muscle with the use of pharmaceutic agent, to stabilize
refraction.
• Cycloplegic refraction is done in young hyperopes to
avoid overcorrection.
• Cycloplegic drugs: Atropine sulfate 1% ointment 3 times
a day for 3 days; cyclopentolate 1 % drop 2-3 times .
Treatment
• No treatment for low hyperopia in young.
• Spectacle correction with plus lenses in symptomatic adult.
• Correction of hyperopia plus addition for near in presbyopic
age.
• Contact lenses
• Hyperopic LASIK
• Phakic intraocular lens
• Holmium : YAG laser thermokeratoplasty
Correction of Hyperopia
Accommodation
• Accommodation is the mechanism by which
the eye changes refractive power by altering
the shape of its crystalline lens by mechanism
described by Helmholtz.
Mechanism of accommodation
• Contraction of ciliary muscle in response to
parasympathetic stimulation.
• Relaxation of the zonular fibres.
• Lens becomes more convex. The process involves
primarily the front surface of the lens.
• Accommodation occurs all round the circumference
and simultaneously in both the eyes.
• Near point: Nearest point where small objects
can be clearly distinguished is called the near
point.
• Near point varies with static refraction and age.
Amplitude of accommodation: diopters in the
change of lens power during accommodation.
Range of accommodation: distance between
the far point and the near point.
Average amplitude of accommodation
• Age in years In dioptres (D)
8 years 14 ± 2
20 years 11 ±2
40 years 6± 2
60 years 1.5±1
Amplitude of Accommodation and Age
Accommodation and convergence
• Accommodation convergence complex
• Accommodation / convergence ratio (AC/A
ratio)
• Accommodation convergence dissociation
Clinical accommodative problems
• Presbyopia
• Accommodative insufficiency
• Accommodative excess
Presbyopia
• Presbyopia is gradual loss of accommodative
response resulting from loss of elasticity of the
lens.
• It becomes a clinical problem when
accommodative amplitude becomes insufficient
for the patient for near work and reading.
Presbyopia
• Age : usually after 40 years
• Onset depends upon preexisting refractive
error, patients visual task and pupillary size.
Correction of presbyopia
• Convex lens for near work.
• The weakest convex lens is prescribed.
• May be prescribed as bifocal along with
distance correction.
Accommodative insufficiency
• Accommodative insufficiency is premature
loss of accommodation( premature
presbyopia)
• Clinical feature: blurring of near object or,
inability to sustain accommodative effort.
Premature presbyopia: Cause
• Concurrent or past debilitating illness
• Drugs : Parasympatholytic drugs ,tranquillizers
• Neurological disorders e.g. encephalitis
• Head trauma
• Glaucoma
• Diabetes mellitus
Presbyopia
• Treatment : Correction for near vision with
convex lenses.
Accommodative excess
• Spasm of Accommodation
• Mechanism: Ciliary muscle spasm
• Symptoms: Headache, brow ache, variable
blurring of distance vision, abnormally close
near point.
Accommodative excess
Etiology
• Iridocyclitis
• Use of anticholinesterases being used for
glaucoma
• Uncorrected refractive error, hyperopia,
astigmatism
• Prolonged and intense near work
Points to Remember
• Definition, optics, clinical features, diagnosis,
treatment of hyperopia.
• Definition, clinical features and correction of
presbyopia
• Accommodative excess