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Contact Lenses > Week 10 > Flashcards

Week 10 Flashcards

1
Q

Threshold for high ametropia

A

Myopia and hyperopia above and equal to 10D
High astigmatism more than 4D

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2
Q

What’s the problem with a high minus lens and what’s the carrier used

A

Thicker in the edges and lens hitch under upper eyelid, carrier is Plano or positive to reduce high riding lens

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3
Q

What is the issue with high plus lens and what carrier is used

A

Thicker in centre, gravity makes lens drop, negative carrier provides lid attachment

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4
Q

Fitting soft lenses in high ametropia

A

SiHy,
modality frequent replacement 3/12ly
, highest power available minus 30D.
TD larger to help with centration = larger by 0.30-0.50mm

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5
Q

What are the long term issues using hydrogel lenses for high ametropia

A

Oedema and neovascularisation

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6
Q

Fitting strategies for RGP lens for high ametropia

A

Fit the mean K
fluorescein shows apical clearance
Aim for Lid attachment to assist with centration
Larger TD- instead of -2mm do -1.50mm from HVID

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7
Q

RGP lens fitting for aphakic corneas

A

BOZR between mean and steepest k to help with stability and centration
Fluorescein- apical clearance
TD large between 8.8-10.5
Lenticular - Negative carrier
Centration -often superior or temporal
If sits low increase TD
Avoid BST
Toric peripheries for high astigmatism
Need tint and UV block

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8
Q

What is the BOZR AND TD OF Corneoscleral lenses in aphakic corneas

A

TD- 11.5-13mm - larger
BOZR- usually 0.50 flatter than K - apical touch

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9
Q

Soft lens fitting in aphakia

A

Hy ( med to high wc)
Large TD 13-16mm
BOZR 0.3mm flatter than K for TD upto 14mm
Can be continuous wear- 3-6/12ly replacement
SiHy-flatter due to high modulus so stiffer

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10
Q

Things to consider with aphakic children

A

Initially EW/CW until DW can be an option ( handling issues)
RGP above 5 years old
School children need over specs (bifocals,PPLS)

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11
Q

Advantages of cosmetic contacts - tints

A

Decreases adaptive photophobia (albinism or aphakia)
Increases handling
Enhances colour vision/ perception
Enhances or change natural eye colour

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12
Q

Disadvantages of cosmetic contacts tints

A

Decreases night vision
Decreases comfort
RGP limited options
Photochromic - light/ dark transition speed is slow

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13
Q

Advantages of hand painted cosmetic contacts

A

Aniridia
Trauma
Specialist needs

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14
Q

Disadvantages of hand painted cosmetic lenses

A

Limited material compatibility with rigid and soft
Lower Dk and Dk/t
Lower comfort and WT as len thicker
High risk of corneal oedema and neovascularisation
Tunnel effect can restrict FOV
Can’t use fluorescein to asses opaque rgp lenses
Rgp may need fenestrations as increase in dimpling /deposits /frothing and reduced comfort

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15
Q

Parameters needed for cosmetic contact lenses

A

RGP: TD larger than 11.5 (bigger)
Soft: iris diameter standardised TD 11.5
Pupil size: 5-6mm (bigger)
Black pupil: occlusion or prosthetic purposes

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16
Q

Options for cosmetic cls

A

Opaque or semi opaque
- laminated insert rgp
Iris matching to photograph of other eye or iris buttons

Tints
Depends on iris colour and ambient lighting - hard to change brown iris
- can be solid tint or printed matrix ( natural effect)

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17
Q

How is Colour vision enhanced in cosmetic lenses

A

For colour blind people or people with colour deficiency
X- chrome lenses help perceive the difference in colours by increasing contrast

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18
Q

Irregular corneas

A

Corneal ectasia - thinning of stroma and loss of elasticity of connective tissue fibres
-Keratoconus - conical and central cornea
-Keratoglobus - whole cornea
- pellucid marginal degeneration - peripheral cornea

Corneal distortion
- scarring and refractive surgery

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19
Q

What is keratoconus

A

Progressive, non-inflammatory corneal disease characterised by central or paracentral corneal thinning and ectasia of the cornea resulting in a high degree of irregular astigmatism

