Loss of Vision

Question 1

Main categories of vision loss (3)

Answer 1

• Acute persistent visual loss
  
  • Acute transient visual loss
  • Chronic visual loss

Question 2

Acute Persistent Visual Loss Causes

Answer 2

• Media problems
  
  • Retinal problems
  • Neural visual pathway problems

Question 3

Media Causes of Acute Persistent Visual Loss

Answer 3

• Keratopathy
  
  • Hyphema
  • Lens changes
  • Vitreous haemorrhage
  • Uveitis
  • Endophthalmitis

Question 4

Retinal Causes of Acute Persistent Visual Loss

Answer 4

• Vascular occlusion
  
  • Retinal detachment
  • Acute maculopathy

Question 5

Neural Visual Pathway Causes of Acute Persistent Visual Loss

Answer 5

• Optic nerve
  * Ischaemic Optic Neuropathy
  * Optic neuritis
  * Papilloedema
  
  • Chiasmal
  • Retrochiasmal
    
    • Homonymous hemianopia
    • Cortical blindness

Question 6

Overview of Keratitis

Answer 6

Definition
Keratitis is inflammation of the cornea due to trauma, abrasive exposure, allergy or infection

Presentation
The eye is cloudy, irregular and may have loss of epithelial cells demonstrated by fluorescein dye, creating a green glow under cobalt blue light

Question 7

Overview of Corneal Oedema

Answer 7

Definition
Corneal swelling results in loss of corneal clarity

Aetiology
Acute angle-closure glaucoma (mostly)
See Glaucoma notes

Question 8

Overview of Hyphema

Answer 8

Definition
A hyphema is blood in the anterior chamber

Aetiology
Due to blunt trauma or may occur spontaneously in conditions with minor trauma leading to neovascularisation or anterior chamber structures (diabetes mellitus, retinoblastoma or melanoma) or bleeding tendency (clotting disorders or warfarin)

Pathophysiology
Blunt force to the eye results in intraocular pressure and posterior pressure being transferred to the iris and its roots, mechanically disrupting the angle. Bleeding results from tears in the vessels of the ciliary body or iris.

Question 9

Overview of Lens Changes

Answer 9

Definition
Changes in size, clarity or positioning of the crystalline lens may alter the focus of light onto the retina, resulting in visual disturbance

Aetiology
Trauma or a variety of congenital conditions can lead to lens dislocation. Lens clouding (cataract) doesn’t occur acutely. Elevated blood glucose can cause increased lens tumescence, altering the refractive error. Normalisation of blood glucose resolves vision.

Question 10

Overview of Vitreous Haemorrhage

Answer 10

Definition
Bleeding into the vitreous humour

Aetiology
Trauma, spontaneous retinal tear, spontaneous vitreous detachment, in any condition with retinal neovascularisation (poorly controlled diabetes).

Presentation
Visual reduction is proportional to the amount of blood in the vitreous

Question 11

Overview of Uveitis (Endophthalmitis)

Answer 11

Definition
Inflammation inside the eye. Only serious bacterial or fungal endophthalmitis by surface pathogens (recent ocular surgery) or blood-borne agents will cause vision loss

Presentation
The eye is red, tearing and painful. Microscopic examination reveals WBCs in the anterior chamber, vitreous space or both. A layer of pus (hypopyon) may collect in the anterior chamber.

Question 12

Overview of Retinal Artery Occlusion

Answer 12

Definition
Thrombosis, embolism or arteritis of the central retinal artery results in retinal ganglion cell damage leading to severe, sudden, painless, central vision loss.

Aetiology
Carotid artery atherosclerosis (commonest) and giant cell arteritis

Question 13

Overview of Retinal Vein Occlusion

Answer 13

Definition
Thrombus leading to disc swelling, diffuse nerve finer layer and pre-retinal haemorrhage and cotton wool spots creating “blood and thunder” fundus

Classification
Depends on the site of the retinal vein involved. Branch RVO when distal vein occluded, Central RVO when central vein occluded, leading to involvement of entire retina.

Question 14

Overview of Retinal Detachment

Answer 14

Definition
Detachment of the neurosensory retina may occur spontaneously or in the setting of trauma

Aetiology
Tear or break in retina (common)

Presentation
Onset of new floaters or black dots in vision, often accompanied by flashes of light (photopsias). In early stages there may be persistent missing portion of monocular visual field. Not painful nor does it cause red eye.

