WORD ORIGIN- Η Πρεσβυωπ?α
The term “Presbyopia” itself comes from two Greek words: Presbys which means “old man” and -opia which means “see”. So it literally means “trying to see as old men do.”
Presbyopia is an eye condition that is likely to hit us all sooner or later. If you are over 45 years old and reading this on your smartphone or tablet, the chances are, you are doing so via corrective lenses such as contact lenses or reading glasses. According to the World Health Organization (WHO), in 2005, there were more than 1 billion people worldwide with presbyopia.
We’ve all seen it (or even experienced it ourselves) firsthand. Whether it’s one of your parents who forgot their reading glasses at a restaurant and still attempt to read the menu, or a friend struggling to read the small print on the back of a medicine bottle, they hold whatever they are trying to focus on, at arm’s length. That is very likely Presbyopia. It’s a result of natural aging and stems from a gradual thickening and decrease in elasticity of the lens inside the eye.
To add to the complication, there is also what is known as the halo effect. This is basically a glow or color light pattern observed when looking at a bright source of light in front of a dark background. It is mostly experienced at night when people who suffer from it, see halos around street lamps and car headlights and can make driving at night unsafe or even impossible in extreme cases.
This optical phenomenon is mainly caused by interaction of light with matter. It is enhanced by the diffraction of light when interacting with the eye, e.g. passing through the eye pupil, eye tissue, or even contact lenses (including intra-ocular lenses that are used after cataract surgery).
Hallo Presbyopia - goodbye Halo Effect!
Although Presbyopia may be unavoidable, the good news is that scientists from the Bar-Ilan University in Israel have presented a new concept that significantly reduces the halo effect that is generated when using multi focal (contact and intra-ocular) lenses and looking at bright point sources in dark conditions.
Prof. Zeev Zalevsky from the Faculty of Engineering, Bar-Ilan University, explains: “Our solution involves smoothening the surface structure of a contact lens or an intra-ocular lens that has extended depth of focus or multi focal capabilities. The smoothening does not complicate the fabrication complexity of the lens and yet yields the same optical performance in treating presbyopia and assisting people after cataract surgery, but with about one order to magnitude smaller halo effect. This allows people that use such lenses to be able to use them also at night.”
Figure 1: Experimental results of measuring the intensity map of light passing through the lens with respectively the first pattern and the second pattern in logarithmic scale.Preliminary in-vivo trials
As part of the investigation of the proposed solution, preliminary in-vivo trials were also performed. The trial group was of 16 people (10 men, 6 women) for which three types of spectacles were used. The test group of people was an average age of 66 years old with a standard deviation of 5 years.
They performed trials with what they called “phase plates”: they took a piece of glass and realized on its surface, the EDOF structure for contact lens design. Those glasses were placed in the frame of spectacles and the subjects looked through them on the point sources to test the resulted performance.
Three types of set-ups were used:
1. Apodized diffractive extended depth of focus (EDOF) lenses
2. the same lenses after applying on them the proposed concept while preserving their EDOF properties (denoted by D++)
3. conventional monofocal lens (having no EDOF capabilities).
The patients had to estimate the size of the halo pattern both its main lobe as well as its first side lobe size. One can see from the results presented in Fig. 2 that the size of the halo rings are smaller when applied the proposed concept and that the obtainable halo approaches the inherent hallo existing in regular monofocal lens.
Figure 2 Clinical trials demonstrating the reduction of the halo effect via using the proposed concept.A clearer future
More and more commercial ophthalmic products incorporate technologies such as extended depth of focus (EDOF) and multi focal technologies in contact and intra-ocular lenses to solve presbyopia. Until now, such lenses were very problematic when used in dark illumination conditions and people with such lenses had severe difficulty e.g. to drive at night. The proposed concept can resolve the above difficulties and make the existing products even more applicable and useful.
Read the full article
Ofer Limon, Zeev Zalevsky: Ophthalmic halo reduced lenses design
Optics Communications, Volume 342, 1 May 2015, Pages 253–258
doi:10.1016/j.optcom.2014.12.049