Craig Blackwell, MD

Santa Cruz, CA
Diplomate: American Board of Ophthalmology
Fellow: American Academy of Ophthalmology

Welcome to the Website of Craig Blackwell, MD

An Ophthalmology Practice in Santa Cruz, CA

Microscope Exam of the Front of the Eye

Microscope Exam of the Front of the Eye

A specialized “slit lamp” microscope is used to examine the fine details of the eye

Exam at the Slit Lamp Microscope

View of the front of the eye through the microscope. The slit beam of light is seen as it passes through the clear cornea and illuminates the iris. The space in between is called the anterior chamber and is filled with a watery liquid called aqueous humor.

The illustration shows the structure of the front of the eye, called the Anterior Segment.

The Cornea is the clear window in front. The Iris is the colored ring surrounding the dark Pupil. The Anterior Chamber is the space between the Cornea and the Iris.

The Conjunctiva is an external covering layer, not shown.

Aqueous Humor

The blue arrows show the circulation of aqueous fluid in the eye.

Aqueous is watery fluid produced by the Ciliary Body as a filtrate from blood, making it like plasma except for less protein and more ascorbate.
Aqueous is important because it supplies nutrients to the lens and cornea which have no blood vessels of their own.
The aqueous circulates around the lens and through the Pupil. It exits the eye by filtering through the pores of the Trabecular Meshwork where it collects in Schlemm’s Canal and then returns to the venous circulation.

Exam of the Anterior Segment

Starting at the surface, we check the white part of the eye, the clarity of the cornea, the depth of the anterior chamber and the details of the iris.
A pterygium is a common wedge-shaped thickening of the outer covering layer of the eye. It is located between the lids where the eye is exposed to sun and wind. If it grows onto the cornea far enough to threaten vision it can be removed. (The Spanish word for pterygium is carnocidad.)

Red Eye

If the eye is red we are commonly considering allergy, infection and other causes of inflammation.

  • Itching and watering suggest allergy.
  • A sandy, gritty feeling suggests dryness.
  • A red eye with discharge likely has an infection.
  • Eye pain and photophobia in the absence of injury suggest primary inflammation, called iritis.

There are so many possible causes of a red eye, including vision threatening causes like corneal ulcer, that it is important to search for confirmatory findings with the microscope, so appropriate treatment can be chosen.


Clouding of the cornea would commonly occur as the result of injury or infection.

Of particular note here are contact lens related infections. Contacts, particularly with overnight wear, trap extra bacteria on the surface of the eye and are associated more infections.

If bacterial infection invades the substance of the cornea it is called an ulcer. All ulcers will leave some degree of scarring. If the scarring is in the center of the cornea it will cause clouding of vision. The only way to remedy significant clouding is with corneal transplant.

Anterior Chamber

Depth estimate of the anterior chamber is important. If the chamber is too shallow there is risk that the normal circulation of fluid within the eye will be blocked and the pressure will rise. This is the mechanism of narrow angle glaucoma. People with narrow angles are the target of the medication warning labels that say do not take if you have glaucoma.

If the chamber appears narrow we do an additional exam with a special mirrored contact lens that lets us look directly into that space and assess the risk of closure. This is called “gonioscopy.” If we judge there is a significant risk of closure we will discuss a laser procedure to make a small opening of the iris to bypass the potential blockage.
See Laser Iridotomy in the Photo Gallery.