Associated
Trauma, diabetic retinopathy or previous surgery

Treatment
Surgery

Question 15

Overview of Acute Maculopathy

Answer 15

Definition
Conditions that affect the macula have a central blind spot (scotoma), blurred vision or visual distortion

Aetiology
Fluid leakage, bleeding, infection or acute worsening of chronic disease (new oedema in dry diabetic retinopathy or new bleeding in dry macula degeneration)

Question 16

Causes of Optic Nerve Visual Pathology

Answer 16

• Ischaemic Optic Neuropathy
  
  • Optic neuritis
  • Papilloedema

Question 17

Overview of Ischaemic Optic Neuropathy

Answer 17

Generally classified as anterior (affecting the optic disc) or posterior (retrobulbar) and as arteritic or nonarteritic. Infarction at the optic nerve head due to thrombosis or transient hypotension leads to monocular superior or inferior visual defect or diffusely reduced vision.

Question 18

Overview of Optic neuritis

Answer 18

Definition
Inflammatory, demyelinating condition of the optic nerve associated with a variety of conditions, most notably multiple sclerosis and occurs at some time during the course in 50%

Presentation
Pain on eye movement, reduced acuity in one eye and washed out colour

Investigations
Rule out giant cell arteritis

Question 19

Overview of Papilloedema

Answer 19

Definition
Elevated intracranial pressure can lead to transient visual obscurations or mild persistent blurred vision.

Differentials
Cerebral oedema, intracranial mass lesion, increased CSF, hydrocephalus, obstruction of venous outflow and idiopathic intracranial HTN
Examination

Reveals bilateral optic nerve swelling without relative afferent papillary defect

Question 20

Overview of Chiasmal Visual Pathology

Answer 20

Description
Involvement of the chiasm is suggested by visual loss of any type associated with pituitary dysfunction or by a monocular or bitemporal hemianopia. Sudden chiasmal vision loss is less common and implies a rapidly expanding mass or an infectious, vascular or inflammatory cause.

Presentation
Cause gradual decline in vision, as they impinge upon the chiasm, optic nerve or optic tract. Peripheral vision loss is often asymptomatic until visual acuity is compromised

Question 21

Causes of Retrochiasmal Visual Pathology

Answer 21

• Homonymous hemianopia

* Cortical blindness

Question 22

Overview of Homonymous hemianopia

Answer 22

Definition
Brain lesions in the region of optic tract and more distal produce a loss of vision on one side of both visual fields

Aetiology
Stroke or haemorrhage into a brain tumour

Question 23

Overview of Cortical blindness

Answer 23

Definition

Extensive bilateral damage to the cerebral visual pathways may result in complete loss of vision

Question 24

Monocular vs Binocular Visual Loss

Answer 24

• Monocular implies a disorder anterior to the optic chiasm (ie, the eye or optic nerve) including ocular disease or ischaemia due to ipsilateral carotid artery disease.
  
  • Binocular suggests a more posterior process involving the optic chiasm, tracts, radiations, or the visual cortex.

Question 25

Acute Transient Visual Loss Causes

Answer 25

• Monocular ischaemia, carotid disease, other embolic source
  
  • Giant cell arteritis
  • Papilloedema
  • Idiopathic retinal vasospasm
  • Migraine
  • Vertebrobasilar ischaemia
  • Seizure : Ictal
  • Postictal

Question 26

Causes of Chronic Visual Loss

Answer 26

• Cataracts
  
  • Chronic glaucoma
  • Trachoma
  • Macula degeneration
  • Presbyopia
  • Diabetic retinopathy

Question 27

Overview of Cataracts incl Pathophysiology and Risk Factors

Answer 27

Definition
A cataract is an opacity of the lens of the eye that causes partial or total blindness, 50% of world blindness may be due to this

Pathophysiology
Unlike epithelia, the less does not shed its nonviable cells, hence there is a build-up of proteins causing lens opacity. The exact mechanism is not known. Most cases occur in those > 60 years of age.

Risk factors
Age, smoking, alcohol, metabolic syndrome, diabetes mellitus.

Question 28

Presentation, Investigations and Treatment of Cataracts

Answer 28

Presentation
The vast majority are senile or age-related with a few for acquired cataracts. The development of age-related cataracts is painless, progressive and can be highly variable. Typically it is bilateral although it can be monocular. Patients usually complain of night driving, reading road signs or difficulty with fine print.

Investigations
A lens opacity can be confirmed by non dilated fundus examination with ophthalmoscope; there may be darkening of red reflex, opacities within red reflex or obscuration of ocular fundus examination.

Treatment
Cataract surgery is the only treatment and the opacified lens is surgically removed. It is a low-risk procedure and should be sought when there is interference in the ability of daily living.

