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Axial length a factor in phaco of microphthalmos, nanophthalmos eyes
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Despite a series of challenges and risks, phacoemulsification with IOL implantation proved safe in eyes with microphthalmos and nanophthalmos, according to a study.
The retrospective analysis included 103 eyes with axial length less than 21 mm that underwent phacoemulsification and IOL implantation. The median follow-up interval was 6.3 months.
Mean axial length was 20.05 mm, and mean anterior chamber depth was 2.7 mm.
Study results showed that intraoperative or postoperative complications occurred in 16 cases (15.5%); the most common complications were zonular dehiscence, severe uveitis and aqueous misdirection.
Shorter axial length, IOP of 22 mm Hg or higher, and IOP treated with topical medications were the only significant independent risk factors linked to complications.
Data showed significant associations between abnormal IOP and shorter axial length (P = .013), shorter anterior chamber depth (P = .012) and lower spherical equivalent refraction (P = .009).
The risk of complications was 4.2 times higher in eyes with axial length less than 20.5 mm, 14.6 higher in eyes with axial length less than 20 mm, and 21.3 times higher in eyes with axial length less than 19 mm, the authors said.
Perspective
Back to TopJack T. Holladay, MD, MSEE
In a study we performed in the late 90s for IOL calculations, especially for piggy-back IOLs up to 64 D, we found that in eyes from 20 mm to 14.96 mm, they fell into two groups: nanophthalmic eyes and axial hyperopes. The nanophthalmic eyes had short axial lengths and horizontal corneal diameters (white-to-white) of 10.5 ± 1.0 mm or less, and the axial hyperopes had normal corneal diameters averaging 11.7 ± 1.0 mm. The nanophthalmic eyes also had thickened sclera over the ciliary body, explaining the reduced uveo-scleral outflow and elevated pressure. The short axial length and elevated pressures are critical indicators, but a small horizontal corneal diameter is also diagnostic of nanophthalmos, in which exudative retinal detachment with prolonged surgery is known to occur. In the axial hyperopes, the surgery was no different than normal, but the IOL power for the same axial length had to be much higher to account for the deeper effective lens position (ELP) with the normal anterior segment. In the nanophthalmic eyes, the required power for the same axial length was lower, because the anterior segment was smaller and the IOL was closer to the cornea with a shorter ELP. Measuring the horizontal corneal diameter is an important parameter in addition to axial length and IOP for differentiating these two conditions. With nanophthalmos, raising the phaco bottle to the ceiling, pretreating with mannitol and Diamox (acetazolamide, Duramed Pharmaceuticals) to decompress the vitreous and minimizing surgery time are all helpful in reducing complications.
References:
Holladay JT, et al. Ophthalmology. 1996;103:1118-1123.
Holladay JT, et al. Ann Ophthalmol. 1998;30:203-206.
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