Albert & Jakobiec's Principles & Practice of Ophthalmology, 3rd Edition

CHAPTER 214 - Nanophthalmos: Guidelines for Diagnosis and Therapy

Chandrasekharan Krishnan,
Tom C. Hsu,
Omah S. Singh

INTRODUCTION

Key Features: Nanophthalmos

  

.   

In nanophthalmos, eyes are reduced in volume but function normally. Axial length is less than 20.5 mm.

  

.   

The most common problems that occur with nanophthalmos are angle-closure glaucoma (acute and chronic) and choroidal effusions.

  

.   

With the advent of small incision phacoemulsification, the risk of intraoperative and postoperative complications has declined dramatically.

The term 'nanophthalmos' is derived from the Greek word nano, meaning, 'dwarf'. It is a rare form of pure microphthalmos that results from arrested development of the globe after closure of the embryonic fissure.[1] Nanophthalmos is usually bilateral and may be inherited in sporadic, autosomal dominant, or autosomal recessive fashions.[1-13] Microphthalmos, conversely, represents a spectrum of phenotypes with variable penetrance (Table 214.1). Unlike other forms of microphthalmos, nanophthalmic eyes are reduced in volume, but otherwise normal in form and function.[1-8,10]


TABLE 214.1   -- Types of Microphthalmos

Primary anophthalmos with lack of a clinically detectable eyeball

Microphthalmos with cyst, caused by failure of the embryonic fissure to close at the 7 to 14 mm stage

Complicated microphthalmos, associated with ocular and systemic anomalies

Pure microphthalmos (also referred to as nanophthalmos) which is not generally associated with ocular or systemic anomalies

 

 

 

CLINICAL CHARACTERISTICS

Clinical characteristics of the nanophthalmic eye include a narrow palpebral fissure with a deeply set eye in a small orbit (Fig. 214.1). Marked hypermetropia is usual, but lesser ranges of hypermetropia, emmetropia, and (rarely) myopia have been reported.[1-8] The nanophthalmic patient is often extremely hyperopic but has good corrected visual acuity.

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FIGURE 214.1  (a-d) A 64-year-old woman exhibiting external characteristics of nanophthalmos including deeply set eyes in small bony orbits, narrow palpebral fissures, and hyperopic refractive correction resembling aphakic spectacles.

 

 

Nanophthalmic eyes by definition have reduced total axial lengths (14-20.50 mm), small equatorial and transverse diameters, and ocular volume reduced to about two-thirds of an average eye (Tables 214.2 and 214.3).[1,15] Corneal diameter may be normal or reduced (10-11.5 mm), and the crystalline lens is normal in volume. Goldmann applanation tensions may reveal a wide ocular pulse (8-12 mmHg) consistent with thickened sclera and impaired drainage of vortex veins. Although nanophthalmos is not characteristically associated with systemic abnormalities, the association of nanophthalmos and cryptorchidism has been reported.[16] This is hypothesized to result from abnormal forebrain development leading to failure of the fetal hypothalamic gonadotropin axis. The most common abnormalities in nanophthalmos involve the posterior pole and the anterior segment angle, and are discussed in detail later in this chapter.


TABLE 214.2   -- Nanophthalmos Data[*]

Sex

n = 40 patients

16 patients (male)

24 patients (female)

Age?

n = 40 patients

Average = 55.2 years; median = 58 years; range = 25-77 yr

Corneal Diameter (mm)

n = 47 eyes of 24 patients

Average = 10.56; median = 10.50; range = 9.5-12.00

Anterior Chamber Depth (mm)?

n = 48 eyes of 25 patients

Average = 1.91; median = 2.25; range = 0.50-4.60

Refractive Error

n = 74 eyes of 37 patients

Average = 10.00; median = 10.00; range = ?3.50±24.00

Axial Length (mm)

n = 78 eyes of 40 patients

Average = 18.83; median = 19.50; range = 15.00-20.50

Crystalline Lens Anterior-Posterior Diameter (mm)

n = 42 eyes of 23 patients

Average = 4.68; median = 4.25; range = 3.0-5.9

Crystalline Lens; Eye Volume Ratio

n = 46 eyes of 23 patients

Average = 24.68%; median = 23.60%; range = 16.60-37.60%

Combined Thicknesses of Scleral and Choroidal Layers (mm)

n = 22 eyes of 12 patients

Average = 2.80; median = 2.25; range = 1.37-4.00

 

*

Patients composing nanophthalmos subset originated through a variety of referral networks over ?30 yr of practice and include but are not limited to:1. Patients referred for the evaluation or treatment of angle-closure and openangle glaucoma.2. Patients referred as blood relatives of an index case affected by nanophthalmos.3. Patients with posterior segment findings consistent with the diagnosis of nanophthalmos (e.g., choroidal effusion or nonrhegmatogenous retinal detachment) referred from a retinal practice.

