From Leeches to Lasers: The Bizarre, Untold History of Keratoconus

Keratoconus Group

From Leeches to Lasers: The Bizarre, Untold History of Keratoconus

To understand keratoconus, one must first understand the delicate optical architecture of the human eye. The cornea, the clear, dome-shaped window covering the front of the eye, provides nearly two-thirds of the eye's total refractive power. In a healthy eye, it is smooth, rigid and symmetrically curved. Light passes through it cleanly, bending precisely onto the retina at the back of the eye to produce sharp images.

In a patient with keratoconus, that delicate architecture collapses. The structural collagen matrix within the middle layer of the cornea (the stroma) weakens, causing normal intraocular pressure to push the tissue outward. The cornea thins, warps and bulges into an irregular, asymmetric cone. As light enters this conical surface, it scatters into a chaotic web of visual distortions known as higher-order aberrations.

Today, optometrists and ophthalmologists can map the front and back of a cone-shaped cornea down to the single micron in seconds and freeze its progression during a routine outpatient procedure. But for nearly three centuries, the condition was a sight-stealing mystery that baffled medical science and inspired some of the most harrowing treatments in surgical history.

An Ectatic Mystery of the 18th Century

Before the invention of specialized magnifying equipment, early physicians struggled to distinguish keratoconus from other conditions that caused corneal swelling, scarring or inflammatory bulging, such as corneal staphylomas or post-traumatic hydrops.

In 1736, Benedict Duddell, an English oculist, recorded one of the earliest documented descriptions of the disease. He observed a 14-year-old boy whose transparent corneas protruded forward like prominent glass cones. Confused by the crystal-clear nature of the bulging tissue, Duddell labeled the condition cornea diaphanum.

In 1748, Burchard Mauchart, a German professor of anatomy and surgery, published a doctoral dissertation describing a similar conical protrusion, dubbing it staphyloma diaphanum (and later staphyloma pellucidum). Lacking precise diagnostic tools or an understanding of corneal biomechanics, early European physicians incorrectly assumed these shapes were caused by an overaccumulation of fluid swelling the eyeball from within.

19th-Century Detectives and the Birth of Corneal Optics

By the mid-19th century, clinical practice began shifting from vague guesswork to systematic clinical observation. Practitioners recognized that the disorder was not a generic fluid swelling, but a distinct, non-inflammatory progressive pathology of the corneal tissue.

In 1854, Dr. John Nottingham, a British physician, published a seminal 270-page monograph titled Treatise on the Conical Cornea. Nottingham's work was the first to systematically catalog the hallmark features that eye care providers still evaluate today:

  • Onset typically occurring during puberty or early adulthood.
  • Progressive worsening of visual distortion and irregular astigmatism despite frequent spectacle changes.
  • Polyopia, or seeing multiple "ghost" images or multiple moons with a single eye (monocular diplopia).
  • The complete failure of traditional spherical and cylindrical spectacle lenses to correct visual acuity.
  • The physical thinning of the central cornea at the peak of the cone.

Visual diagnostic capabilities advanced rapidly over the next three decades. In 1857, William Bowman, a prominent British surgeon, used Hermann von Helmholtz's newly invented ophthalmoscope to inspect light reflecting off conical corneas. Bowman described a distinct, dark parabolic shadow reflection—an observation that laid the clinical groundwork for modern retinoscopy and the shadow test.

A decade later, in 1869, Johann Horner, a Swiss ophthalmologist, published a treatise titled On the Treatment of Keratoconus, officially giving the disease its modern name by combining the Greek words kerato (cornea) and konos (cone).

By 1880, Portuguese ophthalmologist Antonio Placido introduced the Placido disc—a handheld disk painted with alternating concentric black and white rings. By projecting these rings onto a patient's cornea and observing their reflected distortion through a central viewing hole, physicians could visually map the irregular curvature of a cone, laying the foundation for modern corneal topography.

Leeches, Cauterization and Water Goggles

While diagnostic capabilities improved in the 1800s, treatment options remained rudimentary and often dangerous. Before the advent of modern contact lenses or non-invasive surgery, physicians attempted a wide spectrum of systemic and invasive interventions.

Systemic Cures and Eyelid Bleeding

Believing keratoconus stemmed from systemic physical weakness or fluid pressure in the head, 19th-century doctors routinely prescribed internal doses of heavy metal compounds, including arsenic, zinc sulfate and calomel (a mercury compound). To reduce localized blood pressure around the orbit, physicians regularly applied live leeches directly to patients' eyelids and temples.

