MICROPHTHALMOS AND NANOPHTHALMOS

 

MICROPHTHALMOS:

A congenital condition in which the affected eye is smaller at birth.

(Less than 15mm in greatest diameter. Normally the diameter varies from 16-19mm at birth.)

PLEASE ALSO VISIT THE OTHER POST ON NANOPHTHALMOS=

https://ourgsc.blogspot.com/2026/04/nanophthalmos.html

TYPES:

1. PURE MICROPHTHALMOS alone (NANOPHTHALMOS/SIMPLE MICROPHTHALMOS): Eye is smaller than normal size, but there are no other gross abnormalities, except for a high lens/eye volume.
2. Microphthalmos with CYST
3. Microphthalmos associated with other SYSTEMIC ANOMALIES, eg. In Trisomy 13 and congenital rubella.

1

Greek= nanos= Dwarf

DEFINITION: Represents an eye reduced in volume, but otherwise grossly normal in form and function.

Male:Female ratio= 1:1.

Bilateral, in cases of general dwarfism.

In unilateral cases the affected side of the body and face is undeveloped.

Inheritance: Sporadic/AD/AR

CLINICAL FEATURES:

1. Narrow palpebral fissure with deeply set eyeball in small orbit.
2. Marked hypermetropia (+18 to 20 D)
3. Lesser hypermetropia, emmetropia or myopia (occasionally, up to -20D) can occur depending upon the shape of the cornea and lens.
4. Usually, the visual acuity is good. Spectacles resemble aphakic glasses.
5. Anterior chamber angle: In young patients, the angle is open with prominent iris convexity. Progressive anterior chamber shallowing and narrowing of angle occurs with the onset of angle closure glaucoma during the 4^th-6^th decades of life.

Lens:Eye Volume ratios:

Lens volume= 4/3AB (A= ½ thickness of lens) (B=radius of globe)

Eye volume= 4/3R (R= radius of globe)

The lens:eye volume is greater (10-32%) in nanophthalmic eyes, compared to normal eyes (where it is 3-4%).

CLASSIFICATION OF NANOPHTHALMOS ON GONIOSCOPY AND IOP:

(Use pediatric goniolens if corneal diameter is reduced)

CATEGORY 1	Angle completely open with marked iris convexity. IOP= ≤ 20mmHg	Management= Observation at 3-4 monthly intervals.
CATEGORY 2	Angle appears partially closed. IOP= ≤ 20mmHg	More frequent observations. Treatment is initiated when there is evidence of progression in angle closure.
CATEGORY	Angle partially or totally closed. IOP= > 20mmHg

 

TREATMENT:

1. MEDICAL
2. LASER
3. SURGICAL

 

MEDICAL:

• Steroids to reduce choroidal effusions which cause angle closure. Oral Prednisolone in the dose of 1-2 g/kg BW/ day, followed by tapering regimen.
• Pilocarpine= Apparently the mainstay of therapy. Start with 1% four times daily (QID), then increase to higher dose (upto 4%) and frequent administration (2 hourly). However, the response is unpredictable.
• Mydriatic and cycloplegic therapy= Cycloplegics → tighten the zonules→ lens-iris diaphragm moves posteriorly→ deepens anterior chamber, reduces relative pupillary block→ restores normal pathway for aqueous flow anteriorly.
• Beta blockers, carbonic anhydrase inhibitors, and sympathomimetics = decrease aqueous production.
• Hyperosmotic agents can be used for short-term control of IOP during acute attacks.

LASERS:

• Iridotomy
• Iridoplasty (Gonioplasty)= low power argon laser therapy to contract the peripheral iris stroma → flattening iris → widening of angle.

SURGICAL STRATEGIES:

• Prophylactic posterior segment surgery= Posterior scleral resection ± posterior sclerectomy.
• Vortex vein decompression.
• Prophylactic anterior segment surgery= Anterior sclerotomies.
• Cataract surgery= Surgical pearls to improve cataract surgery outcomes include: anterior vitrectomy, medical dehydration of the vitreous and scleral lamellar resection. 