 

?

Patient age refers to the age at time of initial presentation, which may or may not correlate with the age at the time of diagnosis of nanophthalmos.

 

?

20 additional eyes showed clinically shallow chamber depths measuring less than two corneal thicknesses.

 


TABLE 214.3   -- Comparative Ocular Anatomy

Parameter

Normal Adult Human Eye[10]

1990 Nanophthalmos Eyes

Horizontal corneal diameter (mm)

11.7 mm

n = 47 eyes of 24 patients

 

 

Average = 10.56; median = 10.50; range = 9.50-12.00

Anterior chamber depth

3.5 mm

n = 48 eyes of 25 patients

 

 

Average = 1.91; median = 2.25; range = 0.5-4.60

Axial length (mm)

23.6 mm

n = 78 eyes of 40 patients

 

 

Average = 18.83; median = 19.50; range = 15.00-20.50

Crystalline lens with anterior-posterior diameter (mm)

4.11-4.77 mm[14]

n = 42 eyes of 23 patients

 

 

Average = 4.68; median = 4.25; range = 3.0-5.9

Crystalline lens; eye volume ratio[11]

3.1-4.4%[11]

n = 46 eyes of 23 patients

 

 

Average = 24.68%; median = 23.60%; range = 16.60-37.60%

Combined thicknesses of scleral and choroidal layers (mm)

1.01 mm

n = 22 eyes of 12 patients

 

 

Average = 2.80; median = 2.25; range = 1.37-4.00

 

GENETICS

While nanophthalmos has demonstrated sporadic, autosomal recessive, and autosomal dominant inheritance patterns, genetic subsets predisposing the development of the condition have been established. Othman and colleagues[17] have isolated defects at a particular locus (NNO1) on chromosome 11 within large kindred of autosomal dominant nanopthalmic patients; however, the gene has yet to be identified. More recently, Sundin and colleagues[18] reported on the localization of an autosomal recessive nanophthalmic locus to a separate area of chromosome 11, correlating with null mutations in MFRP, a Frizzle-related transmembrane protein. Other members of this protein family are involved with cellular mediation of growth and development, which has significant implications for regulation of the final dimensions of the developing globe.[19] As a potential mechanism for regulation of nanophthalmos and hyperopia, the MFRP gene will likely become pivotal to our understanding of this and other related disorders.

 

 

HISTOPATHOLOGY

Pathological studies of eyes with nanophthalmos have largely centered on the formation of choroidal effusions. The choroid often shows maldevelopment, and the sclera is abnormally thickened with reduced permeability to protein.[20] This maldevelopment predisposes eyes to spontaneous choroidal effusion and nonrhegmatogenous retinal detachments.[1,5] Laboratory investigations have revealed abnormalities in nanophthalmic sclera that may explain the reduced protein transport and the subsequent development of uveal effusion. Light and transmission electron microscopy demonstrate a disordered arrangement of collagen lamellae, coupled with a disorganization of collagen bundles. The fibrils of the collagen show increased stratification in fibril diameter, with noticeable fraying of larger fibril ends. On cross section, differing fibrils with dark and light stained centers are also noted. Histologic analysis has shown increased levels of proteoglycans surrounding collagen fibrils, which may influence their abnormal arrangement.[20,21,6] Histochemical studies of nanophthalmic sclera have shown increased fibronectin staining, with higher fibronectin levels confirmed by tissue culture compared with normal sclera.[22,23]Increased levels of proteoglycans, especially proteodermatan sulfate and proteochondroitin sulfate, have been identified in the nanophthalmic sclera.[22-28] Subretinal fluid analysis in one case of massive uveal effusion with secondary retinal detachment demonstrated a protein content more than threefold greater than plasma, an absence of cells, low potassium concentration, and one type of acid phosphatase enzyme. This suggests derivation from plasma and not from inflammation.[29] Absence of hyaluronic acid in the subretinal fluid strongly suggests a nonrhegmatogenous origin.[5]

 

 

