Embryology of eye mnemonic

Hello friends!

Here's is the simplest way to remember embryology of eye.

*Out of all layers (ecto,meso, endo), the endoderm doesn't contribute to the embryology of eye.

* Mesoderm forms - extraocular muscles

* Rest of the structures are derived from ectoderm.

* Surface ectoderm forms the structures which are visible to us from outside like Corneal epithelium

Conjunctival epithelium

 Lacrimal gland

 Lens ( important)

*Neuroectoderm forms neural structures like

Retina

Ciliary body ( not muscles)

Iris - both sphincter and dilator pupillae

Optic nerve

* Neural crest derivatives are 

Meninges of optic nerve

Schwann cells

Ciliary ganglion

Ciliary muscles 

For the remaining derivatives, watch the following picture.

Thank you.

Dr. Madhuri Reddy. 

Automated Perimetry

 HUMPHREY FIELD ANALYSER (HFA)

1.Perimetry should be performed in a distraction-free environment, to enable the patient to concentrate on the perimetric test.

2.The perimeter is automatically calibrated each time it is turned on. Ideally, patient data (date of birth, refraction, etc.) are entered before the patient enters the room.

3.Before putting the patient onto the machine, the requirements of the test itself are clearly explained and the patient is instructed as follows.

4. Before fully positioning the patient, the eye not being tested should be covered with an eye patch that allows the patient to blink freely.

INSTRUCTIONS TO PATIENT

• Perimetry tests your central and peripheral vision

• Be relatively still once positioned

• Always look straight ahead at the fixation target. Do not look around the bow for stimuli.

• Press the response button whenever you see the stimulus 

• The stimulus in a flash of light

• Only one stimulus is presented at a time

• The stimulus might appear from anywhere. Some stimuli are very bright. Some are very dim and sometimes no stimulus is presented. You are not expected to see all stimuli

• Do not worry about making mistakes

• Blink regularly to avoid discomfort. Don't worry about missing a point the device does not a measure while you blink

• If you feel uncomfortable or are tired close your eye for a moment the test will automatically stop. The test will resume once you open your eye.

• If you have a question, keep the response button pressed this will pause the test

5. The patient is positioned appropriately and comfortably against the forehead rest and chin rest. The lens holder should be as close as possible to the patient’s eye to prevent artefacts. 

6.The Analyser projects a series of white light stimuli of varying intensities (brightness), throughout a uniformly illuminated bowl.

 

 

7.The patient uses a handheld button that they press to indicate when they see a light. This assesses the retina's ability to detect a stimulus at specific points within the visual field. This is called retinal sensitivity and is recorded in 'decibels' (dB).

 

 

8.The Analyser currently utilises the Swedish Interactive Thresholding Algorithm (SITA); a complex mathematical formula which allows the fastest and most accurate visual field assessment to date.

For more information, see the youtube video (link below)

 https://youtu.be/TqL5KvvYJu4 

Written by our guest author - Jignesh Bhadarka

#Ae(ONE)INTERN

Sickle cell retinopathy

 What is the hallmark of sickle cell retinopathy?

Sea fan neovascularization.

All patients with SCD should have dilated funduscopic examinations every 1 to 2 years beginning at age 10, preferably by a retina specialist.

Treatment is usually Laser photocoagulation.

Anti-VEGF medications such as bevacizumab or ranibizumab may lead to partial regression of sea-fan neovascularization.

Sickle cell anemic retinopathy is seen mostly in heterozygous S-C trait and S-Thal trait. 

Fun fact: Sea fans are beautiful soft corals.

-IkaN

Clinical correlate: Sildenafil contraindicated for pilots

Hello

Not just type-5, but Sildenafil is also a phosphodiesterase type-6 inhibitor.

PDE-6 is present in the eyes.

A compilation of similarities between corneal dystrophies

Many dystrophies have commonalities. Following are enumerated as under-

1. Associated with TGF Beta1 mutations-

       - Epithelial basement membrane dystrophy

       - Reis- Bückler's 

       - Thiel- Behnke 

       - Lattice and granular(type1) dystrophies

2. Associated with mutations on 5q31 locus-

         - Reis- Bückler's

         - Lattice and granular(types 1 and  2)

3. Autosomal recessive -

          - Gelatinous drop like

          -.macular

          - Congenital hereditary endothelial( type 2)

4. X linked- 

           - Lisch ( X linked dominant) 

-All others are autosomal dominant. 

