Ocular Diseases Assoc w/LV Px

Albinism

A congenital condition characterised by lack of pigment. Can be oculocutaneous (skin and eyes) or just ocular. 1 in 20000 of general population. Cat. into Tyrosinase +ve or -ve, -ve has more severe effect on vision 6/60-6/120, +ve better 6/24 which improves over time.

• VF appear full
• Blue irises - transillumination
• Photophobia
• Nystagmus
• Hypoplasia of macula
• High incidence of strab
• Poor stereo
• High refractive error
• SYSTEMIC - white or yellowish hair, eyebrows, eyelashes, pink skin, sensitive to sun damage
• Assoc w/Hermansky-Pudlack syndrome - genetic metabolic disorder

Low vision management involves corrective Rx, aperture control contact lenses, tints, UV protection, magnification for distance and near

Cataracts

The opacification of the crystalline lens, classified according to area affected - ant/post subcapsular, ant/post cortical, equitorial, nuclear. Caused by trauma, metabolism, toxic cause, 2ary to inflammation, drugs, hereditary, age-rel. 95% of those over 65 have some form of lens opacification

• VA varies w/degree and location of opac, most often bilat but asymmetric, nucscler not often assoc w/vision loss - more myopic. Posterior subcap has profound effect on VA especially with small pupil
• VF - ok
• Dull/abnormal ret reflex, refraction more myopic, reduced acuity, increased glare, distortion, monoc diplopia, altered colour perception. Treated by removal

LV management centres around lighting, filters and AR coat for glare and magnification

Diabetes Mellitus (I = juvenile onset, II = adult onset)

Signs and Symptoms are excessive thirst, urination, hunger, fatigue w/weight loss and recurrent infections. DR is the biggest single cause of registered blindness in the UK amongst working age people. Smoking and obesity increase the risk. Type I will tend to show retinopathy within 10 to 12 years, type II after 20. 60% will show some degree of retinopathy.

• VA from 6/6 to total blindness, fluctuates dude to blood sugar level if poorly controlled, lens changes (myopic) and CMO (hyperopic)
• VF - 2ary complications can cause loss - laser burns, retinal detachment, Glaucoma, CMO - macular degen.
• Other complications - accomm insuff, Diplop, Cats, Glau (rubeosis), RD, MD/CMO, decreased corneal sensitivity, neovasc, haemorrhages

LV Vision management - refraction, sunglasses and filters, increased illum, mag/minification, flashlight/torch, non-optical, mobility services support groups.

Glaucoma

Open angle - asymptomatic, closed angle pain, blurred vision, photophobia, halos, nausea, vomiting

• VA generally unaffected until end stage
• VF typically respects horizontal midline, arcuate defects, nasal step. Gradually spreads to periphery and centrally
• Diagnostic testing - ON head, VF, IOP, ant chamb angle

LV management w/magnification, lighting indoors & out, glare control, contrast enhancement, minification, peripheral awareness systems, other professional services

Macular Holes

Round red spots in centre of macula 1/3 to 2/3 DD in size, may have grey halo around it where RD happened. May be caused by trauma, myopia, CMO, inflammation but most are idiopathic.

• VA depending on location 6/9-6/120
• VF full thickness holes = dense central scotoma
• Metamorphopsia and reduced VA

LV management with magnification, eccentric viewing, lighting and filters to increase contrast

Macular Disease

Any degenerative condition affecting the macular area. Eg ARMD, Stargardt's, Best's Disease

• Reduced VA D&N, metamorphopsia, central field loss, reduced colour vision, increased glare and photophobia
• Test w/VF, colour testing (D15 usually shows RG loss), flu angiog

LV management with refraction, magnification, lighting, glare control, non-optical, support groups

Myopic Degeneration

This is excessive stretching and expansion of the posterior segment, with scleral and choroidal thinning.

