Midterm 2 Flashcards
Computer Vision
The complex of eye and vision problems related to near work which are experienced during or related to computer use
Prevalence of CVS
Eye and vision problems are the most frequently reported health-related problems for computer workers. Poor vision caused or aggravated by computer use
Why is working at a computer more visually demanding?
Traditional BV problems with near work, frequent saccadic eye movements, continuous eye focusing, alignment demands.
Problems specific to the computer: Poorer contrast, increased glare (direct light, not reflected), different working distance (further than reading), Different viewing angles
When do problems with CVS occur?
When the visual demands of the task exceed the visual abilities of the individual to comfortably perform the task
Is CVS a diagnosis?
No, not in ICD-9/10. Patients with CVS have one or more of the symptoms listed later, symptoms will determine diagnosis.
Symptoms of CVS
Eyestrain/eye fatigue, dry eyes, burning eyes, light sensitivity, blurred vision, HAs, pain of shoulders, neck, back.
Factors to Consider in resolving CVS
- Take a thorough history
- Ergonomics
- Refractive Error
- Illumination
- Dry eye symptoms
- Plus at near
Taking a thorough history (for CVS)
Consider using a pre-exam questionnaire: How many hours a day do you spend on the computer, how far away is the screen, is it at/above/below the eye level. What type of room lighting do you have, do you get up and down from the desk frequently.
Ergonomics
Adjustment of the workstation to the individual needs of the operator is important for overall performance and comfort. Inadequate viewing distances and angles can impose the necessity of awkward postures, contributing to musculoskeletal problems.
Proper viewing distance at the computer
20-26 inches away
Proper viewing angle down at the computer
10-20 degrees
20/20/20 rule
Every 20 mins look at least 20 feet away for 20 secs
Correcting refractive error for CVS
The presence of even a minor vision problem can often significantly affect worker comfort and productivity. If they have small amounts of astigmatism or hyperopia that you wouldn’t normally correct and they are complaining of CVS, this could be the issue.
Illumination and Glare with CVS
Many problems related to lighting may be caused by the introduction of computers into offices where the lighting was originally designed for traditional desktop work. Shouldn’t be in complete darkness, but need to reduce the room light. Bright lights in the peripheral field of view may cause discomfort glare.
Fixing glare for CVS
Faint tint on glasses? Pink/red/yellow- not really proven significantly. Or AR coating, visors on the computer. Anti-glare screens: Antireflective screens, privacy filters.
Dry eye syndrome with CVS
Many office environments contribute to eye irritation for workers because of the dry atmosphere. Use of computers is associated with a decreased frequency of blinking and increased tear evaporation. Tell patients to blink more! Give them tear products.
Plus at near for CVS
Accommodative disorders are the prevalent among symptomatic computer users. Test accommodation: NRA/PRA, accommodative facility, FCC, PRIO testing
PRIO computer testing
Duplicates the accommodative demand of a computer screen, and the light characteristics. Device is placed on the nearpoint rod at the computer working distance. Use dynamic retinoscopy to determine add
Comparing PRIO vs. MEM
Accommodative response is the same.
Study involving most accurate nearpoint test.
Presbyopes: Similar results between methods. No matter what test used, the results were predictable
Prepresbyopes: highly variable with NRA/PRA, and Snellen VA, lowest variability with dynamic ret and FCC.
Computer glasses
Common computer lenses: single vision for intermediate, occupational/computer progressives, Bifocals (inter/near), Trifocals with a large intermediate.
Intermediate add
About half the add power added to the distant power (for single vision glasses). Air on side of weaker rather than stronger. For intermediate/near bifocals, the other half of the add will be in the segment. For trifocals, part of the segment will have half the add, the other part will have the full add.
Computer progressives
Have a much larger intermediate area, less distance.
3D vision syndrome
The intentional mismatch between vergence and accommodative distance. Similarities between this and CVS (this difference is this is at near)
Ways to see 3D
Anaglyph, passive polarized, active shutter, glasses free
Why is seeing 3D important?
It helps develop efficient reading skills, it increases participation as more schools adopt 3D as a teaching tool, increasingly utilized in a growing lift of professions
Causes of 3D viewing challenges
Refractive problems: nearsightedness, farsightedness, astigmatism.
Lack of BV: two eyes not properly aligned, strabismus is present, inputs from the two eyes not successfully combined in the brain and 3D stereoscopic perception will not occur.
Amblyopia, Eye coordination problems, accommodation problems, dizziness and nausea from rapid motion effects (disagrees with balance system)
3D benefits as a public health tool
AOA says there is no evidence that viewing or attempting to view 3D will harm a child’s eyes. Difficulties with 3D can unmask undiagnosed deficiencies and lead to treatment
Treatment Options for 3D vision
Glasses/contact lenses for simple refractive error, glasses to improve eye-focusing or eye coordination, treatment for amblyopia or strabismus, optometric vision therapy to teach eye coordination
UVA, UVB, UVC
UVA: 320-400nm
UVB: 290-320nm
UVC: 100-290nm
The longer the wavelength the more into the skin. UVB (absorbed by cornea/lens)is most dangerous as UVA (may be absorbed by lens) doesn’t go into skin, and UVC is mostly absorbed by the ozone
Benefits of UV
Minimum exposure required to maintain vitamin D adequacy. Prevents ricketts, osteomalacia, and osteoporosis
Sun protection factor
Higher SPF blocks more UVB rays. Just applies to UVB. The SPF number is the theoretical amount of time you can stay in the sun compared to without it.
