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First, keep your index finger about 20-30cm in front of your nose. Now look at the tip of your nose. This simulates convergent squint. You will now be able to see the finger as 2 separate images – one on the left and another on the right. Keeping your eyes fixated at the tip of your nose, close your left eye. The image on the left side disappears. Open your left eye and close your right eye. Now the image on the right side disappears.

Explanation: In convergent squint, the eyeball is rotated inward. Instead of falling on the fovea, the light from the object falls on the nasal side of the retina. Nasal side of the retina is is supposed to receive light from the temporal side of the visual field. So the image formed on the nasal side of the retina will be perceived by the brain as being on the temporal side of the visual field. So in convergent squint, instead of seeing a single image, 2 images will be seen in the temporal fields of each eye. The left eye sees the image on the left and the right eye sees the image on the right – This is UNCROSSED diplopia.

Now we can experience crossed diplopia. Keep your eyes fixated on the computer monitor. Keep your index finger about 15 cm in from of your eye. You can see 2 images of your finger. This is a simulation of divergent squint. Close your left eye. The image on the right side disappears! Open your left eye and now close your right eye. The image on the left will disappear. This is crossed diplopia!

Explanation: The mechanism acts in reverse in case of divergent squint. The eyeball being rotated outward, the image falls on the temporal side of the retina. Images formed on the temporal side of the retina is perceived as being from the nasal field by the brain. So the image seen by the left eye will be perceived as being on the right side and that seen by the right eye will be perceived as being on the left side – CROSSED diplopia.

It took me some time to understand the concept of crossed and uncrossed diplopia. So I decided to write this article to help other learn about them. I have tried my best to explain the concept. If you have any doubts regarding, please leave a comment below.

1. Causes of uniocular diplopia
2. Mastectomy left breast – Xray
3. Massive pleural effusion

Ref : Comprehensive Ophthalmology, 4th edition by A.K.Khurana; page 230

1. AIIMS November 2011 – MCQ 99
2. Pupillary signs in a comatose patient
3. Ophthalmology – MCQ 29 – Topical treatment of open angle glaucoma

1. Ophthalmology – MCQ 14 – Prevention of the endophthalmitis in cataract surgery
2. SPM – MCQ 96 – Smoking and risk of coronary heart disease
3. Seroma – Cause, Mechanism, Management and Prevention

1. Ophthalmology – MCQ 12 – Mucin layer tear film deficiency
2. PGIMER November 2011 – MCQ 12
3. Biochemistry – MCQ 78 – Transmembrane region of protein

Contributed by Prepg Preparation

1. Wool sorters disease
2. Orthopaedics – MCQ 10 – 60 yrs old male with bony abnormality at upper tibia and hearing loss
3. RGUHS Karnataka PGET 2011 – MCQ 53

ARP stands for:

• Accommodation Reflex Present (read forwards)
• Pupillary Reflex Absent (read in reverse)

1. Clinical features of Bell’s palsy – Mnemonic
2. Features of AIDS Dementia Complex – Medical mnemonic
3. Asherman syndrome – Features – Mnemonic

• Optic disc drusen
• Hypermetropia
• Persistent hyaloid tissue

1. Vitreous humor anatomy
2. Optic cup
3. Cup disc ratio

1. Hangout interval – Mechanism, significance
2. Dermatology – MCQ 22 – Factor worker with itchy, annular plaques
3. Anterior Ischemic Optic Neuropathy (AION) – Etiology, Clinical features, Investigations, Treatment

Clinical significance:

• It is closely related to the infundibulum and may compromise the ostium of the maxillary sinus
• Hence it is a proposed cause of recurrent maxillary sinusitis

Reference:
Otorhinolaryngology, Head and Neck Surgery By Matti Anniko, Manuel Bernal-Sprekelsen, Patrick Bradley

1. Onodi cells
2. Hurthle cells or Askanazy cells
3. Pathology – MCQ 23 – Function of Natural killer cells

Clinical importance:

• Attempt to remove the onodi cells during sinus surgery may cause injury to the optic nerve
• The onodi cells are a potential cause for incomplete sphenoidectomy
  • The anatomical landmarks of the sphenoid sinus correlate with that of onodi cells
  • Hence, the surgeon may mistakenly believe that the sphenoid sinus has been reached

Reference:
Otorhinolaryngology, Head and Neck Surgery By Matti Anniko, Manuel Bernal-Sprekelsen, Patrick Bradley