• VA decreases as condition progresses, may lead to NPL from 2ary complications
• VF varies w/structures involved
• Blurred Dv, flashes/floaters, thinning of RPE, posterior staphyloma, Fuch's spot, Retinal detachment
• Associated syndromes - Down's, Marfan's syndrome, Stickler's Syndrome

LV Management refraction, magnification, lighting and contrast enhancement, glare control and photophobia protection, torch @ night, other professional services

RP

1 in 3000-4000 of the population. Most common in males - autosomal recessive/dominant/x-linked

• VA from 6/6 to NLP
• VF starts in mid-periphery and goes inward and outward
• Nyctalopia, light/dark adaptation affected, attenuated BV, bony spicule pigmentation, waxy disc, posterior subcapsular cataracts, CMO

LV Management - minification, peripheral field awareness, magnification, sunlenses, lighting control, torch at night, genetic counselling

Retinopathy of Prematurity

Abnormal proliferation of retinal blood vessels in premature infants receiving oxygen therapy. About 7% of babies in UK born prematurely.

• VA from 6/6 to NLP
• VF variable depending upon which part of the retina is involved
• High myopia, strabismus, RD, glaucoma, cataract, corneal scarring, glare and photophobia, CVI

LV Management - refraction, magnification, sunlenses, filters, lighting control

Causes of Visual Impairment

Global

• 47.8% Cataract
• 13% other -trauma etc
• 12.5% Glaucoma
• 10.6% AMD
• 3.3% Corneal Opacity
• 4.8% DR
• 3.9% Childhood Blindness
• 3.6% Trachoma
• 0.8% Onchocerciasis

Cataract

• Affects about 16m worldwide
• An IOL costs about 10 dollars

Onchocerciasis

• Control programme in west africa over 11 countries which protected 30m people including children, costs $1 per person

Vit A Deficiency

• Xerophthalmia (dry eyes) causes 350,000 children to become blind per annum
• Prevented by good diet with fruit and veg etc

Diabetes

• 2% of the UK pop are known to have it, 10% will have DR that requires ophthalmological intervention
• Untreated 6-9% of those with prolif. DR would become blind each year
• Affects working age group
• Screening and treatment is expensive

Preventing Blindness Worldwide

• Immunisation
• Nutrition & Education
• Personal Hygiene
• Sanitation
• Training and local medical facilities

Support for the Visually Impaired in the YooKay

• Social work - centre for sensory impaired people provides info, advice, equipment, training, certification/registration eye clinic, technical services & library
• RNIB - charity, provides training and rehab, wide range of non-optical LVAs, braille, talking books, advice & campaign for equal rights eg lobbies for provision of new drugs, computer training, funding/carrying out research
• RNIB training courses - goal to provide VIPs with skills, qualifications and confidence to remain in work or obtain employment. Have learning resource centre with study and library area, classrooms, training rooms, recording studio, interview suite, guide dog facilities, cafe_bar, sports facilities, accommodation
• RNIB talking book service - Annual subs, NVA is
• Royal National College for the blind - skills for independent living, academic studies, GCSE/A-Level/AS Levels/BTEC, GNVQ, AVCE
• Royal Blind School in Edinburgh - day/residential school for pre-, primary and 2ary. Scottish braille press there too
• Talking Newspaper Assoc of UK - local volunteers, local press, weekly editions, national newspapers and magazines, annual subs
• Calibre - adult and children's compact cassette library, 6000 adult and 1000 children's books
• National Library Of The Blind 350,000 braille and Moon books, 13,500 music scores, electronic books
• Playback - Glasgow City Council 1976 centre for sensory impairment, registered charity w/80 volunteers, 46,000 cassettes a month. Magazines, newspapers, tape library and reading service
  

Low Vision Rehabilitation

Psychological barriers to process of rehab

• Concealment - px still pretends vision is fine - the eyes still look normal. They may feel the vision loss is seen as a general cognitive decline by others. They may reduce social contact, stay indoors. Younger px may fear losing their job/loss of independence
• Px refusing LVAs - think new glasses will do it. Equate VI with 'blind' and give up. They may have unrealistic expectations as well as other worries like caring for partner/money etc. Practitioner must explain that aids can be difficult to use but be encouraging and REALISTIC - ie don't give them aids they won't use

Prognostic Factors in Predicting Success w/LVA use

You have to wonder what constitutes successful LVA use/assessment - increased VA/confidence/performance of required tasks? Stuff that can be measured: VA, reading speed/acc, frequency of use of LVA.