UV radiation increases:
Closer to the equator, higher the altitude, between 10am and 2pm in the Summer
Factor involved in determining the UV index
Elevation of the sun in the sky, amount of ozone n the stratosphere, cloud conditions.
UV Index range
0 (nighttime) to 15/16 (tropics at high elevations and clear skies). 1-2 (low), 3-5 (moderate), 6-7 (high), 8-10 (very high, UV levels dangerous), 11+ (extreme, light skin can burn in minutes)
UV index
The next day’s forecast of the amount of damaging UV radiation expected to reach the time when the sun is highest in the sky (solar noon)
UV and the eye
The entire eye is subject to damage, UV has direct DNA damage and or phosensitixing reactions causing production of free radicals and eventual oxidative damage. IR has higher potential for tissue damage. Tissue must absorb energy to cause damage. UV may cause pterygium/pinguecula
Studies about UV exposure and eye
Most studies state that many eye diseases are caused by sunlight. Especially Photokeratitis–> caused by UV
Outcomes associated withe UVR with strong evidence of causality
Immune effects (activation of latent virus infection) Effects on skin (types of skin cnacer and sunburn) Effects on eye (photokeratitis and conjunctivitis, solar retinopathy, pterygium, cancer of cornea and conjunctiva, cortical cataract)
Cornea and UV light
Corneal epithelium plays a significant role in protecting eye from UV. Anterior layers of cornea are believed to be twice as effective at absorbing UVB as the posterior layers
Photokeratitis
CAUSED BY UV
Really akin to a sunburn of the cornea and conjunctiva, presents with tearing, pain, photophobia. Not apparent until at least several hours after exposure.
Peripheral Light focusing
Obliquely incident light is refracted from the peripheral cornea to concentrated sites inside the anterior segment. Can create areas of concentrated light in the nasal corneal limbus and the lens cortex. May be implicated in pterygium and age-related cortical cataracts. Only wraparound sunglasses or UV blocking contact lenses may provide protection against PLF.
Lens and UV light
Age-related cataracts. Clear association between UVB and CORTICAL cataracts, NOT nuclear cataracts
Choroid and Retina and UV light
Uveal melanoma, solar retinopathy, maybe AMD
Light blocking capabilities of lens materials
Crown glass about 39%, polycarb, trivex, CR-39 100% of UVB, CR-39 lets in about 10% of UVA
UV coatings
For plastic lens, submerge into a hot UV dye, just like you would tint a lens.Glass lenses have certain lenses
AR coatings and UV reflection
Near complete protection against all frontal UV exposure. AR coatings may reflect UV radiation off the back side of the lens into the eye.
Preferred sunglas frame recommendations
Ensure sufficient pantoscopic tilt and faceform wrap. Fit very closely to wearer’s head and face
ANSI standard for nonprescription sunglasses
Impact-resistant standards, flammability standards, Cosmetic (lens free of pits, scratches, grayness, water marks, bubbles), Refractive (zero power in any meridian: plano with tolerance of +.12 to -.25, cylinder less than .12, prism less than 1/4) Transmittance depends on color and other factors
Transmittance standard for nonprescription for sunglasses
Light: 40%, Med 8%-40%, Dk 3-8%, have to let in 6-8% light from traffic signal. 1% max UV
Contact Lenses and UV
UV-blocking contact lenses (class 2) must absorb 70% UVA and 95% UVB. Class 1 blockers must block 90% of UVA and 99% UVB. Should be able to reduce PLF
Does UV transmission increase through contact lens wear?
Wearing contact lenses does not significantly affect the transmission of UV through the lens
Advantages of Contact lenses as UV protection
Protects limbal stem cells, reduces PFL, no back side UV reflections, worn all day
Disadvantages of CL as UV protection
No protection to eyelids or most of the conjunctiva
High energy violet/blue light
Has been implicated as having a role in ARMD. Has non visual functions in mammals, regulates the circadian cycle. Present outdoors from sun, all year long. Present indoors from LED light in most modern lighting and display systems
Ciracadian Rhythms
Physical and mental behavior and mental behavior changes following a 24 hour cycle. Nerve cells in the hypothalamus above the optic chiasm in the suprachiasmatic nucleus. less light= more melotonin, more blue light=less melatonin= more wakefullness
IOLs and UV
IOLs need to be UV blocking, there has been support that they need to be blue filter too especially if the person has ARMD
Corneal Ectasia
Thinning of cornea. Genetic disorder (keratoconus) Refractive surgery, Trauma, Keratitis.
Corneal Collagen Cross-linking
Indicated for Corneal ectasia. Safer than corneal transplant. Increases rigidity of cornea to prevent further deformation. Use riboflavin to absorb UVA and induce photochemical reaction. This interaction produces oxygen reactive free-radical species. Results in covalent bonds between collagen fibers
