Various laser lenses have been introduced following Goldmann 3- mirror and Goldmann fundus contact lens for retinal photocoagulation. Below described some of the time-tested lenses in widespread use. Precise knowledge of these lenses is necessary for safe retinal photocoagulation.

2. Various laser lenses have been introduced following Goldmann
3- mirror and Goldmann fundus contact lens for retinal
photocoagulation.
Below described some of the time-tested lenses in widespread
use. Precise knowledge of these lenses is necessary for safe
retinal photocoagulation.
Activation of the laser can be done by :
• Lens-mirror contact lens system used with a slit lamp
• Fiber optic system (endophotocoagulation)
• Indirect ophthalmoscope with a handheld +20 or +28 diopter
(D) lens

3. For optimal visualization and treatment of retinal structures, the
accessory lenses are used.
They are used to image these structures at a point where they
can be reimaged by the slit lamp.
In a Haag- Streit Model 900, the stereoscopic slit lamp is in
focus at about 9 mm in front of the objective lens of the
microscope or about 280 mm from the examiner's eye.
The slit lamp cannot focus directly on the patient's retina due to
the intervening optical system of the patient's eye.
So, accessory optical aids are required in the form of lenses in
front of the patient's eye to nullify the optical effects of the
various intervening optical systems of the patient's eye.
Laser should be delivered through a Slit-Lamp system for
optimal viewing.

4. Coupling solution like Hydroxypropyl methylcellulose (2- 2.5%) is
commonly used to form a bond between the cornea and the contact
lens.
Several contact lens solutions have been described that provide
excellent post contact lens examination clarity for subsequent clinical
examinatio or photography.
1% carboxymethylcellulose sodium has a viscosity and adherence
greater than saline and at the same time provides excellent optical
clarity after contact lens removal.
Types of Lens Design
Non- contact: Hruby lens, +90 diopter (D) lenses and +60 (D) diopter
lenses.
+90 and +60 lenses has been used for retinal photocoagulation in
retinal tears, post-vitrectomy laser treatment of a giant retinal tear and
for treating proliferative diabetic retinopathy.
Treatment of macular lesions is not encouraged as the surgeon has
less control over patient eye movement.

5. The Hruby lens (Figure 1 & 2) is a high
minus (originally - 58.6 D) non-contact
lens mounted on the slit lamp for stability.
It provides a high resolution, upright
image of structures in the posterior pole.
But, the small field of view makes it
difficult to be certain of the relationship of
nearby structures.
Visualization of more peripheral
structures is limited by the entrance pupil,
which is minified by the negative optics.
This lens should be used only for
observation purposes and not laser
surgery.

6. The +90 D lens (Figure 3 & 4) is also more commonly being used as a
diagnostic lens as it is a noncontact lens thereby avoiding contact lens
solutions and potential compromise in corneal clarity.
It shows a relatively wide field of view with a good resolution.
However, subtle amounts of clinically significant fluid associated with a
choroidal neovascular membrane or central serous retinopathy may be
missed.

7. Contact: Pan retinal laser lenses, Focal laser lenses.
Two types of laser lenses are available to assist in slit-
lamp delivery of photocoagulation:
Plano-concave lenses: provide an upright image with
high resolution of small retinal area.
The plano-concave lenses have mirrors angulated at
590 , 690 and 730.
High plus power lenses: provide an inverted image with
mild loss of fine resolution, but provide a wide field of view,
making these lenses very suitable for pan-retinal
photocoagulation. These are also called indirect lens.

8. Some common characteristics of the laser lenses are:
Concave posterior surface conforming to the corneal
curvaturev and a flat or convex anterior surface
Planar mirrors allowing observation of the anterior chamber
angle or peripheral retina.
A prism to allow visualization of the mid-periphery of the retina.
A flange to stabilize the lens and prevent blinking
Knurled edge to facilitate lens manipulation.
Laser lenses generally consist of a conical
polymethylmethacrylate or aluminium shell
Glass anterior surface, lenticular elements and mirrors.

