ERRORS OF REFRACTION ACCOMMODATION

ERRORS OF

REFRACTION AND

REFRACTION

 _{IT IS CHANGE IN DIRECTION OF}

LIGHT AS IT ENTERS A MEDIUM OF DIFFERENT DENSITY

DEFINITIONS

 _EMMETROPIA  AMETROPIA:

– AXIAL: 22-24mm.2.5-3.00D/mm

– CURVATURE: K.conus, spherophakia

– INDEX: N.sclerosis, vitrectomy with silicon oil.

MYOPIA

 _{Developmental myopia –10D at birth}

 Pathological axial myopia: starts at 5-10 yr of age and goes on increasing till 25 . May achieve 15-25D or more.

 _{Pathological curvature myopia. K.conus}

 Index myopia i.e. nuclear sclerosis, DM, drugs: Hydralazine, chlorthalidone and phenothiazines.

CHANGES IN MYOPIA

adversely as compared to ant half.

 _{Pale tessellated fundus}

 _{Myopic crescent, PPA, Tilted disc}  Focal Choroidoretinal atrophy

FINDINGS IN MYOPIA CONTINUED

 Lattice degeneration.

 Mac. Hole. Vitreous degeneration:

 Laquer’s crackes, Coin haemorrhage.

 haemorrhages and thromboses leading to Foster-Fuchs spot.

 _{Peripheral retinal degenerations leading to} thinning, hole formation and ret. detach.

CHANGES IN MYOPIA--- CONTINUED---

 AC deep and pupils wide.

 Rhegmatogenous retinal detachment.

 Choroidal neovascular membrane CNV.

 Foveal retinochisis. Macular hole.

 Amblyopia. Poor visual acuity in spite of optical correction. Centra/peripheral scotomas.

Pre-senile cataract, Ectopia lentis.

Increased prevalence of POAG, PDS/PDG, steroid responsiveness.

Down, Marfan’s, Stickler, Ehlers-Danlos and Pierre-Robin….Syndromes.

SYMPTOMS

 Indistinct distant vision.

 Disproportionate accommodation and

convergence may lead to discomfort in near work.(High myopia)

TREATMENT OF MYOPIA

 SPECTACLES, CONTACT LENS & SURGICAL TREATMENT.

– Radial keratotomy

– Photorefractive keratectomy

– LASIK and LASEK

– Clear lens extraction.

– Phakic IOL Implantation (implantable c.lens).

RADIAL KERATOTOMY

 PROCEDURE:

Multiple deep stromal radial cuts starting from optical zone (Central 4mm) up to limbus by diamond knife. Causes bulging of peripheral cornea and flattening of the central.

 INDICATIONS:

Static myopia upto 5D of adults with no or little astigmatism.

 _{CONTRA-INDICATIONS:}

Before 21 year of age, significant astigmatism and corneal opacity.

RADIAL KERATOTOMY cont..

 _{SUCCESS RATE:}

50% stable by about six month.

 PER-OPERATIVE COMPLICATIONS: Accidental perforation, involvement of visual

axis and incisions of wrong direction.

 POST -OPERATIVE COMPLICATIONS: Bacterial keratitis, endophthalmitis,

intrastromal inclusion cyst, globe rupture and cataract formation.

PHOTOREFRACTIVE KERATECTOMY

 PROCEDURE:

Optical zone anterior stromal ablation by Excimer Laser after epithelial removal. This thins central cornea and reduces its diaptoric power.

 _INDICATIONS:

Static myopia upto 6D , astigmatism upto 3D.

 _{CONTRA-INDICATIONS:}

PHOTOREFRACTIVE KERATECTOMY cont..

 _{SUCCESS RATE:}

90% achieve final refractive error of 1D. Long term drift especially in high myope.

 COMPLICATIONS:

Mild pain and watering for few days. Corneal scarring 3% of cases. Night glare.

LASER IN-SITU KERATOMILEUSIS

 PROCEDURE:

Same as PRK except that laser is applied after a hinged corneal flap by micro keratome.

 INDICATIONS:

S myopia upto 12D , astigmatism upto 5D.

 _{CONTRA-INDICATIONS:}

LASER IN-SITU KERATOMILEUSIS cont..

 SUCCESS RATE:

Results are better than PRK.

 _{COMPLICATIONS:}

Buttonholing, amputation, incomplete irregular flaps and corneal perforation.

Wrinkling, distortion or dislocation of flap. Epithelial in growth under flap. Keratitis, anterior segment ischaemia and optic neuropathy.

 _{Axial, Curvature, Index}

 Symptoms:

May be asymptomatic. Accommodative asthenopia (poor health, long near work, old age ), esotropia, early onset of presbyopia.

Hyperopia continued…….

SIGNS:

• Ant. Segment is affected more.

• Smaller Corneal diameter, shallow AC.

• Higher incidence of ACG.

• Retina looks like watered silk, blurring of disc margins mimicing papilloedema and papillitis.

Treatment of Hyperopia

 Spectacles

 Contact lens

 PRK (2D) LASIK (4D)

 Holmium laser thermal keratoplasty(1 to 2.5D) and Conductive Keratoplasty

ASTIGMATISM

 When the refracting system cannot make a punctate image due to differing powers in different meridians.

 _{Regular / Irregular. With the rule / against the}

rule.

 Simple myopic / hypermetropic, compound myopic / hypermetropic and mixed astigmatism.

More prone to Asthenopic symptoms

 Astigmatic fan and crossed cylinder 7.12-p.

 Keratometry may reveal different K readings.

 Corneal topography(5.15,5.16-K)

 Abnormally oblong looking disc on fundoscopy.

 Ectopia lentis, corneal tear repair, cataract surgery, tight corneal suturing.

TREATMENT OPTIONS-ASTIGMATISMT

 _SPECTACLES

 RIGID CONTACT LENS

 _{ARCUATE KERATOTOMY}  _{PRK (3D)}

 LASIK (5D)

APHAKIA

 Absence of eye lens i.e cat surgery, traumatic rupture and removal.

 High Hypermetropia.

 _{Correcting lens usually +10D}

 Linear magnification about 30% leading to diplopia. Some spherical aberration causing pin cishion effect. Jack in the box phenomenon due to prismatic effect. Faulty judgment of distance. Irregular or wavy looking flat surfaces. Reduced fields and poor eccentric visual acuity. Physical inconvenience and cosmetic deficiency of heavy plus spectacles lenses.

Pseudophakia

 _{Spherical over or under correction,}

 _{Surgical wound induced astigmatism and}  _{Loss of accommodation (unless the IOL is}

ANISOMETROPIA

 When the two eyes differ in their refractive power.

 _{Up to 2.5D permissible.}  _{Higher may require :}

CONTACT LENS MONOVISION

ANOMALIES OF ACCOMMODATION

 _Presbyopia

 Paralysis of accommodation  Spasm of accommodation

PRESBYOPIA

 _{Near point of accommodation recedes.}

 _{Weakness of ciliary muscle and hardening of lens.}  _{Age, fatigue, debility, disease , toxemia . Latent}

hypermetropia and glaucoma.  RAF-rule

PARALYSIS OF ACCOMMODATION

 _{Paralysis of accommodation}

 Drugs e.g atropine+++(0.5%-1.0%- 3days to 10days), Cyclopentolate+(0.5%1.0% -30min to 24 hr), tropicamide.

 ₃rd _{nerve paralysis, diphtheria and botulism}

Spasm off accommodation

 _Miotics

 Some error of refraction and a stressful near work for long hours, bad illumination,

anxiety, etc. Esotropia and bilateral miosis.  _{Cyclopegics and bifocals.}