The visual system Macleod’s 14th edition, chapter 8

Anatomy and physiology

Eye is situated the in the Bony orbit. Covered by: Eyelid (protection from injury / maintain tear film/ facial expression)

*Opening: elevated by: 1- levator palpebrae superiosis.(Cranial Nerve lll) 2-Müller’s muscle (smpathetic autonomic system) *Closure : mediated by orbicularis oculi(cranial nerve VII) The orbit houses the :

1- lacrimal gland 2-blood vessels 3-autonomic nerve fibers 4-cranial nerves (ll , lll , lV , Vl) The contents are cushioned by orbital FAT ( enclosed anteriorly by the orbital

septum and eyelids).

Refractive elements of the eye :

• refractive power: The degree to which a transparent body deflects a ray of light from a straight path.

• the major refractory elements:

1-Tear film 2-cornea 3-crystalline lens

• cornea posses The greatest refractive power and the main refracting element of the eye

• Lens (biconvex):provides additional controllable refraction, causing the light to focus on to the retina.

When light is :

1. Precisely focused on the retina … emmetropia

2. Focus point falls behind the retina .. Hypermetropia (long slightness) .. Eye is too short in infants, youngs can compensate by contracting ciliary muscle

3. Focus in front of the retina .. Myopia (short sightedness) .. Eye is too long start in childhood and worsen during growing age.

These errors (2 and 3 ) can be corrected with

1) Lenses.. For point num 2 use a convex (plus) lens & for point num 3 use a concave (minus) lense

2) Pinhole

-Presbyopia: impaired accomodation, >45 -Astigmatism: cornea irregularly curved

https://www.youtube.com/watch?v=VDehC_Txa1U

Vision altered by intraocular diseases which leads to :

1. change in the optical or refractive properties of the eye.

2. Prevent the incident light rays from being clearly focused on the retina.

Alternatively, it may results from extraocular factors associated with :

damage to the visual pathway , which runs from the optic nerve to the optical lobe.

1) Altered vision • History

Establish whether the change in vision is : 1) Sudden 2) gradual - Both of them have their own specific set of differential diagnosis

vision may be not just reduced but also distorted,

this results from disruption to the normal structure of the macula , the central part of the retina ..

The most common cause is macular degeneration.

but also may frequently stem from an epiretinal membrane ,vitreous traction or central serous retinopathy

This results from disturbance of the vitreous and the retina , occurring most commonly in posterior vitreous detachment Usually found in older patient as the vitreous gradually degenerates and liquefies , causing it to peels from the retina. The vitreous is attached to retina in certain regions , in these regions the vitreous either : 1)detaches with traction … resulting in flashing light 2) Detaches by tearing the retina .. Releasing retinal pigment cells, Patient will see either of these as floaters

• Haloes : are colored lights seen around bright light Occurs with corneal edema and mostly associated with angle-closure glaucoma.

*Pain on eye movement usually indicates either optic neuritis (white eye) or scleritis (red eye) • Cornea is one of the highly innervated regions of the body

When corneal nerves are activated it leads to 1)Pain 2)sensation of a foreign body 3)reflex watering 4) photophobia

2) Pain

3) Red eye The eye is covered with a network of vessels in the conjunctiva ,episclera and sclera . Ciliary vessels are also found around cornea causes leads to red eye :

1) Dilation or hemorrhage in these vessels 2) uveitis , in acute angle closure glaucoma and corneal irritation: the ciliary vessels around the cornea become more prominent ( ciliary flush) The appearance is distinct from conjunctivitis , in which there is blanching of vessels towards the cornea

Clinical pictures in different types of congestion:

Whether it is :

1)Monocular .. Results from intraocular disease in one eye

2)Binocular .. Results from imbalance in eye movement

• Test the eye movement and use your knowledge of the functions to of the extraoclear muscles to work out which cranial nerve is affected in binocular diplopia

4) Double vision (diplopia)

Increase in discharge from the eye results from : 1)Increase in production 2) Decrease in drainage from the ocular surface Irritation of corneal nerves activates cranial nerve V1 and

results in reflex tearing response. Tears normally drain through the punctum at the medial end

of the lower eyelid into the nasolacrimal duct, which opens below the inferior turbinate into the nasal cavity. Blockage of tear drainage or abnormal lid position can also result in excessive discharge.

