I commend Jung and associates for describing the results of phacoemulsification cataract surgery under topical anesthesia observed in nanophthalmos and relative anterior microphthalmos. The authors investigated the refractive outcomes, describing a poorer prediction of the postoperative refraction in nanophthalmos, which could be attributable to at least 2 factors.
First, the manufacturers are allowed to commercialize intraocular lenses (IOL) with a given power tolerance from the nominal power, which is directly related to the nominal IOL power (a greater IOL power tolerance for highly powerful implants). The authors could be able to confirm that a significantly higher percentage of eyes requiring an IOL of at least 30 diopters was observed in the nanophthalmos group. I believe that such information would be important to the manufacturers and would urge them to indicate the effective power, as opposed to the nominal power, for the most powerful IOLs.
A second important point regards the accuracy of axial length (AL) measurements: a systematic error attributable to the employed technology would produce more noticeable errors in shorter eyes, which were the nanophthalmic eyes. In fact, the use of a 10 MHz ultrasound transducer, although with immersion technique, leads to greater inaccuracy in AL measurements in comparison to what is achievable with partial coherence interferometry (PCI), as the latter technology is negligibly affected by velocity assumptions and consistently measures along the visual axis. The error of PCI biometry for normal eyes is 0.02 mm, a sixth of the systematic error of acoustic biometry. In addition, the ultrasound waves propagate more quickly through the lens than through the vitreous, and it would be theoretically more likely to have a greater inaccuracy in AL measurements in nanophthalmos, which is characterized by an increased lens thickness–to–ocular axial length ratio.
In light of the above-discussed reasons, PCI has been considered to be the gold standard technology for AL measurements in nanophthalmos over the last decade.
I would challenge the authors to elucidate their rationale for employing the ultrasound technology with immersion technique in their series of eyes operated on between 2007 and 2010, and to add details regarding the ultrasound velocity adopted and whether they used gated or not-gated ultrasounds.