Shallow anterior chamber with short axial length
Nanophthalmos/simple microphthalmos
Colobomatous microphthalmos
Complex microphthalmos
Shallow anterior chamber with normal axial length
Relative anterior microphthalmos
Normal anterior chamber depth with short axial length
Axial hyperopia
20.1.1 Shallow Anterior Chamber with Short Axial Length
Proposed by Duke-Elder in 1964, this type of microphthalmos includes three subtypes, i.e., simple microphthalmos, colobomatous microphthalmos, and complex microphthalmos [9].
20.1.1.1 Nanophthalmos/Simple Microphthalmos
Nanophthalmos refers to the ocular condition of short axial length without other congenital ocular defects or systemic anomalies [1, 9]. Typically, the total axial length is at least two standard deviations below the mean when adjusted for age. For example, in nanophthalmic children aged 3 years or older, the mean axial length is less than 20.5 mm. Clinically, nanophthalmos is extremely rare and usually occurs bilaterally [10]. No racial difference has been observed in terms of incidence [11]. The clinical characteristics of microphthalmos in children are listed as follows:
- 1.
Often accompanied by microcornea, with a horizontal corneal diameter of 9.5–11 mm (Fig. 20.1).
Fig. 20.1
Microcornea
The horizontal diameter of the cornea of the right eye in this patient is less than 10 mm.
- 2.
The volume of a nanophthalmic eye is homogeneously reduced to approximately two thirds of normal ocular volume with an increased lens to total eye volume ratio and normal or slightly increased lens thickness.
- 3.
Both the peripheral and central ACDs are shallow. The peripheral iris bulges anteriorly. The anterior chamber angle, however, remains open in nanophthalmic children. They usually have poorly dilating pupils and significant IOP fluctuations.
- 4.
High hyperopia ranging from +7.25D to +20.00D.
- 5.
An interesting finding in nanophthalmic children is the absence of uveal effusion, one of the cardinal pathologies in nanophthalmic adults [12]. Not a single case of uveal effusion has been reported in these children [3–6]. The underlying mechanism for this finding might be that compression on vortex veins is not so significant as to cause uveal effusion because the nanophthalmic sclera in children is softer, thinner, more permeable to fluid egress, and more flexible than in adults.
20.1.1.2 Colobomatous Microphthalmos
Colobomatous microphthalmos is associated with defective closure of the embryonic fissure during early development of the eye. Normally, complete closure of the embryonic fissure occurs by the sixth week of gestation. Incomplete closure may result in colobomatous microphthalmos, often accompanied by other ocular developmental anomalies such as coloboma of iris or choroid, or even hypoplasia of the visual pathway and visual cortex [9].
20.1.1.3 Complex Microphthalmos
Complex microphthalmos is associated with systemic diseases and concurrent anterior/posterior segment abnormalities other than incomplete closure of the embryonic fissure. In such patients, microphthalmos is merely one of the clinical manifestations of their hereditary syndromes with other ocular and systemic pathologies [2]. Syndromes associated with complex microphthalmos are listed in Table 20.2 [8].
Table 20.2
Microphthalmos-related syndromes
Microphthalmos-related syndromes |
13 trisomy syndrome (Patau syndrome) |
Chromosome 18 deletion syndrome |
Congenital rubella syndrome |
Hallermann-Streiff syndrome |
LSD (lysergic acid diethylamide) embryopathy |
Goldenhar syndrome |
Oculodentodigital dysplasia (ODD) syndrome |
Micrognathia-glossoptosis syndrome |
Oculo-cerebro-renal syndrome (Lowe’s syndrome) |
Focal dermal hypoplasia (FDH) |
Francois syndrome |
Ullrich syndrome |
20.1.2 Shallow Anterior Chamber with Normal Axial Length
Naumann created the term relative anterior microphthalmos (RAM) for eyes with a shallow anterior chamber and a normal axial length in 1980. These eyes are characterized by a total axial length of >20 mm, a horizontal corneal diameter of 9–11 mm, and a decreased anterior segment volume. RAM is more common than nanophthalmos [13].
20.1.3 Normal Anterior Chamber Depth with Short Axial Length
The main manifestation of this subtype of microphthalmos is high axial hyperopia with a normal ACD. As there are no morphological deformities of the eye, the risk of complications associated with pediatric cataract surgery is not increased in this population.
20.2 Surgical Indications, Timing, and Preoperative Evaluation
Children with nanophthalmos, colobomatous microphthalmos, and complex microphthalmos appear to be at a higher risk when undergoing cataract surgery. Cataract surgery in RAM is also associated with certain complications. Pediatric cataract patients with normal ACDs and short axial lengths have a lower risk. Therefore, for cataract children complicated with microphthalmos, a complete assessment should be performed to determine the specific type of microphthalmos. The ophthalmologist should practice rigorous control of the surgical indications in an effort to achieve maximum visual outcomes of the affected child. When planning surgery for microphthalmic children who meet the indications, the ophthalmologist should be well aware of all the possible intraoperative and postoperative complications, so that necessary preventive measures are taken to mitigate these risks.
20.2.1 Surgical Indications and Timing
20.2.1.1 Indications and Timing of Cataract Extraction
The surgical indications and timing of cataract extraction in microphthalmic children are similar to that in other children with cataracts. See Chap. 12, Sect. 12.1 “Indications and Timing of Pediatric Cataract Surgery” for a detailed discussion.
20.2.1.2 Indications and Timing of IOL Implantation
Microphthalmic eyes with cataract have a more crowded anterior chamber and a smaller capsular bag compared with cataractous eyes that have a normal axial length and without RAM. It is recommended that IOL implantation should be delayed in microphthalmic children to reduce risks of complications such as posterior synechia and glaucoma [3, 14]. Another concern is the availability of IOL with extreme powers (≥ +30.0D) for microphthalmic infants with extremely short axial lengths [15], which can also be avoided by delaying IOL implantation until the affected eye has reached an acceptable axial length with a less crowded anterior chamber. It should be noted that compared to aphakia correction by contact lenses, early implantation of an IOL produces similar visual outcomes at the cost of increased complications and adverse events in infant eyes with a normal axial length, according to the long-term results of the Infant Aphakia Treatment Study (IATS) [16, 17]. Therefore, the authors believe that it is also advisable to leave the microphthalmic children aphakic until the eyes grow longer. Of the current studies on IOL implantation in microphthalmic children, the majority of cases remained aphakic until >3 years of age [14, 15]. The general recommendation for aphakia after cataract extraction in these children is wearing spectacles or contact lenses and choosing the timing of secondary IOL implantation based on the growth of the aphakic eye [3, 4, 6]. The option of piggyback IOL implantation, one of the recommended solutions to aphakia in microphthalmic adults with cataract [18], is not yet supported by strong clinical evidence for this use in the cataract surgery of microphthalmic children, whose ocular structures are yet to develop with an even more crowded anterior segment. The authors believe that piggyback IOL implantation is inadvisable in young children with microphthalmos.
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