How aquatic water-beetle larvae with small chambered eyes overcome challenges of hunting under water

A particularly unusual visual system exists in the visually guided aquatic predator, the Sunburst Diving Beetle, Thermonectus marmoratus (Coleoptera: Dytiscidae). The question arises: how does this peculiar visual system function? A series of experiments suggests that their principal eyes (E1 and E2) are highly specialized for hunting. These eyes are tubular and have relatively long focal lengths leading to high image magnification. Their retinae are linear, and are divided into distinct green-sensitive distal and UV and polarization-sensitive proximal portions. Each distal retina, moreover, has many tiers of photoreceptors with rhabdomeres the long axis of which are peculiarly oriented perpendicular to the light path. Based on detailed optical investigations, the lenses of these eyes are bifocal and project focused images onto specific retinal tiers. Behavioral experiments suggest that these larvae approach prey within their eyes' near-fields, and that they can correctly gauge prey distances even when conventional distance-vision mechanisms are unavailable. In the near-field of these eyes object distance determines which of the many retinal layers receive the best-focused images. This retinal organization could facilitate an unusual distance-vision mechanism. We here summarize past findings and discuss how these eyes allow Thermonectus larvae to be such successful predators.

Randomized trial of multifocal intraocular lenses versus monovision after bilateral cataract surgery

OBJECTIVE

To compare spectacle independence in patients randomized to receive bilateral multifocal intraocular lenses (IOLs) or monofocal IOLs with the powers adjusted to produce monovision.

DESIGN

Randomized, multicenter clinical trial.

PARTICIPANTS

A total of 212 patients with bilateral, visually significant cataract.

METHODS

Before bilateral sequential cataract surgery, patients were randomized (allocation ratio 1:1) to receive bilateral Tecnis ZM900 diffractive multifocal lenses (Abbott Medical Optics, Santa Ana, CA) or Akreos AO monofocal lenses (Bausch & Lomb, Rochester, NY) with the powers adjusted to target -1.25 diopters (D) monovision. Outcomes were assessed 4 months after the second eye underwent operation.

MAIN OUTCOME MEASURES

The primary outcome was spectacle independence. Secondary outcomes included questionnaires (VF-11R, dysphotopsia symptoms, and satisfaction) and visual function measures (near, intermediate, and distance logarithm of minimum angle of resolution [logMAR] visual acuity, stereoacuity, contrast sensitivity, and forward light scatter).

RESULTS

A total of 212 patients were randomized, and 187 patients (88%) returned for assessment 4 months after surgery. Uniocular distance refractions in the monovision arm showed a mean spherical equivalent of +0.075 D in the distance eye and -0.923 in the near eye. In the multifocal arm, the mean distance spherical equivalents were -0.279 D and -0.174 D in the right and left eyes, respectively. A total of 24 of 93 patients (25.8%) in the monovision arm and 67 of 94 patients (71.3%) in the multifocal arm reported never wearing glasses (P<0.001, Fisher exact test). The adjusted odds ratio of being spectacle free was 7.51 (95% confidence interval, 3.89-14.47). Binocular uncorrected acuities did not differ significantly for distance (0.058 logMAR for monovision vs. 0.076 for multifocal, P = 0.3774) but were significantly worse in the multifocal arm for intermediate acuity (0.149 vs. 0.221, P = 0.0001) and in the monovision arm for near acuity (0.013 vs. -0.025, P = 0.037). In the first postoperative year, 6 patients (5.7%) in the multifocal arm underwent IOL exchange (4 had a bilateral and 2 had a unilateral exchange). No patients in the monovision arm underwent IOL exchange.

CONCLUSIONS

Patients randomized to bilateral implantation with the diffractive multifocal Tecnis ZM900 were more likely to report being spectacle independent but also more likely to undergo IOL exchange than those randomized to receive monofocal implants (Akreos AO) with the powers adjusted to give low monovision.