Surgery in Short and Eyes

Definitions

• The average axial length of the adult eye is approximately 23.8 mm.

• Microphthalmia refers to an eye with an axial length (AL) that is 2 standard deviations below the mean, or < ~21 mm in adults. ²

• Simple microphthalmos is a small eye with no ocular abnormalities, a normal anterior chamber depth (ACD), and normal scleral thickness.

• Complex microphthalmos is a small eye with anatomic abnormalities but also a normal scleral thickness.

• Nanophthalmos refers to an eye with thickened sclera, small ACD, and short AL, often reported as <18 mm, although there is a lack of consensus on the upper limit for AL. ^1,2

Comorbidities

Slit Lamp Exam

Examination of short eyes should be particularly attentive to the relative size and depth of the anterior segment, which can vary markedly in this patient subset. Guttae may be more common in these eyes; even in the absence of guttae, the endothelial cell count may be reduced, perhaps by prior intermittent angle closure episodes. In shallower anterior segments, gonioscopy is advisable, especially if there is any hint of angle closure history.

The examiner should be attentive on fundus evaluation to the possible presence of choroidal folds or retinoschisis, both of which are seen more often in these cases than in eyes of normal axial length. Macular OCT can be especially useful to detect subtle choroidal folds or thickening.

IOL Selection

• Notoriously challenging

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    In very short eyes, the relative size of the anterior segment to the posterior segment is highly variable, unlike eyes with “normal” axial lengths.

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    Some of these eyes will have normal-sized anterior segments with normal depth.

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    Others may have exquisitely shallow and/or small chambers.

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    Variability makes effective lens position (ELP) prediction postoperatively difficult.

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    Relative rarity of these eyes yields less normative data from which to draw conclusions.

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    Because the IOL powers tend to be much higher in this subgroup of patients, any error in ELP estimate will have a greater impact on the final refraction than in normal or longer-eyed counterparts.

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    Artificial intelligence-based calculation methods such as the Hill-RBF formula tend to perform better in this subgroup and should continue to improve with each formula iteration as more data is acquired.

• A more detailed discussion of IOL calculation method is included in Chapter 3 of this text.

  IOL power availability in commercially marketed lenses does not always go as high as needed for emmetropia in very short eyes.

• The highest IOL power currently available in the United States in a foldable model is 40.0 diopters.

• For eyes that require much higher powers, several strategies are available. One common approach is to select a 40D IOL and have the patient understand that they will remain highly hyperopic postoperatively.

• At the time of this publication, only one European manufacturer still makes ultra-high-powered IOLs:

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    HumanOptics AG (Erlangen, Germany) manufactures hydrophilic acrylic IOLs up to 60.0 diopters.

This high-powered IOL has relatively soft and thin haptic material and is more vulnerable to movement with bag contraction. Accordingly, insertion of a capsular tension ring (CTR) is advisable, even if no zonulopathy is identified.

Because of the risks of iris chafe, pigment dispersion, and uveitis-glaucoma-hyphema syndrome with sulcus IOL placement in short eyes, we strongly discourage the use of piggyback IOLs in this setting.