31

Nanophthalmos

Diagnosis and Treatment

Zvia Burgansky-Eliash, MD and Richard J. Simmons, MD

Nanophthalmos is a relatively rare bilateral condition characterized by small ocular volume, typically associated with marked hyperopia and shallow anterior chamber.¹ The axial length is between 14 and 20.5 mm.^2,3 Exceptionally, nanophthalmic eyes may be emmetropic or myopic. The globe has a small equatorial diameter and a small corneal diameter, but the size of the lens is normal. The disproportion between lens and ocular volume contributes to iris convexity and ante rior chamber shallowing. In nanophthalmos, the lens may occupy 10% to 30% of the volume of the globe, compared with approximately 4% in normal adult eyes.

In many cases, visual acuity is reduced due to macular hypoplasia presented with lack of foveal light reflex, lack of a normal foveal pit on optical coherence tomography, and abnormal or absent foveal avascular zones on fluorescein angiography.⁴ Retinal pigmentary dystrophy can accompany nanophthalmos as well.^5–7 A case of retinitis pigmentosa and optic nerve drusen associated with nanophthalmos was described.⁸

INHERITANCE

In some cases, nanophthalmos is inherited; in other cases, it is a sporadic occurrence. If inherited, transmission may be either autosomal recessive or autosomal dominant.^7,9,10 In one autosomal dominant nanophthalmos family, the abnormality was located on NNO1 locus on chromosome 11.¹¹ Often, the inheritance is unknown, but the patients have relatives who are blind from angle-closure glaucoma.^1,12 There is a controversy regarding female predominance.^1,13,14 Although nanophthalmos is usually not associated with systemic abnormalities, there are reports on cases with coexisting cryptorchidism,¹⁵ Hallermann-Streiff syndrome,¹⁶ and oculo-dento-digital syndrome.¹⁷

GLAUCOMA CHARACTERISTICS

Nanophthalmos is complicated by angle-closure glaucoma in many cases, which usually develops between 20 and 50 years of age.² In younger patients, the most characteristic findings are hyperopic eyes with small corneas and bulging forward of the lens and iris into a shallow anterior chamber. As the lens enlarges with age, there is an increase in relative pupillary block, and the anterior chamber becomes shallow, with progressive narrowing of the angle. This is the most common cause of angle-closure glaucoma in nanophthalmic eyes, which eventually leads to peripheral anterior synechiae formation.

Angle closure can also develop secondary to spontaneous choroidal thickening and effusions.¹⁸ These choroidal changes may cause a forward rotation of the ciliary body that pushes the peripheral iris forward, allows the lens to move forward, and increases relative pupillary block. Severe uveal effusion and exudative retinal detachment is a frequent complication of anterior segment surgery. Choroidal effusion and exudative retinal detachment were reported also after laser peripheral iridotomy.^19,20

HISTOPATHOLOGY

The sclera in eyes with nanophthalmos is both thicker and disorganized compared to normal sclera.^16,21–23 The collagen fibrils bundles are larger, less ordered, and more interwoven than normal.21 High levels of fibronectin found in these cases affect the packing of collagen fibers and lead to thickening of the sclera and occlusion of the vortex veins.¹⁶ The thickened sclera reducing its permeability to protein²⁴ together with the constriction of vortex veins both contribute to uveal effusion in the nanophthalmic eye.

TREATMENT

In general, medication and laser therapy offer a safe and often sufficient option for treatment of nanophthalmic angle-closure glaucoma.^10,25

Medical Treatment

Intraocular pressure elevation is managed by aqueous suppressants: beta-blockers, alpha adrenergic agonists, and carbonic anhydrase inhibitors. Miotics may make the pupillary block worse by relaxing the lens zonules in these patients.¹⁰

Laser Iridectomy

It is recommended to perform a preventive peripheral iridectomy (PI) when angles are still open but so slit like that angle closure is threatened. When glaucoma develops, laser iridotomy is beneficial to eliminate the pupillary block component in the early stage of glaucoma before the occurrence of peripheral anterior synechiae.^3,10

Argon Laser Peripheral Iridoplasty

If angle remains narrow or becomes worse progressively with time, laser iridoplasty is the next step, providing widening of the angle in up to 91.6% of patients.^10,13 The widening effect of iridoplasty may gradually disappear. Therefore, a patient should have a slit-lamp examination and gonioscopy every 3 months. Iridoplasty is used repeatedly, attempting to open as much of the angle as possible.