EXAMINATION OF THE NANOPHTHALMIC PATIENT

The diagnosis of nanophthalmos is based on the clinical criteria mentioned previously. The patient often presents with decreased vision precipitated by choroidal effusion, retinal detachment, or acute angle-closure glaucoma. Conversely, in a glaucoma referral practice, nanophthalmic patients are often seen because of narrow angle glaucoma caused by phakomorphic angle narrowing, pupillary block angle narrowing, or anterior rotation of the ciliary body due to choroidal effusion. There may be a family history of blindness from angle-closure glaucoma or a history of prior surgical complications in the fellow eye.[30] Refractive error is determined by standard refraction techniques. Ruler or calipers are used to measure the external horizontal corneal diameter. The presence of nystagmus or strabismus is noted and documented by Hirschberg measurement[31] or by prisms. Anterior chamber depth is measured axially and peripherally at the slit lamp by the method described by Van Herrick and associates.[32]Measurements may be supplemented by pachymetry, A-scan or B-scan ultrasonography,[35] magnetic resonance imaging, and ultrasonographic biomicroscopy.[36,35] (Cheng HM, Singh OS, Kwong K, et al: Morphometric analysis of nanophthalmos and narrow angle glaucoma using MRI. Poster presentation, ARVO, Sarasota, FL, May 1992.) Intraocular pressure readings are obtained by Goldmann applanation tonometry, and the width of the ocular pulse is noted. The degree of iris convexity and the anterior chamber angle configuration is evaluated by gonioscopy (Fig. 214.2). Angle closure in eyes affected by nanophthalmos may progress over time, and Zeiss lenses are especially helpful in identifying areas of synechial closure via indentation gonioscopy. Ultrasonographic biomicroscopy provides useful information about the configuration of the ciliary body and iris (Fig. 214.3), the angle and the presence of anterior choroidal effusions.

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FIGURE 214.2  (a and b) Koeppe gonioscopy demonstrates prominent iris convexity and asymmetric stages of angle closure in both eyes.

 

 

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FIGURE 214.3  (a and b) Ultrasound biomicroscopy demonstrates pupillary block and angle crowding in a nanophthalmic eye.
Courtesy of C. J. Pavlin, M.D., Toronto, Ontario, Canada.

 

 

A-scan and B-scan ultrasonography are helpful in measuring the axial length of the globe; dimensions of the crystalline lens; the condition of the posterior segment, including choroidal and scleral thickness measurement; and the presence and extent of choroidal effusion or retinal detachment.[33] Lens:eye volume ratios can be calculated in the manner described by Kimbrough and associates.[15] The lens:eye volume ratio is greater (10-32%) in nanophthalmic eyes than in emmetropic eyes (3-4%).[13]

Dilated fundus evaluation should be performed to evaluate the posterior segment if the angle looks open by gonioscopy. The optic disks are characteristically small, pink, and without a well-defined cup, unless there has been glaucomatous damage. Baseline stereo disk photographs, automated visual fields and nerve fiber layer analyses are important for evaluation and future management. Posterior segment changes may include bone-spicule changes that resemble retinitis pigmentosa, and low-lying peripheral choroidal detachment with or without associated nonrhegmatogenous retinal detachment. In some cases, choroidal detachment create macular folds and reduce visual acuity.[36] In eyes that cannot be dilated or in which media opacification limits the view, B-scan ultrasonography can assist in accurately determining the thickness of the scleral and choroidal layers as well as the presence of posterior segment abnormalities associated with nanophthalmos.

 

 

ANGLE CLOSURE IN NANOPHTHALMOS

In the young nanophthalmic patient, there is marked iris convexity and the anterior chamber angle is open. With age, progressive anterior chamber shallowing and narrowing of the angle occurs, leading to phakomorphic and/or pupillary-block angle-closure glaucoma during the fourth to sixth decades of life (Fig. 214.4).[29,37] In two-thirds of these patients, the attack is bilateral.[30] Chronic open-angle glaucoma may also occur in these eyes.[30,38,39] Anatomic characteristics that predispose to angle closure include small corneal diameter, shallow anterior chamber, reduced axial length, iris convexity, and a normal-sized crystalline lens (which causes anterior segment crowding by occupying a disproportionately large volume of the globe.)[3,15,30] These factors can lead to phakomorphic angle closure, pupillary-block angle closure, synechial angle closure or a combination of these. Spontaneous choroidal detachments also occur and can cause angle closure. Choroidal effusion contributes to angle closure with elevation and forward rotation of the ciliary body, which relaxes tension on the crystalline lens zonules.[5,15,30] This allows anterior movement of the crystalline lens, increased iridolenticular apposition, and relative pupillary block (Fig. 214.5). The development of choroidal effusion in nanophthalmic patients between the ages of 40 and 70 years correlates well with the frequent occurrence of angle-closure glaucoma.[5]

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FIGURE 214.4  (a and b) The parallelopiped of light demonstrates asymmetric stages of anterior chamber shallowing by slit-lamp examination.

 

 

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FIGURE 214.5  (a and b) The anterior segment examination demonstrates superior corneal opacification corresponding to areas of iridocorneal apposition during acute angle-closure glaucoma in the right eye. Patent iridotomies that are present inferiorly in the right eye and superiorly in the left eye were created by argon and subsequent Nd:YAG lasers.

