Table 4  Intraoperative, early and late postoperative complications

*Tobramycin+Dexamethasone: topical tobramycin(0.3％)+dexamethasone (0.1％)

＃ AIR was documented in the form of flare and/or cells ≥ grade 2 by Hogan's criteria

△Dexamethasone sodium phosphate: intravenous dexamethasone sodium phosphate 5-10 mg daily

In our study, there were no complications in the majority (60.67％) of cases (if TCE and AIR were excluded), and improvement of BCVA was achieved in 94.38％ of cases. Nonetheless, significant risks are still associated with phacoemulsification surgery on nanophthalmic eyes． Compared with a previous study10, we achieved a limited gain in BCVA, with greater deviation (from 0.1 logMAR to 1.4 logMAR). This suboptimal visual acuity could be caused by two factors. Firstly, the majority of patients with nanophthalmos came from remote rural regions in China, and had poor visual acuity when they were teenagers or suffered from preexisting ocular diseases such as refractive amblyopia and foveal underdevelopment. Secondly, most of the eyes included in our study had glaucoma which could damage the optic nerve before cataract surgery.
Postoperative BCVA in nanophthalmos was less favorable compared with that in normal eyes. This was also true for the refractive results. The target refraction of ±0.50 D was not reached in 52 eyes (58.43％), most of which remained hyperopic. Several factors may be responsible for this discrepancy, including discrepancies in AL measurement and IOL power calculation. IOL calculations could be inaccurate, with the Holladay Ⅱ formula typically being preferred although it is not readily available^11-12. The Hoffer Q formula which performed as well as the HolladayⅡ formula for small eyes¹³ is readily available and therefore was our method of choice. Although Gayton et al¹⁴ demonstrated 2 IOLs , in a piggyback manner, can be successfully implanted, we considered that the zonules in those small eyes may be too weak to support insertion of 2 IOLs. Oshika et al¹⁵ modified the technique by implanting 1 IOL in the capsular bag and another IOL in the sulcus. We determined that insufficient space was available for 2 IOLs, and more importantly, that piggyback IOLs would produce marked hyperopic drift¹⁶. Based on all of these factors, we used a single highpower IOL instead of piggyback IOLs.
Phacoemulsification lens surgery of nanophthalmic eyes is associated with a high risk of perioperative complications, such as corneal decompensation, severe iritis, explosive choroidal hemorrhage, uveal effusion, retinal detachment, malignant glaucoma and CME¹⁷. In our cases, TCE, AIR, CME and uveal effusion accounted for the majority of early postoperative complications, while CME, uveal effusion glaucoma and PCO accounted for the majority of late postoperative complications. Nuclear hardness was a major risk factor for TCE and AIR. Once CME occurred, it was difficult to treat.In our study 2 eyes of 2 patients developed malignant glaucoma, presumably because of capsular block and aqueous misdirection and required YAG-capsulotomy combined with anterior vitrectomy to manage the IOP. Both patients had intractable IOP elevation (1 eye had cyclophotocoagulation) before surgery. We deemed that additional surgical interventions were often required as soon as complications were detected, emphasizing the necessity for careful follow-up.
In our study, there were no severe complications. One of the reasons for this may be that the percentage of high-risk eyes (approximately ＜18 mm¹⁸) was low (17.98％). More importantly, we believed the reduction of severe complications was closely related to surgical technique, and the surgery should always be handled by an experienced surgeon. To protect the corneal endothelium, we injected low density vis coelastic (VISCOAT, Alcon Laboratories Inc, Texas, USA) before capsulorrhexis. The coaxial micro-incision technique with a 2.2 mm corneal incision reduced the trauma around the corneal incision site. A stop and chop technique was performed to divide the lens as small as possible (approximately 6-8 pieces). We created paracentesis to make a “stab” incision for the first step, and made the viscoelastic advancing towards the paracentesis to gradually replace the aqueous humor. This may help reduce the aqueous outflow and naturally maintain ACD. We surmised that a 95 cm bottle height may be suitable, as it could maintain normal ACD without causing ocular hypertension or ischemia during surgery. We preferred topical anesthesia to retrobulbar anesthesia, because it reduced the vitreous pressure. Preoperative administration of mannitol may be important in preventing unexpected complications¹⁹. As expected, we noticed that previous surgical intervention may be helpful for postoperative ACD and IOP, and may protect against the development of complications. The risk for complications in nanophthalmos was greater with reducing AL, ACD, ACV or ACA and with higher nuclear hardness or Km.
Our study represented a fairly comprehensive case series. A previous study indicated that when the AL cut off to define nanophthalmos was ＜20.9 mm, 0.1 mm less than the 21 mm AL we used to defined nanophthalmos, the sample size of the present study would reduce the by nearly 25％20. By and large, the outcomes that we report were gratifying. Our experience may be useful to surgeons and patients at the time of perioperative preparation and preoperative counseling. The present study was related to the techniques and skills of an individual surgeon, potentially limiting the generalization of our results. IOLs with a power greater than 34 D were not readily available. This could leave nanophthalmos eyes with a higher postoperative refractive diopter receiving less powerful IOLs. Further studies may be more valuable if we included even short eyes. The decision to use ocular hypotensive agents was based on clinical judgment, and patients were not randomized into groups. We only considered the risk factors correlated with the surgery when we studied the incidence of PCO, ignoring the influence of previous holopathy such as diabetes and hypertension. Therefore, our results may be somewhat biased. Future largescale multicenter randomized controlled clinical trials are recommended to generalize our outcomes.

Conclusion