Glaucoma surgeries=

• Surgical peripheral iridectomy (PI).
• Trabeculectomy
• Cyclocryotherapy and other cyclodestructive procedures.

Nanophthalmos showing thick sclera

NEUROVASCULAR COUPLING

 

 

"Neurovascular coupling" appears to be a critical mechanism in the regulation of ocular blood flow (OBF).

Increased activity of the neurons subserving vision leads to higher blood flows to the neural elements, a response called “functional hyperemia”. This intertwined association of the nerves and blood flow is called “neurovascular coupling”. This phenomenon is defined as the "vascular response to increased neuronal activity". 

According to the negative feedback principle, increased neuronal activity causes accumulation of vasoactive catabolites, such as H+, K+, and adenosine. These substances decrease vascular resistance and increase the blood flow, until the normal hemostasis is achieved. Studies have found that stimulation of nerves, such as that with flicker stimuli, leads to activity-dependent regulation of OBF in the retina and ONH. In glaucomatous eyes, astrocytic dysfunction in the ONH can disrupt this coupling, leading to retinal ganglion cell stress and degeneration independently or in association with changes in IOP. Malfunctioning of the astrocytes and disturbed neurovascular coupling triggers structural remodeling in the ONH, which appears as optic disc cupping.

Neurogenic Control of Vessels

The eye has a rich supply of autonomic nerves within the uvea, the posterior ciliary arteries, and the extraocular portion of the central retinal artery. Vessels in the retina and the prelaminar portion of the optic nerve have no neural innervation. Consequently, stimulation of the sympathetic nerve system might influence retinal and optic nerve head perfusion indirectly, at most. Nevertheless, α- and β-adrenergic receptors have been demonstrated in the retinal vessels.

The autonomic nervous system supplies a network of vasomotor nerve fibers. The nerve fibers form a plexus in the adventitia of the resistance vessel walls and send extensions to form varicosities on the outer surface of the media.

The nerve fibers consist of three kinds of fibers: (a) adrenergic; (b) cholinergic; and (c) non-adrenergic/non-cholinergic (nitric oxide).

Neurotransmitters are released from the varicosities towards the smooth muscle cells. Norepinephrine produces vasoconstriction by stimulating alpha-receptors, and acetylcholine evokes vasodilatation by stimulating M3-receptors. In addition to these classical neurotransmitters, several substances are released in the nerve terminals.

Stimulation of the sympathetic superior cervical ganglion elicits constriction of the uveal blood vessels and increases the uveal vascular resistance. Surprisingly, electrical stimulation of parasympathetic fibers of the ciliary ganglion induces intense miosis, without notably changing the uveal vascular resistance. Intracranial stimulation of the oculomotor nerve produces vasoconstriction in the anterior uvea and vasodilation in the choroid.

Uveal vasodilation is also seen on stimulation of the facial nerve and ophthalmic and maxillary divisions of the trigeminal nerve.

Vasoactive intestinal polypeptide (VIP)-immunoreactive nerves have been demonstrated in the choroid, indicating that VIP may be involved in the vasodilation produced by nerve stimulation.

The dense vasodilative innervation of the choroid, might be important to increase choroidal blood flow under certain conditions such as high light intensity.

Microvascular unit techniques combining bi-directional laser Doppler velocimetry and retinal vessel analyzer (RVA) confirmed human retinal blood flow response to flicker light measuring an increase of retinal blood flow in the magnitude of 53--59%.

 

REFERENCES:

• Shen W. Retinal Neurovascular Coupling: From Mechanisms to a Diagnostic Window into Brain Disorders. Cells. 2025 Nov 16;14(22):1798. doi: 10.3390/cells14221798. PMID: 41294851; PMCID: PMC12651437.
• Buerk DG, Riva CE, Cranstoun SD. Frequency and luminance-dependent blood flow and K+ ion changes during flicker stimuli in cat optic nerve head. Invest Ophthalmol Vis Sci. 1995;36:2216–27.
• Gugleta K, Fuchsjäger-Mayrl G, Orgül S. Is neurovascular coupling of relevance in glaucoma? Surv Ophthalmol. 2007 Nov;52 Suppl 2:S139-43. doi: 10.1016/j.survophthal.2007.08.009. PMID: 17998039.
• Daniele Prada, Alon Harris, Giovanna Guidoboni, Brent Siesky, Amelia M. Huang, Julia Arciero. Autoregulation and neurovascular coupling in the optic nerve head. Survey of Ophthalmology.  2016;61:164-186. https://doi.org/10.1016/j.survophthal.2015.10.004.
• Naixing Huang, Tristan T. Hormel, Siyu Chen, David Huang, Thomas S. Hwang, Steven T. Bailey, and Yali Jia, "Retinal neurovascular coupling evaluation with circular-scan OCTA," Opt. Express 33, 31295-31306 (2025)