• VA Studies - success rates vary consid. depending on criteria. Up to 95% of px achieve improvement
• Quality of life studies - Manchester Low Vision Questionnaire
• Attending LV Clinic - 67% px benefit 'a great deal', 22.8% a little, 10.5% not at all

WRT to a successful predictor of LVA use

• VA - poor, improved VA doesn't necess mean that LVA will be any good
• VF - good, extent and location of remaining field important, restricted field tends to have poor prognosis
• Stability of eye cond - good, better chance of success if stable
• Duration of VI - poor prognosis if recent (loss model)
• Cause of VI - poor, depends more on motivation
• Age - Good, younger = better prognosis
• Education/Intelligence, poor, people w/good intel tend to do better, but it's more fluid intel (ie adaptability to new task)
• Motivation - good. PROBABLY THE MOST IMPORTANT FACTOR! Self img/psychological barriers

Px Prefers

• Simple stuff! High spec adds, hand mags, stand mags, illuminated mags

Non-Optical and Sensory LVAs

These make the best use of residual vision/work via sensory substitution. Non-optical aids include daily living aids, environmental design, lighting and contrast and tints.

• Self threading needles, liquid level indicators, talking watches, large number telephones or microwaves, 'bump ons' or 'hi marks' and coloured stickers
• READING - making object bigger (large print books/bills/clocks/watches etc), talking watches or books or newspapers, reading stands, typoscopes, good lighting
• WRITING - felt tips, yellow paper, lined paper, writing frames

Braille was developed in 1824 and consists of 3x2 grid pattern of 6 dots giving 63 characters, 26 letters & contractions & punctuation. There are two levels - in grade 1 every word is spelt out and in grade 2 there are approved contractions for stuff like 'and' and 'with'. 20% of those registered blind can use braille. Books are thick and bulky and it isn't good for the elderly due to loss of sensation in their fingertips. It can be generated by a computer.

Moon is another tactile language that was developed in 1847. It was designed for people who previously had sight, featuring curves and lines that are more approximate to actual letters.

Electronic Aids for reading and writing

• CCTV, video magnifiers, head mounted devices
• Computers - scanners, speech synthesis, braille keyboards/printers, PDAs, USB cameras
• Built into OS - Windows has accessibility, Mac OSX has 'universal access' which enlarges icons, arrow, alters contrast and has voice output.
• Screen magnification software eg Zoomtext is also available.

Mobility Aids

• Canes and Sticks
• Electronic Aids (ultrasound, sonar)
• Dogs (see later)
• People (guides)
• Talking Signs
• Built Environment

White Sticks (if has red stripes this indicates px is deaf too)

1. Symbol Cane - lightweight, folds up, indicated px is VI
2. White walking stick - as above but aids support
3. Long Cane - most common. Developed by war vets in US following world war 2. Needs extensive training (+150hrs). Made of lightweight aluminium, held at chest height at 30 degree angle and swung in L to R arc as foot goes forward. Touches ground at end of travel and may have roller on tip
4. Guide Cane - Shorter/stronger than long cane, used as back up for those with residual vision

Trailing

Technique to help locate door, walk in straight line, detect posn of objects in front of the px on the same side of his body as the extended arm. This can provide useful info about everyday objects, obstacles and potential hazards. In familiar environment the px moves close to the wall with knuckles against it using the other hand in front to detect obstacles

Electronic Mobility Aids

• Ultrasonic - ultracane, hand held (miniguide, palmsonar), head mounted (sonic pathfinder), Bat K sonar-cane
• Laser - laser cane which has three beams (ground, waist, up) and alerts with tones and vibration
• GPS - MOBIC (mobility of blind and elderly people interacting with computers), braille note GPS, Trekker

Dogs

Guide dogs for the blind started in 1931. Running cost is 45m pa and they get no Govt funding. The dogs guide the owner and avoid obstacles, stop at kerbs/steps, find doors, road crossings and frequently visited places and lead across roads. The owner is basically responsible for encouraging the dog while directing and informing it.