Invasive Surgical Interventions

When oral medications and leeches failed to stop the bulging cornea, eye surgeons turned to invasive surgical experiments:

  • Iridodesis (Pupil Displacement): William Bowman devised a procedure in which he inserted a fine metal hook through a peripheral corneal puncture, hooked the sphincter of the iris, and tied it into the incision. This pulled the pupil into a narrow vertical slit away from the optical center, intended to redirect light around the distorted apex of the cone.
  • Chemical and Thermal Cauterization: Albrecht von Gräfe, a leading German eye surgeon, popularized searing the peak of the corneal cone with a stick of silver nitrate in 1866. Later surgeons used hot cautery irons. The goal was to burn a deliberate lesion into the cone apex, creating a dense central scar that would contract as it healed, physically pulling the bulging tissue flat.
  • Elliptical Excision: Surgeons attempted full-thickness surgical cuts to remove wedge-shaped sections from the peak of the corneal cone, subsequently sewing the remaining corneal edges back together. Performed before the invention of delicate ophthalmic micro-sutures or antibiotics, these procedures frequently resulted in ruptured globes, severe intraocular infections and permanent blindness.

Early Optical Experiments

Optical inventors simultaneously tried to create external devices capable of neutralizing the irregular optical surface of the cone:

  • The Hydrodiascope (1896): Invented by German physician Dr. Lohnstein, this device consisted of a heavy, metal-framed glass goggle filled with a warm saline solution that bathed the eye directly. The liquid neutralized the irregular refraction of the cone, allowing light to pass smoothly into the eye. While optically functional, the apparatus leaked constantly, was cosmetically alarming and was impossible to wear outside a laboratory.
  • Blown-Glass Scleral Shells (1888): Working independently, French physician Eugène Kalt, German physiologist Adolf Fick, and Swiss physician August Müller produced the world's first glass contact lenses. Kalt placed thick, blown-glass shells directly over the corneas of keratoconus patients. The tears trapped between the glass lens and the cornea created a liquid layer that masked the irregular corneal surface—the direct physical ancestor to modern scleral lens technology.

The 20th Century: From Rigid Plastics to Corneal Transplants

The 20th century transformed keratoconus management from high-risk surgical experimentation into a precise optical science.

In 1936, Dr. Ramón Castroviejo performed the first successful penetrating keratoplasty (corneal transplant) specifically for a patient with advanced keratoconus. Using circular trephines to remove the diseased central cornea and replacing it with full-thickness donor tissue, Castroviejo proved that end-stage keratoconus could be cured surgically, offering sight to patients facing total functional blindness.

For patients who did not require surgery, optical correction saw a massive leap forward with the invention of polymethyl methacrylate (PMMA) hard contact lenses in the 1940s, followed by rigid gas-permeable (RGP) corneal lenses in the 1970s. These hard lenses rested over the central cornea, holding a tear layer beneath them that filled in the irregular valleys of the cone.

However, small RGP corneal lenses presented significant clinical challenges. Because they rested directly on the peak of the cone, hard lenses frequently caused mechanical friction, leading to apical scarring, corneal abrasions and localized tissue hypoxia. Fitting a rigid corneal lens on a steep, unstable cone was often an agonizing process of trial and error for both doctor and patient.

In 1984, Stephen Klyce introduced video-keratoscopy, utilizing computer algorithms to process reflections from Placido disc rings and generate color-coded topographic maps of corneal elevation and curvature. For the first time, eye care providers could view the exact contours of a cone and detect subclinical, asymptomatic keratoconus long before physical bulging occurred.

The Biochemical Breakthrough: Freezing the Cone in Place

Despite advances in contact lenses and topography, doctors throughout the 20th century faced a fundamental limitation: they could measure and optically correct keratoconus, but they could not stop the underlying ectasia from worsening.

That changed in the late 1990s at the Technical University of Dresden in Germany. A research team led by Prof. Theo Seiler, Dr. Eberhard Spoerl and Dr. Gregor Wollensak developed a procedure known as Corneal Collagen Cross-Linking (CXL).

The procedure relies on basic photochemistry. The outer epithelial layer of the cornea is removed or permeable, and liquid riboflavin (vitamin B2) drops are applied to the stroma until the tissue is saturated. The cornea is then exposed to controlled ultraviolet-A (UV-A) light at a wavelength of 365 nanometers.

