spectacles and contact lenses1
DESCRIPTION
TRANSCRIPT
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