Allergic Conjunctivitis (Treatment, causes)

Allergic Conjunctivitis refers to the inflammation of the conjunctiva. The conjunctiva is the tissue that covers the inside of the eyelids and the white parts of the eyeball as well. It is usually caused by allergens and irritants, such as pollen, dust mites, pet dander or other allergy causing agents. 

Allergic Conjunctivitis is a common condition of the eye and very important as a topic for your Ophthalmology paper. Read this blog post thoroughly to learn all about this condition and boost your NEET PG preparation. 

Allergic Conjunctivitis

• It is a form of ocular allergy that primarily presents irritation and excessive watering in the eyes due to immunoinducive agents. 
• It can be acute, seasonal, or perennial allergic reactions.

The types of allergic conjunctivitis are vernal keratoconjunctivitis, atopic and phlycenular keratoconjunctivitis.

Phlyctenular Conjunctivitis

• Allergy caused by endogenous antigens→ Staphylococcus aureus and tuberculosis infections. 
• Presents watering and itching. 
• Characteristic of phlyctenular conjunctivitis→ nodule of phycten near the limbus and conjunctival congestion
• Involvement of cornea leads to a fascicular ulcer, which later develops into ring ulcer. 
• It is a type 4 hypersensitivity reaction→ treated with steroids
• Recurrence of PC due to infection→ antibiotics, such as tetracycline.

Vernal Conjunctivitis

It is a type 1 hypersensitivity reaction caused by exogenous allergens, such as pollen, dust, etc.

• Common in summer and children.
• Presents itching, watering, and ropy discharge containing mucin.
• It does not develop follicular reactions but only papillary reactions.

Three forms of vernal conjunctivitis

Three forms are palpebral, limbal and mixed. 

Papebral form 

• It is characterised by papillary reaction with cobblestone appearance

Limbal form

• It develops horner trantas spots: white dots containing eosinophils
• When it involves the cornea, it forms the cupid’s bow, also known as pseudogerontoxon.

Important Information Gerontoxon is another name for arcus senilis. The epithelial lesion in vernal conjunctivitis appears like arcus senilis. Hence the name.

• Later stages lead to shield ulcer: deposition of mucus and calcium phosphates in micro-erosions
• Maxwell Lyon’s sign is a pseudomembrane formed due to excessive deposition of mucus on the papilla.

Treatment 

• Antiallergic mast cell stabilisers and antihistamines: olopatadine and azelastine
• Mast cell stabiliser: sodium cromoglycate and nedocromil sodium
• Antihistamines: apenastin and bepotastine.
• Mild steroids: fluorometholone and loteprednol etabonate, when others do not work. 
• Acetylcysteine to dissolve mucus

Atopic Keratoconjunctivitis

• Common temperate regions and winters.
• Predominant in adults with no gender predilection.

Findings in Atopic keratoconjunctivitis

• Shield cataract
• Dennie morgan folds: skin folds under the eyes due to excessive rubbing.
• Keratoconus: due to rubbing
• Madarosis: loss of eyebrows and eyelashes.
• Hertoghe’s sign: loss of lateral one-third eyebrows

Treatment for atopic keratoconjunctivitis

In case of severe allergic reactions: immunomodulators such as cyclosporin and calcineurin inhibitors, such as tacrolimus.

Side notes:

Other causes of Hertoghe’s sign

• Leprosy
• Myxedema

Xerophthalmia

It is a spectrum of ocular diseases due to Vitamin A deficiency.

WHO grading of xerophthalmia

The grading helps determine the severity of the condition. The signs are denoted by X and a subscript. They are 

• X_n → night blindness nyctalopia: the earliest sign
• X_1a → conjunctival xerosis
• X_1b → bitots spot
• X₂ → corneal xerosis
• X_3a → keratomalacia in less than one-third of the cornea
• X_3b → keratomalacia in more than one-third of the cornea (keratomalacia is liquefactive necrosis of cornea)
• X_s → cornea scarring
• X_f → xerophthalmia fundus → white spotted fundus and decreased amplitude in electroretinogram

Q. why do we see decreased amplitude in ERG?

Ans. ERG represents the activity of layers of rods and cones. Since xerophthalmia affects rods and bipolar cells, ERG shows a dip in amplitude.

Side notes:

More about bitots spot

Bitots spot: is keratinised epithelia and infection by corynebacterium xerosis. It is more common on the temporal side:

Pathological changes in xerophthalmia

• Loss of goblet cells
• Squamous metaplasia with keratinisation.

Treatment for xerophthalmia  

• Child more than one year: one lakh IU of vitamin A on the 0th, 1st, and 14th day
• Less than one year: half the dose
• Oral: double the dose of injectival vitamin A.  

Local treatment for xerophthalmia

• Intense lubrication: eyedrops containing methylcellulose derivatives or sodium hyaluronate
• Topical: retinoic acid 

Side note:

Other causes of nyctalopia

• Retinitis pigmentosa
• High myopia
• Late stage of primary open-angle glaucoma
• Congenital stationary night blindness (CSNB)
• Choroidal dystrophy: choroideremia and gyrate atrophy

Side notes:

Two forms of CSNB

1. fundus albi punctatus: night blindness with white spots in the fundus
2. Oguchi’s disease: night blindness with pale spots on the fundus.

Mezov’s phenomenon

Pale fundus restores its appearance when a person suffering from Oguchi’s disease stays in darkness for about an hour. The cause of the phenomenon is the overstimulation of rods.