 

 

Although nanophthalmos is characteristically associated with angle-closure glaucoma, associations with open-angle glaucoma and pseudoexfoliation glaucoma have also been reported.[38,40]

 

 

RETINOCHOROIDAL INVOLVEMENT IN NANOPHTHALMOS

The fundus may exhibit bone-spicule changes of the retinal pigment epithelium, resembling retinitis pigmentosa and may represent changes induced by resolved nonrhegmatogenous retinal detachment. (Fig. 214.6)[1,41,42,43] The posterior segment may appear normal, but varying degrees of macular hypoplasia associated with nystagmus and strabismus, cystic macular degeneration, and retinal degeneration have been described.[37,41] Optic nerve head drusen have also been found in patients with nanophthalmos. Young children with nanophthalmos have been reported to have consistent yellowish pigmentation within the macula, along with prominent chorioretinal folds and crowded optic nerve heads. These findings may reflect disparate growth rates between the sclera and the retina.[17]

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FIGURE 214.6  The nanophthalmic eye can have some or all of these ocular features: (1) reduced corneal diameter, (2) shallow anterior chamber with thickened iris and prominent iris convexity, (3) impending angle closure with peripheral anterior synechiae formation, (4) a crystalline lens of normal size occupying a disproportionately large percentage of intraocular volume, (5) a thickened uveal tract with choroidal effusion occurring posteriorly, (6) a thickened scleral wall, (7) nonrhegmatogenous retinal detachment affecting the posterior pole region, and (8) reduced total axial length of 18.83 mm (compared with the normal axial length of 23.50 mm, average).

 

 

The association of retinal detachment with high degrees of hyperopia was first reported by Witmer[44] in 1951. Brockhurst[5] noted the association of uveal effusion and nonrhegmatogenous retinal detachment with nanophthalmos. Shaffer hypothesized that the abnormally thickened sclera found in nanophthalmic eyes impedes outflow through the vortex veins, resulting in an increased predisposition to choroidal effusion and subsequent nonrhegmatogenous retinal detachment.[45] This theory is supported by the wide ocular pulse pressure frequently noted in the nanophthalmic eye.[30,45] Gass[48] described the idiopathic uveal effusion syndrome in nine patients. He and others[47,48] hypothesized that aging and hormonal changes in collagen and ground substance of patients with abnormal congenitally thickened sclera may inhibit transscleral protein transport, and postulated that the barrier effect of the sclera was more important than vortex vein obstruction.

Choroidal effusion and retinal detachment may occur spontaneously, intraoperatively, or postoperatively and lead to decreased visual acuity that does not respond to conventional therapy.[5,49,50]Preoperatively, intraocular pressure offsets the elevated venous pressure in the choroidal space seen in nanopthalmic eyes. When intraocular pressure suddenly decreases during glaucoma or cataract surgery, choroidal effusion and subsequent retinal detachment may occur, since hydrostatic forces favor fluid influx into the choroidal space. Alternatively, choroidal detachment also occurs spontaneously in asymptomatic nanophthalmic eyes during the third to fifth decades of life.[5] The pathophysiology of choroidal effusion involves increased transudation of fluid and protein molecules from the intravascular choriocapillaris to the suprachoroidal space. The volume of effusion increases when water molecules enter the extravascular space to balance the osmotic gradient. Nonrhegmatogenous retinal detachments with 'shifting fluid' phenomena may occur. Causes of choroidal effusion include hypotony, inflammation, trauma, and increased orbital or elevated episcleral venous pressure.[5,51]

There have been numerous papers describing attempts to prevent or correct choroidal effusions in nanophthalmic eyes. In some cases, oral steroid therapy can aid resolution of choroidal effusion and nonrhegmatogenous retinal detachments.[5] In a case reported by Lesnoni and colleagues,[52] uveal effusion in a nanophthalmic eye was noted after argon laser treatment for retinoschisis, and intravenous prednisolone provided resolution of effusions and a return of visual acuity. Brockhurst introduced the vortex vein decompression technique[53,54] which permits controlled drainage of the suprachoroidal space, allowing spontaneous retinal reattachment and reducing the risk of a disastrous visual outcome at the time of planned intraocular surgery. These eyes should be followed carefully by B-scan ultrasonography, and if choroidal effusion persists, anterior sclerotomies are recommended at the time of glaucoma or cataract surgery.[30] Gass[47] achieved successful resolution of uveal and retinal detachments by performing 5 × 7 mm, two-third thickness sclerotomies in four quadrants, avoiding the vortex veins. Central 1-mm sclerotomies, without choroidal puncture, were placed to decompress the suprachoroidal space, but no drainage of subretinal fluid was attempted. This technique, along with modifications, has been applied successfully in some cases of nanophthalmic uveal effusion.[55,56]

 

 

MEDICAL TREATMENT

MIOTICS

Historically, pilocarpine was the mainstay of initial therapy and was used in most eyes before laser or surgical intervention. For the treatment of suspected angle-closure glaucoma, in addition to other pressure-reducing agents, a test dose of topical 1% pilocarpine solution was applied. Repeat evaluation by slit lamp and gonioscopy was performed 45-90 min thereafter. A favorable clinical response was evidenced by anterior chamber deepening and a wider angle configuration. If shallowing of the anterior chamber or exacerbation of angle closure occurred, pilocarpine was not readministered. For the treatment of pressure elevation in open-angle glaucoma, pilocarpine therapy was usually initiated with 1% topical solution on a qid basis, but a higher concentration (e.g., 4%) and more frequent administration (e.g., every 2 h while awake) were titrated according to the clinical response. Approximately half of the eyes require continued miotic therapy after successful laser iridotomy or goniophotocoagulation.