9. Antireflection coatings
They are usually applied to each optical surface in a laser lens that reduces
reflected white light (from the slit lamp source) that could decrease contrast or the
slit lamp image, and laser light (from the treatment beam) that could pose a
potential hazard to an observer standing behind the laser operator.
The hazard distance is 7 meters for an uncoated lens and 1.6 meters for a coated
lens. Most laser lenses use broad-spectrum, multilayer, antireflection coatings that
reduce reflected light between 400 nm and 700 nm from approximately 4 per cent
to less than one per cent.
Mirror lenses
Mirror lenses provide high magnification and high resolution but only a
small part of the fundus or chamber angle can be viewed at any one
time.
Therefore, the mirrors at various degrees of inclinations are necessary.
e.g.Goldmann 3 mirror lenses. The image formed in the Goldmann 3
mirror lens is the mirror image of the area focused.

10. Lenses without Mirrors
The field of view may be increased to a variable extent by use of biconcave
contact lenses based on the simple Goldman lens (without mirrors).
Another entirely different way of increasing the field of view involves using
contact lenses based on the EL Bayadi lens.
Both Rodenstock Panfundoscope and Mainster lens are excellent examples
of such lenses.
All wide-angle systems of this category are derived from the principle of
indirect ophthalmoscopy and the common denominator of all these lenses is a
large and inverted field of view.
Thus both the panfundoscope and the Mainster lenses produce inverted real
images.
Magnification and field of view
Magnification and field of view are critical parameters for determining which
lens is best for a particular clinical problem. The three main lenses -
Goldmann three mirror lenses, Panfundoscope and Mainster lens - are
compared in Table.

11. Focal Laser Lenses
Goldmann Lens (Figure 5 & 6)
The premier lenses to be used for retinal
lasers are the Goldmann fundus lens and the
Goldmann three -mirror lens.
The Goldmann fundus lens with either a
single mirror inclined at 620, or the three-
mirror style with the Gonioscopy mirror angled
at 590 provides a large field of view but must
be rotated 3600 to view the angled structures.
It has a flat anterior surface and produces
an erect, virtual ophthalmoscopic image
located near the posterior surface of the
crystalline lens.
The chief disadvantage of the Goldmann
lens is its limited field of view without rotation.

12. Yannuzzi fundus lens (Figure 7).
It is a modification of an earlier
model developed by Krieger in 1966
designed to facilitate macular
photocoagulation.
It has a concave corneal surface
which is steeper and of greater
diameter, so also has a better optics
than a simple Goldman fundus lens.
The concave corneal surface
allows posterior lens pressure to be
transmitted to the sclera without
distorting the cornea.
It produces an erect, virtual
ophthalmoscopic image located in
the anterior vitreous humor.

13. Volk Area centralis lens (Figure 8).
This is an indirect contact lens that provides a good
field of view with an excellent magnification.
The field of view is 700/840. Image magnification is
1.06x. Laser spot magnification is 0.94x.

15. Volk PDT lens (Figure 9).
The field of view is 1150/1370.
Image magnification is 0.67x.
Laser spot magnification is 1.5 x which
allows treatment of Choroidal neovascular
membranes upto maximum spot size of
6400um with providing excellent
visualization of the CNVM.
The Volk PDT lens comes standard with
SupraCoat whic covers the 689nm laser
wavelength indicated in this type of
procedure.

16. Volk Transequator lens (Figure 10)
It is designed for focal laser therapy and mid-to-far
peripheral fundus diagnosis.
Its unique optical design presents a realistic
contour of the retinal concavity, offering an
impressive wide-field of view of the entire posterior
pole extending to the equator.
Its superior optics allow dynamic movement on
the globe, therefore increasing its functional field of
view.
The field of view is 1100/1320.
Image magnification is 0.70x.
Laser spot magnification is 1.44x.

17. Mainster:
 Introduced in 1986, this lens has more field of view (58%
greater than Goldman) and a greater magnification.
Although the field of view is 14% less than the Panfundoscope,
but the lateral and axial magnification are better which makes it
useful for detecting retinal thickening.
It has a biconvex, aspherical anterior lens element and a
concave lens element to fit the corneal curvature.
It produces an inverted, real image located in front of its
biconvex aspheric anterior lens element (Figure 11a).

