Microspherophakia

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Article initiated by:

Pratima Vishwakarma

All contributors:

Manoj Marathe, Neha Gandhi, Alpa S. Patel, M.D., Derek W DelMonte, MD, Pratima Vishwakarma, Kourtney Houser, MD, Brandon Baartman, MD, Michael Wildes, MD, Yashovardhan Singh Siwach, M.S.

Assigned editor:

Michael Wildes, MD

Review:

Assigned status Update Pending

 by Michael Wildes, MD on June 10, 2024.

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Contributing Editors:	add

Microspherophakia (MSP) is characterized by increased anteroposterior diameter and reduced equatorial diameter of the crystalline lens. It is a rare condition, usually bilateral.

On slit lamp examination- Whole lens is visible with full mydriasis Photo Courtesy- LVPEI, Bhubaneswar

Disease Entity

Disease

Microspherophakia has the following characteristics:

• It is usually bilateral
• Small diameter of the lens
• Increased anteroposterior diameter of the lens
• Equator of the lens is visible with full mydriasis
• Movement of lens with change in posture
• May be associated with lens dislocation/ subluxation , high myopia, defective accommodation, glaucoma

Genetics

Mutations in following genes have been noted:

• Latent TGF β-binding protein-2 (LTBP2) gene
• 

  Microspherophakia with posterior synechiae. Image Courtesy :Dr. Yashovardhan Singh Siwach, ASG Eye Hospitals, Jodhpur Rajasthan
  ADAMTS17

LTBPs are a family of proteins showing structural homologies with fibrillins and is expressed in trabecular meshwork, ciliary processes and lens capsule/epithelium layer. It might have a role in regulation of elastic fibre assembly.

ADAMTS17 is part of same family of metalloproteinases as ADAMTS10 which is the main gene associated with Weill-Marchesani syndrome.

Associations

Microspherophakia may occur as an isolated defect, may be familial or it might be associated with systemic / local anomalies as follows:

Entities associated with microspherophakia

Systemic
Weill-Marchesani syndrome
Marfan Syndrome
Lowe Syndrome
Homocystinuria
Alport Syndrome
Microspherophakia-metaphyseal dysplasia
Axenfeld Rieger syndrome
Klinefelter’s syndrome
Rhizomelic form of Chondrodysplasia punctata
Metaphyseal dysplasia
Cri du chat syndrome
Hyperlysinemia
Peters Anomaly
Mandibulofacial dystosis
Congenital rubella
Local
Aniridia
Iridocorneal endothelial syndrome
Megalocornea
Optic disc colobomata

Familial microspherophakia is not associated with systemic abnormalities. Pattern of inheritance is mainly autosomal recessive, but it can also be autosomal dominant.

General Pathology

In histopathological study it has been found that zonular fibers may be abnormally long and somewhat rudimentary. In addition there may be abnormal development and distribution of secondary lens fibers. Later on hyaloid degenerations are noted due to changes in shape of lens affecting the lens fibers.

Pathophysiology

Following mechanisms has been suggested :

• Arrest in development or abnormal insertion of secondary lens fibers both of which may be secondary to a nutritional deficiency from defects in tunica vasculosa lentis and may occur in the fifth and sixth month of embryonic life as the lens is normally spherical at this stage
• Zonular fibers may also be rudimentary due to lack of tension and arrest in lens development so that it may remain spherical instead of gradually converting to a normal biconvex shape

Diagnosis

History

A thorough family history and history of systemic anomalies is required.

Symptoms

Zonular instability might lead to lens dislocation/ subluxation or secondary angle closure glaucoma. Patients might present with diminution of vision or acute eye pain.

Signs

Classically, signs of microspherophakia include the triad of angle closure glaucoma, shallow anterior chamber, and refractive myopia. Other findings can include:

• Thick crystalline lens with smaller diameter and defective accommodation
• Entire equatorial margin of the lens is seen with full mydriasis which will move with change in posture
• Posterior staphyloma, myopic crescent, ectopic pupil, or blue sclera
• Signs associated with complications like ectopia lentis, glaucoma, high myopia, retinal detachment, etc.

Diagnostic procedures

UBM (ultrasound biomicroscopy) might be useful in diagnosis of microspherophakia. This imaging technology uses ultrasonic waves to produce two dimensional cross sectional images of the anterior segment. It provide morphological details of anterior chamber angle, iris, ciliary body, zonules & lens and is specially useful in challenging cases like those having small and fixed pupil.

Screening tests may be required for associated systemic conditions like serum homocysteine levels and urine screening test for homocysteinuria.

Complications

Microspherophakia with minimal to mild lens subluxation Photo courtesy - LVPEI Bhubaneswar

Glaucoma is common in microspherophakia and has been reported in up to 51% of patients. Secondary angle closure glaucoma is the most common sight threatening complication of microspherophakia.

Glaucoma in microspherophakia may be caused via:

• Acute pupillary block mechanism caused by forward movement of spherical lens or anterior subluxation of lens due to weak and long zonules.
• Peripheral anterior synechiae formation due to unrelieved pupillary block causing synechial angle closure and irreversible trabecular meshwork damage.
• Chronic pupillary block leading to crowding of anterior chamber angle by the spherical lens
• Developmental anomaly of the anterior chamber angle

Progressive microspherophakia is also responsible for severe and progressive lenticular myopia while zonular instability might lead to lens dislocation or subluxation.

The probability of developing glaucoma increases with age for patients with microspherophakia.

Management

Slitlamp photograph of the right eye of the patient with microspherophakia with  shallow anterior chamber
Photo courtesy: LVPEI, Bhubaneswar

Medical and surgical management of complications seen with microspherophakia may be difficult.

Cycloplegics are the treatment of choice. Miotics if given in microspherophakia might lead to pupillary block glaucoma.

Stepwise protocol for treatment of glaucoma in microspherophakia:

1. Nd: Yag Laser Peripheral iridotomy (although this may have limited effect)
2. Clear lens extraction with or without goniosynechiolysis
3. Filtering surgery
4. Tube shunt surgery

Indications of clear lens extraction in patients with microspherophakia:

• Corneo-lenticular contact
• Unilateral high myopia
• Pupillary block
• Secondary intractable glaucoma

Intraoperative complications associated with clear lens extraction in these patients include difficulty in performing capsulorhexis and implanting IOL due to smaller bag size.