The response of nanophthalmic eyes to pilocarpine is unpredictable, and in some eyes cause increased relative pupillary block.[57]

 

 

MYDRIATIC AND CYCLOPLEGIC THERAPY

Unlike other eyes with narrow-angle glaucoma, nanophthalmic eyes may exhibit a paradoxic effect to mydriatic and cycloplegic therapy, with deepening of the anterior chamber and reduction of intraocular pressure. Cycloplegics relax the ciliary muscles and tighten the zonules, thus moving the lens-iris diaphragm posteriorly. This tends to deepen the anterior chamber, decrease relative pupillary block (in some cases), and restore the normal pathway for aqueous flow anteriorly.

 

 

SYMPATHOMIMETICS AND ?-BLOCKERS

Topical ?-blockers lower intraocular pressure by reduction of aqueous production, but have no significant effect on angle configuration. In some cases, Epinephrine and its derivative medications deepen the anterior chamber, widen the angle and reduce intraocular pressure. Apraclonidine (Iopidine) and brimonidine tartrate (Alphagan) are selective ?2-agonists that decrease aqueous production and increase uveoscleral outflow.

 

 

CARBONIC ANHYDRASE INHIBITORS

Oral and topical carbonic anhydrase inhibitors reduce aqueous production. They are used in conjunction with other medications, in the medical treatment of glaucoma and before laser or surgical intervention. Some nanophthalmic eyes have demonstrated deepening of the anterior chamber with widening of the angle after treatment with acetazolamide.[30]

 

 

PROSTAGLANDIN ANALOGUES

Several medications in this class have recently been introduced including latanoprost (Xalatan), travoprost (Travatan), and bimatoprost (Lumigan). These medications are thought to function mainly by increasing aqueous outflow via the uveoscleral pathway. Because of the overall efficacy and ease of application, these medications have become the first choice in treatment for most types of glaucoma. In theory, since nanophthalmic eyes have increased scleral and choroidal thickness, there may be a limitation to the benefits of this class of medication due to extrinsic resistance to uveoscleral outflow. In practice, however, this does not seem to limit the effect of this class of medication in nanophthalmic eyes.

 

 

HYPEROSMOTICS

Hyperosmotic agents, including oral glycerol (Osmoglyn), isosorbide (Ismotic), and intravenous mannitol, can be successfully used on a short-term basis to improve pressure control (e.g., during an acute attack of angle closure). They can also be useful preoperatively to dehydrate the vitreous and decrease positive pressure.

 

 

STEROIDS

When choroidal effusion contributes to angle closure, oral steroids in doses of 1-2 mg/kg of body weight per day on a tapering regimen have been used with some success.[5] Intravenous steroids may be beneficial.[52]

 

 

LASER TREATMENT

LASER IRIDOTOMY

Laser iridotomy combined with appropriate medical therapy is the procedure of choice to relieve pupillary block and deepen the anterior chamber in the treatment of angle-closure glaucoma. Iridotomy should also be performed in nanophthalmic eyes suspected to have phakomorphic glaucoma, to relieve any component of pupillary block that may be exacerbating the situation. The iridotomy (Figs 214.7a and 214.8a) is checked for patency by slit-lamp evaluation, including retroillumination. Nanophthalmic irides are clinically thicker than normal, and several treatment sessions may be required to achieve a patent opening. Brown irides may require argon pretreatment or higher power settings when compared with lighter blue irides, and previously patent iridotomies can undergo subsequent spontaneous closure. Usually, an iridotomy that remains patent 6 weeks after therapy will not close. Both neodymium:yttrium-aluminum garnet (Nd:YAG) and argon lasers can be used to create iridotomies, being careful to create an iridotomy peripherally to avoid damage to the lens of a phakic eye.

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FIGURE 214.7  (a and b) Anterior segment examination displays asymmetric shallowing of the anterior chambers associated with angle closure in both eyes. A patent laser iridotomy is present superonasally in the right eye, and prominent gonioplasty markings were placed in the midperipheral iris in the left eye to widen the angle.

 

 

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FIGURE 214.8  (a and b) The anterior segment in the right eye shows patent peripheral iridotomies superiorly, whereas the left eye shows an anterior sclerotomy inferonasally formed before proceeding with cataract extraction.

