1st lecture Contact Lenses what can help you in optic

1 lecture for contact lense

1. Contact Lenses
Prof Dr Asmaa Ibrahim

2. Definition and Scope
•Contactlensesarethin,curved
opticaldevicesplaceddirectlyon
thesurfaceoftheeye.
•Theyaremedicaldevices
designedtocorrectrefractive
errors,improve cosmetic
appearance,orservetherapeutic
anddiagnosticpurposes.
•Unlikespectacles,contactlenses
movewiththeeye,providinga
widerfieldofviewandmore
naturalvision.

3. Historical Background
•Thedevelopmentofcontactlensesspansoverfivecenturies.
•LeonardodaVinci(1508)firstdescribedalteringcornealrefractionwith
water.
•RenéDescartes(1636)proposedaglasstubefilledwithwater.
•In1887,F.A.Müllerproducedthefirstwearableglasscontactlens.
•WilliamFeinbloomintroducedplasticlensesinthe1930s.
•Softhydrophiliclensesappearedinthe1960s,revolutionizingcomfort
andweartime.
•Modernsiliconehydrogellensesofferhighoxygenpermeabilityand
advanceddesignssuchasmultifocal,toric,andsmartlenses.

4. Advantages of Contact Lenses Compared to Spectacles
Advantages Explanation
WiderFieldofView Nospectacleframestoobstructperipheral
vision.
BetterOpticalQuality Reducesimagedistortionandaberrations
inhighprescriptions.
NoFogging Idealforhumidorrainyenvironments.
ImprovedAesthetics Naturalappearanceandincreasedself-
esteem.
SportsandOccupationalSafety Donotsliporbreaklikeglasses.

5. Indications and Contraindications
Indications Contraindications
Refractiveerrors(myopia,
hyperopia, astigmatism,
presbyopia)
Activeeyeinfectionor
inflammation
Therapeuticuse(bandage
lensesforcornealdisease)
Severedryeyeoruncontrolled
systemicdisease
Cosmetic use
(colored/prostheticlenses)
Poorhygieneorinabilityto
followcareinstructions

6. Ocular Anatomy & Physiology Relevant to
Contact Lenses

7. 1-The cornea
•Thetransparent,avascularfrontstructureofthe
eyeprovidingapproximately43dioptersof
refractivepower.
•Itishighlyinnervatedandsensitive,makinglensfit
andoxygenpermeabilitycritical.
•Layersincludeepithelium,Bowman’slayer,stroma,
Descemet’smembrane,andendothelium.
•Softlensesmayreduceoxygensupplytothe
cornea,whileRGPlensesallowmoretearexchange
andoxygenation.
Ocular Anatomy & Physiology Relevant to
Contact Lenses

8. Layer KeyFunction
Epithelium Barrierand rapid
regeneration
Bowman’sLayer Structuralsupport
Stroma Maintainstransparency
andshape
Descemet’sMembrane Basementmembranefor
endothelium
Endothelium Pumpsfluid,maintains
cornealclarity

9. 2.TearFilm
•Thetearfilmiscomposedoflipid,
aqueous,andmucinlayers.
•Itprovideslubrication,nutrition,
andwasteremoval,andisvitalfor
lenscomfortandmovement.
•TearexchangeisgreaterwithRGP
lensesthanwithsoftlenses.
•Tearbreakuptime(TBUT)andtear
volumeareassessedduringlens
fittingtopredicttolerance.

10. 3-Conjunctiva & Limbus
•Theconjunctivacoversthesclera
(bulbar)andlinestheeyelids
(palpebral).
•Gobletcellsproducemucin
essentialfortearfilmstability.
•Thelimbus,thetransitionzone
betweencorneaandsclera,houses
stemcellsnecessaryforcorneal
epithelialregeneration.
•Contactlenswearcaninduce
limbalstemcelldeficiencyif
oxygentransmissionisinadequate.

11. 4 Sclera
•Thescleraisthedense,
fibrousoutercoatof
theeyeproviding
rigidity.Sclerallenses
restonthesclera,
vaultingoverthecornea
andcreatingatear
reservoir.

12. 5-Eyelids and Blink
Mechanism
•Eyelids distribute the tear film,
protect the ocular surface, and
aid in lens positioning.
•Incomplete blinking and
meibomian gland dysfunction
can cause dry spots on lenses,
leading to discomfort.

13. 6 Lacrimal System
•Thelacrimalsystem
maintainsahealthytear
filmanddrainstears.
•Contactlensesmay
altertear flow,
contributingtodryness
ordebrisbuildup.
Evaluationoftear
quantityandqualityis
essentialpriortofitting.

14. Tear Film Layers and Functions
TearFilm
Layer
Function
LipidLayerPreventsevaporation
Aqueous
Layer
Providesnutrientsand
hydration
MucinLayerPromotestearadherence
tocornealepithelium

15. Contact Lens Design & Nomenclature
•Understandingbasecurves,diameters,sagittal
depth,andedgeprofilesenablespractitionersto
matchlensespreciselytotheocularsurface.

16. Parameters
•Contactlensesaredefinedbyseveralparameters
includingbasecurve,diameter,sagittaldepth,
centralthickness,andedgedesign.
•Eachparameteraffectscomfort,movement,and
oxygentransmission.