1. Haller’s cells (infraorbital ethmoid cells)
2. Optic nerve sheath fenestration
3. Papillomacular bundle

• Visual Display Terminal Syndrome

1. BPES – Acronym
2. NARES – Acronym
3. HRC – Acronym

• Defective vision is one of the important symptoms of acute iridocyclitis
• Initially there is slight blurring of vision with progressive deterioration
• There are multiple causes of defective vision in acute iridocyclitis
• They are: (from anterior to posterior of eyeball)
  • corneal oedema and keratic precipitates
  • Aqueous humour turbidity
  • Exudates in pupillary area
  • Myopia as a result of ciliary spasm
  • Complicated cataract
  • Cyclitic membrane
  • Vitreous haze
  • Macular oedema
  • Papillitis
  • Secondary glaucoma

Image credits: The eyes have it

1. Ophthalmology – MCQ 42 – 25 year old male with sudden painless loss of vision
2. Vision 2020 – The right to sight
3. SPM – MCQ 47 – Vision 2020 “The right to sight”

Causes of aphakia

• Congenital aphakia
• Surgical aphakia – removal of lens as in cataract extraction
• Aphakia due to absorption of lens – sometimes seen in children after trauma
• Traumatic extrusion of lens
• Posterior dislocation of lens into the vitreous causes optical aphakia

Optics in aphakia

• The lens is important in refraction and hence its removal results in considerable decreased in the refractory power of the eye
• The eye becomes highly hypermetropic
• The power of eye decreases from +60D to +44D
• The power of accomodation lost
• The posterior focal point lies behind the eyeball

Clinical features

• Symptoms
  • Defective vision – due to high hypermetropia and loss of accomodation
  • Erythropsia and cyanopsia – due to entry of infrared and ultraviolet rays in the absence of the crystalline lens
• Signs (anterior to posterior)
  • Limbal scar in case of surgical aphakia
  • Deep anterior chamber
  • Iridodonesis – tremulousness of the iris due to loss of support of lens
  • Jet Black pupil
  • Loss of 3rd and 4th purkinje images
  • Fundus examination reveals a small hypermetropic fundus
  • Retinoscopy shows high hypermetropia

Treatment:

• Spectacles
  • Spectacles should be prescribed with about +10D lens for correction of aphakia
  • It should also include correction for surgical astigmatism and +3-4D for near vision
  • Nowadays spectacles are not preferred for use in aphakia due to its many disadvantages
  • Advantages of using spectacles in aphakia
    • Cheap
    • Easy to use
    • No complications
  • Disadvantages
    • The images are magnified – about 30% – hence not useful in unilateral aphakia as it causes diplopia
    • The field of vision in decreased considerably
    • Spherical and chromatic aberration of high power lenses
    • Roving ring scotoma (Jack in the box phenomenon)
    • Prismatic effect of the thick lenses
    • High power are cosmetically not acceptable
• Contact lenses
  • Advantages over spectacles:
    • Produces less magnification
    • Better field of vision
    • Less chromatic and spherical aberration
    • No prismatic effect
    • Cosmetically more acceptable
  • Disadvantages
    • Costly
    • More care in required usage of contact lenses – may not be suitable for use in young children and elderly
    • Complications related to use of contact lenses
• Intraocular lens implantation
  • This is the preferred method nowadays
  • The lens can be implanted in the capsular bag or in the anterior chamber
  • It eliminates most of the disadvantages associated with the use of spectacles or contact lenses
  • Disadvantage include the complications associated with surgery
• Refractive surgery – This is a newly emerging treatment for aphakia
  • Keratophakia
    • a lenticule prepared from the donor cornea is placed within the lamellae of the patient’s cornea
  • Epikeratophakia
    • a lenticule prepared form the donor cornea is stitched to the patients cornea after removing the epithelium
  • Hyperopic Lasik

1. Anterior Ischemic Optic Neuropathy (AION) – Etiology, Clinical features, Investigations, Treatment
2. Ophthalmology – MCQ 44 – Effects of contact lens wear.
3. Episcleritis – Etiopathogenesis, Clinical features, Treatment

1. Intercanthal distance
2. Forensic medicine – MCQ 29 – Singeing, Blackening and tattooing
3. Medicine – MCQ 153 – Pulmonary function test in kyphoscoliosis