 

 

The technique of laser iridotomy is modified for eyes with acute angle closure because the iris is often closely apposed to the cornea. In this situation, argon laser is used initially to benefit from the anterior chamber deepening that occurs from the gonioplasty effect, while avoiding potential endothelial damage that can result from pulsed laser energy in close proximity to corneal tissue. In eyes with iridocorneal touch or very shallow anterior chambers, the iridotomy is placed more centrally. Once pupillary block is relieved and the anterior chamber is deepened, it is often possible to perform a second iridotomy at a more peripheral location. If laser iridotomy cannot be performed, then surgical iridectomy should be performed. However, the development of choroidal effusion, retinal detachment, malignant glaucoma, and decreased visual acuity have all been reported after surgical iridectomy in nanophthalmic eyes in acute angle closure.[30]

After laser iridotomy, patients are maintained on miotics and preoperative glaucoma medications. Intraocular pressure is rechecked in 1 and 24 h postoperatively to detect any pressure spike, and iridotomies are examined for patency. If the iridotomy shows evidence of early closure, laser therapy is repeated and the postoperative steroid regimen is continued.

 

 

LASER TRABECULOPLASTY

Laser trabeculoplasty can be difficult in nanophthalmic eyes because the angle is frequently narrow. In some cases, laser gonioplasty can improve angle visualization and allow for trabeculoplasty.

 

 

LASER GONIOPLASTY (IRIDOPLASTY)

Laser gonioplasty (iridoplasty) uses low-power argon laser therapy to contract the peripheral iris stroma and the iris with subsequent widening of the angle (Fig. 214.7b).[58-69] Standard laser settings of 500 ?m spot size, 200-400 mW power, and 0.2-0.5 s duration are used. The Goldmann mirrored lens is used to stabilize the eye and permit visualization of the angle during laser application. Alternatively, the Abraham lens can be used. The energy level is titrated to the iris response with an end point of blanching and contraction of the peripheral iris without bubble formation and pigment liberation. Conservative treatment of one to two quadrants at any one time is advocated because treatment of larger areas may result in ballooning of the iris in opposite clock hours with exacerbation of angle closure. Gonioplasty is relatively atraumatic and can be repeated as often as needed. There is minimal inflammation, and topical steroid therapy is tapered and discontinued over a period of 1 week unless there is evidence of persistent inflammation. Topical steroids and continuance of glaucoma medications help reduce intraocular inflammation while controlling intraocular pressure, thus enhancing the safety of subsequent ocular surgery.

In general, glaucoma medications are continued after any laser procedure. It must be noted, however, that several authors have reported on the development of choroidal or uveal effusions after varied laser procedures to the nanophthalmic eye.[52,70,71] While these effusions are more characteristically linked to surgical approaches, the ophthalmologist should be aware that these complications are a possible consequence of laser.

 

 

SURGICAL STRATEGIES IN NANOPHTHALMOS

When anterior segment surgery is necessary, posterior segment consultation should be considered. Choroidal effusions should be dealt with prior to surgery by systemic steroid therapy or choroidal drainage.[5] Prophylactic scleral resection (with or without vortex vein decompression) should be performed 2 months before the planned anterior segment procedure. Elective posterior segment procedures, as well as anterior sclerotomies at the time of the anterior segment surgery, should be performed in the following situations:

  

1.   

Choroidal effusion associated with nonrhegmatogenous retinal detachment that causes loss of central visual acuity or constriction of the visual field.

  

2.   

Impending angle-closure glaucoma with annular choroidal detachment. They should be considered in the following additional situations if the anterior chamber is very shallow, intraocular pressure is elevated, or choroid thickened.

  

3.   

Before elective cataract surgery with or without an intraocular lens (IOL).[72]

  

4.   

Before elective glaucoma filtration surgery.

  

5.   

Before elective cataract and filtration surgery with or without an IOL.

With the safety of small incision phacoemulsification, it may be less necessary to perform prophylactic procedures prior to cataract operation. For detailed information regarding the surgical techniques of scleral resection and vortex vein decompression,[53,54] the reader is referred to Chapter 220.

At the time of planned anterior segment surgery, when choroidal thickening (with or without choroidal effusion) is present, anterior scleral resection with sclerotomy should be considered to decrease the risk of vision-threatening posterior segment complications (Fig. 214.8b).

Anterior sclerotomies should be considered in the following three situations:

  

1.   

If the eye shows signs of anterior chamber shallowing related to positive vitreous pressure during the procedure, our recommendations are to close the eye and perform anterior sclerotomies with the intention of resuming the planned procedure after the pressure differential resolves.

  

2.   

In the presence of thickened sclera and choroid, with or without uveal effusion, scleral resection with or without vortex vein decompression should be considered 2 months before surgery, and anterior sclerotomies should be performed at the time of the planned anterior segment surgery.

  

3.   

In acute or chronic angle-closure glaucoma unresponsive to laser iridotomy in nanophthalmic eyes, anterior sclerotomy may be indicated to drain the suprachoroidal space before proceeding with surgical peripheral iridectomy.