18. Mainster Standard lens (Figure 11b)
This lens is designed for focal and grid laser treatment from the posterior pole to
the midperiphery.
The field of view is 900/1210. Image magnification is 0.96 x. Laser spot
magnification is 1.05x.
High resolution, high magnification of image allows appreciation of subtle intra-
retinal details and retinal thickening.
So, it is excellent for diagnosis and treatment of macular oedema, branch retinal
vein occlusion, choroidal neovascular membrane in age-related macular
degeneration and presumed ocular histoplasmosis.

19. PRP Lenses
Mainster wide field lens (Figure 11c)
This allows a very wide range of slit lamp magnification to be used.
It has excellent ophthalmic resolution and image binocularity is maintained
across the entire field of view.
It is used for panretinal photocoagulation in proliferative diabetic retinopathy.
The field of view is 1180/1270. Image magnification is 0.68x. Laser spot
magnification is 1.50 x.

20. Mainster Ultrafield PRP lens:
This lens has the widest field of view available for pan retinal
photocoagulation. It has a unique optical design to provide a clear, bright
image across the entire field.
It is light- weight, has a secure fit flange for easy manipulation besides
having a high efficiency laser light anti-reflective coating.
The field of view is 1650/1800. Image magnification is 0.51 x. Laser spot
magnification is 1.96x.
Rodenstock Panfundoscopic lens (Figure 12 & 13)
Introduced in 1969 by Schlegel this lens is used for panretinal
photocoagulation from the posterior pole to beyond the equator without the
use of mirrors.
It gives a panoramic view, produces an inverted, real image located in its
spherical biconvex anterior lens element. Thus, the biomicroscope must be
located further from the patient's eye than using a Goldman lens.

21. This low biomicroscopic magnification
produces adequate magnification with a large
field and acceptable depth of focus.
The working field is 84% greater than a
Goldman but lateral magnification is 24% lesser
than a Goldman.
The spot size is 40% larger than the
photocoagulator setting or twice large than the
conventional contact lens.
Disadvantage of this lens is that it produces
peripheral distortion.
It can produce marked laser beam
astigmatism while treating the peripheral retina.
Reflexes compromise retinal image thereby
causing oblong burns when treating through the
periphery of the lens.

22. Common Features of Mainster and Panfundoscopic lens
Large areas of the fundus may be treated in Panretinal
photocoagulation without lens rotation.
Visualization of the optic disc and macula during
peripheral treatment prevents disorientation.
The experienced laser surgeon can achieve a more
peripheral view by tilting the lens off-axis.
The field of view is increased in myopes and decrease in
hyperopes and will lead to differences in how far
peripherally laser photocoagulation can be applied.
Working distance on these lenses are greater.
Anterior segment irradiance becomes excessive with large
spot sizes (1000μm) but should be acceptable at a spot size
of 500μm.

23. Volk Quadraspheric lens (Figure 14)
The original 130 Quadraspheric lens has grown
in popularity since its introduction in 1989 as the
preferred wide field fundus laser lens for diagnosis
and treatment of the retina.
The four aspheric surfaces also employ high-
efficiency antireflection coatings thereby improving
lens performance by reducing astigmatism across
the entire field of view.
It also enhances visualization through a small
pupil. It produces an inverted and reversed image.
Its sleek 28.6mm diameter housing provides a
definite advantage over competitive wide field
lenses for peripheral retinal viewing, reflection
displacement and ease of use.
The laser spot magnification is 1.97x and the
image magnification is 0.51x.

24. Volk Super Quad 160 lens (Figure 15)
This lens offers the widest field of view. Its
ideal 0.5x image magnification provides
simultaneous visualization of the posterior pole
to the peripheral retina providing a greater
margin of safety even during extreme wide angle
panretinal photocoagulation.
The field of view is 1600/ 1650 , image
magnification is 1.97x and laser spot
magnification is 2.0x.
This has become the ideal lens for
visualization and treatment of proliferative
diabetic retinopathy, ischaemic retinal vein
occlusion and peripheral retinal holes and tears.
Laser beam transmission and fundus image
quality are sharp and undistorted to the full
extent of the viewing field.