Surgery
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Surgery has long been considered the last resort, however, this was in an era when the only option to patients was a corneal graft. Thankfully newer treatments such as collagen cross linking has advanced the thinking around surgical options for the keratoconic patient.
Still most surgery is reserved for those patients who struggle with all other options as recovery time and procedural risks must be carefully considered. With the exception of cross linking surgery is still considered a grave step and not a panacea to treat all forms of the condition. If patients can cope with contact lenses or glasses then the consensus is to continue with that form of treatment.
There are occasions, however, when patients cannot continue with glasses or contact lenses where vision is not significantly improved or that the they become intolerant to contact lenses. Generally being atopic (allergic) patients this can be an issue. In these cases surgery can become a lifeline to patients who really struggle with their vision. In this section I have attempted to outline some of the options available currently but first i think it worth understanding a little about the corneal structure.
Still most surgery is reserved for those patients who struggle with all other options as recovery time and procedural risks must be carefully considered. With the exception of cross linking surgery is still considered a grave step and not a panacea to treat all forms of the condition. If patients can cope with contact lenses or glasses then the consensus is to continue with that form of treatment.
There are occasions, however, when patients cannot continue with glasses or contact lenses where vision is not significantly improved or that the they become intolerant to contact lenses. Generally being atopic (allergic) patients this can be an issue. In these cases surgery can become a lifeline to patients who really struggle with their vision. In this section I have attempted to outline some of the options available currently but first i think it worth understanding a little about the corneal structure.
The cornea is made up of five main layer or structures. The epithelium is the very front surface exposed to the air. This is a rapidly regenerating surface as it has to cope with all this injury's and minor scratches that usually occur on a daily basis.
Below this is Bowman's layer, which provides a base for the epithelium and a transition to the layer below (the stroma). It is also quite rigid in nature, therefore, provides a significant amount of rigidity to the cornea as a whole. If damaged it will result in scarring. |
The Stroma forms close to 90% of the overall thickness of the cornea and consist of carefully arranged collagen fibers parallel to the corneal surface. These fibers are held in position by a series of bonds between each fiber. The arrangement of the fibers is crucial, if disrupted by scar tissue formation, swelling, etc the the clarity of the tissue can be lost leading to a loss of vision.
Separating the stromal collagen fibers with the final layer of the cornea is the basement layer know as Descement's membrane. This layer provides a base for the stroma but also a structure from which the endothelium can be supported.
The Endothelium is a single layer of cells which perform a very important function for the overall clarity of the cornea structure. They act as little water pumps and continually dehydrate the cornea. If they were to fail in this function the corea would swell and become hazy and eventually opaque leading to loss of vision. If you can recall waking up of a morning and being "bleary eyed" this is as a result of the natural swelling of the cornea overnight causing blurred vision, After a few minutes the vision becomes clearer, this is because the endolthelium has caught up by pumping the excess water out of the cornea. The endothelium consists of around 3000 cells per square mm at birth. This number gradually reduces over time as the cells are not regenerated. In order to function properly we need around we require at least 750 cells/mm2 otherwise the water stagnates in the cornea causing swelling and visual disturbance.
Separating the stromal collagen fibers with the final layer of the cornea is the basement layer know as Descement's membrane. This layer provides a base for the stroma but also a structure from which the endothelium can be supported.
The Endothelium is a single layer of cells which perform a very important function for the overall clarity of the cornea structure. They act as little water pumps and continually dehydrate the cornea. If they were to fail in this function the corea would swell and become hazy and eventually opaque leading to loss of vision. If you can recall waking up of a morning and being "bleary eyed" this is as a result of the natural swelling of the cornea overnight causing blurred vision, After a few minutes the vision becomes clearer, this is because the endolthelium has caught up by pumping the excess water out of the cornea. The endothelium consists of around 3000 cells per square mm at birth. This number gradually reduces over time as the cells are not regenerated. In order to function properly we need around we require at least 750 cells/mm2 otherwise the water stagnates in the cornea causing swelling and visual disturbance.