It has been found that not all nanophthalmic eyes develop posterior segment complications. In the absence of preexisting glaucoma, with normal angle configuration and normal posterior segment findings, intraoperative and postoperative complications are uncommon, and prophylactic anterior sclerotomies do not appear to be indicated before proceeding with planned cataract surgery.

 

 

OPERATIVE TECHNIQUE OF ANTERIOR SCLEROTOMY AND ANTERIOR SCLERAL RESECTION WITH SCLEROTOMY

Figures 214.9 to 214.13 demonstrate the steps to performing anterior sclerotomy. Figures 214.14 to 214.16 refer to anterior scleral resection with sclerotomy. Table 214.4 lists the instruments used for these techniques.

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FIGURE 214.9  The globe is rotated superiorly and fixated with a Bishop-Harmon forcep while a radial conjunctival incision is created in the inferior temporal (or nasal) quadrant to expose the underlying sclera. A full-thickness equilateral triangular scleral flap is created with its apex directed anteriorly and centered 5 mm posterior to the surgical limbus overlying the pars plana region.

 

 

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FIGURE 214.10  The apex of the triangle is grasped with a Pierse-Hoskin forcep and the flap is dissected posteriorly with a Bard-Parker No. 15 blade to expose the underlying choroid.

 

 

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FIGURE 214.11  Meticulous hemostasis is achieved with the aid of monopolar diathermy (MIRA, Inc.).

 

 

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FIGURE 214.12  The cyclodialysis spatula is advanced along a course tangential to the sclera (nasally and temporally) to drain sequestered pockets of fluid in the suprachoroidal spaces.

 

 

  

 

FIGURE 214.13  The conjunctival incisions are closed with 10-0 nylon sutures in interrupted fashion.

 

 

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FIGURE 214.14  The apex of the partial-thickness scleral triangle is grasped with forceps and dissected posteriorly. The scleral flap is then resected.

 

 

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FIGURE 214.15  A radial sclerotomy is created to expose the underlying choroid.

 

 

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FIGURE 214.16  A Kelly-Descemet punch is used to remove adjacent semicircular scleral crescents and create a circular opening into the suprachoroid.

 

 


TABLE 214.4   -- Instruments and Supplies Used for Anterior Sclerotomy

Sharppoint knife

Blunt, 5/8-inch, 25-gauge needle

Control syringe of 5 mL volume filled with balanced salt solution

Pierse-Hoskin tissue forceps

Sharp Westcott scissors

Calipers

Bipolar pencil cautery (Mentor)

Monopolar underwater diathermy (MIRA, Inc.)

Elschnig fixation forceps

No. 15 Bard-Parker blade

10-0 nylon suture

8-0 Vicryl suture

Needle holders

Simmons-Kimbrough cyclodialysis spatula (0.5 mm)

 

 

 

SURGICAL PERIPHERAL IRIDECTOMY

In cases involving angle closure that do not respond to laser intervention, the technique of surgical peripheral iridectomy is performed in the manner described by Chandler and Grant.[73] In nanophthalmic eyes that require glaucoma surgery, operative gonioscopy and anterior chamber deepening are useful adjuncts in selective cases for determining whether a peripheral iridectomy or filtration surgery would be most likely to succeed (Figs 214.17 and 214.18). Based on the findings of Chandler and Simmons, if there are four clock hours or less of synechial closure, with satisfactory pressure control on maximally tolerated medical therapy, peripheral iridectomy is the procedure of choice. If six clock hours or more are closed, with inadequately controlled pressures on maximally tolerated medical therapy, then filtration surgery should be performed.[73,72]

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FIGURE 214.17  A beveled paracentesis is created in the peripheral cornea with the aid of a sharp, pointed knife.

 

 

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FIGURE 214.18  Anterior chamber deepening is accomplished by introducing balanced salt solution contained in a 5-mL syringe through the beveled paracentesis.

 

 

 

 

GLAUCOMA SURGERY

Indications for glaucoma surgery in nanophthalmic eyes are essentially the same as for normal eyes. When glaucoma filtration surgery is performed in eyes affected by nanophthalmos, there is an increased risk of posterior segment complications, even after prophylactic posterior scleral resection and anterior sclerotomies have been created. The creation of a 'tight trabeculectomy' is currently advocated, with a gradual reduction of intraocular pressure during the postoperative period by laser suture lysis (Fig. 214.19)[74] or releasable suture techniques. This helps avoid sudden decompression of the globe and reduces the risk of postoperative choroidal effusion and retinal detachment. As in other types of glaucoma, antifibrotic medications (mitomycin C or 5-fluorouracil) inhibit the fibrovascular response often associated with bleb failure, which in turn enhances the ultimate success of the filtration procedure.[75-77] Graded digital pressure maneuvers during the postoperative period can assist in achieving target intraocular pressure control.[78] Additional details regarding the strategy and techniques of glaucoma filtration surgery are provided in Chapter 220.

