About two-thirds of your eye's focusing power comes from a transparent dome roughly half a millimetre thick at its centre. The lens inside the eye gets most of the attention because it is the one we replace in cataract surgery, but the cornea in front of it does more of the work. It also has no blood vessels at all, and that one unusual fact explains almost everything else about it.
No blood vessels means nothing to scatter light, which is why the cornea is clear. It also means the cornea is fed slowly, by tears from the front and by fluid from inside the eye behind, so it heals slowly and defends itself against infection poorly. A scratch on your skin is a nuisance. A scratch on your cornea that gets infected can cost you the eye's vision in a week.
How it is built, and why that matters
Think of three working parts. The outer skin, the epithelium, is a few cells thick and replaces itself completely every week or so. It is why a simple abrasion heals in two days without a mark. Beneath it sits the stroma, which is nine-tenths of the thickness and made of collagen fibres laid down in a precise lattice. That lattice is the reason the tissue is transparent. Disturb the arrangement, with a scar or with swelling, and the cornea goes hazy. At the back is a single layer of endothelial cells that continuously pump water out of the stroma to keep it from waterlogging. These cells never divide again after you are born. You spend your whole life on the stock you started with.
So there are three distinct ways for a cornea to fail: the surface gets infected, the shape goes wrong, or the pump at the back runs out. Each has a very different treatment.
When the surface gets infected
A corneal ulcer is an infected crater in the cornea, and it is one of the genuine eye emergencies. In and around Telangana the classic story is a farm injury, where a stalk of paddy or a leaf whips the eye during harvesting. Vegetative injuries frequently seed a fungal infection, which is slower, more stubborn and harder to treat than a bacterial one. The other classic story is contact lenses: sleeping in them, topping up old solution instead of replacing it, or rinsing the case with tap water.
What should send you to an eye hospital the same day, not next week:
- A red, painful eye with a white or grey spot visible on the coloured part.
- Pain that is out of proportion to how the eye looks, with heavy watering and a real dislike of light.
- Vision that has dropped in the last day or two in one eye.
- Any eye injury with plant material, mud, or a metal fragment.
Two things make ulcers worse and both are common. The first is steroid eye drops bought at a pharmacy for a red eye, which will calm the redness beautifully while the infection eats deeper. Never use a steroid drop in a red eye without an eye doctor having looked at it under a microscope. The second is delay. An ulcer treated on day one usually heals with a small scar off the visual axis. The same ulcer treated on day ten may need a transplant. We keep emergency cover running at Masab Tank around the clock on 040-4245 6666 precisely for this.
When the shape goes wrong
Keratoconus is a progressive thinning and forward bulging of the cornea into a cone, usually starting in the teens or early twenties. The early signs are easy to dismiss: a spectacle number that keeps changing, particularly the cylinder, ghosting or streaking around lights at night, and glasses that never quite give clear vision even when new. Chronic eye rubbing, which often traces back to untreated allergy, makes it progress faster. If your child has itchy eyes and rubs them constantly, treat the allergy.
The important part is that keratoconus is now largely a manageable condition, provided it is caught while it is still moving. Collagen cross-linking uses riboflavin and controlled ultraviolet light to stiffen the corneal fibres and halt progression. It does not sharpen your vision and it is not meant to. Its job is to stop the cornea getting worse, which it does in the great majority of cases. Vision itself is then handled with spectacles, rigid or scleral contact lenses, or in some eyes with corneal ring segments.
Keratoconus is also the reason every laser vision correction workup includes corneal topography. An eye with an early, undetected cone that undergoes LASIK can destabilise badly. If a scan shows an irregular shape, laser correction is off the table, and that refusal is protecting you rather than obstructing you. There is more on how those decisions are made on our refractive surgery page.
When the pump at the back fails
Because endothelial cells never regenerate, anything that kills them off is permanent. Fuchs dystrophy, an inherited condition, slowly reduces their numbers over decades. Complicated cataract surgery or long-standing high pressure can do the same faster. When the count drops below what is needed, fluid accumulates in the stroma and the cornea turns hazy, worst in the morning and clearing a little through the day. That morning pattern is a useful clue.
Treatment used to mean replacing the whole thickness of the cornea. Today it usually does not. Modern transplants are selective: only the failed back layer is exchanged in a DSEK or DMEK, or only the front layers in a DALK for scarring and keratoconus, leaving the patient's own healthy tissue in place. The advantages are real: faster recovery, better final vision, and a much lower risk of the graft being rejected. Full-thickness grafts are still used, mainly for deep scars and severe ulcers.
All corneal transplants depend on donated tissue, and demand in India comfortably exceeds supply. Eye donation costs a family nothing and takes a few minutes after death, and it is worth telling your relatives now what you would want.
If you have a red painful eye today, treat it as urgent. If your spectacle power has been changing every few months, or you have been told your astigmatism is unusual, ask for a corneal topography scan rather than another new pair of glasses. Our cornea service covers all of the above, and appointments at any centre can be made on 90001 80035.