Trabeculectomy

Filtration surgery alone is not advised as it is associated with high risk of permanent loss of vision caused by disastrous complications after the surgery.^10,26 Sudden decompression of the globe during surgery triggers the rapid progression of massive uveal effusion, which may lead to secondary retinal detachment, intraocular hemorrhage, and loss of vision (Figure 31-1). Therefore, glaucoma filtration surgery is considered as the last choice in the treatment of angle-closure glaucoma.^10,13 Prophylactic sclerectomy, anterior sclerotomy, or vortex vein decompression are needed to reduce disastrous complications.

During trabeculectomy, an effort is made to avoid intraoperative and postoperative hypotony to minimize the chance for choroidal effusions and exudative retinal detachments. This is achieved by filling the anterior chamber with viscoelastic agent prior to performing the sclerotomy, preplacing of trabeculectomy flap sutures so that they may be closed immediately, and tight suture closure.

When the glaucoma is such that trabeculectomy can be deferred, preoperative prophylactic sclerectomy is performed, preferably 4 to 6 weeks before the trabeculectomy to allow full recovery. In these cases, 2 inferior posterior sclerectomies are done, sparing the superior conjunctiva.

If the glaucoma is so severe that immediate surgery is necessary, anterior V-shaped sclerotomies can be done at the time of the trabeculectomy before the eye is opened. In a study of 20 patients who had trabeculectomy with mitomycin C application and inferior sclerotomy, the cumulative probability of success was 85% at 1 year and 47% at 5 years after surgery. Complications were common and include uveal effusion in 50%, cataract formation in 35%, and late choroidal detachment in 25%.³ In another small report, 2 patients underwent a similar procedure successfully.²⁵

Sclerectomy and Sclerotomy

Several methods have been proposed to open areas in the sclera that allow drainage of existing uveal effusion and as a prophylactic measure before or at the beginning of filtration surgery.

Brockhurst²⁷ recommends including vortex vein decompression with lamellar scleral resection and posterior sclerotomies. In his description, 80% of participants had a reattachment of the retina after this procedure. However, intraoperative bleeding may occur during scleral dissection around the vortex vein.³

The technique for posterior sclerectomies described by Gass²⁸ includes lamellar scleral resection and sclerotomy. Gass advocates the removal of a two-thirds thickness rectangle (5 mm × 7 mm) of sclera with the additional removal of a 1-mm full-thickness piece of sclera from the scleral bed.

The use of absorbable gelatin film to cover the sclerectomized area was tried successfully in one case of partial-thickness sclerectomy with a central sclerotomy. The gelatin film may prevent regeneration of scleral tissue and recurrence of the exudative retinal detachment.20

Jin and Anderson¹³ described a V-shaped full-thickness sclerotomy anteriorly over the pars plana, leaving it unsutured to provide ongoing drainage postoperatively. The authors of this chapter recommend a similar technique with excising the flap completely at the base in high-risk cases, because the unsutured flaps may reseal within 7 days. The full-thick ness V-shaped scleral flaps (4 mm × 4 mm) are made in the inferior nasal and temporal quadrants (the point of the V should be 5 mm from the limbus directed to ward the limbus). There is a risk related to large areas of uvea unprotected by sclera; however, anterior site is better protected than posterior area by thicker uveal layer and firm vitreous base.³ Moreover, these eyes face certain blindness unless surgery is successful. Simple linear sclerotomies similar to that made for drainage of choroidal effusions are inadequate in true nanophthalmos.

PROGNOSIS

Although angle-closure glaucoma secondary to nanophthalmos can be treated with various techniques, the prognosis remains guarded.

REFERENCES

1.      Brockhurst RJ. Nanophthalmos with uveal effusion. A new clinical entity. Arch Ophthalmol. 1975;93(12):1989-1999.

2.      Ritch R, Chang BM, Liebmann JM. Angle closure in younger patients. Ophthalmology. 2003;110(10):1880-1889.

3.      Yalvac IS, Satana B, Ozkan G, Eksioglu U, Duman S. Management of glaucoma in patients with nanophthalmos. Eye (Lond). 2008;22(6):838-843.

4.      Walsh MK, Goldberg MF. Abnormal foveal avascular zone in nanophthalmos. Am J Ophthalmol. 2007;143(6):1067-1068.

5.      Mandal AK, Das T, Gothwal VK. Angle closure glaucoma in nanophthalmos and pigmentary retinal dystrophy: a rare syndrome. Indian J Ophthalmol. 2001;49(4):271-272.

6.      Ghose S, Sachdev MS, Kumar H. Bilateral nanophthalmos, pigmentary retinal dystrophy, and angle closure glaucoma—a new syndrome? Br J Ophthalmol. 1985;69(8):624-628.

