Contact lenses-2

1. Contact lenses-2 Advanced Applications of Contact Lenses-1 31/12/2009 Instructor: Areej Okashah

2. Presbyopia & Contact lenses • Presbyopia is a gradual decrement of visual functions @ near among elderly (40 years or older) • Bifocal & multifocal contact lenses (either GP or soft designs) are designed to substitute bifocal or multifocal glasses; respectively. • Bifocal contact lenses: provide two corrections (distance & near) • Multifocal contact lenses: provide correction for more than two distances; usually in a progressive design.. • Either bifocal or multifocal contact lenses use simultaneous or alternating vision technique. • Monovision: means that one lens corrects distance vision in one eye; & another lens corrects near vision in the fellow eye

3. Which is more effective for our patients ? • Monovision • Multifocal • Or bifocal designs & • GP or • Soft material Answer: you should evaluate your individual patient: consider tear, tear film, lids, …..etc.

4. A good candidate for bifocal or multifocal contact lenses is the good candidate for contact lens wear in general…. Case history: surgical history; medications (e.g. antihistamines); visual requirements; occupational requirements….. Discuss with patients External (anatomical) measurements: pupil size; lid position; palpebral fissure size; blink rate & quality Tear quality & volume Corneal integrity Refraction K/ corneal topography Are very important preliminary evaluations

5. Patient satisfaction with presbyopic lenses starts after 6weeks of the initial application

6. Single-vision CL & reading glasses • i.e. a CL (GP or soft; sphere or toric) for distance correction; & a spectacle for near add. • Provides good bilateral vision at D & N • Low cost • Simplicity of fitting

7. Monovision • i.e. anisometropic contact lens correction; one eye is corrected for distance ; the other eye is corrected for near.. So, patients will be able to see D & N as they keep both eyes open • Using conventional lens designs • Decrease professional effort • < expense for patients • This design is thinner than bi-or-multifocal CL Howevere It impairs stereoscopic depth perception & one eye produces a dominant response (ocular dominancy) usually the one for distance; reduce the contrast sensitivity If the patient has strong dominancy in one eye; it then be difficult to ignore the out of focus monovision image

8. Check for VA for both D & near Patient comfort & adaptation are important to consider Consideration in fitting monovision

9. Bifocal CLs • 70% of presbyopes who wear CLs are fitted with monovision; 30% are fitted with bifocal designs ???? • Bifocals are either simultaneous vision, or alternating vision designs

10. Simultaneous vision i.e. bivision • Simultaneous vision is achieved when the D & N power are positioned within the pupil at the same time; the patient will selectively suppress the most blurred image at the selected distance • Three designs are available with simultaneous vision………cont

11. cont …..1) aspheric : has a gradual change of curvature along one surface 2) concentric/annular : has small central zone (the central zone either for D or N; but D is more often) 3) diffractive : available in soft design only & is independent on the pupil size; central diffractive zone that focuses image at distance by refraction of light & at near through diffraction principle)

12. Alternating/translating vision • i.e. vertical movement results in one power zone to position in front of the pupil at any one time (the distance zone is in front of the of the pupil when viewing @ D; & the near zone when viewing at N) • Intentional shifting of lens position in which separate discrete images formed by the two power segments in the lens focus on the retina with a change of gaze from distance (up) to near (down) or vice versa.. • Prism ballast or truncation are usually involved in this design to maintain lens stability

13. Therapeutic Cls • Trauma • Disease • Surgery • Bandages • Corneal reshaping

14. Ocular trauma • Contact lenses can cause trauma which causes visual impairment and participate in rehabilitation • Trauma can be caused mostly by metallic injury & motor vehicle accidents • Always check the corneal topography • Corneal staining; abrasion; scarring • Cls may give a protective benefit against ocular trauma • Cls is a useful tool to heal corneal & conjunctival wounds by allowing the regeneration of affected cells; & by the prevention of direct contact with lids while blinking

15. Cls also help in vision rehabilitation after trauma or injury • It also help manages aphakia; irregular astigmatism; iris/pupil abnormalities; amblyopia management (e.g. instead of patch); gross disfigurement (e.g. lids)= post-trauma • Bandage Cls: (soft, GP, or piggyback designs): after penetrating-keratoplasty; post-refractive surgery : to improve healing or to prevent infection or contamination; corneal abrasion

16. Paediatric contact lenses • Usually CL wear in children is elective • Either to improve vision or to improve appearance • Correction of refractive errors among children depends on the refractive error type; age; requirements; & parents motivation • Myopia: is rare among children; & if low-to-moderate occasionally causes amblyopia • Spectacle correction of high myopia results in image minification; peripheral distortion; reduced field of view;  CLs reduce these effects

17. Rigid CLs slow the progression of myopia in children …. “controversial” • Hyperopia: the most common refractive error among children; however refractive error correction doesn’t alter emmetropization; many practitioners recommend correction of hyperopia to improve vision & to prevent the onset of accommodative esotropia • With spectacle correction of hyperopia: plus lenses are heavy; magnify the patients eyes & the viewed object & they distort the peripheral vision… Cls avoid these

18. Cls in paediatric can be used to correct astigmatism as in adults; anisometropia (to reduce the retinal image disparity & to prevent amblyopia) as well as aphakia • Children can be fitted with smaller diameter e.g. RGP OAD/ OZD = 9.2/7.88 mm because they have smaller palpebral fissure… • Children can be fitted with larger diameter lenses because they may fall while on their eyes

19. BCR selection:

20. Keratoconus • Is a progressive disorder in which the cornea has irregular shape • Onset: around puberty • Autosomal dominant • Usually bilateral; but assymetrical • Systemic association: e.g. Down syndrome; Turner syndrome; Marfan syndrome • Ocular association: e.g. retinitis pigmentosa; vernal keratoconjunctivitis;

21. According to morphology can be classified into Nipple cones: small size 5mm; steep curvature; the apex of the cone is central or infero-nasally

22. Oval cones: 5-6mm size; ellipsoid (oval) & displaced inferotemporally

23. Globus cones: the largest >6mm

24. Presentation: visual impairment due to progressive myopia & astigmatism (usually reported for one eye); changes in spectacle Rx; decrease tolerance to contact lens wear; • Signs: central or paracentral stromal thinning; apical protrusion; irregular astigmatism; steepening of the cornea graded according to keratometry readings (mild <48D, moderate 48-54D, severe >54D) Early in the disease: oil droplet reflex on ophthalmoscopy; irregular scissor reflex on retinoscopy; Vogt lines (i.e. deep vertical stromal striae) on slit-lamp exam; irregular astigmatism on keratometry; abnormal corneal topography

25. Vogt striae (i.e. line) in keratoconus

26. Late in the disease: Munson sign (i.e. bulging of the lower lid on downgaze); visual acuity worsens; watering; oedema; stromal scarring after beaks healing; Munson sign in keratoconus

27. Treatment: spectacles to correct regular & mild irregular astigmatism; contact lenses (e.g. rigid; toric); Keratoplasty • http://www.youtube.com/watch?v=8jDBvjbKMR4 • http://www.youtube.com/watch?v=Kwv9juznA7c • http://www.youtube.com/watch?v=QRNzDC5xlc8