Week 10 Flashcards
Threshold for high ametropia
Myopia and hyperopia above and equal to 10D
High astigmatism more than 4D
What’s the problem with a high minus lens and what’s the carrier used
Thicker in the edges and lens hitch under upper eyelid, carrier is Plano or positive to reduce high riding lens
What is the issue with high plus lens and what carrier is used
Thicker in centre, gravity makes lens drop, negative carrier provides lid attachment
Fitting soft lenses in high ametropia
SiHy,
modality frequent replacement 3/12ly
, highest power available minus 30D.
TD larger to help with centration = larger by 0.30-0.50mm
What are the long term issues using hydrogel lenses for high ametropia
Oedema and neovascularisation
Fitting strategies for RGP lens for high ametropia
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
RGP lens fitting for aphakic corneas
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
What is the BOZR AND TD OF Corneoscleral lenses in aphakic corneas
TD- 11.5-13mm - larger
BOZR- usually 0.50 flatter than K - apical touch
Soft lens fitting in aphakia
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
Things to consider with aphakic children
Initially EW/CW until DW can be an option ( handling issues)
RGP above 5 years old
School children need over specs (bifocals,PPLS)
Advantages of cosmetic contacts - tints
Decreases adaptive photophobia (albinism or aphakia)
Increases handling
Enhances colour vision/ perception
Enhances or change natural eye colour
Disadvantages of cosmetic contacts tints
Decreases night vision
Decreases comfort
RGP limited options
Photochromic - light/ dark transition speed is slow
Advantages of hand painted cosmetic contacts
Aniridia
Trauma
Specialist needs
Disadvantages of hand painted cosmetic lenses
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
Parameters needed for cosmetic contact lenses
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
Options for cosmetic cls
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)
How is Colour vision enhanced in cosmetic lenses
For colour blind people or people with colour deficiency
X- chrome lenses help perceive the difference in colours by increasing contrast
Irregular corneas
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
What is keratoconus
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
Features/ causes of keratoconus
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
Clinical features and management of keratoglobus
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
Symptoms of keratoconus
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
Early Signs of keratoconus
Progressive myopia and irregular astigmatism
Scissoring ret reflex
Distorted keratometry mires
Distorted placido rings
Inferior steepening in topography graphs
Later signs of keratoconus
Vogts striae (vertical lines)
Fleishers ring (partial or complete iron ring surrounding corneal periphery)
Prominent corneal nerves
Other/worse signs of keratoconus
Corneal scarring
Munsons sign
Thinned cornea
Acute hydrops (corneal oedema)
2 Types of keratoconus
- Nipple or centred cone- within 2mm of centre of cornea. As it progresses the cone becomes steeper and smaller in diameter (like a football)
- 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)
Classification of keratoconus
Mild is less than 48D (k is 7.03mm)
Moderate 48-54D (7.03-6.25mm)
Severe is above 54D (6.25 and steeper)
Surgical Management of keratoconus
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
Non surgical management of keratoconus
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
Clinical features and management of pelucid marginal degeneration
Rare, progressive peripheral corneal thinning
Bilateral
Adulthood
Features: effects inferior cornea
NO FLEISCHER RING OR VOGTS STRIAE
Management: spectacle and CLs
CXL
keratoplasty
What astigmatism does PMD induce
ATR because it’s steeper in the 180 degrees and flatter in 90 degrees
Inferior thinning so ATR
Advantages of Soft lenses for irregular corneas
Standard soft toric in early stages
Excellent comfort, disposability and lower initial cost
Disadvantages of soft lenses for irregular corneas
Inability to mask moderate/ severe irregular astigmatism
High order aberrations
Compromise quality of vision?
Advantages of RGPS cls for irregular corneas
Provide better vision
Correct astigmatism and optical aberration Better than soft
High O2 transmissibility
Greater tolerance in px with dry eyes
Disadvantages of RGP for irregular corneas
Poor fitting can damage cornea
Do not fit FLAT cls !
What are the risks of a flat fit RGP on an irregular cornea
Cause abrasions and scarring
What are the risks of a steep RGP on an irregular cornea
Risk of corneal steepening, imprinting of mid periphery, 3 and 9 o clock staining, poor vision
What is a 3 point touch for a RGP fitting on irregular cornea
Ideal fit
Lens support and bearing shared between the corneal apex and the para central cornea
Advantages of corneo-scleral cls
Comfort since lens edges tuck under the lids -larger than standard RGP
More stable vision
Not easily lost
larger BOZD
Disadvantages of corneo-scleral cls
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
What are scleral cls
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
Advantages of scleral cls
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
What conditions can scleral cls be beneficial
Severe dry eye sjorgren syndrome
Exposure keratitis
Filamentary keratitis
Persistent epithelial defects
Neutrophic cornea
How to fit scleral lenses
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
What are hybrid CLs
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)
How to fit hybrid CLs
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
What are piggy back CLs
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.
Uses of therapeutic/ bandage cls (6)
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
What is Billous kertopathy and how do therapeutic cls help
Chronic corneal edema caused by endothelial dysfunction
Continues soft CL wear to reduce the pain
How do therapeutic cls help recurrent corneal erosions
Due to trauma or epithelial basement membrane dystrophy
Cls promote healing and re-epithelialisation
Cls should be worn in CW
Soft lenses most used
How do therapeutic cls help in post -refractive surgery (PRK/ LASIK)
Reduces symptoms
How do therapeutic cls help severe dry eye
SiHy improve discomfort and blurred vision
Modern scleral and mini scleral retainer fluid reservoir which facilitates both hydration and protection of cornea
How do therapeutic cls help trichiasis
Soft CL reduce symptoms and damage before ocular surgery
How do therapeutic cls help and what causes
corneal thinning/ perforations
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)
What is the materials and Fitting of bandage lenses
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