1. Canthus
2. Sparrow’s foot marks
3. Distant direct ophthalmoscopy

1. BPES – Acronym
2. Intercanthal distance
3. Telecanthus

1. Telecanthus
2. Forensic medicine – MCQ 29 – Singeing, Blackening and tattooing
3. Ophthalmology – MCQ 41 – 30 year old man with blurring of vision

Alternate names (synonyms):

• Palpebral commissures

1. Epicanthus inversus
2. Olfactory slit
3. Bicanthal plane

• Blepharophimosis Ptosis Epicanthus Inversus Syndrome (Ophthalmology)

1. Epicanthus inversus
2. VDTS – Acronym
3. NARES – Acronym

• Levator Palpebrae Superioris

1. Cause of enophthalmos in Horner’s syndrome
2. Ophthalmology – MCQ 7 – Occulomotor nerve palsy
3. Horner’s syndrome

1. Horner’s syndrome
2. LPS – Acronym
3. Annulus of Zinn

1. Cause of enophthalmos in Horner’s syndrome
2. Medicine – MCQ 13 – Bernard soulier syndrome
3. Ophthalmology – MCQ 40 – Components of horner’s syndrome

1. Surgery – MCQ 49 – Acquired (secondary) megacolon
2. Tear film – Layers and formation
3. Obstetrics & Gynaecology – MCQ 40 – PCOS

• Subluxated clear lens
• Subluxated intraocular lens
• Keratoconus (irregular refraction from corneal surface)
• Double pupil (congenital / large iridectomy / iridodialysis)
• Incipient cataract (this usually causes polyopia – due to irregular refraction due to multiple water clefts within the lens)

1. Crossed and Uncrossed diplopia simplified!
2. Aphakia – Causes, Optics, Clinical features and Treatment
3. Ophthalmology – MCQ 34 – Contraindication for intraocular lens after cataract surgery

1. Tobacco amblyopia
2. AIIMS November 2011 – MCQ 166
3. Relative scotoma

1. CPM – Acronym
2. Etiology of papilledema
3. Anaesthesia – MCQ 19 – Allodynia

• Conditions affecting the functioning of rods (as rods are involved in night / scotopic vision)
  • Vitamin A deficiency
  • Retinitis pigmentosa (and other tapetoretinal degenerations)
  • Oguchi disease (congenital stationary night blindness)
  • Congenital high mypoia
  • Familial congenital night blindness
• Certain conditions affecting transparency of visual media
  • In dim light, the pupils dilate so as to allow more light to reach the retina
  • In case of peripheral corneal opacities and paracentral lenticular opacities, there is obstruction to the passage of light when pupils are dilated
• Conditions causing delayed dark adaptation
  • Advanced primary open angle glaucoma

1. WHO definition of ‘blindness’
2. SPM – MCQ 16 – Cause of blindness in children in India
3. Ophthalmology – MCQ 5 – Common causes of childhood blindness

Etiology:

• AION occurs due to blockage of Short posterior ciliary arteries which supply the optic nerve
• The different types of AION are:
  • Idiopathic – most common – thought to be due to atherosclerotic changes in the vessels
  • Arteritic – associated with giant cell arteritis
  • Miscellaneous – associated with various conditions like
    • Severe anemia
    • Malignant hypertension
    • Papilledema
    • Migraine
    • Massive haemorrhage
    • Collagen vascular disorders

Clinical features:

• Sudden visual loss
  • involving the upper or lower (more common) half of the visual field – altitudinal hemianopia
• Fundus changes – disc
  • oedematous (segmental / diffuse)
  • pale or hyperemic

Investigations:

• ESR and C reactive protein may be elevated in the arteritic variety
• Definitive diagnosis of arteritic AION is by temporal artery biopsy

Treatment:

• High dose steroids (prednisolone 80mg daily) – taper it by 10mg every week
• Low dose steroids may have to be given for 3 months to 1 year

1. AION – Acronym
2. Bronchiolitis obliterans – Etiology, Pathogenesis, Clinical Features, Investigations and Management
3. Episcleritis – Etiopathogenesis, Clinical features, Treatment

• Anterior Ischemic Optic Neuropathy

1. Anterior Ischemic Optic Neuropathy (AION) – Etiology, Clinical features, Investigations, Treatment
2. CZH – Acronym
3. AIIMS November 2011 – MCQ 166