Guide dog owners have to be over 16, have VI which makes safe independent travel difficult - marked decrease in VA, CS or VF. 43% of guide dog users are totally blind, mainly due to congenital or early onset degenerative disease. RP makes up 18% and optic atrophy 10%. The average age is 53.

Guide Dog Assessment

General Info Visit

• Info on services and training provided

Mobility Assessment

• Medical Status, cause and degree of VI, options (long cane or other, guide dog assess, non guide dog mobility aids)
• Contrainds - sufficient sight, age, dislike of dogs

Guide Dog Assessment

• Instructor assesses appropriate aid/suitability
• Work with dog to determine whether px can walk with it, follow movements, keep control, react etc
• Assessment of home environment

Breeding

1200 guide dogs are bred each year, mostly labs/lab-golden retr. cross. There has been a programme going since the 60s to reduce health probs and regulate supply. The dogs have x-ray health checks and eye exams

Makin the dog guide

• Puppy walking at 6 weeks old w/volunteer walkers who teach dog to ignore distractions or other dogs, walk on LHS and in straight line, centre of pavement, and stand and wait at kerb. 75% of puppies can do this, the other 25% are killed. No not really they are used as dogs for therapy, for the disabled, RAF, Customs & Excise, Prisons etc
• At 10-12 weeks the clever dogs go to a training centre where a proper dog trainer becomes involved, dog is fitted with harness and does tasks in busier environment etc
• At 3 months advanced training starts and dog is tailored to individ. needs

Pairing

Priority system. At 5 months dog attached to owner then 3-4 weeks intensive training, px taught to take care of dog. The owner pays a nominal 50p for the dog and the dog actually costs 35000 over its lifetime

Working

Continuing support is provided, with regular health checks, food/vet bills, third party insurance. Most dogs work 7-8 yrs. Guide dogs are allowed anywhere thanks to disability discrimination act 1995

Retiring

This is caused by health problems, increased mistakes, loss of concentration, slower walking speed, loss of confidence. The dog can stay with the owner as a pet or be rehoused.

Environmental Design

Simple things

• TV away from windows
• Sit close to TV/blackboard
• Location of reading lights
• At one side of teacher/TV if hemianopic px
• Colour schemes - Light paint on walls, dark round doors, lighter door with contrasting handle, dark flooring, hard flooring - for the sound, contrasting skirting boards for stairs

Architectural Design

• Features to aid VIPs eg lighting contrast
• Wide/sliding doors
• Auditory indicators eg in lifts
• Handrails
• Enclosed Staircases
• Tactile elements like on floors
• Avoid stuff like glass doors
  

LV: Lighting

Lighting

The goal of lightning is to provide adequate lighting in the appropriate places without any glare

• General lighting - there should be an even distribution of light with extra for hazardous areas. Ceilings and walls should be light coloured and non-reflective. Patients should face away from the window in daylight to avoid glare
• Local lighting - take into account inverse square law and also cosine law (put paper as close to 90 degrees to light source as possible to get maximum illuminance
• NB 60yr old needs 3 times the illumination of a 20 yr old due to senile miosis, media opacities and loss of neurons

Glare

• Discomfort Glare - subjective visual discomfort - px feels visually uncomfortable or fatigued. VA not affected by glare and discomfort relieved by tints. EG In uveitis, ocular albinism, cone-rod dystrophy, RP. Can be measured by getting patient to adjust light to a certain level of unpleasantness. No clinical relevance tho
• Disability Glare - Loss of retinal image contrast as a result of intraocular light scatter or stray light. This reduces visual performance. The degree of glare depends on the angle between the task and the glare source & the relative luminance
• Media opacs lead to IO light scatter and veiling luminance across retinal image and a reduction in contrast. Eg ageing, cataract, pos. chamber IOL, PCO, Keratoconus, Corneal Oedema, RK, vit opac

Disability glare can be measured objectively - px viewing an acuity/low contrast chart under controlled lighting conditions. This allows for simulation of everyday situations like flu overhead lighting, sunlight on cloudy day etc. Optom measures VA while shining penlight into pxs eye at a fixed distance and angle (eg 10cm and 30 degrees). Drop in VA of 2 lines or more indicates a significant degree of glare.