7.      MacKay CJ, Shek MS, Carr RE, Yanuzzi LA, Gouras P. Retinal degeneration with nanophthalmos, cystic macular degeneration, and angle closure glaucoma. A new recessive syndrome. Arch Ophthalmol. 1987;105(3):366-371.

8.      Buys YM, Pavlin CJ. Retinitis pigmentosa, nanophthalmos, and optic disc drusen: a case report. Ophthalmology. 1999;106(3):619-622.

9.      Neelakantan A, Venkataramakrishnan P, Rao BS, et al. Familial nanophthalmos: management and complications. Indian J Ophthalmol. 1994;42(3):139-143.

10.    Singh OS, Simmons RJ, Brockhurst RJ, Trempe CL. Nanophthalmos: a perspective on identification and therapy. Ophthalmology. 1982;89(9):1006-1012.

11.    Othman MI, Sullivan SA, Skuta GL, et al. Autosomal dominant nanophthalmos (NNO1) with high hyperopia and angle-closure glaucoma maps to chromosome 11. Am J Hum Genet. 1998;63(5):1411-1418.

12.    Kimbrough RL, Trempe CS, Brockhurst RJ, Simmons RJ. Angle-closure glaucoma in nanophthalmos. Am J Ophthalmol. 1979;88(3 pt 2):572-579.

13.    Jin JC, Anderson DR. Laser and unsutured sclerotomy in nanophthalmos. Am J Ophthalmol. 1990;109(5):575-580.

14.    Calhoun FP Jr. The management of glaucoma in nanophthalmos. Trans Am Ophthalmol Soc. 1975;73:97-122.

15.    Barad RF, Nelson LB, Cowchock FS, Spaeth GL. Nanophthalmos associated with cryptorchidism. Ann Ophthalmol. 1985;17(5):284-286, 288.

16.    Yue BY, Kurosawa A, Duvall J, Goldberg MF, Tso MO, Sugar J. Nanophthalmic sclera. Fibronectin studies. Ophthalmology. 1988;95(1):56-60.

17.    Widder RA, Engels B, Severin M, Brunner R, Krieglstein GK. A case of angle-closure glaucoma, cataract, nanophthalmos and spherophakia in oculo-dento-digital syndrome. Graefes Arch Clin Exp Ophthalmol. 2003;241(2):161-163.

18.    Wu W, Dawson DG, Sugar A, et al. Cataract surgery in patients with nanophthalmos: results and complications. J Cataract Refract Surg. 2004;30(3):584-590.

19.    Thapa SS, Paudyal G. Choroidal effusion following laser peripheral iridotomy for the treatment of angle closure glaucoma in a patient with nanophthalmos. Nepal Med Coll J. 2005;7(1):81-82.

20.    Krohn J, Seland JH. Exudative retinal detachment in nanophthalmos. Acta Ophthalmologica Scandinavica. 1998;76(4):499-502.

21.    Trelstad RL, Silbermann NN, Brockhurst RJ. Nanophthalmic sclera. Ultrastructural, histochemical, and biochemical observations. Arch Ophthalmol. 1982;100(12):1935-1938.

22.    Stewart DH 3rd, Streeten BW, Brockhurst RJ, Anderson DR, Hirose T, Gass DM. Abnormal scleral collagen in nanophthalmos. An ultrastructural study. Arch Ophthalmol. 1991;109(7):1017-1025.

23.    Shiono T, Shoji A, Mutoh T, Tamai M. Abnormal sclerocytes in nanophthalmos. Graefes Arch Clin Exp Ophthalmol. 1992;230(4):348-351.

24.    Jackson TL, Hussain A, Morley AM, et al. Scleral hydraulic conductivity and macromolecular diffusion in patients with uveal effusion syndrome. Invest Ophthalmol Vis Sci. 2008;49(11):5033-5040.

25.    Kocak I, Altintas AG, Yalvac IS, Nurozler A, Kasim R, Duman S. Treatment of glaucoma in young nanophthalmic patients. Int Ophthalmol. 1996;20(1-3):107-111.

26.    Huang S, Yu M, Qiu C, Ye T. The management of secondary glaucoma in nanophthalmic patients. Yan Ke Xue Bao. 2002;18(3):156-159.

27.    Brockhurst RJ. Vortex vein decompression for nanophthalmic uveal effusion. Arch Ophthalmol. 1980;98(11):1987-1990.

28.    Gass JD. Uveal effusion syndrome. A new hypothesis concerning pathogenesis and technique of surgical treatment. Retina. 1983;3(3):159-163.