5. Chromosome 12- Meesman's, congenital 

                                     hereditary stromal.

6. Chromosome 20- Posterior polymorphous, 

                                    congenital hereditary 

                                     endothelial.

7. Chromosome 1- Gelatinous drop like,

                                   posterior polymorphous.

8. Amyloid deposition is seen in- 

                   - Gelatinous drop like

                   - Lattice

                   - Granular (type2) 

                   - Congenital hereditary endothelial.

9. Bowman's membrane is lost in- 

                   -Gelatinous drop like

                   - Reis-Bückler's (replaced by irregular

                       material

                   - Thiel-Behnke's ( replaced by a

                       fibrocellular layer)

10. Recurrence after keratoplasty-

                    -  Reis-Bückler's

                    -. Lattice, granular, and macular

                    - Schynder 

                     -  Congenital hereditary stromal.

11. Association with glaucoma and keratoconus-

                    - Posterior polymorphous

                    - Fuch's endothelial. 

Now don't blame me for the list being too exhaustive 🙄

Source- Postgraduate ophthalmology by Zia Chaudhari and M Vanathi 

-Sushrut 

Mnemonic for head posture in A-V pattern squints

Chin up in what? Chin down in what? The vexing never ends. Well, as it turns out, the word 'vex' itself is here to save the day.

Chin up- V exotropia (VEx). Remember that squint is very 'vexing'. So you stare in the sky to remember at least a fraction of what you stuffed in your brain the day before. 

Other will be A esotropia. By exclusion, it's easy to remember. 

Chin down- V esotropia or A exotropia. Again, by exclusion, these get placed naturally under this heading.

So, just remember 'VEX' and you won't be vexed anymore! 

-Sushrut 

Ocular Alzheimer's disease

A paper published in 2003 has dubbed glaucoma as 'ocular Alzheimer's disease' because some of the pathophysiological elements are similar.

Cataract in Rubella- interesting fact

The progressive nuclear cataract in Rubella may harbor live virus particles.

Types of glare and mnemonic

There are 4 different types of glare-

1. Direct glare- When the source of light is placed in the same or nearly the same direction as the object of fixation.

2. Discomfort glare- Glare which produces discomfort without interfering with vision. One experiences it when the overall illumination of the surroundings is too bright. 

3.Indirect glare- When an intense light source is placed in a direction other than the object of fixation.

4. Disability glare- Glare which reduces visual performance without necessarily causing discomfort. It refers to the reduced visibility of a target due to the presence of light elsewhere in the visual field. Contrast is reduced, and thus the visibility of the target. 

Now. How to remember all four? 

You are familiar with direct and indirect ophthalmoscopes. 

Suppose an ophthalmologist begins with direct ophthalmoscopy, which causes discomfort, both, to the patient as well as himself, because it involves going too close to the face. The ophthalmologist then starts using an indirect ophthalmoscope with the patient in a supine position, but after a while ends up having cervical spondylosis. Thus, getting a disability.

That's all!

-Sushrut 

Mnemonic for ocular axes and angles

This one is for the PGs. The 4 axes and 3 angles are pretty confusing to remember plainly. Here's how I do it.

Mnemonic for Cherry 🍒 Red spots in Eye

Hello everyone….

" Story of Cherry 🍒 from farm to crowd "

From Farmer ( Mr.Tay Sachs ) 

Quintal of GM Cherry 🍒 storage (GM = Genetically modified ) 

Picked up 

By Dapper Gentleman (Mr.Sandhoff ) 

for selling to 

Crowd 

In Berlin 

(Like Cherry blossoms in Berlin... Google it.. ) 

IOLs- most important optical zone

Most common answer would be the centre.

That however is not the case as the light rays pass undeviated right through the centre.

In fact, phakic IOLs have an opening right in the centre for aqueous to circulate.

The most important part is the pericentral area, as the refracted rays through this area get focussed on the macula.