AS-OCT in Childhood Glaucoma

 

Anterior segment optical coherence topography (AS-OCT) is a non-contact imaging modality that uses low-coherence interferometry to visualize the ocular anterior segment structures.

AS-OCT has demonstrated its ability in adults to accurately measure corneal thickness, epithelial thickness, angle opening distance (AOD), angle recess area (ARA), anterior chamber depth (ACD), and lens vault.

Hand-held OCT (HH-OCT) has emerged as a valuable tool in the diagnosis and management of various pediatric optic neuropathies.

A comprehensive literature search was performed in October 2024 across four major databases: PubMed, Web of Science, EBSCOhost, and Google Scholar.The objective was to identify original studies evaluating the clinical application of AS-OCT—including HH-AS-OCT—in the assessment of childhood glaucoma.

15 studies including 406 glaucomatous eyes with diverse etiologies such as primary congenital, juvenile open-angle, post-cataract, and syndromic glaucoma published between 2012 and 2025 were included in the review.

AS-OCT enabled high-resolution visualization of the trabecular meshwork, Schlemm canal, iris, and anterior chamber angle. Several studies proposed diagnostic thresholds for iris thickness and angle width, with area under the receiver operating characteristic curves ranging from 0.69 to 0.87. Postoperative imaging documented drainage device position and angle anatomy, while HH-AS-OCT facilitated imaging in infants and uncooperative children, revealing subclinical abnormalities undetectable by gonioscopy; however, these structural findings do not consistently predict clinical outcomes. Heterogeneity in devices, imaging protocols, and glaucoma phenotypes limits standardization, and no definitive AS-OCT biomarker has yet emerged in childhood glaucoma. [1]

In a study by Kaushik et al, no visibility of the trabecular meshwork structures was the most specific sign for glaucomatous eyes. [2]

Byline:

Regarding posterior segment OCT, Lever is of the opinion that the OCT measurements of the pRNFL and macular thickness have a strong ability to diagnose paediatric glaucoma. However, OCT should be used in addition to conventional diagnostic tools rather than as a standalone method. [3]

REFERENCES:

1. Abdelaal A, Kawji A, Gad W, Alzein A, Chang TC, Bitrian E, El Sayed YM, Gawdat GI, Hassan AK, El-Fayoumi D, Elhusseiny AM. Utilization of anterior segment optical coherence tomography in childhood glaucoma: A systematic review. Surv Ophthalmol. 2026 Jun 27:S0039-6257(26)00086-X. doi: 10.1016/j.survophthal.2026.06.011. Epub ahead of print. PMID: 42364735.
2. Kaushik S, Singh AK, Thattaruthody F, Suresh V, Gera A, Yadav S, Pandav SS. Utility of Swept-Source Anterior-Segment OCT as an In-Office Biomarker for Early Childhood Glaucoma. JAMA Ophthalmol. 2025 Jul 1;143(7):553-560. doi: 10.1001/jamaophthalmol.2025.1009. PMID: 40402480; PMCID: PMC12100509.
3. Lever M, Halfwassen C, Unterlauft JD, Bechrakis NE, Manthey A, Böhm MRR. The Paediatric Glaucoma Diagnostic Ability of Optical Coherence Tomography: A Comparison of Macular Segmentation and Peripapillary Retinal Nerve Fibre Layer Thickness. Biology (Basel). 2021 Mar 25;10(4):260. doi: 10.3390/biology10040260. PMID: 33805903; PMCID: PMC8064387.