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FIGURE 214.19  Placement of interrupted 10-0 nylon sutures through the scleral flap creates a 'tight trabeculectomy' that allows gradual reduction of intraocular pressure through sequential laser suture lysis during the postoperative period.

 

 

Options for glaucoma control in eyes with poor visual potential or after several unsuccessful attempts to establish adequate filtration include cyclocryotherapy, Nd:YAG or diode external cyclophotocoagulation to the ciliary body, and endoscopic cyclophotocoagulation. Glaucoma drainage implants[79] are an option, but since the anterior chamber is shallower than normal, there is an increased risk of tube-related complications (such as corneal decompensation or iris plugging of the tube ostium). Placing the tube in the vitreous after vitrectomy has been successful. Nonpenetrating deep sclerectomy and viscocanalostomy procedures offer the advantage of not entering the eye, thus theoretically preventing an abrupt drop in intraocular pressure. The efficacy of these procedures needs to be further studied.

 

 

CATARACT AND GLAUCOMA SURGERY

In the presence of visually significant cataract with glaucoma uncontrolled on maximally tolerated medical therapy, and in the absence of choroidal thickening or effusion, combined phacoemulsification, posterior chamber lens implantation, and 'tight' trabeculectomy are indicated.[74]

The technique of 'phacofiltration' involves cataract extraction by phacoemulsification combined with the creation of a trabeculectomy and implantation of an IOL through a small incision. If there is marked choroidal thickening or choroidal effusion in conjunction with anterior chamber shallowing, elective posterior scleral resection should be considered 2 months before the phacofiltration procedure, and anterior sclerotomy at the time of surgery. Some eyes with visually significant cataract formation and uncontrolled glaucoma lack sufficient conjunctiva for conventional filtration surgery. Visual restoration and glaucoma control through combined cataract extraction with IOL implantation and cyclodialysis[90] is useful, but use of a glaucoma drainage implant lessens the risk of hypotony. The Baerveldt[79] and Molteno (Parrish RK, personal communication, 1997) valves have been used. A valved or a modified nonvalved implant (i.e., ligature around the Baerveldt tube) decrease the incidence and complications of hypotony. There have been recent reports of success with phacoemulsification and goniosynechialysis[91,92] in patients with elevated intraocular pressure due to chronic angle-closure glaucoma and peripheral anterior synechiae. Traditionally, it was believed that the synechiae should be present for no more than 1 year in order for goniosynechialysis to be effective.[93] However, further studies need to be performed to validate this claim.

 

 

POSTOPERATIVE CARE

At the completion of anterior segment surgery, sub-Tenon's antibiotic and steroid are injected. Standard postoperative care after cataract or combined cataract and glaucoma surgery involves generous application of topical steroids to reduce inflammation and ocular congestion. Topical antibiotic therapy is initiated and adjunctive therapies such as 5-fluorouracil, laser suture lysis, and digital massage may be used to enhance filtration success.[74-78] Glaucoma medications may be introduced, as needed, to achieve adequate pressure control. For a thorough discussion of postoperative care after glaucoma filtration surgery, refer to Chapter 220.

 

 

COMPLICATIONS

Frequent observation is indicated during the postoperative period after anterior segment surgery in eyes affected by nanophthalmos. These eyes may have crowding of the anterior segment or angle closure that may require additional peripheral iridotomies. Retained peripheral cortical material after cataract extraction may effectively occlude small, peripheral laser iridotomies, but larger surgical peripheral iridectomies usually remain patent and facilitate stabilization of fluid dynamics. Pseudophakic malignant glaucoma after cataract surgery has been reported in four eyes with reduced axial lengths, implanted with posterior chamber IOL optics measuring 7 mm in diameter. [94] To avoid this rare complication, the use of posterior chamber lenses with optic diameter measuring 6 mm or less is recommended. Other complications of surgery in nanophthalmos include corneal decompensation, flat anterior chamber, choroidal effusion, cystoid macular edema, hypotony maculopathy, retinal detachment, failed filtration, malignant glaucoma, endophthalmitis, and blindness. For a thorough discussion regarding further management, the reader is referred to Chapter 220.

 

 

CONCLUSION

Nanophthalmos is a rare and frequently unrecognized ocular condition, which can be associated with disastrous complications spontaneously or during or after routine surgery for glaucoma and cataract. Early detection requires a high index of suspicion and appropriate testing by the examiner. With the advent of small-incision phacoemulsification, the complications associated with cataract surgery have diminished significantly. Prophylactic posterior scleral resection with optional posterior sclerotomy, vortex vein decompression, and anterior scleral resection are some techniques that can be employed to make surgery safer in some of these eyes. Timely diagnosis and implementation of therapeutic guidelines has improved the outcome of the management of nanophthalmos.

 

 

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