Nanophthalmos is part of the clinical spectrum of microphthalmos, which encompasses heterogeneous “small-eye” phenotypes1 varying from the extreme of anophthalmos to simple microphthalmos,2,3 pure microphthalmos or nanophthalmos,4 partial microphthalmos,5 complicated microphthalmos,4 posterior microphthalmos,6 and relative anterior microphthalmos (RAM).7 Auffarth et al.7 define RAM as a corneal diameter smaller than 11.0 mm, an axial length greater than 20.0 mm, and no other morphologic malformation. In RAM, the posterior segment findings with respect to choroidal–scleral thickening have not been described. Posterior microphthalmos is described as a “disproportionate foreshortening of the posterior segment.”6 This variety of nomenclature reflects the clinical spectrum of the small-eye phenotype. For the small eye without ocular malformations, which is typically considered nanophthalmos, the salient clinical features include thickened sclera,8–10 a normal to large lens with a high lens:eye volume ratio,11 a shallow anterior chamber,12 and a shorter than average total axial length.12 These 4 basic clinical features can account for glaucoma and retinal complications in these eyes.
Although scleral thickness is not routinely measured clinically, the variation in scleral thickness of the globe is known. The sclera is normally thickest posteriorly and measures approximately 1.0 mm in an eye of average size.10 It is typical that the sclera thins anteriorly and is approximately 0.6 mm at the equator and is thinnest (0.3 mm) posterior to the rectus muscle insertions.10 When the inner scleral surface cannot be distinguished from the adjacent retinal–choroidal tissues, such as in the setting of inflammation, hypotony, and infiltration processes, these normally thin tissues are included in the assessment of eye-wall thickness. Based on these known scleral measurements and the normally thin retinal–choroidal tissues, an eye was determined to have increased retinal–choroidal–scleral thickening if the measurement on echography was greater than 1.7 mm.
We describe our surgical experience at a university-based practice with 14 eyes of 8 patients with nanophthalmos that was diagnosed based on increased retinal–choroidal–scleral thickening on echography.
Patients and Methods
Patients with the diagnosis of nanophthalmos who had ocular surgery were identified by a review of the surgical logs of 5 surgeons between June 1978 and April 2002. Nanophthalmos was diagnosed based on a shorter than average axial length (usually less than 21.0 mm), typically a shallow anterior chamber, hyperopia, and retinal–choroidal–scleral thickening greater than 1.7 mm determined by B-scan echography. Patients who were still being followed at the institution gave informed consent and enrolled as part of a protocol approved by the Institutional Review Board of the University of Michigan Medical Center. Inclusion criteria were based on a clinical diagnosis of nanophthalmos and ocular surgery for cataract. Charts were reviewed for sex, age at initial consultation, family history, refraction, corneal diameter, keratometry, B-scan ultrasound (Innovative Imaging Inc), comorbid ocular diagnoses, ocular surgeries, preoperative and postoperative visual acuities, and intraoperative and postoperative complications. In addition, high-frequency ultrasound biomicroscopy (Paradigm Medical Industries, Inc.) was performed in case 5. The best corrected visual acuity was assessed 2 to 6 months postoperatively. Given the limited number of patients in this series, the results were examined qualitatively.
Because cataract surgery can affect intraocular pressure (IOP)13,14 and is advised in eyes with a phacomorphic component to narrow-angle glaucoma,15 the IOP was measured in the 10 eyes that had cataract surgery at our institution; cases 5 and 7 (right eye) had cataract surgery elsewhere. The mean IOP at the 5 visits before cataract surgery was compared with the mean IOP at the 5 visits after cataract surgery, if available. Otherwise, the single preoperative IOP was compared with the mean IOP at the 5 visits after cataract surgery.
Twelve cataract surgeries were performed using a peribulbar or retrobulbar anesthetic block except in case 7, which was performed using general anesthesia as profound chemosis from an anesthetic block was noted in the 2 preceding surgeries. Case 7 was also treated with intravenous mannitol. Phacoemulsification alone was conducted through a temporal clear cornea or limbal approach in 10 eyes. Phacoemulsification was combined with trabeculectomy at 1 site in 1 eye. Extracapsular cataract extraction (ECCE) through a superior 11.0 mm limbal incision was done in 1 eye. Pupil stretching was accomplished by sphincterotomy, mechanical stretching, or iris hooks. One eye received a poly(methyl methacrylate) posterior chamber intraocular lens (IOL), and the rest received a single foldable acrylic IOL (MA30, MA60, or SA60, Alcon).
