Spectacles and contact lenses1

Spectacles and contact Spectacles and contact lenseslenses

Spectacles Spectacles

Optical appliances comprising of lenses Optical appliances comprising of lenses and a frame, with sides extending towards and a frame, with sides extending towards the earsthe ears

Spectacles Spectacles

Optical correction for refractive errorsOptical correction for refractive errors

Lens materials:Lens materials:– TransparentTransparent– Impact resistantImpact resistant– Low weightLow weight– Scratch resistantScratch resistant– Easy to manufactureEasy to manufacture– Inexpensive Inexpensive

Materials:Materials: GlassGlass::

- crown glass of refractive index 1.52. crown glass of refractive index 1.52. - Provide optimum visual clarity Provide optimum visual clarity - Heavy / break easilyHeavy / break easily

PlasticPlastic: : eg PMMA, CR-39 (RI: 1.49)eg PMMA, CR-39 (RI: 1.49)

- lighter than glass, lighter than glass, - does not shatter but can does not shatter but can easily get scratchedeasily get scratched• Polycarbonate: • lighter, thinner and stronger. lighter, thinner and stronger. • high refractive index (1.58)high refractive index (1.58)• Unbreakable Unbreakable

High index glassesHigh index glasses::- Used for high refractive errorsUsed for high refractive errors- Have a high refractive index of 1.56-1.67, Have a high refractive index of 1.56-1.67,

as compared to 1.52 for crown glassas compared to 1.52 for crown glass- These lenses, therefore, are thinner, flatter These lenses, therefore, are thinner, flatter

and lighterand lighter- Eg flint glass (1.62)Eg flint glass (1.62)

Frames:Frames:

DurableDurable

Non allergicNon allergic

Resistant to corrosionResistant to corrosion

InexpensiveInexpensive

Non inflammableNon inflammable

MetalMetal

PlasticPlastic

NylonNylon

CombinationCombination

Tortoise shellTortoise shell

Lens shapesLens shapes

Meniscus lensesMeniscus lenses: : - Small to moderate degree of Small to moderate degree of

refractive errorsrefractive errors- The standard lenses are ground The standard lenses are ground

with base curveswith base curves- + lens uses negative base curve+ lens uses negative base curve- - lens uses positive base curve- lens uses positive base curve- The prescription is ground onto The prescription is ground onto

the other ‘combining surface’the other ‘combining surface’

Lenticular form:Lenticular form:- Used for high refractive Used for high refractive

errorserrors- The central portion of The central portion of

the lens is corrective the lens is corrective and the peripheral and the peripheral surfaces are parallel to surfaces are parallel to each othereach other

Aspheric lenses:Aspheric lenses:

- - Lens curvature flattens peripherally Lens curvature flattens peripherally thereby reducing aberrations and thereby reducing aberrations and hence providing better peripheral hence providing better peripheral visionvision

Single vision and multiple power Single vision and multiple power lenseslenses

Single vision lenses (monofocal): Single vision lenses (monofocal): - Lenses having the same refractive power Lenses having the same refractive power

over the entire surfaceover the entire surface- Used to correct myopia, hypermetropia, Used to correct myopia, hypermetropia,

astigmatism, presbyopiaastigmatism, presbyopia

Multifocal, varifocal or progressive Multifocal, varifocal or progressive advancement lenses: advancement lenses:

Tinted, coated and photochromatic Tinted, coated and photochromatic lenseslenses

Tinted: Tinted: – tints prevent damaging UV rays from entering tints prevent damaging UV rays from entering

the eyesthe eyes– reduce the amount of light entering the eye reduce the amount of light entering the eye

thereby making the patient more comfortable thereby making the patient more comfortable in bright sunlightin bright sunlight

Photochromatic lensPhotochromatic lens– Lenses that darken on exposure to UV raysLenses that darken on exposure to UV rays– Once UV is removed (eg. Walking indoors), Once UV is removed (eg. Walking indoors),

the lenses become clearthe lenses become clear– Silver halideSilver halide

Anti reflective coating:Anti reflective coating:– Destructive interferenceDestructive interference– Prevents annoying reflexes from anterior / Prevents annoying reflexes from anterior /

posterior surfaces of the lensposterior surfaces of the lens– Driving at night, working at the computerDriving at night, working at the computer