Question 29

Overview of Glaucoma incl Pathophysiology and Classification

Answer 29

Definition
Glaucoma is a group of eye diseases that are traditionally characterised by the intraocular pressure (IOP) exceeding optic nerve threshold. Usually due to a raised IOP.

Pathophysiology
Excessive IOP leads to optic nerve damage and consequent visual loss. Can be primary or secondary to uveitis, trauma, glucocorticoid therapy, vasoproliferative retinopathy or ocular syndromes

Classification
Defined as open-angle or angle-closure.
* Open-angle is characterised by progressive peripheral visual field loss, followed by central field loss. It is associated with increased aqueous production and decreased outflow.
* Angle-closure is where the drainage pathway of aqueous humour is blocked with anatomical predisposition

Question 30

Presentation, Diagnosis, Investigations and Treatment of Glaucoma

Answer 30

Presentation
In open angle there are rarely symptoms. The visual loss occurs but the painful red eye is only a presentation of angle-closure.

Diagnosis
Nerve damage on fundus examination, visual field testing and elevated IOP.

Investigations
Gonioscopy is the gold-standard using a special lens for a slit lamp to visualise the angle and diagnose angle closure.

Treatment
Immediate laser iridotomy, decreases IOP (topical beta-blockers, adrenergics, carbonic anhydrase, hyperosmotic agents) and miotic drops (pilocarpine).

Question 31

Overview of Trachoma including how they present (two phases)

Answer 31

Definition
Trochoma is a contagious eye infection of Chlamydia trachomatis and is the leading cause of worldwide blindness. C. trachomatis is transmitted by intimate social or sexual contact.
Presentation
The manifestations can be divided into two phases:
* Active trochoma - causes a mild, self-limited follicular conjunctivitis (relatively asymptomatic) usually in childhood.
* Cicatricial disease - causes scar tissue leading to entropion (inward rolling of the eyelid) and subsequent trichiasis (ingrown eyelashes). Eyelash abrasion on the cornea leads to corneal oedema, ulceration and scarring. If untreated this results in blindness.

Investigations
PCR of swab

Treatment
Surgery (reduce eyelash irritation), Antibiotics (azithromycin), Facial cleanliness and Environmental improvement is the tool for global trachoma elimination. (F & E reduce transmission)

Question 32

Overview of Macula Degeneration

Answer 32

Definition
Age-realted macula degeneration is a degenerative disease of the central portion of the retina (the macula) that results in primarily in loss of central vision. It is classified as dry (atrophic) or wet (neovascular or exudative) for clinical purposes.

Epidemiology
Of those > 40yo the prevalence is 1.5%. Risk factors include age and smoking
Presentation
* Dry (atrophic)
* Gradual loss of vision in one or both eyes.
* Wet (neovascular or exudative)
* Acute distortion in vision, especially straight lines or loss of central vision usually in one eye, may be acute.

Investigations
On fundus examination:
Dry (right) - small, bright drusen are visible
Wet (left) - areas of vessel leakage are present with large disci form scar

Treatment
Complicated. Stop smoking. If there is wet degeneration then laser the new blood vessels

Question 33

Overview of Presbyopia

Answer 33

Definition
Presbyopia “ageing sight” is a non-refractive error that also affects visual acuity.

Pathophysiology
Occurs when the lens loses its normal accommodating power and can no longer focus on objects viewed at arms length or closer. The cause of accommodation loss includes increased form deprivation, excessive accommodation, scleral stretching (second to raised IOP) and autonomic deficits.

Presentation
It begins after age 40 when the patient starts to appreciate the inability to focus objects at reading distance. The eye’s focusing power for reading is lost progressively and fully by 65.

Treatment
Corrective lenses

Question 34

Overview of Diabetic Retinopathy

Answer 34

Definition
Diabetic retinopathy is a global term for vision loss secondary to macular oedema (retinal thickening and oedema involving the macula), haemorrhage from new vessels, retinal detachment or neovascular glaucoma.

Classification
Termed non-proliferative or proliferative (presence of abnormal new blood vessels emanating from the retina)

Aetiology
Chronic hyperglycaemia. It is not sure how. VEGF?

Presentation
The vast majority have no symptoms until late stages
* Non-proliferative (left) - has variable nerve-fibre layer infarcts (cotton wool spots), intraretinal haemorrhages and hard exudates
* Proliferative (right) - has neovascularisation arising from the disc and/or retinal vessels.

Prevention
Good glycaemic and blood pressure control