MYOPIA INDIAN EYES: COMPARING CALCULATED AND MEASURED AXIAL LENGTH IN YOUNG PATIENTS

Myopia is the leading cause of preventable blindness in children and young adults in the world. As age increases axial length increasing risks of myopia for causing ocular morbidity including retinal detachment, glaucoma, myopic macular degeneration, and cataracts. In India, much patient eye examination done at primary eye clinic, where to estimate axial length is difficult. Our aim of the study was to assess the reliability of formula by comparing Predicted Axial Length (AL) uses corneal radius and Spherical equivalent (SE) to the measured AL using Ocular Biometry. Method: 96 myopic eyes were included, Comprehensive eye examination with Auto-refractokeratometer using TOPCON-800 and Axial length with Ocular Biometry (IOL Master-500) Calculated Axial length with formula by using AVE-K and SE which is obtained from original Gullstrand simplified Schematic eye: AL= (24.00×AVE-K/7.80–SE×0.40) for both K-reading. Result: Mean Calculated AL(mm) was 24.67 ± .90 and Measured AL (mm) which was 24.28 ± .96mm in 9-25yr age (P<0.001) with Mean difference 0.3±0.4. All groups show statistically significant correlation between Calculate AL and Mean AL (p<0.01, r>0.9). The coefficient of determination (R2) was 82% in 9-25yr age group. Conclusion: Study provides strong agreement between Measured AL and Calculated AL. Alternate method of AL measurement with a calculated formula can be implemented in all primary eye care for predicting Axial length and managing myopic patients for monitoring myopia control.

New method to improve the quality of vision in cataractous keratoconus eyes

To analyze using optical simulations if the proper use of a segmented intraocular lens (IOL) can improve the visual outcomes compared to the implantation of a spherical monofocal IOL. The wavefront profile of the Mplus (Oculentis) and a monofocal IOLs with the phase transformation introduced by each IOL were calculated using a Hartmann-Shack wavefront sensor. In addition, the wavefront profile of schematic eye models of various keratoconus conditions was obtained and was propagated to the IOLs. The optical performance of such combination was obtained after combining ray tracing and Fourier optics. A pre-clinical validation was also evaluated incorporating clinical data from three different keratoconus eyes of three patients. The implantation of the Mplus IOL can compensate or reduce the overall coma of the eye with keratoconus improving the quality of vision compared with a spherical monofocal IOL due to lower displacements of the retinal image or tilting in keratoconus. All theoretical simulations were confirmed afterwards by mean of a preclinical validation. The use of a standard toric segmented IOL with a proper orientation and selection of the addition can improve the optical quality of the keratoconus eye compared to the use of a monofocal spherical IOL.

Optical Coherence Tomography Reveals Sigmoidal Crystalline Lens Changes during Accommodation

This study aimed to quantify biometric modifications of the anterior segment (AS) during accommodation and to compare them against changes in both accommodative demand and response. Thirty adults, aged 18–25 years were rendered functionally emmetropic with contact lenses. AS optical coherence tomography (AS-OCT) images were captured along the 180° meridian (Visante, Zeiss Meditec, Jena, Germany) under stimulated accommodative demands (0–4 D). Images were analysed and lens thickness (LT) was measured, applying a refractive index correction of 1.00. Accommodative responses were also measured sequentially through a Badal optical system fitted to an autorefractor (Shin Nippon NVision-K 5001, Rexxam, Japan). Data were compared with Dubbelman schematic eye calculations. Significant changes occurred in LT, anterior chamber depth (ACD), lens centroid (i.e., ACD + LT/2), and AS length (ASL = ACD + LT) with accommodation (all p < 0.01). There was no significant change in CT with accommodation (p = 0.81). Measured CT, ACD, and lens centroid values were similar to Dubbelman modelled parameters, however AS-OCT overestimated LT and ASL. As expected, the accommodative response was less than the demand. Interestingly, up until approximately 1.5 D of response (2.0 D demand), the anterior crystalline lens surface appears to be the primary correlate. Beyond this point, the posterior lens surface moves posteriorly resulting in an over-all sigmoidal trajectory. he posterior crystalline lens surface demonstrates a sigmoidal response with increasing accommodative effort.

Peter Orlebar Bishop. 14 June 1917—3 June 2012

Peter Orlebar Bishop was an Australian neurophysiologist renowned for his ingenious quantitative approach to the study of the mammalian visual system and his great ability to attract a large number of talented people to visual research. Peter’s research was based on specially designed, precise instrumentation and data quantification applied mainly to analysis of the response properties of single neurones in the principal dorsal thalamic visual relay nucleus, the dorsal lateral geniculate nucleus (LGNd) and the primary visual cortex. This quantitative bent was evident throughout Peter’s entire research career: starting with the design and construction of innovative DC amplifiers; to his quantitative analysis of optics, ‘schematic eye’ for the cat, which rivalled Gullstrand’s schematic eye for humans; to creating and demonstrating validity of the concept of ‘projection lines’ in the representation of contralateral visual field in different cellular layers of the LGNd of mammals with frontally positioned eyes and discovery of massive binocular input to single LGNd neurones. Peter’s engineering approach was probably at its heuristic peak when it revealed many details of binocular interactions at the level of single neurones in the primary visual cortex—the interactions which appear to underpin overall mechanisms underlying stereopsis, the high precision binocular depth sense.

Peter Orlebar Bishop 1917–2012

Peter Orlebar Bishop was an Australian neurophysiologist renowned for his ingenious quantitative approach to study of the mammalian visual system and great ability to attract a large number of talented people to visual research. Peter's research was based on specially designed, precise instrumentation and data quantification applied mainly to analysis of the response properties of single neurones in the principal dorsal thalamic visual relay nucleus, the dorsal lateral geniculate nucleus (LGNd) and the primary visual cortex. This quantitative bent was evident throughout Bishop's entire research career:starting with the design and construction of innovative DC amplifiers; through to his quantitative analysis of optics—‘schematic eye' for the cat, which rivaled Gullstrand's schematic eye for humans; to creating and demonstrating validity of the concept of ‘projection lines' in the representation of contralateral visual field in different cellular layers of the LGNd of mammals with frontally positioned eyes and discovery of a very substantial binocular input to single LGNd neurones. The engineering approach of Peter was probably at its heuristic peak when it revealed many details of binocular interactions at the level of single neurones in the primary visual cortex—the interactions that appear to underpin overall mechanisms underlying stereopsis, the high precision binocular depth sense.