Collagen type in various ocular structures
Driving Criteria
(In order to be eligible for a car/motorcycle license)
- Read a post-September 2001 number plate at 20m
- Visual acuity ≥ 6/12
- Horizontal visual field of 120° with 50° of extension in either direction
- No visual field defects within 20° of the horizontal meridian
If diagnosis which is unlikely to satisfy these conditions, the DVLA must be notified.
Revise occular structures and their germ tissue of origin
How are visual impairments classified
The department of health in the UK classifies patients with visual impairments as severe (blind) or partial.
Severe Sight Impairment (blind)
One of:
- VA < 3/60
- VA 3/60-6/60 AND a severe VFD such as tunnel vision
- VA ≥ 6/60 with significant VFD, particularly affecting the lower fields
Sight Impaired (partial impairment)
One of:
- VA 3/60-6/60 with full VF
- VA 6/18-6/24 with moderate VFD or loss of central vision
- VA ≥ 6/18 with a significant VFD such as hemianopia
Most common cause of blindness in the world
Cataract
Most common cause infective blindness in the world
- Trachoma (1st)
- Onchocerciasis (2nd)
Most common cause of visual impairment in the world
Refractive error
Most common type of colour blindness
Red-green
Most common cause of nutritional blindness
Vitamin A deficiency → nyctalopia
Most common cause of irreversible blindness in the world
Glaucoma
Mitochondrial Inheritance
Mitochondria are inherited on the X chromosome, meaning a father with mitochondrial disease cannot pass it to his son.
- Kearns-Sayre syndrome
- Leber Hereditary optic neuropathy
Kearns-Sayre syndrome
- Increased concentration of mitochondria in muscles
- Causes to myopathy, ophthalmoplegia, ptosis, salt and pepper retinopathy and cardiac conduction defects
Leber Hereditary optic neuropathy
- Ganglion cell degeneration leads to optic atrophy.
- Presents in young men with progressive painless vision loss and a fundoscopic triad of pseudo-oedema, telangiectasia and tortuous vessels.
List 4 X-linked Recessive conditions
A son can only be affected if the mother is also affected.
- Congenital Retinoschisis
- Ocular Albinism
- Fabry Disease
- Lowe Syndrome
List 2 Autosomal Recessive conditions
- Oculocutaneous albinism
- Stargardt’s disease
List 4 Autosomal Dominant conditions
- Congenital Cataracts
- Corneal Dystrophies
- Marfan Syndrome
- Stickler Syndrome: defective collagen 2 syntheses leading to an empty vitreous, RD, deafness and systemic marfanoid and facial abnormalities.
- Neurocutaneous disorders: tuberous sclerosis, Von-Hippel Lindau and neurofibromatosis
Revise diseases associated with specific chromosomes
Coloboma
A coloboma is a hole in the structure of the eye, most commonly the iris. It is uncommon but high-yield in exams.
Revise 3 types of colobomas
Revise organisms and culture mediums
Classsification of Fungi
- Yeast (unicellular)
- Filamentous (grow in branches)
- Dimorphic (features of both yeast and filamentous types)
Candida infection
The yeast Candida albicans infects the retina of immunocompromised people and it is also the commonest endogenous cause of endophthalmitis.
It typically presents with fluffy white retinal lesions.