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20
Q

Features/ causes of keratoconus

A

Presents in teens
Bilateral but asymmetric
Progressive
Autosomal dominant
Systemic causes: downs, EDS, marfans
Ocular causes: vernal KC, blue sclera, aniridia, eye rubbing, floppy eyelid syndrome, RP

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21
Q

Clinical features and management of keratoglobus

A

Extremely rare and from birth or acquired onset

Severe version of oval cone ( late stage)

Clinical features: globular ectasia and acute hydrops (sudden onset of corneal oedema) is rare
Cornea more prone to rupture or mild trauma

Management: surgical management is difficult
CL often unsatisfactory
Intacts and corneal cross linking CXL can be useful
Protect eyes from trauma

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22
Q

Symptoms of keratoconus

A

Asymptomatic in early stages
Visual distortion/ visual loss in one eye due to irregular astigmatism
Myopia and many cases corneal scarring
Ghosting/ monocular diplopia due to irregular astigmatism
Photophobia and flare especially at night

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23
Q

Early Signs of keratoconus

A

Progressive myopia and irregular astigmatism
Scissoring ret reflex
Distorted keratometry mires
Distorted placido rings
Inferior steepening in topography graphs

24
Q

Later signs of keratoconus

A

Vogts striae (vertical lines)
Fleishers ring (partial or complete iron ring surrounding corneal periphery)
Prominent corneal nerves

25
Q

Other/worse signs of keratoconus

A

Corneal scarring
Munsons sign
Thinned cornea
Acute hydrops (corneal oedema)

26
Q

2 Types of keratoconus

A
  1. Nipple or centred cone- within 2mm of centre of cornea. As it progresses the cone becomes steeper and smaller in diameter (like a football)
  2. Oval cone- centre outside the central 2mm of the cornea (usually temporal). As it progresses it becomes steeper and larger in diameter (like a rugby)
27
Q

Classification of keratoconus

A

Mild is less than 48D (k is 7.03mm)
Moderate 48-54D (7.03-6.25mm)
Severe is above 54D (6.25 and steeper)

28
Q

Surgical Management of keratoconus

A

Corneal cross linking (CXL) slows progression
Intact- when KC is stable but px can’t achieve good vision with specs or CLs
Corneal transplantation-severe KC or when stable but px can’t achieve good vision or intolerant to CLs

29
Q

Non surgical management of keratoconus

A

Px education
No rubbing eyes
Ocular lubricants
Topical anti allergics for allergic pxs
CLs for better vision - corneo rgp , corneo-scleral , scleral , hybrid , piggy-back

30
Q

Clinical features and management of pelucid marginal degeneration

A

Rare, progressive peripheral corneal thinning
Bilateral
Adulthood

Features: effects inferior cornea
NO FLEISCHER RING OR VOGTS STRIAE

Management: spectacle and CLs
CXL
keratoplasty

31
Q

What astigmatism does PMD induce

A

ATR because it’s steeper in the 180 degrees and flatter in 90 degrees
Inferior thinning so ATR

32
Q

Advantages of Soft lenses for irregular corneas

A

Standard soft toric in early stages

Excellent comfort, disposability and lower initial cost

33
Q

Disadvantages of soft lenses for irregular corneas

A

Inability to mask moderate/ severe irregular astigmatism
High order aberrations
Compromise quality of vision?

34
Q

Advantages of RGPS cls for irregular corneas

A

Provide better vision
Correct astigmatism and optical aberration Better than soft
High O2 transmissibility
Greater tolerance in px with dry eyes

35
Q

Disadvantages of RGP for irregular corneas

A

Poor fitting can damage cornea
Do not fit FLAT cls !