Contact lensesContact lensesAn artificial device An artificial device substituting the anterior substituting the anterior surface of the corneasurface of the cornea

Concept of contact lensesConcept of contact lenses

Types Types

Hard contact lensesHard contact lenses

Soft contact lensesSoft contact lenses

Rigid gas permeable lensesRigid gas permeable lenses

Hard contact lensesHard contact lensesMade of PMMA (poly methyl-methacrylate)Made of PMMA (poly methyl-methacrylate)

Comfort: Comfort: – Do not allow enough oxygen to reach the eye Do not allow enough oxygen to reach the eye – Therefore patients find it difficult to adapt to Therefore patients find it difficult to adapt to

themthem

Quality of vision:Quality of vision:– visual clarity is goodvisual clarity is good– can be used in astigmatic corneascan be used in astigmatic corneas

Deposit formation:Deposit formation:– Relatively resistantRelatively resistant

Soft contact lensesSoft contact lenses

Made from HEMA ( hydroxyethyl-methacrylate)Made from HEMA ( hydroxyethyl-methacrylate)

Contain Contain ~ 70% water~ 70% water

Comfort: betterComfort: better

Prone to formation of deposits.Prone to formation of deposits.– discomfort may occur on long term use. Therefore discomfort may occur on long term use. Therefore

disposable contact lenses ( daily, weekly or monthly) disposable contact lenses ( daily, weekly or monthly) have been introducedhave been introduced

Oxygen permeable or Rigid gas Oxygen permeable or Rigid gas permeable lenses (RGP)permeable lenses (RGP)

Made of copolymer of PMMA, silicone and Made of copolymer of PMMA, silicone and CAB ( cellulose acetate butyrate )CAB ( cellulose acetate butyrate )This polymer transmits oxygenThis polymer transmits oxygenDeposit formation: resist deposit formation Deposit formation: resist deposit formation and less likely to cause infectionand less likely to cause infectionQuality of vision: retain shape better and Quality of vision: retain shape better and provide sharper visionprovide sharper visionEasy to clean and disinfect, last longer Easy to clean and disinfect, last longer than soft C Lsthan soft C Ls

Types: wear timeTypes: wear time

Daily wearDaily wear

Extended wearExtended wear

Continuous wearContinuous wear

Type: frequency of replacementType: frequency of replacement

Daily disposablesDaily disposables

MonthlyMonthly

QuarterlyQuarterly

Annual / conventionalAnnual / conventional

IndicationsIndications

1.1. Optical: refractive errors(I huka)Optical: refractive errors(I huka)– Irregular astigmatismIrregular astigmatism– High myopiaHigh myopia– U/L aphakiaU/L aphakia– Keratoconus Keratoconus – AnisometropiaAnisometropia

Advantages Advantages

Less alteration of image sizeLess alteration of image size

Less aberrationsLess aberrations

Retain binocular vision in case of high Retain binocular vision in case of high anisometropiaanisometropia

Cosmetically more acceptableCosmetically more acceptable

Normal field of visionNormal field of vision

2. Therapeutic 2. Therapeutic • Recurrent epithelial erosions, exposure keratitis, Recurrent epithelial erosions, exposure keratitis, • Drug delivery system-pilocarpineDrug delivery system-pilocarpine• Aniridia –absence of irisAniridia –absence of iris

3. Diagnostic 3. Diagnostic • GonioscopyGonioscopy• Fundus examinationFundus examination

4. Cosmetic 4. Cosmetic – ColorColor– Disfigured corneaDisfigured cornea

Complications Complications

Corneal Corneal – Epithelial oedemaEpithelial oedema– AbrasionsAbrasions– Superficial punctate keratitisSuperficial punctate keratitis– Neovascularisation Neovascularisation – Corneal ulcerationsCorneal ulcerations

Conjunctival:Conjunctival:– Allergic conjunctivitisAllergic conjunctivitis– Giant papillary conjunctivitisGiant papillary conjunctivitis– Superior limbic keratoconjunctivitisSuperior limbic keratoconjunctivitis

Contact lens relatedContact lens related– Scratch / tearScratch / tear– DiscolorationDiscoloration– Lens depositsLens deposits– Loss of lensLoss of lens