M. Redondo

Optical aberrations of the human cornea as a function of age

We investigated how the optical aberrations associated with the anterior surface of the human cornea change with age in a normal population. Aberrations were computed for a central part of the cornea (4, 5, and 6 mm in diameter) from the elevation data provided by a videokeratographic system. Measurements were obtained in 59 normal healthy, near-emmetropic [spherical equivalent lower than 2 diopters (D)] subjects of three age ranges: younger (20-30 years old), middle-aged (40-50 years old), and older (60-70 years old). The average corneal radius decreased with age and the cornea became more spherical. As a consequence, spherical aberration was significantly larger in the middle-aged and older corneas. Coma and other higher-order aberrations also were correlated with age. The root mean square of the wave aberration exhibited a linear positive correlation (P < 0.003) with age for the three ranges of pupil diameter. Despite a large intersubject variability, the average amount of aberration in the human cornea tends to increase moderately with age. However, this increase alone is not enough to explain the substantial reduction previously found in retinal image quality with age. The change in the aberrations of the lens with age and the possible loss of part of the balance between corneal and lenticular aberrations in youth may be the main factors responsible for the reduction of retinal image quality through the life span.

Laser in situ keratomileusis disrupts the aberration compensation mechanism of the human eye.

PURPOSE To study how changes induced on corneal optics by myopic and hyperopic laser in situ keratomileusis (LASIK) refractive surgery affect the aberration compensation mechanism. DESIGN Interventional case series and modeling theory. METHODS We measured ocular, corneal, and internal aberrations for a 6-mm pupil in 15 myopic and 6 hyperopic eyes with similar age range before and 6 months after standard LASIK. Ocular aberrations were measured using our own developed Hartmann-Shack wavefront sensor, whereas corneal aberrations were calculated by using the elevation data obtained by corneal topography. Ocular, corneal, and internal root mean square (RMS), spherical aberration (SA), coma, and compensation factor were compared for each patient. RESULTS After myopic LASIK, we obtained an average 1.6-fold increase in ocular RMS, mainly positive SA, and coma, associated with a similar increase in corneal aberrations. In the hyperopes, we found a higher (2.3-fold) induction of ocular aberrations after surgery, mainly negative SA and coma, but without net increases of corneal aberrations. Aberration compensation clearly decreased or even inverted after hyperopic LASIK, decreasing the ocular optical quality in a higher level than myopic LASIK. CONCLUSIONS Although ocular aberrations after myopic LASIK usually were smaller than corneal aberrations because of partial compensation of SA, after hyperopic LASIK, because of induction of negative SA and change in coma, disruption of the compensation mechanism lead to a larger increase of ocular aberrations. Customized procedures should maintain the natural compensation to achieve improved visual outcomes.

Temporal evolution of ocular aberrations following laser in situ keratomileusis

Citation information: Benito A, Redondo M & Artal P. Temporal evolution of ocular aberrations following laser in situ keratomileusis. Ophthalmic Physiol Opt 2011, 31, 421–428. doi: 10.1111/j.1475‐1313.2011.00854.x

The behavior of two cell lines obtained from murine (B16-F10) and human (G-361) melanomas implanted into the eyes of New Zealand white rabbits, and their microscopic, immunohistochemical and ultrastructural appearances

A transcleral inoculation of 15×106 melanocytes of the B16-F10 and G-361 cell lines was carried out in the anterior chamber of one eye in New Zealand white rabbits. Tumor growth occurred in 24 eyes (77%) of the B16-F10 group and in 22 (73%) of the G-361 group. The tumors of the latter group were mostly amelanic and showed local aggression with ocular perforation and extrascleral growth one month post-implant, while the tumors of the B16-F10 group were intensely pigmented and grew over the iris although they did not perforate the eyeball. Microscopically, the tumors of both groups were of the mixed type, made up of epithelioid and fusiform melanocytes. S-100 protein and Nki C3 monoclonal immunohistochemical techniques showed a positive immunoreaction in all cases of tumor growth. Ultrastructurally, the G-361 melanocytes showed a few melanosomes corresponding to maturity state II and, occasionally, state III, while totally melanized state IV cells predominated in the B16-F10 group. Aberrant melanosomes were common in both groups. The inoculation of 15×106 melanocytes of either cell line was useful to produce ocular melanomas.