5) Discharge

6) Swollen eyes Orbit is an enclosed structure except anteriorly, so any swelling inside the orbit will results in :

Anterior displacement of the globe (Proptosis)

• Past ocular history • Past medical history : Focus on systematic diseases that could affect the eyes ( directly / side effect of treatment ) :

1) Diabetis or HTN .. Especially in the context of visual loss or double vision

2) Thyroid disease in the context of red, swollen eyes and double vision

3) asthma or COPD or peripheral vascular disease if starting glaucoma medications

• Drug and allergy history The eyes may be affected by medications for other conditions .. Like glaucoma exacerbation by conjunctival absorption of nebulised anticholinergic drugs in COPD. Medications for the eyes (like beta blocker eye drops) can aggrevate other conditions like asthma Ask History of fever or allergy .. If the patient has itchy eyes

•Family history Several eye diseases have an inherted predisposition Ask: 1)glaucoma in first order relatives 2)Genetic diseases Includes retinitis pigmentosa 3)Thyroid eye disease

• Social histoty: Visual impairment has a wide range of effects on daily life Ask: 1) Daily activities require good vision: reading, Tv, sport, hobbies, … 2) Driving 3) Occupation .. Certain professions including drivers of heavy good vehicles / pilots require specific visual acuity criteria 4) Smoking and alcohol use: this may affect vascular and optic nerve function within the eyes

Carefully and systematically examine:

1) Posture and gait

2) Head position

3) Facial asymmetry and dysmorphic features

4) Eyelid position and periocular skin

General examination:

Physical examination • General Examination • Visual Acuity • Orbital and Periorbital Exam • Pupils • Visual Field • Opthalmoscopy

Visual aquity:

Mandetory to assess in all patients.

Each eye should be assessed separately .. The most common method is using snellen chart (displays a random selection of letters at diminishing font size in successive lines )

• Firstly positioned at 6 metres If the patient cannot see the largest font, reduce the test distance to 3 metres, then to 1 metre. If cannot see the largest font, document instead whether they can count fingers, see hand movement or just perceive the difference between light and dark.

• On the Snellen chart, lines of decreasing font size are numbered according to the distance in metres that a person with normal vision could read them. Express visual acuity as the distance at which text is read (usually 6 metres) over the number of the smallest font line read correctly on the chart. For example, 6/60 means that the patient sees at 6 metres the font size that is seen at 60 metres by a person with normal vision.

Orbit and periorbital examination • swelling, erythema or any other skin changes.

• ptosis

• asymmetry in the position of the eyeballs.

• Eyeball protrusion (proptosis).

• Palpate for any masses.

• eye movements.

• ophthalmoscope examination .

Pupils Examine

• squint and ptosis shape and symmetry .

- Physiological anisocoria (unequal pupil size) is seen in 20% of population .

Relative afferent pupillary defect (RAPD)

is an important clinical sign that occurs when disease of the retina or optic nerve reduces the response of the eye to a light stimulus

• In normal patients, this results in symmetrical constriction of both pupils. In RAPD, light in the affected eye causes weaker constriction (apparent dilatation) compared to light shone in the normal eye

Accommodation

• There should be constriction of the pupil on near gaze.

• Failure to constrict to light but constriction on near gaze is referred to as light-near dissociation.

Anisocoria:

The eyes should be assessed to determine which is the abnormal pupil.

• If the degree of anisocoria is greater in brighter lighting, then it is the larger pupil that is abnormal; if it is more pronounced in dim lighting, the smaller pupil is the abnormal one.

An equal degree of anisocoria in all levels of lighting indicates physiological anisocoria.

Visual fields • The normal visual field extends 160 degrees horizontally and 130 degrees vertically.

• Fixation is the very centre of the patient’s visual field.

• The physiological blind spot is located 15 degrees temporal to the point of visual fixation and represents the entry of the optic nerve head into the eye.

Ocular alignment and eye movements

• The eyes are normally parallel in all positions of gaze except for convergence.

• Any misalignment is referred to as a squint (strabismus).

• Squints are described as manifest (tropia) if present with both eyes open, or latent (phoria) if revealed only by covering one eye.

• In addition, they can be concomitant (where the angle of squint remains the same in all positions of gaze) or incomitant (where the angle of squint deviation is greatest in a single position of gaze).

• The latter is commonly the result of paralysis of particular extraocular muscles

Oculocephalic (doll’s-eye) reflex

• This reflex is the ability of the eyes to remain fixated while the head is turned in the horizontal plan

• An impaired reflex indicates a brainstem abnormality.

Ophthalmoscopy

• The direct ophthalmoscope is a useful tool for assessing both the anterior and the posterior segments of the eye.

• Pharmacological pupil dilatation is essential, though the optic disc can be examined sufficiently without dilatation.

• If epithelial defects are suspected, fluorescein can be administered and a cobalt blue filter used to reveal these.

The End….