Microspherophakia - Causes, Pathophysiology, Symptoms, Diagnosis, and Treatment

What Is Microspherophakia?

Microspherophakia is a rare congenital condition characterized by a bi-convex spherical lens having reduced equatorial diameters due to increased anteroposterior thickness of the lens. It is a triad of angle-closure glaucoma, a small spherical crystalline lens, and lenticular myopia. This may be caused as a result of developmental anomalies of zonules. The condition is mostly associated with lens subluxation, anterior or posterior dislocation, high myopia, accommodation deficits, or increased intraocular pressures. Rarely, microspherophakia has been associated with retinitis pigmentosa, Axenfeld-Rieger anomaly, and XYY syndrome.

Who Is Susceptible to Microspherophakia?

Mostly, microspherophakia has been observed in association with severe different developmental abnormalities and syndromes, especially in association with Weil Marchesani syndrome. The prevalence of Weill Marchesani syndrome has been estimated at 1 in 100,000. Microspherophakia has been observed as an isolated condition in various ethnic groups. Among the Indian population, microspherophakia has been seen in 1.2 percent of children with any kind of lens abnormality.

What Causes Microspherophakia?

The primary cause of microspherophakia lies in the development of zonules during embryogenesis. The condition is caused due to mutations in the latent-TGF-β-binding protein 2 (LTBP2), ADAMTS17, and FBN1 genes. The LTBP2 gene is present in the trabecular meshwork, ciliary processes, and lens capsule and is structurally similar to fibrillin proteins. The gene encodes components for elastic fiber assembly. The other two genes-ADAMTS17, and FBN1, are primarily implicated in Weill Marchesani syndrome.

What Is the Pathophysiology of Microspherophakia?

Congenitally, the crystalline lens is almost spherical at birth, anteroposteriorly measuring 3.5 mm and equatorially 6.5 mm in diameter. By adulthood, the measurements increase to 5 mm in thickness and 9 to 10 mm in equatorial diameter. Due to weak zonules, the equatorial plane lacks tension resulting in a lens that is more spherical and convex. The acquired shape, along with zonular weakness, results in high lenticular myopia and subluxation.

The two pathophysiological mechanisms associated with microspherophakia are:

• Developmental delay or pathological insertion of lenticular fibers during the fifth to the sixth week of intrauterine life. This occurs due to malnutrition and defects in tunica vasculosa lentis.

• The lens remains spherical due to the zonules becoming rudimentary, which is preceded by abnormal development of lenticular fibers.

What Is the Histopathology of Microspherophakia?

Under the microscope, histopathological studies reveal:

• Rudimentary zonules that are unusually elongated.

• Developmental defects in secondary lenticular fibers.

• Abnormal distribution of secondary lenticular fibers.

• Hyaloid degeneration of the lens.

• Changes in lens shape.

• Disruption of the lenticular fibers.

What Are the Signs and Symptoms of Microspherophakia?

The signs of microspherophakia present as:

• Bilateral presentation.

• Poor vision.

• Accommodation problems.

• Acute pain.

• Redness.

• Acute angle closure.

• Unilocular diplopia.

• Lens subluxation.

• Flashes and floaters.

• Amblyopia (lazy eye).

• Myopic disc.

• Myopic crescent.

• Posterior staphyloma.

• Myopic macular degeneration.

• Blue sclera.

• Ectopic pupil.

• Retinal detachment.

• Tears.

• Retinal holes.

• Lattice degeneration.

• Lenticular myopia.

• Mean refractive index of -11.07 dioptres.

• Glaucoma.

• Increased intraocular pressure.

• Angle-closure glaucoma.

• Anterior lens displacement.

How to Diagnose Microspherophakia?

After a preliminary clinical observation, a detailed slit lamp examination can be performed and closely monitored for signs of retinoscopy, best-corrected visual acuity, intraocular pressure, anterior chamber angle and depth, gonioscopy, lens morphology, and signs of subluxation.

Dilated fundus examination is done to identify any glaucomatous disc changes, myopic retinal changes, or co-existing retinal pathology. Further investigations like measurement of lens thickness, axial length, ultrasound biomicroscopy, and anterior segment optical coherence tomography can be done to understand the mechanism of angle closure. iTrace has been used to analyze the underlying cause of decreased pre-operative visual acuity and also aids in foreshadowing surgical outcomes. Electron microscopy can be done to detect any reduction in endothelial cells which is required prior to surgical planning. Apart from that, a detailed systemic examination must be done to detect any systemic conditions or pre-existing syndromes.

How to Treat Microspherophakia?

The treatment regime for microspherophakia involves managing each of the presenting clinical features.The protocol is as follows:

• Lenticular Myopia: Refractive error correction to prevent any amblyopia.
• Pupillary Block: Prevented by prophylactic Nd-Yag laser iridotomy. Any acute attack can be treated by cycloplegics that relax the ciliary muscles, tighten the zonules, and posteriorly pull the lens iris diaphragm. Mannitol, administered intravenously, causes vitreous shrinkage, relieving any pupillary block.
• Angle-Closure Glaucoma: The patients may regain normal intraocular pressure with YAG iridotomy and antiglaucoma medications. Advances cases might require glaucoma surgery in the form of a filtration procedure or glaucoma drainage device. Surgery further lowers the intraocular pressure, preventing any additional disc damage. Treatment may involve combined surgical therapy with lensectomy, vitrectomy, and transversal ciliary body photocoagulation.
• Lens Subluxation: This can be treated with precise lens extraction followed by IOL (intraocular lens) placement. Furthermore, the surgeon might use capsular tension rings. Capsulorhexis, with a double-flanged modification, using a femtosecond laser followed by standard capsular ring insertion. Clear lens extraction (goniosynechialysis with possible secondary IOL-scleral fixated intraocular lens) can be done with corneal-lenticular touch or posterior dislocation into the vitreous cavity. Clear lens exaction is indicated in cases of high myopia, cornea-lenticular touch, high myopia in one eye, and pupillary block glaucoma.
• Poor Vision: Can be managed by low-vision assistive devices.
• Predisposing Systemic Conditions: Requires holistic inter-professional management.

What Is the Prognosis of Microspherophakia?

The prognosis of microspherophakia is completely dependent on the severity of the clinical features. Trabeculectomy has shown an over 86 % success rate by six months and around 77 % by the first year. Blindness was reported in about 20 % of the eyes on presentation.

What Is the Differential Diagnosis of Microspherophakia?

• Aniridia.

• Megalocornea.

• Iridocorneal endothelial syndrome.

• High lenticular myopia.

• Disc coloboma.

• Retinal detachment.

Microspherophakia has also been reported in association with several systemic disorders:

• Alport syndrome.

• Weill Marchesani syndrome.

• Homocystinuria.

• Marfan syndrome.

• Axenfeld-Rieger syndrome.

• Metaphyseal dysplasia.

What Are the Complications of Microspherophakia?

• High myopia.

• Complete anterior or posterior dislocation.

• Corneo-lenticular touch.

• Endothelial decompensation.

• Vitreous tractions.

• Retinal detachment.

• Subluxation of the lens.

• Shallow anterior chamber.

• Intermittent irido-lenticular touch.

• Chronic pupillary block glaucoma.

• Malignant glaucoma.

• Permanent loss of vision or phthisis.

• Painful blind eye.

Conclusion

Microspherophakia is a rare congenital ocular disorder that requires early recognition which is essential in obtaining a good prognosis. The severity of the clinical features can be greatly reduced by early diagnosis. Surgical interventions are commonly used to decompress intraocular pressures and lens relocation. But the most important regime is to manage any underlying syndromes or systemic conditions.