36
Q

What are the risks of a flat fit RGP on an irregular cornea

A

Cause abrasions and scarring

37
Q

What are the risks of a steep RGP on an irregular cornea

A

Risk of corneal steepening, imprinting of mid periphery, 3 and 9 o clock staining, poor vision

38
Q

What is a 3 point touch for a RGP fitting on irregular cornea

A

Ideal fit
Lens support and bearing shared between the corneal apex and the para central cornea

39
Q

Advantages of corneo-scleral cls

A

Comfort since lens edges tuck under the lids -larger than standard RGP
More stable vision
Not easily lost
larger BOZD

40
Q

Disadvantages of corneo-scleral cls

A

Limbal impingement (interfere with limbus stem cells) from the lens periphery and with the risk of stem cell damage
More complicated to design and fit

41
Q

What are scleral cls

A

Scleral cls rest solely on the sclera. It is intended to vault the cornea and in its entirely to retain a fluid reservoir between the lens and the eye

Small diameter 14.5-18mm
Large diameter 19-24mm

42
Q

Advantages of scleral cls

A

Large TD eliminates lid sensation and issues associated with lens movement
Lower risk of corneal damage compared to RGP due to absence of corneal contact and minimal movement
The liquid reservoir keeps ocular surface hydrated, reduces ocular discomfort and protects the cornea

43
Q

What conditions can scleral cls be beneficial

A

Severe dry eye sjorgren syndrome
Exposure keratitis
Filamentary keratitis
Persistent epithelial defects
Neutrophic cornea

44
Q

How to fit scleral lenses

A

According to fitting guide
Based on sagital height of lens and eye
Lenses have to be inserted full in saline solution (without preservatives) and fluorescein to assess the fit

45
Q

What are hybrid CLs

A

Central RGP material for good vision
Peripheral soft material (siHy or Hy) for good comfort
Useful for KC, PMD, post-LASIK, corneal transplant
Special lens care solutions suitable for soft and RGP lenses needed
Careful when cleaning (risk of seperation between both zones)

46
Q

How to fit hybrid CLs

A

According to CL guide
Based on saggital height of the eye and lens
Lenses have to be inserted full of saline solution (without preservatives) and high weigh fluorescein to assess the fit

47
Q

What are piggy back CLs

A

Consist of a soft lens underneath a corneal RGP to act as a cushion to a well fitting RGP
DD siHy used
The power of the soft Cls can be altered to help in the RGP fitting
Use of 2 cls= more cost and reduce O2 permeability.

48
Q

Uses of therapeutic/ bandage cls (6)

A

Promote epithelial/ corneal healing
Wound coverage
Pain relief
Mechanical protection of the ocular surface
Maintaining corneal hydration
Drug delivery

SiHy are the most common used

49
Q

What is Billous kertopathy and how do therapeutic cls help

A

Chronic corneal edema caused by endothelial dysfunction
Continues soft CL wear to reduce the pain

50
Q

How do therapeutic cls help recurrent corneal erosions

A

Due to trauma or epithelial basement membrane dystrophy
Cls promote healing and re-epithelialisation
Cls should be worn in CW
Soft lenses most used

51
Q

How do therapeutic cls help in post -refractive surgery (PRK/ LASIK)

A

Reduces symptoms

52
Q

How do therapeutic cls help severe dry eye

A

SiHy improve discomfort and blurred vision
Modern scleral and mini scleral retainer fluid reservoir which facilitates both hydration and protection of cornea

53
Q

How do therapeutic cls help trichiasis

A

Soft CL reduce symptoms and damage before ocular surgery

54
Q

How do therapeutic cls help and what causes
corneal thinning/ perforations

A

Common cause of perforation: accidental injury and surgical trauma
Lens can prevent the extrusion of the ocular content before surgery

Common cause of corneal thinning: RA results in keratolysis that destroys corneal stroma
Lens prevent perforation by reinforcing cornea and preventing distension by the IOP (prevents swelling from increasing pressure)

55
Q

What is the materials and Fitting of bandage lenses

A

Materials-
biomimetic (better for tear film production issues), exposure keratitis

high water content hydrogel (better for painful eye needing several weeks of cw like bullous keratopathy)

SiHy (wound healing) like persistent epithelial defect

rigid (severe dry eye and corneal exposure/ trichiasis) - large corneal; limbal diameter TD 12.50 and scleral

Fitting: Plano, BOZR and TD are flatter with higher water content hydrogels, CW with lenses replaces every 4-8 weeks

Contact Lenses (4 decks)

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