Lamellar scleral resections were performed in preparation for cataract surgery in cases 1, 2, and 7. In case 1, the scleral window resections were conducted simultaneously with the cataract surgery. In cases 2 and 7, the scleral resections were performed approximately 2 weeks to 2 months before cataract surgery. Two or 4 quadrants were exposed, and lamellar scleral dissections were performed with various dimensions depending on the surgeon and case.
Over 24 years, 8 patients (6 women, 2 men; all white) with nanophthalmos based on echography had cataract surgery. Four had not been previously diagnosed with nanophthalmos. The mean age at the initial consultation at our institution was 59 years ± 14.4 (SD) (range 30 to 70 years). Comorbid ocular diagnoses included hyperopia, amblyopia, angle-closure glaucoma, cataract, pseudoexfoliation glaucoma, plateau iris (determined by ultrasound biomicroscopy), retinoschisis, pigmentary retinopathy, macular edema, and uveal effusion. There was variable hyperopia of +1.25 to +12.50 diopters (D) spherical equivalent (mean +7.69 ± 3.35 D). The mean corneal diameter in 13 eyes of 7 patients was 10.90 ± 0.99 mm (range 8.0 to 12.0 mm). The mean keratometry was 47.20 ± 2.91 D (range 43.00 to 52.00 D). The mean axial length in all 16 eyes was 18.4 ± 1.65 mm (range 15.82 to 21.30 mm). B-scan ultrasound mode to examine the retinal–choroidal–scleral thickness and determine the presence of uveal effusions in all patients except case 2 showed maximum retinal–choroidal–scleral thickness in 12 eyes of 6 patients; the mean thickness was 2.41 ± 0.40 mm (range 2.0 to 2.8 mm). In some eyes, the retinal–choroidal–scleral thickness was quite variable. Table 1 shows the demographic information, ocular diagnoses, refraction on initial consultation, and biometric parameters.
Twelve eyes had cataract extraction with posterior chamber IOL implantation, 11 by phacoemulsification and 1 by ECCE. Four eyes had lamellar scleral resections. The decision to perform lamellar scleral resections for cataract surgery was based on the ocular history of the patient. If the patient had a documented history of uveal effusions (2 eyes in case 2), lamellar scleral resections were performed. In the other 2 eyes (cases 1 and 7), the surgeon was concerned about intraoperative and postoperative choroidal effusions; thus, sclerotomies were performed. All cases were complex, and the total number of surgeries (including laser and operative procedures) in all 8 patients was 36, with a mean of 2.5 surgeries per eye (range 1 to 6 surgeries) (Table 2). Other surgeries included glaucoma laser procedures (8 eyes), cyclocryotherapy (2 eyes), trabeculectomy with scleral resections (1 eye), lamellar scleral resections for uveal effusion (2 eyes), trabeculectomy combined with phacoemulsification (1 eye), and neodymium:YAG laser capsulotomy (4 eyes).
No eye lost vision after surgery. The change in visual acuity from preoperatively to postoperatively ranged from no improvement to 20/25 (Table 2). The variation in postoperative visual acuity may be explained by preoperative clinical diagnoses (Table 1) related to amblyopia, retinal pathology, and glaucoma. Of the 10 eyes that had cataract surgery at our institution (cases 5 and 7 [right eye] had cataract surgery elsewhere), 5 (cases 1, 2, 3, 4, and 7) were treated medically for glaucoma with an average of 1.8 glaucoma medications per eye (range 1 to 3 medications in the operated eye). The mean preoperative IOP was 17.2 ± 5.8 mm Hg (range 11 to 27 mm Hg). Two months postoperatively, the mean IOP was 14.4 ± 3.1 mm Hg (range 9 to 18 mm Hg) and the mean number of glaucoma medications in the previously treated eyes was 1 (range 0 to 3 medications in the operated eye).
Eight eyes had no complications (excluding posterior capsule opacity). No eye that had cataract surgery developed postoperative choroidal serous effusions. The cumulative complications in 4 of the 12 eyes included unresponsive to prednisone and subsequent phthisis (case 1), broken IOL haptic with vitreous loss (case 4), choroidal hemorrhage and glaucoma progression (case 5), and severe iritis and phthisis (case 7).