The interaction between the UV-A light and the riboflavin generates reactive oxygen species, which induce the formation of new covalent chemical bonds among adjacent collagen fibrils in the corneal stroma. This biological reinforcement increases the mechanical rigidity of the corneal tissue, effectively freezing the cornea in its current shape and halting further progression.

Modern Diagnostics, Lasers, and the Scleral Lens Renaissance

Today, the management of keratoconus bears almost no resemblance to the invasive procedures of the past. Modern eye care centers rely on non-invasive 3D Scheimpflug tomography and Optical Coherence Tomography (OCT) to analyze the anterior and posterior surfaces of the cornea, measuring structural changes at the microscopic level long before visual symptoms develop.

When progressive keratoconus is caught early, corneal cross-linking stabilizes the tissue, preventing the need for corneal transplants in the vast majority of patients. When surgery or vision refinement is necessary, modern ophthalmologists utilize advanced femtosecond lasers to create precise tissue channels for Intacs (intracorneal ring segments) or to cut donor tissue during laser-assisted keratoplasty, as well as excimer lasers for topography-guided PRK combined with cross-linking.

For optical rehabilitation, eye care providers have embraced custom gas-permeable scleral contact lenses. Unlike the painful RGP lenses of the 20th century, modern scleral lenses have a large diameter that vaults entirely over the sensitive, conical cornea without touching it, landing softly on the insensitive sclera (the white part of the eye).

The space between the scleral lens and the warped cornea is filled with a sterile saline reservoir. This liquid layer neutralizes all corneal surface irregularities, creating a smooth, optically perfect front surface that routinely restores crisp 20/20 vision to patients with severe structural deformities.

After nearly three centuries of trial, error and medical horror, science has successfully tamed keratoconus. The silver nitrate has been retired, the hydrodiascope sits in museum display cases, and leeches have returned to the history books where they belong.

References & Historical Sources

  • (/1736). A Treatise with Respect to the Diseases and Cures of the Cornea, or Horny Coat of the Eye (with 1736 Appendix). London: J. Roberts. (Provides the earliest documented English reference to a conical cornea, termed cornea diaphanum).
  • and (). De Staphylomate Diaphano. Doctoral dissertation, University of Tübingen. (Early classification describing conical corneal ectasia under staphyloma diaphanum).
  • (). Practical Observations on Conical Cornea, and on the Short Sight, and Other Defects of Vision Connected with It. London: John Churchill. (The seminal 270-page monograph defining monocular polyopia, onset at puberty, and optical limitations of spectacles).
  • (). "On Conical Cornea, and its Treatment by Operation." Ophthalmic Hospital Reports and Journal of the Royal London Ophthalmic Hospital, 2, 154–167. (First recorded use of ophthalmoscopy to observe parabolic shadow reflections and early description of pupil relocation via iridodesis).
  • (). "Ueber die Behandlung des Keratoconus." Archiv für Ophthalmologie, 12(2), 215–220. (First documentation of apex chemical cauterization using silver nitrate to flatten conical tissue).
  • (). "Zur Behandlung des Keratoconus." Klinische Monatsblätter für Augenheilkunde, 7, 329–333. (Official coining of the modern medical term keratoconus).
  • (). "Novo instrumento para analyse da curvatura da cornea." Periodico Ophthalmologico Pratico, 5, 27–30. (Introduction of the Placido disc for visual mapping of corneal irregular astigmatism).
  • (). "Du traitement du kératocône par les verres de contact." Archives d'Ophtalmologie, 8, 541–556. (First recorded clinical application of blown-glass scleral contact shells to mask corneal irregularities).
  • (). "Keratoplasty for the Treatment of Keratoconus." Transactions of the American Ophthalmological Society, 46, 127–153. (Clinical demonstration of penetrating keratoplasty specifically for end-stage keratoconus).
  • (). "Computer-assisted corneal topography: High-resolution graphic presentation and analysis of keratoscopy." Investigative Ophthalmology & Visual Science, 25(12), 1426–1435. (Development of computerized video-keratoscopy and color-coded topography maps).
  • , , and (). "Riboflavin/ultraviolet-A-induced collagen crosslinking for the treatment of keratoconus." American Journal of Ophthalmology, 135(5), 620–627. (Landmark study establishing the safety and efficacy of Corneal Collagen Cross-Linking).