17. Parameter Definition / Clinical
Significance
BaseCurve(BC) Posteriorcurvatureradiusof
thelens;matchescorneal
curvature.
Diameter(OAD) Overalllens diameter
determineslenscoverageand
centration.
SagittalDepth Heightfromthechordtothe
backsurface;affectslensvault.
CentralThickness Varieswithpower;influences
oxygentransmissionandlens
rigidity.
EdgeDesign Roundedortaperededge
affectscomfortandtear
exchange.

18. Base Curve (BC)
•Posterior curvature radius of
the lens; matches corneal
curvature.
Diameter (OAD)
Overall lens diameter determines
lens coverage and centration.

19. Sagittal Depth
•Height from the chord to the back surface; affects lens vault.

20. Central Thickness
•Varies with power; influences oxygen transmission
and lens rigidity.

21. Edge Design
•Rounded or tapered edge affects comfort and tear
exchange.

22. •Lens Shapes and Designs
•Contact lenses can be classified by their front and back surface
curvatures and optical zones.
•Key designs include spherical, aspheric, toric, multifocal,
progressive, and reverse curve lenses.

23. Lens Shape/Design Clinical Application
Spherical Standard corrections for
myopia/hyperopia.
Aspheric Reduces spherical
aberrations; mimics corneal
asphericity.
Front Surface Toric Corrects astigmatism on
front surface.
Back Surface Toric Aligns with corneal toricity;
improves stability.
Bitoric Both surfaces toric for high
astigmatism.
Multifocal/ProgressivePresbyopia correction with
near and distance zones.
Reverse Curve Used in orthokeratology and
post-refractive surgery fits.

24. Tear Lens Concept
•The tear lens is the thin layer of
tears between the posterior
surface of a contact lens and
the anterior cornea.
•It can neutralize corneal
astigmatism if thicker in
steeper areas.
• Rigid lenses use the tear lens
to correct irregularities,
whereas soft lenses conform to
the cornea and provide
minimal neutralization.

25. Types of Contact Lenses
•Contact lenses are available in a wide variety of
materials and designs to meet diverse visual,
therapeutic, and cosmetic needs.

26. Soft Contact Lenses
•Soft lenses are made of hydrogel or silicone
hydrogel materials.
They are flexible, conforming to the corneal
surface and offering high comfort.
•Types of Soft Contact Lenses:
•Daily Wear: Inserted in the morning and
removed before sleep.
•Extended Wear: Approved for overnight use
(increased risk of infection).
•Disposable: Daily, biweekly, monthly
replacement schedules.
•Toric: Designed to correct astigmatism.
•Multifocal: Provide near and distance
correction for presbyopia.
•Colored/Decorative: Change or enhance eye
color, may be prescription or cosmetic.

27. Rigid Gas Permeable (RGP) Lenses
•RGP lenses are smaller, firmer lenses made from oxygen-permeable
polymers.
They provide sharper vision for high astigmatism or irregular corneas but
require adaptation.
•Indications: Keratoconus, irregular astigmatism, post-refractive surgery
fits, myopia control.
•Advantages: High oxygen transmission, excellent visual acuity, durable.
•Disadvantages: Initial discomfort, adaptation period, may dislodge
with vigorous activity.

28. Hybrid Contact Lenses
•Hybrid lenses combine a rigid gas-permeable center
with a soft skirt.
They provide the clarity of RGP lenses with the comfort
of soft lenses.
Indications: Irregular corneas, astigmatism with
comfort demands.

29. Scleral Contact Lenses
•Scleral lenses are large-diameter gas-permeable lenses that vault over
the cornea and rest on the sclera.
They create a tear reservoir between the lens and the cornea, providing
excellent comfort and visual quality for irregular corneas.
•Indications: Severe dry eye, keratoconus, post-keratoplasty, ocular
surface disease.

30. Therapeutic & Specialty Lenses
•Therapeutic lenses protect the cornea and promote healing. Specialty
designs serve unique purposes in special populations:
•Paediatric Lenses: Aphakia, congenital anomalies, nystagmus.
•Bandage Lenses: Post-surgical healing, epithelial defects.
•Orthokeratology Lenses: Worn overnight to reshape the cornea.
•Prosthetic/Coloured Lenses: Improve appearance of disfigured eyes or
occlude light in coloboma.

31. Contact Lens Types and Their Key Features
Lens Type Key Features Main Indications
Soft Lenses
Flexible, high comfort, various
replacement schedules
Myopia, hyperopia, mild
astigmatism, presbyopia, cosmetic
use
RGP Lenses
Rigid, high oxygen permeability,
small diameter
Keratoconus, irregular corneas, high
astigmatism
Hybrid Lenses RGP center with soft skirt
Astigmatism, corneal irregularities
with comfort needs
Scleral Lenses
Large diameter vaulting cornea, tear
reservoir
Severe dry eye, keratoconus, post-
PKP
Therapeutic/Bandage
No prescription, protect or heal
cornea
Post-surgery, epithelial defects
Orthokeratology
Reverse curve design, worn
overnight
Temporary myopia control

32. Advantages and Disadvantages of Different
Lens Types
Lens Type Advantages Disadvantages
Soft Lenses
Comfortable, easy
adaptation
Less oxygen transmission,
deposits
RGP Lenses Sharp vision, durable
Initial discomfort,
adaptation required
Hybrid Lenses Best of both worlds Complex fitting, cost
Scleral Lenses
Great for irregular corneas,
tear reservoir
High cost, specialized fitting
Therapeutic Lenses Protection and healing
No vision correction unless
combined design