Given the use of the terms RAM7 and posterior microphthalmos,6 there is growing recognition of the wide clinical spectrum of the small-eye phenotype. Nanophthalmos is a relatively rare anomaly characterized by a small eye without other malformations.4 Clinical features that have been described include a narrow palpebral fissure, a deeply set globe in a small orbit, a short axial length, axial hyperopia, a small to normal corneal diameter, a shallow anterior chamber, thickened choroid and sclera, and a high lens:eye volume ratio.4,11,12,16 Although some studies use hyperopia as a defining feature, refraction is determined by the axial length and the combined refractive power of the cornea and crystalline lens. Hence, it is not surprising that the degree of hyperopia is variable and that myopia is rarely reported in these eyes.4
Absolute axial length has also been used to define nanophthalmos, but this may be too simplistic. Uyama et al.17 divided eyes with uveal effusion based on absolute axial lengths; however, most eyes had thickened sclera on magnetic resonance imaging and intraoperatively (Table 1 in Uyama et al.). Similarly, Johnson and Gass' series of idiopathic uveal effusion9 showed that 17 of 18 eyes examined by echography had posterior choroidal thickening in eyes with an axial length greater than 20.5 mm and hyperopia less than +7.50 D. In the same series, 17 of 20 eyes that had lamellar scleral resections had “thicker than normal” sclera. In these 2 case series, these eyes may be considered nanophthalmic based on the clinical diagnosis of uveal effusion and choroidal–scleral thickening determined by various imaging studies and intraoperatively.
In our case series, we diagnosed nanophthalmos based on a crowded anterior segment, hyperopia, a shorter than average axial length (less than 21.0 mm), and increased retinal–choroidal–scleral thickening (greater than 1.7 mm) determined by echography. In particular, the crowded anterior segment and the increased retinal–choroidal–scleral thickening can account for the potential glaucoma and retinal complications in predisposed eyes. These complications include acute angle-closure glaucoma, uveal effusion syndrome with or without exudative retinal detachment, cystoid maculopathy, and aqueous misdirection or malignant glaucoma.18 Given the variety of nomenclature for the clinical spectrum of the small-eye phenotype, additional quantitative measures of these eyes and comparison to other eyes in the spectrum of normal and myopic eyes would be useful. Specifically, biometric data on corneal curvature, corneal diameter, pachymetry, anterior chamber depth, lens thickness, retinal–choroidal–scleral thickness, and vitreous cavity depth are helpful quantitative considerations as part of the clinical spectrum of nanophthalmos, RAM,7 and posterior microphthalmos.6
There are no typical fundus findings in eyes with nanophthalmos. The following have been described in cases of nanophthalmos and microphthalmos: retinal cysts,4 macular hypoplasia,4 retinoschisis,8,19 papillomacular folds and “drusen-like” deposits,6,20 retinitis pigmentosa and disc drusen,21 pigmentary retinopathy,6,22,23 and geographic pigment epithelial disturbance.8,12,19,24–26
During this study, we performed anterior segment surgery in 3 additional patients with nanophthalmos who did not require cataract surgery. They ranged in age from 24 to 54 years and had +7.00 to +24.00 D of hyperopia. Retinal–choroidal–scleral thickness ranged from 2.3 to 3.4 mm. One eye required removal of a hyperopic epikeratophakia graft, 3 eyes had scleral resection or vortex vein decompression for choroidal effusion, 2 eyes required laser iridotomy, and 1 eye had chelation removal of band keratopathy.
In summary, our cataract surgery experience in 12 eyes of 8 patients is encouraging given the current treatment approach to cataracts and uveal effusion. Scleral lamellar resections were not performed in every case depending on the surgeon; however, in eyes with a history of uveal effusion, it is prudent to consider resections to enhance posterior uveoscleral flow. In eyes without a history of uveal effusion, the results in our small series indicate that phacoemulsification cataract surgery without the use of lamellar resections is safe. In addition, the pupillary block component and appositional closure of narrow-angle glaucoma can be treated by laser iridotomy and peripheral laser iridoplasty, respectively.11,27–30 New classes of glaucoma medications also provide improved pharmacologic treatment for lowering IOP in these high-risk eyes. With advances in phacoemulsification and IOLs for cataract surgery7,31–35 and surgical approaches to enhance posterior uveoscleral outflow,9,17,27,30,36–38 surgical outcomes in eyes with nanophthalmos are improving.
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