 Pterygium

It is conjunctival degeneration characterised by triangular fibrovascular subepithelial ingrowth of bulbar conjunctiva over the limbus. It occurs commonly on the nasal side.

Clinical features

• Ugly appearance if it is not covering the pupil; otherwise, harmless. 
• Astigmatism
• Diminished vision when it encroaches on pupils.

Histopathology

• Elastotic degeneration of conjunctival stroma: similar to pinguecula.

Structure of Pterygial Formation

• Body: part from the triangle's base to the border of the pupil.
• Head: apical part of pterygium that protrudes into the pupil. and
• Avascular halo: the region around the tip: the destruction of bowman’s membrane by metalloproteinases.
• Stocker’s line occurs due to iron deposition near the head.

Causes  

• Exposure to UVB rays

Side note:

What else does UVB cause?

In addition to pterygium, it can cause phot ophthalmia, also called snow blindness → UVB rays reflect off the snow and cause corneal epithelial erosion.

Pseudo Pterygium

• It is a scarring that appears like pterygium.
• How to differentiate it from pterygium?
  • Glass rod test: if the glass rod passes through scarring, it is pseudo-pterygium.

Treatment

1. Bare sclera technique

• The recurrence rate after the bare sclera technique is 30 to 40%..
• Mitomycin C, an antimitotic drug administered preoperatively reduces the recurrence. 

2. Autografting

• It is the most effective modality  
• Procedure:

cut a portion of the conjunctiva in the upper or superior temporal quadrant, including limbal stem cells: 

↓

Stitch it over the affected area: conjunctiva at excised region regenerates.

3. Perfect 

• It stands for Pterygium Extended Resection Followed By Extended Conjunctival Transplantation.
• It is a modified version of autografting wherein the conjunctiva excised is much larger.

Pinguecula

It is a yellowish-white mound near the limbus formed by elastotic degeneration of conjunctival stroma

• It is commonly nasal.
• It does not extend on to the cornea.

Treatment

• Not needed: if asymptomatic.
• Mild steroids or lubricants: if presents itching
• Excision is an option but not preferable.

Dry Eye

• It is a condition caused by impaired functions of any layer of the tear film. It becomes a disease with the onset of ocular inflammation.
• Dysfunction of any of the three layers of tear film causes inadequate volume, unstable secretion, or dysfunction in the tear.

Layers of Tear Film After Cornea

1. Mucin layer: formed of goblet cells of conjunctiva → helps spread tear over the ocular surface
2. Aqueous layer: thickest layer: formed of lacrimal and accessory lacrimal glands→ lubrication.
3. Lipid layer: formed by meibomian glands in the lens → prevents evaporation of tear.

Keratoconjunctivitis Sicca

Keratoconjunctivitis sicca is the deficiency of the aqueous layer.

• KCS + Xerostomia primary: Sjogren syndrome.
• Primary Sjogren syndrome + connective tissue disorder: secondary Sjogren syndrome

Side note:

Ocular features of rheumatoid arthritis

Rheumatoid arthritis is a connective tissue disorder, and its association with keratoconjunctivitis sicca leads to secondary Sjogren syndrome. Hence, patients with rheumatoid arthritis experience dry eye disorder.

 Clinical Manifestations of Dry Eye

• Burning sensation
• Gritty sensation of foreign bodies
• Excessive mucus deposition
• Diminished vision when precorneal tear film involved
• Tear meniscus height lesser than 0.25 mm.
• Punctate epithelial keratitis
• Mucus filaments

Investigation of Dry Eye Disorder

• Slit lamp examination

To visualise tear meniscus height, which is the length of a triangular cross-section between lower lid margin and cornea. 

• Schirmer’s test
  • Schirmer’s test 1 
    It involves placing Whatman paper No. 41 under the lower lid for 5 minutes: 
    Wet length of less than 15mm indicates dry eye. 
    It measures both basal and reflex secretion.
• Schirmer’s test 2
  Measures only basal secretion using topical anaesthesia.
• Phenol red thread test
  Yellow-colored thread is brought in contact with the eye for 15 seconds, and the length of the stain that turns red is measured.
  Less than 6 mm indicates severe dry eye.
• Tear film break-up time 
  • It is the time taken for a dry spot to appear from the last blink.
  • Less than 10 seconds indicates severe dry eye.

Important Information While Schirmer’s and phenol red thread tests help diagnose aqueous layer dysfunction, TBUT helps diagnose deficiency in the meibomian and lipid layer.

• Rose Bengal or lissamine green staining

They help visualize dead cells and mucus.

• Tear constituent

Low levels of lactoferrin indicate dry eye.

• Impression cytology

Measures the number of goblet cells.

• Tear osmolality measurement

A high value indicates a dry eye.

Treatment

Treatment is either medical or surgical

Medical	Surgical
Lubricating eye drops containing methylcellulose derivatives, polyvinyl alcohol with povidone, and hyaluronate derivatives.Acetylcysteine to dissolve mucus.Cyclosporin for inflammation	Lacrimal punctal occlusion.For temporary measure Collagen plug that can be dissolved in a few weeks.Silicone plugs for prolonged occlusion.For permanent measure thermal cautery of proximal canaliculate.

That is everything you need to know about Allergic Conjunctivitis for your Ophthalmology preparation. For more interesting and informative blog posts like this download the PrepLadder App and keep reading our blog!