Human Eye

What colour do you perceive?

Complete the Google Form and check out the consolidated poll results below!

Note: You will need to refresh this page after submitting the Google form for your results to be tallied below!

Edit: I am pretty proud of myself for creating this subsection! Reminded me of my excel course I had to attend.

If you are curious to the scientific explanation why the dress (and sandals) were perceived differently by different people, click this link!

LASIK: Laser Assisted In Situ Keratomileusis

Due to travel restrictions in 2020, I went for my LASIK surgery in Dec 2020 and used the school holidays for my recovery.

Here are some of my statistics before LASIK:

  • right eye, left eye

  • myopia degree: 275, 300

  • astigmatism: 75, 50 (apparently doctor said this was considered severe)

  • cornea thickness before LASIK / microns: 504, 508

  • adjustments to cornea thickness / microns: -51, -56

Strangely enough, although my astigmatism was severe when they used a specialised machine to measure the surface of my cornea, when I did the actual eye test (reading numbers & letters on a wall), I displayed minimal astigmatism. This meant that somehow my brain was able to compensate for the really severe astigmatism and still could see things quite clearly.

The doctor and I hypothesised that perhaps I have been using glasses without any astigmatism for years, that some how my brain compensated for it. But who knows!

Structure of the Cornea

In IP and O-level Biology, students are taught simply that the cornea "refracts light". This is true! However, the cornea actually consists of different layers and types of cells.

During LASIK, the excimer laser functions to reshape the cells of the stroma. Which means the upper layers of the cornea need to be removed, either via a cornea flap or by being scrapped off (PRK).

LASIK procedure

The actual LASIK produced for me was subdivided into two parts:

  1. the creation of the cornea flap

  2. the usage of the excimer laser to reshape the cornea

In my case, my cornea flap was created using a laser, so it was classified as a "bladeless" creation of cornea flap. The cornea flap is required as it needs to be folded back to subsequently allow the excimer laser to reshape the cells underneath the cornea.

Before the surgery, I imagined that staring at the laser beam would be similar to staring at a laser pointer, however the "beam" or "spot" I was asked to stare at was actually pretty blurry (I assume due to the folded cornea flap affecting the refraction of light).

LASIK patient's experience

If you are not to squeamish, watch the YouTube video where they show and explain the LASIK procedure being carried out on a patient!

PRK: photorefractive keratotectomy

An alternative to the creation of the cornea flap for the excimer laser to reshape the cornea cells would be the PRK procedure. Instead of a cornea flap being created, the doctor scrapes off the epithelium layer (refer to cornea structure image again). Subsequently, the excimer laser then reshapes the stroma cells the same way as the LASIK procedure previously described.

Part of the recovery of the PRK procedure in this case would then involve the epithelium cells growing back (mitosis in action!).