Overnight Wear (M2) Flashcards
What is the timing of wearing CLs to be considered extended wear? 1. Continuous wear? 2
- 1 to 6 nights of overnight wear
2. 30 days of overnight wear
What are the benefits of overnight wear CLs?
- infrequent application and removal
- good vision at all times
- reduces cost associated with lens care
What was thought to be the primary culprit of microbial keratitis, but was found to be false after SiHy technology saw no dec in prevalence?
hypoxia
What is the Holden Mertz criteria Dk/t value to avoid excess overnight edema and limbal hyperemia?
125
What is the Holden Mertz criteria Dk/t value that can lead to lid and lens edema that is recoverable during eye wear time?
87
What is the Holden Mertz criteria Dk/t value to avoid end of seventh day edema?
35
What is the Holden Mertz criteria Dk/t value that leads to none to trace end of first day edema and is the daily wear criteria?
24
What happens to the Dk of a hydrogel lens with increased water content? 1. Silicone hydrogel lens? 2
- increases Dk
2. decreases DK until about 70% water content and then increases
Do males or females wear their CLs overnight more often?
males
Which GP lenses can be used for extended wear?
- Menicon Z
- Boston XO2
- CRT
What is the follow up schedule for an extended wear patient?
1 day, 1 wk, 1 month, 3 months, 1 yr
What should be done at the initial fit for extended wear patients?
- educate patient on risks and benefits
2. sign informed consent?
What are the conditions that occur when the lids are closed?
- hypoxia
- dec tear exchange
- inc CO2
- acidic pH
- inc in bacterial colonization
What are the possible impacts of CLs on the endothelium?
- polymorphism (diff sizes)
2. pleomorphism (diff shapes)
What are the impacts of CLs on the epithelium?
- thinner epithelium
- dec rate of exfoliation
- dec stem cell turnover if low Dk
What are the dots on the corneal midperiphery and periphery that indicate hypoxic stress? 1. Do these have reversed or non reversed illumination?
- epithelial microcysts
2. reversed illumination
How does switching to SiHy lenses impact the amount of microcysts present?
increases with a spike at first then decreases overall
How much vascularization is considered to be significant? 1. What materials lead to this? 2
- 1mm or more
2. lower Dk materials
What appears in the cornea with 5% edema? 1. With 10%? 2. With 15%? 3. What is the normal percent amount of edema from overnight wear? 4
- loss of transparency
- folds appear
- striae appear
- 3 to 4%
What is the possible impact of low Dk/t (SiHys and hydrogels may too though) on the stroma?
dec keratocyte density
What is the possible impact of low Dk on refractive error?
half saw -0.25 to -0.50 myopic shift
What is a side effect of SiHy lenses that leads to dots on the cornea?
mucin balls
What is the percentage of symptomatic patients for extended wear SiHys?
2.5 to 6%
How does the risk of MK compare for ortho-K, daily wear GP, and soft lenses?
highest to lowest risk: soft lenses, ortho-K, DW GP
