Contact Lens

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"The indications can be divided into ..."

Indications for contact lens

1. Refractive (most common)

2. Therapeutic (see below)

3. Cosmetic

• Leucocoria

• Phthsis bulbi

4. Diagnostic and surgical (goniolens, fundus contact lens)

<ïï> What are the therapeutic indications for contact lens?

1. Optical

• Uniocular aphakia

• Irregular astigmatism — keratoconus

2. Pain relief

• Bullous keratopathy

• Corneal abrasions

• Post photorefractive keratectomy

3. Promote corneal healing

• Recurrent corneal erosion

• Persistent epithelial defect

• Thygeson's keratitis

• Superior limbic keratoconjunctivitis

• Filamentary keratitis

4. Protect cornea

• Exposure keratopathy

• Entropian, trichiasis

• After ptosis operation

5. Perforated corneas

• Descematocoele

6. Pharmaceutical delivery device

Therapeutic indications for contact lens tQ Exam tips:

Section 3: Corneal and External Eye Diseases What ate the materials used in contact lens?

'The ideal material for contact lens should be ..." "The current materials include ..."

Ideal material for contact lens

1. Optically clear

2. High oxygen transmission

• Water soluble

• Related to Dk/L, where Dk = permeability, L = thickness

3. Comfortable

• Surface wettability

4. Low complication rates

5. Durable

• High tensile strength

• Resistant to deformation, tear

6. Ease of sterilization

Current contact lens material

1. Hard — PMMA (polymethylmethacrylate)

• High water content — extended wear soft contact lens (EWSCL)

• Low water content — daily wear soft contact lens (DWSCL)

3. Semi-flexible/rigid gas permeable (RGP)

• CAB (cellulose acetate butyrate)

<§> Tell me about soft contact lens. What are advantages and disadvantages?

"Soft contact lens can be broadly divided into extended wear (EWSCL) or daily wear (DWSCL)." "They are made of hydrogel, with varying water contents ..."

Soft contact lens

1. Advantages of soft CL

• Comfortable

• Greater stability

• Ease of adaptation

• Rarely get overwear syndrome

• Lack of spectacle blur

2. Disadvantages

• Poorer VA in eyes with astigmatism

• Higher risk of complications

• Durability low

3. Indications for DWSCL

• First time wearer

• Part time wearer

• Failed extended wear

4. Indications for EWSCL

• Infants, children and elderly

• Lack of manual dexterity

• Therapeutic indications

<S> What are the pathophysiological changes to the eye with contact lens wear?

"The pathophysiological changes included ..."

Pathophysiological changes to the eye

1. Dessication

2. Microtrauma

3. Hypoxia

4. Hypersensitivity/toxicity

"Contact lens wear complications can be divided into blinding and nonblinding."

Complications of contact lens wear

1. Blinding

• Infective keratitis

• Corneal scarring

2. Nonblinding (note: related to the 4 pathophysiological changes!)

• Related to dessication

Dry eye syndrome

• Related to microtrauma

• Punctate epithelial erosions

• Corneal abrasion

• Superior limbic keratoconjunctivitis

• Related to hypoxia

• Corneal edema

• Epithelial microcysts, acute overwear syndrome (rupture of cysts)

• Corneal vascularization

• Related to hypersensitivity/toxicity

• Giant papillary conjunctivitis

• Allergic conjunctivitis (disinfectant, preservative — thiomersal)

• Sterile infiltrates

3. Contact lens changes

• Distortion, breakage

• Microorganisms — bacteria, fungi

<5> Tell me about giant papillary conjunctivitis

"GPC is one of the common contact lens complication ..." "Secondary to hypersensitivity." "GPC presents in different stages ..."

1. Stages

• Stage 1: Preclinical GPC (symptoms only)

• Stage 4: Subconjunctival scarring

\Nhatare the complications of contact lens wear?

2. Etiology

• Contact lens wear

• 30% of patients with EWSCL

• 15% of patients with DWSCL

• Hypersensitivity (asthma, hay fever)

• Trauma (foreign body and prothesis)

3. Management

• Decrease wearing time

• Reevaluate fit and material/change to RGP if needed

• Topical antihistamines and mast cell stabilizers

• Topic steroids if necessary

• Consider discontinuation of contact lens wear

Contact lens fitting

1. History

• Visual requirements, ocular diseases

2. Fitting procedure for soft contact lens

• Base curve — inversely proportional to the keratometry (K) reading

• Choose from 3 standard curves available (8.1, 8.4, 8.7mm)

• Refraction

Ocular examination

• Palpebral aperture and tightness . SLE

• Select trial lens (base curve/refraction/corneal diameter e.g. 8.4/-4.0D/13.5)

• Tightness (too flat or too steep)

• Over-refract with contact lens on (e.g. if -1.5D gives VA of 20/20)

3. Fitting procedure for hard contact lens

• Choose from different individual curves (7.2 to 8.5)

• Refraction (choose from different powers for each base curve)

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