-Sushrut

Bell's phenomenon

It is the motion of the eyeball during lid closure and is a reflex between the occulomotor and the facial nerves.  There are 4 types-

1. Normal- Upward and outward movement of
                           the eyeball.

2. Inverse- Upward but inward movement.*

3. Reverse- Downward movement.*

4. Perverse- Lateral movement.

*Some authors opine that inverse is downward and outward while reverse is upward and inward.

The Bell's phenomenon is of importance in ptosis and lag ophthalmos surgeries .

-Sushrut

T cells in traumatic optic neuropathy- summoning the devil😈

Traumatic optic neuropathy is a tough nut to crack. High dose steroids and surgical decompression were the empirical modes of management. There is an ongoing search to save the optic nerve in trauma.

The innate adaptive T cell response has been deemed to be protective in traumatic optic neuropathy. It supposedly acts against the self directed antigens in traumatic optic neuropathy. The response can be augmented or induced depending upon an individual.

Other modalities are monisialogangliosides, neurotropic growth factors, and gene transfer of anti inflammatory cytokines.

A new group of steroids, the 'lazaroids' (great name that!) or 21 amino steroids provide free radical binding capability inherent to the group sans the glucorticoid activity.

-Sushrut

Photophobia vs blepharospasm

Both have the same presentation of tight lid closure.

In dark, blepharospasm won't be completely abolished while photophobia would.

Anaesthetisation(topical) reduces greatly the blepharospasm but not photophobia.

-Sushrut

Fuch's s in Ophthalmology

Following this are ascribed to Fuch

1. Fuch's heterochromic iridocyclitis
2. Fuch's corneal endothelial dystrophy
3. Gyrate atrophy of the choroid
4. Ciliary body adenoma

-Sushrut

No Vitamin A in Stargardt's disease

In lipofuscinoses like Stargardt's, fundus flavimaculatus, and Best's disease spectrum, Vitamin A and related compounds are avoided as the metabolites of those is what causes the disease in the first place. Usually, Vitamin A is prescribed empirically by general ophthalmologists for degenerative diseases of the retina.

-Sushrut

Age related macular degeneration- some facts

1. Dry AMD is the most common form, but wet AMD is responsible for 90% of the cases of visual loss.

2. Type 1 choroidal neovascular membrane is 'occult' and type 2 is 'classic'. This might be counter intuitive to remember.

3. In the genome, except for chromosome nos 7,11,13,21, and the Y chromosomes, all the other harbour genetic loci for AMD!

4. Hypermetropic eyes are at a greater risk of AMD. This, again is counterintuitive as myopic eyes are usually more prone to degenerative conditions.

5.Another, (sort of) counter intuitive fact is that 'hard' drusens do not lead to macular degeneration while 'soft' drusens precede macular degeneration.

6.Beta carotene, a treatment modality for AMD increases the risk of carcinoma of the lung in smokers as well as non smokers. Zinc causes genitourinary complications- UTIs, prostatic hyperplasia, and in women,stress incontinence. Also, zinc is ineffective in the prevention of advanced AMD. These results are from the two RCTs- AREDS 1 and 2 .

-Sushrut

Interesting retinal peculiarities

1. The respiratory rate of the retina is twice that of the brain.

2. The retina does not require insulin for glucose to enter the cells!

3. In the retina, glycolysis occurs despite having sufficient oxygen supply.

4. The retina is not just a sensory organ. Much of the image processing occurs at the retinal level itself.

-Sushrut

Fas- fas ligand interactions and uveitis

-Fas ligand/ FasL/ CD95 ligand is a type 2 membrane protein belonging to the TNF superfamily and is found on lymphocytes.

-In the eye, it is expressed on Iris and corneal endothelial cells.

-In the rest of the body, it is expressed on the thymus, testes, and the brain.

-Liver and intestines express this only in periods of severe inflammatory process.

- Apoptosis of the T lymphocytes can be triggered by FasL. Loss of this mechanism is touted to be one of the causes of uveitis.

Mechanism by which it acts is believed to be the selective apoptosis of cells producing TNF or by IL2 activation of lymphocytes.

-Sushrut