Reducing Disability Glare

• Environmental control, task lighting, avoidance of shiny surfaces, tints to reduce retinal illuminance, visors and hats
• People who may benefit from tint - media opac, albino, RP, Cone dystrophies, aniridia (though cone dystrophy may be better), corneal dystrophies, diabetics, uveitis
• Prescribe tints wrt subjective comfort or objective w/low contrast charts vs high contrast charts, varying illumination.

CIBSE Recommended levels for normally sighted px
(in lux)

• Living Room 50, Sewing/Sustained Reading 300, Kitchen 300, Hall/Stairs 150, Bathroom 50, Bedroom 50.
• 50-100% increase in those figures if you're over 65
• 5 times to 10 times increase if you're a VIP. Usually compromise w/1000 lux, adjustable

Bulbz

• Fluorescent is best. Gives poor colour rendering because usually at discreet wavelength but this is irrelevant in a low vision context.
• Discharge tube can be folded to give more compact bulb
• 9w or 11w, high efficacy
• Stays cool even after prolonged application
• NB Px can use any light source and it will not affect the way they read
  

Real Image/Transverse Magnification

M = SIZE OF IMG (on screen) / SIZE OF ORIGINAL OBJECT

CCTV is the most common way of producing this kinda magnification. It's aberration free (with magnification edge of magnifier view = rubbish) but the resolution of the screen determines image quality. Up to 70x mag is possible but usually about 30x is limit. The magnification is variable with a zoom control in a way that just ain't possible with an optical aid. This means if the px requires a change in magnification it remains useful. It has variable camera/task and eye/screen distances so allows for more normal viewing and extended reading. Reading speed is about the same though. Contrast etc is variable too.

Components

• Camera
• Light Source
• X-Y Platform
• Monitor screen (bigger screen = larger FOV - only 4 characters required for reading but up to 15 required for optimum page navigation)
• With the most common design (PORTABLE CCTV) each component is fixed and mounted vertically 'in line', working space is fixed or limited, all the controls are together so easier to set up. Also it's more portable duh.
• Can also add 2nd camera for distance

Advantages

• Zoom on magnification - overall view at low mag then increase for detail
• Adjustable mag if vision changes
• Monochrome/colour monitor allows for real life colour or different combinations
• Contrast reversal 0 >50% of px prefer white on black as it reduces scatter in media opacities
• Reading duration much increased but speed the same
• Binocular viewing from a normal distance
• More psychologically acceptable than a magnifier? Just looks like a computer if it's a kid@school
• Good if Parkinsons or something prevents optical aid usage
• Good if px has extensive vfd. Easier to adapt to steady eye strategy with it
• Split screen for simultaneous tasks

Disadvantages

• Expensive & need continuing service & repair
• Persistence of image on phosphor if CRT style screen
• Requires more practice than optical aids (15-20 sessions of daily practice)
• Bulky/obtrusive/difficult to move around - would need one for home and one for work
• Control posns often better for right handed
• Depth of field is limited (probs with thick books)

A head mounted device works in basically the same way. There are also TV readers which attach to the px's TV. The users of EVE aids are usually young & motivated. Px w/ VA>6/90 seem to gain little benefit from their use (mainly for reading, filling in forms, school tasks and viewing photos.

As regards to obtaining the visual aid, optical aids are usually provided by the HES - free to any px on permenant loan. There's no general formal scheme for electronic aids - they are bought privately. A registered VIP doesn't pay the VAT. Local charities or 'electronic aids for the blind' also supply but most are bought privately. They are available to use in libraries.

Tapermag

• Real image magnifier consisting of a bundle of transparent glass optical fibres
• Each fibre is narrow at the end which rests on the text and expands towards the top edge. The magnification is mainly real image magnification with a bit of relative distance magnification (the image is closer to the eye than the reading material)
• Aberration free but has a limited range of magnification (2.1-2.3x mag)
• Expensive compared to plus lens magnifiers.